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![Nov 26, 2025 11
JAVA vs C++
JAVA
More secure
Java doesn't support multiple inheritance
Java is most likely to be found in Web and
Enterprise applications.
• Java Example
• File: Simple.java
class Simple{
public static void main(String args[]){
System.out.println("Hello Java");
}
}
C++
Less secure
C++ supports multiple inheritance
C++ is more likely to be found in System and
other low level applications.
• C++ Example
File: main.cpp
#include <iostream>
using namespace std;
int main() {
cout << "Hello C++ Programming";
return 0;
}](https://image.slidesharecdn.com/02chaptertwo-overviewofjavaprinciple-251126132708-3f5285f3/75/02Chapter-Two-Overview-of-Java-Principle-pptx-11-2048.jpg)
![Nov 26, 2025 28
Simple Java program: Example #1
/*
This is a simple Java program. Call this file "Example.java".
*/
public class Example1 {
// Your program begins with a call to main().
public static void main(String args[]) {
System.out.println("This is a simple Java program.");
}
}
Objective: Learn how to write, compile, and run your first Java program](https://image.slidesharecdn.com/02chaptertwo-overviewofjavaprinciple-251126132708-3f5285f3/75/02Chapter-Two-Overview-of-Java-Principle-pptx-28-2048.jpg)
![Nov 26, 2025 33
Con’ t…
3. // Your program begins with a call to main().
– This is the second type of comment supported by Java.
– A single-line comment begins with a // and ends at the end of the line.
– As a general rule, programmers use multiline comments for longer remarks and single-line
comments for brief, line-by-line descriptions.
4. public static void main(String args[]) {
This line begins the main( ) method.
As the comment preceding it suggests, this is the line at which the program will begin
executing.
All Java applications begin execution by calling main( ).
Let’s take a brief look at each part now at next slide](https://image.slidesharecdn.com/02chaptertwo-overviewofjavaprinciple-251126132708-3f5285f3/75/02Chapter-Two-Overview-of-Java-Principle-pptx-33-2048.jpg)
![Nov 26, 2025 37
parentheses
– Any information that you need to pass to a method is received by variables specified
within the set of parentheses that follow the name of the method.
– These variables are called parameters.
– If there are no parameters required for a given method, you still need to include the
empty parentheses.
– In main( ), there is only one parameter
– String args[ ] declares a parameter named args, which is an array of instances of the
class String. (Arrays are collections of similar objects.)
– Objects of type String store character strings.
– In this case, args receives any command-line arguments present when the program is
executed.
Con’ t…](https://image.slidesharecdn.com/02chaptertwo-overviewofjavaprinciple-251126132708-3f5285f3/75/02Chapter-Two-Overview-of-Java-Principle-pptx-37-2048.jpg)
![Nov 26, 2025 39
• Valid java main method signature
– public static void main(String[] args)
– public static void main(String []args)
– public static void main(String args[])
– public static void main(String... args)
– static public void main(String[] args)
– public static final void main(String[] args)
– final public static void main(String[] args)
Invalid java main method signature
public void main(String[] args)
static void main(String[] args)
public void static main(String[] args)
abstract public static void main(Strin
g[] args)
Con’ t…](https://image.slidesharecdn.com/02chaptertwo-overviewofjavaprinciple-251126132708-3f5285f3/75/02Chapter-Two-Overview-of-Java-Principle-pptx-39-2048.jpg)
![Nov 26, 2025 50
Byte
The smallest integer type is byte.
It is useful in saving memory for large arrays, it is a signed two’s
complement integer.
It has a size of 8 bits with a range from -128 to 127.
• Example
// Java program to demonstrate byte data type in Java
class byte{
public static void main(String args[]){
byte a = 126;
System.out.println(a);
}
}](https://image.slidesharecdn.com/02chaptertwo-overviewofjavaprinciple-251126132708-3f5285f3/75/02Chapter-Two-Overview-of-Java-Principle-pptx-50-2048.jpg)
![Nov 26, 2025 51
Short
• Short is similar to byte and is used to save memory in large arrays.
• It is also a two’s complement with a size of 16 bit and ranges from -32,768
to 32,767 (inclusive).
• Examples of short variable declarations:
// Java program to demonstrate short data type in Java
class short{
public static void main(String args[]){
short a = 56;
System.out.println(a);
}
}](https://image.slidesharecdn.com/02chaptertwo-overviewofjavaprinciple-251126132708-3f5285f3/75/02Chapter-Two-Overview-of-Java-Principle-pptx-51-2048.jpg)
![Nov 26, 2025 52
int
The most commonly used integer type is int.
It is a signed 32-bit type that has a range from –2,147,483,648 to
2,147,483,647.
Example-
// Java program to demonstrate int data type in Java
class int{
public static void main(String args[])
{
int a = 56;
System.out.println(a);
}
}](https://image.slidesharecdn.com/02chaptertwo-overviewofjavaprinciple-251126132708-3f5285f3/75/02Chapter-Two-Overview-of-Java-Principle-pptx-52-2048.jpg)
![Nov 26, 2025 53
long
• The range of a long is quite large
• long is a signed 64-bit type and ranges from -2^64 to 2^63-1.
• Is useful for those occasions where an int type is not large enough to hold the
desired value.
• Example:
// Java program to demonstrate long data type in Java
class long
{
public static void main(String args[])
{
long a = 100000L;
System.out.println(a);
}
}](https://image.slidesharecdn.com/02chaptertwo-overviewofjavaprinciple-251126132708-3f5285f3/75/02Chapter-Two-Overview-of-Java-Principle-pptx-53-2048.jpg)
![Nov 26, 2025 54
long: Example#2
// Compute distance light travels using long variables.
class Light {
public static void main(String args[]) {
int lightspeed;
long days;
long seconds;
long distance;
// approximate speed of light in miles per second
lightspeed = 186000;
days = 1000; // specify number of days here
• seconds = days * 24 * 60 * 60; // convert to seconds
distance = lightspeed * seconds; // compute distance
System.out.print("In " + days);
System.out.print(" days light will travel about ");
System.out.println(distance + " miles.");
}
}
.
• This program generates the following
output:
• In 1000 days light will travel about
16070400000000 miles.
• Clearly, the result could not have been
held in an int variable](https://image.slidesharecdn.com/02chaptertwo-overviewofjavaprinciple-251126132708-3f5285f3/75/02Chapter-Two-Overview-of-Java-Principle-pptx-54-2048.jpg)
![Nov 26, 2025 56
float
• The type float specifies a single-precision value that uses 32 bits of storage.
• Variables of type float are useful when you need a fractional component, but don’t
require a large degree of precision.
• For example, a float can be useful when representing dollars and cents.
• Example float variable declarations:
– float hightemp, lowtemp;
// Java program to demonstrate float data type in Java
class float {
public static void main(String args[]) {
float a = 4.5541132f;
System.out.println(a);
}
}](https://image.slidesharecdn.com/02chaptertwo-overviewofjavaprinciple-251126132708-3f5285f3/75/02Chapter-Two-Overview-of-Java-Principle-pptx-56-2048.jpg)
![Nov 26, 2025 57
Double
Double precision, as denoted by the double keyword, uses 64 bits to store a
value. Used to manipulate large-valued numbers.
Double precision is actually faster than single precision
All transcendental math functions, such as sin( ), cos( ), and sqrt( ), return double
values.
Ex: double variables to compute the area of a circle:
// Compute the area of a circle.
class Area {
public static void main(String
args[]) {
double pi, r, a;
r = 10.8; // radius of circle
pi = 3.1416; // pi, approximately
a = pi * r * r; // compute area
System.out.println("Area of circle is " +
a);
}
}](https://image.slidesharecdn.com/02chaptertwo-overviewofjavaprinciple-251126132708-3f5285f3/75/02Chapter-Two-Overview-of-Java-Principle-pptx-57-2048.jpg)
![Nov 26, 2025 59
Characters…
• Here is a program that demonstrates char variables:
– // Demonstrate char data type.
class CharDemo {
public static void main(String args[]) {
char ch1, ch2;
ch1 = 88; // code for X
ch2 = 'Y';
System.out.print("ch1 and ch2: ");
System.out.println(ch1 + " " + ch2);
}
}
– This program displays the following output:
ch1 and ch2: X Y
• Notice that ch1 is assigned the value 88, which is the ASCII (and Unicode) value that
corresponds to the letter X.](https://image.slidesharecdn.com/02chaptertwo-overviewofjavaprinciple-251126132708-3f5285f3/75/02Chapter-Two-Overview-of-Java-Principle-pptx-59-2048.jpg)
![Nov 26, 2025 60
Booleans
It can represent only one bit of information, i.e. true or false for logical values.
This is the type returned by all relational operators, as in the case of a < b. boolean.
They cannot be changed either explicitly or implicitly, but the programs for conversion can
be easily written.
• // A Java program to demonstrate boolean data type
class boolean{
public static void main(String args[])
{
boolean b = true;
if (b == true)
System.out.println("true");
}
}](https://image.slidesharecdn.com/02chaptertwo-overviewofjavaprinciple-251126132708-3f5285f3/75/02Chapter-Two-Overview-of-Java-Principle-pptx-60-2048.jpg)
![Nov 26, 2025 66
Class- Example #1
public class School{
// Declaration of a primitive variable.
String name="RSVM"; // Instance variable
public static void main(String[] args){
// Creating an object of the class.
School sc=new School(); // sc is Non-primitive data type i.e Object REFERENCE.
// Print the address of the memory location of an Object.
System.out.println(sc);
// Now we cannot access instance variable directly. We call instance variable by using reference variable sc
which is created above.
System.out.println(sc.name);
}
}
Output: School@1db9742
RSVM](https://image.slidesharecdn.com/02chaptertwo-overviewofjavaprinciple-251126132708-3f5285f3/75/02Chapter-Two-Overview-of-Java-Principle-pptx-66-2048.jpg)
![Nov 26, 2025 69
Array
An array in java is an object which is used to store multiple variables of the same type.
• i.e. a structure that can hold multiple values –but all the values must be of the same
type.
An array is declared by specifying the data type of the values it will hold, followed by []
to indicate that it is an array.
That type can be a primitive data type or an object type.
The example of declaring an array variable of primitive data type int is as follows:
int [ ] scores;
byte[] arrayOfBytes; //array of values of type byte
byte[][] arrayOfArrayOfBytes ; //an array of arrays of byte[] type](https://image.slidesharecdn.com/02chaptertwo-overviewofjavaprinciple-251126132708-3f5285f3/75/02Chapter-Two-Overview-of-Java-Principle-pptx-69-2048.jpg)
![Nov 26, 2025 70
Example #1: Array
Customer[] arrayOfCustomers; //array of objects of the class Customer
In the above Ex, we can say that byte[] and Customer[] are types.
After an array has been declared, it must be created.
Because an array is actually an object in Java,
the new keyword must be used to create the array (new is used to create any object).
The size of the array i.e. how many elements it can hold must be specified.
For example, to declare an array called 'arrayOfBytes' that will hold 1024 bytes and
to create it: byte[] arrayOfBytes = new byte[1024];
To declare an array of 50 strings: String[] lines = new String[50];](https://image.slidesharecdn.com/02chaptertwo-overviewofjavaprinciple-251126132708-3f5285f3/75/02Chapter-Two-Overview-of-Java-Principle-pptx-70-2048.jpg)
![Nov 26, 2025 71
Assigning Values to Arrays
When the array is created, each of the values in the array is initialized to the corresponding default
value (i.e. array default value is null).
The null literal can be used to indicate that an object that is of a reference data type does not yet
exist
i.e. to initialize an object to be empty or null.
Ex: char[] password = null;
• Literal values can also be used to specify the values of an array,
• For Ex:
String[] responses = new String[2];
responses[0] = "Yes";
responses[1] = "No";
//to read the elements
System.out.println ("The answer should be " + responses[0] + " or " + responses[1] + "!");
](https://image.slidesharecdn.com/02chaptertwo-overviewofjavaprinciple-251126132708-3f5285f3/75/02Chapter-Two-Overview-of-Java-Principle-pptx-71-2048.jpg)
![Nov 26, 2025 72
Assigning Values to Arrays…
An array can also be initialized by the following syntax
• int[] someNumbers = {1, 2, 3, 4} **The element values are separated by commas.
The new keyword is not used – but the object is implicitly created.
The length of this array is now 4
The statement above could also be written as:
int[] someNumbers = new int[4];
someNumbers[0] = 1;
someNumbers[1] = 2;
someNumbers[2] = 3;
someNumbers[3] = 4;](https://image.slidesharecdn.com/02chaptertwo-overviewofjavaprinciple-251126132708-3f5285f3/75/02Chapter-Two-Overview-of-Java-Principle-pptx-72-2048.jpg)
![Nov 26, 2025 73
Array of Objects
Unlike traditional array which store values like string, integer, Boolean, etc.
array of objects stores objects.
The array elements store the location of reference variables of the object.
Syntax:
Class obj[]= new Class[array_length]
For Ex, we use a class Student containing a single instance variable mark.
class Student {
int marks;
}](https://image.slidesharecdn.com/02chaptertwo-overviewofjavaprinciple-251126132708-3f5285f3/75/02Chapter-Two-Overview-of-Java-Principle-pptx-73-2048.jpg)
![Nov 26, 2025 74
Array of Objects…
An array of objects is created just like an array of primitive type data items in
the following way. Student[] studentArray = new Student[7];
The above statement:
• creates the array which can hold references to seven Student objects.
• It doesn't create the Student objects themselves.
• They have to be created separately using the constructor of the Student class.
• The studentArray contains seven memory spaces in which the address of seven
Student objects may be stored.
If we try to access the Student objects even before creating them, run time errors would occur.
The Student objects have to be instantiated using the constructor of the Student class and their
references should be assigned to the array elements in the following way.
studentArray[0] = new Student();](https://image.slidesharecdn.com/02chaptertwo-overviewofjavaprinciple-251126132708-3f5285f3/75/02Chapter-Two-Overview-of-Java-Principle-pptx-74-2048.jpg)
![Nov 26, 2025 85
Declaring a Variable
In Java, all variables must be declared before they can be used.
The basic form of a variable declaration is shown here:
type identifier [ = value][, identifier [= value] ...] ;
• The type is one of Java’s atomic types, or the name of a class or interface.
• The identifier is the name of the variable.
• You can initialize the variable by specifying an equal sign and a value.
initialization expression must result in a value of the same (or compatible) type as
that specified for the variable.
To declare more than one variable of the specified type, use a comma separated
list.](https://image.slidesharecdn.com/02chaptertwo-overviewofjavaprinciple-251126132708-3f5285f3/75/02Chapter-Two-Overview-of-Java-Principle-pptx-85-2048.jpg)
![Nov 26, 2025 88
Sample java code that uses a variable
public class Sample {
public static void main(String[] args)
{
int num = 10;
System.out.println("The number is:
"+ num);
}
}
When we run this, we get the output:
The number is: 10
int num = 10;
• int is the type of the variable declared.
• Integers are whole numbers (no decimal point)
and can either be negative, positive, or zero.
num is the name of the variable.
= is the assignment operator.
• It tells to store the value 10 to the variable
num.
• Hence, after the statement, num gets the value
of 10.](https://image.slidesharecdn.com/02chaptertwo-overviewofjavaprinciple-251126132708-3f5285f3/75/02Chapter-Two-Overview-of-Java-Principle-pptx-88-2048.jpg)
![Nov 26, 2025 89
Different variables refers to different data
Consider this example:
public class Sample {
public static void main(String[]
args) {
int a = 50;
int b = 75;
System.out.println("The first
number is: "+ a);
System.out.println("The second
number is: "+ b);
}
}
The output of this is:
• The first number is: 50
• The second number is: 75
a is a variable of type int and
assigned a value of 50
b is another variable of type int and
assigned a value of 75
a and b are different from each
other because they have different
names](https://image.slidesharecdn.com/02chaptertwo-overviewofjavaprinciple-251126132708-3f5285f3/75/02Chapter-Two-Overview-of-Java-Principle-pptx-89-2048.jpg)
![Nov 26, 2025 90
Manipulating variables
The value stored to a variable can be
updated. Consider this example:
public class Sample {
public static void main(String[] args) {
int num = 20;
num = num + 5;
System.out.println("The result is: "+
num);
}
}
• The output of this is: The result is: 25
num is a variable of type int and assigned
a value of 20
num's value is updated with the
statement num = num + 5
num + 5 is evaluated first
num is 20, by adding 5 the outcome is
25
25 is then assigned to num
after the statement, num gets the
value 25](https://image.slidesharecdn.com/02chaptertwo-overviewofjavaprinciple-251126132708-3f5285f3/75/02Chapter-Two-Overview-of-Java-Principle-pptx-90-2048.jpg)
![Nov 26, 2025 91
A Second java Program
This example shows how a variable is declared and how it is
assigned a value. call this file /* Call this file
"Example2.java". */
public class Example2 {
public static void main(String args[]) {
int num; // this declares a variable called num
num = 100; // this assigns num the value 100
System.out.println("This is num: " + num);
num = num * 2;
System.out.print("The value of num * 2 is ");
System.out.println(num);
}
}
• When you run this program,
you will see the following
output
• This is num: 100
• The value of num * 2 is 200](https://image.slidesharecdn.com/02chaptertwo-overviewofjavaprinciple-251126132708-3f5285f3/75/02Chapter-Two-Overview-of-Java-Principle-pptx-91-2048.jpg)
![Nov 26, 2025 96
Local Variable: Example #1
public class Test {
public void pupAge() {
int age = 0;
age = age + 7;
System.out.println("Puppy age is : " + age);
}
public static void main(String args[]) {
Test test = new Test();
test.pupAge();
}
}
Here, age is a local variable.
This is defined inside pupAge() method and its scope is limited to only this
method.
• This will produce the
following result −
• Output Puppy age is: 7](https://image.slidesharecdn.com/02chaptertwo-overviewofjavaprinciple-251126132708-3f5285f3/75/02Chapter-Two-Overview-of-Java-Principle-pptx-96-2048.jpg)
![Nov 26, 2025 97
Local Variable: Example #2
• Following example uses age without initializing it, so it would give an error at the
time of compilation.
public class Test {
public void pupAge() {
int age;
age = age + 7;
System.out.println("Puppy age is : " + age);
}
public static void main(String args[]) {
Test test = new Test();
test.pupAge();
} }
• This will produce the following error while compiling it −
– OutputTest.java:4:variable number might not have been initializedage = age
+ 7; ^1 error](https://image.slidesharecdn.com/02chaptertwo-overviewofjavaprinciple-251126132708-3f5285f3/75/02Chapter-Two-Overview-of-Java-Principle-pptx-97-2048.jpg)
![Nov 26, 2025 100
Instance Variables: Example#2
public class Employee {
// this instance variable is visible for any
child class.
public String name;
// salary variable is visible in Employee class
only.
private double salary;
// The name variable is assigned in the
constructor.
public Employee (String empName) {
name = empName;
}
// The salary variable is assigned a value.
public void setSalary(double empSal) {
salary = empSal;
}
// This method prints the employee
details.
public void printEmp() {
System.out.println("name : " +
name );
System.out.println("salary :" +
salary);
}
public static void main(String
args[]) {
Employee empOne = new
Employee("Abdi");
empOne.setSalary(1000);
empOne.printEmp();
}
}](https://image.slidesharecdn.com/02chaptertwo-overviewofjavaprinciple-251126132708-3f5285f3/75/02Chapter-Two-Overview-of-Java-Principle-pptx-100-2048.jpg)
![Nov 26, 2025 103
Class/Static Variable: Example#2
public class Employee {
// salary variable is a private static variable
private static double salary;
// DEPARTMENT is a constant
public static final String DEPARTMENT = "Development ";
public static void main(String args[]) {
salary = 1000;
System.out.println(DEPARTMENT + "average salary:" + salary);
}
}
• This will produce the following result −
• Output
• Development average salary:1000](https://image.slidesharecdn.com/02chaptertwo-overviewofjavaprinciple-251126132708-3f5285f3/75/02Chapter-Two-Overview-of-Java-Principle-pptx-103-2048.jpg)
![Nov 26, 2025 110
You can include as many import statements as are necessary to import all the classes
used by your program.
• This is the general form of the import statement:
import pkg1[.pkg2].classname; // Import a single class
import pkg1[.pkg2].*; // Import the whole package
• Here,
– pkg1 is the name of a top-level package, and
– pkg2 is the name of a subordinate package inside the outer package separated by a
dot (.).
Import a Class(2)](https://image.slidesharecdn.com/02chaptertwo-overviewofjavaprinciple-251126132708-3f5285f3/75/02Chapter-Two-Overview-of-Java-Principle-pptx-110-2048.jpg)
![Nov 26, 2025 113
Example#1
import java.util.Scanner; // Import the Scanner class
class MyClass {
public static void main(String[] args) {
// Create a Scanner object
Scanner myObj = new Scanner(System.in); System.out.println("Enter
username");
// Read user input
String userName = myObj.nextLine();
// Output user input
System.out.println("Username is: " + userName);
}
}](https://image.slidesharecdn.com/02chaptertwo-overviewofjavaprinciple-251126132708-3f5285f3/75/02Chapter-Two-Overview-of-Java-Principle-pptx-113-2048.jpg)
![Nov 26, 2025 115
Ex #2: different methods to read data of various types:
package inputuser;
import java.util.Scanner;
public class InputUser {
public static void main(String[] args) {
// TODO code application logic here
Scanner sc=new Scanner(System.in);
System.out.print("Enter your name:");
// String input
String userName= sc.nextLine();
System.out.print("Enter your age:");
// Numerical input
int age = sc.nextInt();
System.out.print("Enter salary:");
double salary = sc.nextDouble();
System.out.println("Your name is:"+ userName);
System.out.println("Your age is:"+ age);
System.out.println("Your salary:"+ salary);
}
}](https://image.slidesharecdn.com/02chaptertwo-overviewofjavaprinciple-251126132708-3f5285f3/75/02Chapter-Two-Overview-of-Java-Principle-pptx-115-2048.jpg)
![Nov 26, 2025 117
To create a package, use the package keyword:
MyPackageClass.java
package mypack;
class MyPackageClass {
public static void main(String[] args) {
System.out.println("This is my package!");
}
}
Ex #1: Create package](https://image.slidesharecdn.com/02chaptertwo-overviewofjavaprinciple-251126132708-3f5285f3/75/02Chapter-Two-Overview-of-Java-Principle-pptx-117-2048.jpg)
![Nov 26, 2025 126
Example #1: Widening conversion (int to double)
public class MyClass {
public static void main(String[] args) {
int a = 9;
double d = a; // Automatic casting: int to double
System.out.println(a); // Outputs 9
System.out.println(d) // Outputs 9.0
}
}](https://image.slidesharecdn.com/02chaptertwo-overviewofjavaprinciple-251126132708-3f5285f3/75/02Chapter-Two-Overview-of-Java-Principle-pptx-126-2048.jpg)
![Nov 26, 2025 129
Narrowing or Explicit Conversion: Example#1
public class MyClass {
public static void main(String[] args) {
double d= 9.78;
int a = (int) d; // Manual casting: double to int
System.out.println(d); // Outputs 9.78
System.out.println(a); // Outputs 9
}
}](https://image.slidesharecdn.com/02chaptertwo-overviewofjavaprinciple-251126132708-3f5285f3/75/02Chapter-Two-Overview-of-Java-Principle-pptx-129-2048.jpg)
![Nov 26, 2025 130
Narrowing or Explicit Conversion: Example#2
//Java program to illustrate explicit type conversion
class Test
{
public static void main(String[] args)
{
double d = 100.04;
//explicit type casting
long l = (long)d;
//explicit type casting
int i = (int)l;
System.out.println("Double value "+d);
//fractional part lost
System.out.println("Long value "+l);
//fractional part lost
System.out.println("Int value "+i);
}
} Output: Double value 100.04 Long value 100 Int value 100](https://image.slidesharecdn.com/02chaptertwo-overviewofjavaprinciple-251126132708-3f5285f3/75/02Chapter-Two-Overview-of-Java-Principle-pptx-130-2048.jpg)
![Nov 26, 2025 136
Unary Operators: Example
public static void main(String[] args) {
int result = +1; // result is now 1
result--; // result is now 0
result++; // result is now 1
result = -result; // result is now -1
boolean success = false;
boolean tt = !success; // true
}](https://image.slidesharecdn.com/02chaptertwo-overviewofjavaprinciple-251126132708-3f5285f3/75/02Chapter-Two-Overview-of-Java-Principle-pptx-136-2048.jpg)
![Nov 26, 2025 142
Simple example program demonstrates the arithmetic operators
class BasicMath {
public static void main(String args[]) {
// arithmetic using integers
System.out.println("Integer Arithmetic");
int a = 1 + 1;
int b = a * 3;
int c = b / 4;
int d = c - a;
int e = -d;
System.out.println("a = " + a);
System.out.println("b = " + b);
System.out.println("c = " + c);
System.out.println("d = " + d);
System.out.println("e = " + e);
Output: Integer Arithmetic
a = 2 b = 6 c = 1 d = -1 e = 1](https://image.slidesharecdn.com/02chaptertwo-overviewofjavaprinciple-251126132708-3f5285f3/75/02Chapter-Two-Overview-of-Java-Principle-pptx-142-2048.jpg)
![Nov 26, 2025 143
Modulus Operator
Modulus Operator
– The modulus operator, %, returns the remainder of a division operation.
– It can be applied to floating-point types as well as integer types.
– Example:
• // Demonstrate the % operator.
class Modulus {
public static void main(String args[]) {
int x = 42;
double y = 42.25;
System.out.println("x mod 10 = " + x % 10);
System.out.println("y mod 10 = " + y % 10);
}
}
• When you run this program, you will get the following output:
• x mod 10 = 2 y mod 10 = 2.25](https://image.slidesharecdn.com/02chaptertwo-overviewofjavaprinciple-251126132708-3f5285f3/75/02Chapter-Two-Overview-of-Java-Principle-pptx-143-2048.jpg)
![Nov 26, 2025 146
A sample program that shows several op= assignments
// Demonstrate several assignment operators.
class OpEquals {
public static void main(String args[]) {
int a = 1;
int b = 2;
int c = 3;
a += 5;
b *= 4;
c += a * b;
c %= 6;
System.out.println("a = " + a);
System.out.println("b = " + b);
System.out.println("c = " + c);
} }
• The output of this program is shown here: a = 6 b = 8 c = 3](https://image.slidesharecdn.com/02chaptertwo-overviewofjavaprinciple-251126132708-3f5285f3/75/02Chapter-Two-Overview-of-Java-Principle-pptx-146-2048.jpg)
![Nov 26, 2025 150
Example:Increment and Decrement
The following program demonstrates the increment operator.
// Demonstrate ++.
class IncDec {
public static void main(String args[]) {
int a = 1, b = 2;
int c, d;
c = ++b;
d = a++;
c++;
System.out.println("a = " + a);
System.out.println("b = " + b);
System.out.println("c = " + c);
System.out.println("d = " + d);
}
}
The output of this program follows: a = 2 b= 3 c = 4 d = 1](https://image.slidesharecdn.com/02chaptertwo-overviewofjavaprinciple-251126132708-3f5285f3/75/02Chapter-Two-Overview-of-Java-Principle-pptx-150-2048.jpg)
![Nov 26, 2025 155
Example: boolean logical operators.
class BoolLogic {
public static void main(String args[]) {
boolean a = true, b = false;
boolean c = a | b;
boolean d = a & b;
boolean e = a ^ b;
boolean f = (!a & b) | (a & !b);
boolean g = !a;
System.out.println(" a = " + a);
System.out.println(" b = " + b);
System.out.println(" a|b = " + c);
System.out.println(" a&b = " + d);
System.out.println(" a^b = " + e);
System.out.println("!a&b|a&!b = " + f);
System.out.println(" !a = " + g);
} }
a = true b = false a|b = true a&b = false a^b = true a&b|a&!b = true !a = false](https://image.slidesharecdn.com/02chaptertwo-overviewofjavaprinciple-251126132708-3f5285f3/75/02Chapter-Two-Overview-of-Java-Principle-pptx-155-2048.jpg)
![Nov 26, 2025 158
Operator Precedence: Table
Operators Associativity Type
() [] . left to right highest
++ -- right to left unary postfix
++ -- + - ! (type) right to left Unary & prefix
* / % left to right multiplicative
+ - left to right additive
< <= > >= left to right relational
== != left to right Equality
& left to right boolean logical AND
^ left to right boolean logical exclusive OR
| left to right boolean logical inclusive OR
&& left to right logical AND
|| left to right logical OR
?: right to left Conditional
= += -= *= /= %= right to left Assignment](https://image.slidesharecdn.com/02chaptertwo-overviewofjavaprinciple-251126132708-3f5285f3/75/02Chapter-Two-Overview-of-Java-Principle-pptx-158-2048.jpg)
02Chapter Two- Overview of Java Principle.pptx
- 1. Nov 26, 20251 Chapter- Two Overview of Java Principle
- 2. Nov 26, 20252 Topics we will cover in chapter- Two Overview of Java Programming Definition of Java Application, Java Applets Editing, Compiling and Interpreting Java Development tools The First simple program Basics in Java Programming • Data Type • Variable types and identifiers • Number types, strings, constants • Type Conversion/ Casting • Operators and operator precedence
- 3. Nov 26, 2025 Overviewof Java Programming language • Let's start learning of java from basic questions like: – How java is developed (history of java)? – What is java? – Where it is used? – What type of applications are created in java? – Features of Java (characteristics of java) – How java differ from other programming language (e.g. C++) ? 3
- 4. Nov 26, 20254 History of Java Java was originally developed by Sun Microsystems, a US company, in 1991. Its first name was Oak and it was designed for the development of software for consumer electronic devices such as televisions and video recorders. As such, one of the main goals for the language was that it is simple, portable and highly reliable. In 1995, Oak was renamed Java due to some legal issues – the name does not have any particular meaning.
- 5. Nov 26, 20255 What is java? Java is related to C++, which is a direct descendent of C. Much of the character of Java is inherited from these two languages. From C, Java derives its syntax. Many of Java’s object-oriented features were influenced by C++. Java is object-oriented language.
- 6. Nov 26, 2025 WhyJava is Important JAVA is a platform independent on which programmers can be run. • that is, they can be run on many different platforms • e.g. Windows, Mac, Linux, Solaris. • (Platform any hardware or software environment in which a program runs). Write Once Run Anywhere (WORA). Java is different from other programming languages • because a Java program is both compiled and interpreted but in many other languages, the program is either compiled or interpreted. 6
- 7. Nov 26, 20257 Why Java is Important … Trouble with C/C++ language is that they are not portable and are not platform independent languages. Emergence of World Wide Web, which demanded portable programs. Portability and security necessitated the invention of Java.
- 8. Nov 26, 20258 Where JAVA is used • Desktop Applications – Used to build cross-platform software with graphical interfaces. – Frameworks: JavaFX, Swing, AWT. – Example: IDEs like Eclipse and NetBeans are built with Java. • Web Applications – Java is heavily used for server-side (backend) development. – Frameworks: Spring Boot, Hibernate, Struts, Jakarta EE (Java EE). – Examples: Online banking systems, e-commerce websites, government portals. • Mobile Applications – Android apps are primarily written in Java (or Kotlin, which runs on the JVM). – Android SDK uses Java-based APIs.
- 9. Nov 26, 20259 Where JAVA is used… • Enterprise Applications – Used in banking, insurance, logistics, and healthcare industries. – Frameworks: Spring, EJB, Java EE. • Cloud-Based Applications – Java is used for cloud development because it integrates well with modern cloud platforms. – Platforms: AWS, Google Cloud, Azure. • Game Development – Used for 2D/3D games, especially mobile and indie games. – Libraries: LibGDX, jMonkeyEngine. • Embedded Systems / IoT – Java runs on devices with limited resources (e.g., sensors, smart cards, routers). • Smart Card, Robotics
- 10. Nov 26, 202510 JAVA vs C++ JAVA Java is pure oop language. Java is Platform Independent language. Java has automatic garbage collection Java doesn't support pointers Java compiled programs needs JVM application to be installed to execute java programs. C++ C++ supports both procedural and OOP C++ is a Platform dependent language C++ has no automatic garbage collection C++ supports pointers. C++ compiled programs doesn't need any intermediate application to execute C++ programs.
- 11. Nov 26, 202511 JAVA vs C++ JAVA More secure Java doesn't support multiple inheritance Java is most likely to be found in Web and Enterprise applications. • Java Example • File: Simple.java class Simple{ public static void main(String args[]){ System.out.println("Hello Java"); } } C++ Less secure C++ supports multiple inheritance C++ is more likely to be found in System and other low level applications. • C++ Example File: main.cpp #include <iostream> using namespace std; int main() { cout << "Hello C++ Programming"; return 0; }
- 12. Nov 26, 202512 Characteristics of Java • The features of Java are also known as javabuzzwords.
- 13. Nov 26, 202513 Java Is Simple • Java is partially modeled on C++, but greatly simplified and improved. Java Is Object-Oriented • One of the central issues in software development is how to reuse code. • OOP provides great flexibility, modularity, clarity, and reusability through encapsulation, inheritance, and polymorphism. Java Is Distributed • Distributed computing involves several computers working together on a network. • Java is designed to make distributed computing easy.
- 14. Nov 26, 202514 • The programs are compiled into the Java Virtual Machine code called bytecode. • The bytecode is machine-independent and can run on any machine that has a Java interpreter, which is part of the Java Virtual Machine (JVM). Java Is Interpreted Java Is Robust • Robust simply means strong. • Java uses strong memory management. • There are lack of pointers that avoids security problem. • There is automatic garbage collection in java. • There is exception handling and type checking mechanism in java. • All these points make java robust.
- 15. Nov 26, 202515 Java Is Secure • Java is best known for its security. • With Java, we can develop virus-free systems. • Java is secured because: • No explicit pointer, Java Programs run inside a JVM sandbox Java Is Architecture-Neutral • The goal of JAVA is: write once; run anywhere, anytime, forever • With a Java Virtual Machine (JVM), you can write one program that will run on any platform.
- 16. Nov 26, 202516 Java Is Portable • Because Java is architecture neutral, Java programs are portable. • They can be run on any platform without being recompiled. Java's Performance • Java is faster than other traditional interpreted programming languages because Java bytecode is "close" to native code. • Java enables the creation of cross-platform programs by compiling into an intermediate representation called Java bytecode. • This code can be executed on any system that implements the JVM
- 17. Nov 26, 202517 Java Is Multithreaded • A thread is like a separate program, executing concurrently. • We can write Java programs that deal with many tasks at once by defining multiple threads. • The main advantage of multi-threading is that it doesn't occupy memory for each thread. • It shares a common memory area. • Threads are important for multi-media, Web applications, etc. Java Is Dynamic • Java was designed to adapt to an evolving environment. • New code can be loaded on the fly without recompilation. • There is no need for developers to create, and for users to install, major new software versions. • New features can be incorporated transparently as needed.
- 18. Nov 26, 202518 Definition of Java Application, Java Applets Java can be used to create two types of programs: applications and applets. Application: • is a program that runs on your computer, under the operating system of that computer. • independent program (maybe fully compiled, though more likely byte-code compiled and then interpreted) Applet: is an application designed to be transmitted over the Internet executed by a Java-compatible Web browser. Restricted access to machine on which it is run No access to local file
- 19. Nov 26, 202519 Editing, Compiling and Interpreting of a Java program A .class file does not contain code that is native to your processor; it instead contains bytecodes — the machine language of the Java Virtual Machine (Java VM). In the Java programming language, all source code is first written in plain text files ending with the .java extension. Those source files are then compiled into .class files by the javac compiler. • The java launcher tool then runs your application with an instance of the JVM
- 20. Nov 26, 202520 What is Java Bytecode? Java bytecode is the instruction set for the Java Virtual Machine. As soon as a java program is compiled, java bytecode is generated. In more apt terms, java bytecode is the machine code in the form of a .class file. With the help of java bytecode we achieve platform independence in java.
- 21. Nov 26, 202521 What is JVM (Java Virtual Machine) ? JVM is an abstract machine. It is called a virtual machine because it doesn't physically exist. It is a specification that provides a runtime environment in which Java bytecode can be executed. It can also run those programs which are written in other languages and compiled to Java bytecode. Through JVM, the same application is capable of running on multiple platforms as shown in fig:
- 22. Nov 26, 202522 JVM (Java Virtual Machine) The JVM performs the following main tasks: – Loads code, – Verifies code, – Executes code, – Provides runtime environment. i.e. Just-in-Time The main tasks of JVM:
- 23. Nov 26, 202523 Java Development Tools • Java includes many development tools, classes and methods: – Development tools are part of Java Development Kit (JDK) and. – The classes and methods are part of Java Standard Library (JSL), also known as Application Programming Interface (API). JDK constitutes of tools like java compiler, java interpreter and many. API includes hundreds of classes and methods grouped into several packages according to their functionality.
- 24. Nov 26, 202524 Java Runtime Environment (JRE) JRE is an acronym for Java Runtime Environment. The JRE is a set of software tools which are used for developing Java applications. It is used to provide the runtime environment. It is the implementation of JVM. It physically exists. It contains a set of libraries + other files that JVM uses at runtime.
- 25. Nov 26, 202525 JDK (Java Development Kit) JDK is an acronym for Java Development Kit. JDK is a software development environment which is used to develop Java applications and applets. It physically exists. It contains: JRE + development tools. The JDK contains a private JVM and a few other resources such as an interpreter/loader (java), a compiler (javac), an archiver (jar), a documentation generator (Javadoc), etc. to complete the development of a Java Application.
- 26. Nov 26, 202526 Popular Java Editors To write your Java programs, you will need a text editor. There are even more sophisticated IDEs (Integrated Development Environments) available in the market. But for now, you can consider one of the following: – Notepad : On Windows machine, you can use any simple text editor – Netbeans: is an open-source IDE in Java which can be downloaded from http://www.netbeans.org/index.html. – Eclipse: is another free Java IDE for developers and programmers. – Apache NetBeans 27 is the latest major release (as of August 21, 2025) of the Apache NetBeans integrated development environment (IDE) – https://netbeans.apache.org/front/main/download/
- 27. Nov 26, 202527 The First Java Program How to write the simple program of java? To create a simple java program, you need to create a class that contains the main method. Let's understand the requirement first. For executing any java program, you need to: – download the JDK and install it. – Set path of the jdk/bin directory. http://www.javatpoint.com/how-to-set-path-in-java – Create the java program – Compile and run the java program
- 28. Nov 26, 202528 Simple Java program: Example #1 /* This is a simple Java program. Call this file "Example.java". */ public class Example1 { // Your program begins with a call to main(). public static void main(String args[]) { System.out.println("This is a simple Java program."); } } Objective: Learn how to write, compile, and run your first Java program
- 29. Nov 26, 202529 Entering the Program The first thing that you must learn about Java is that the name you give to a source file is very important. For this example, the name of the source file should be Example1.java. Let’s see why. • The Java compiler requires that a source file use the .java filename extension. • As you can see by looking at the program, the name of the class defined by the program is also Example1. • In Java, all code must reside inside a class. • By convention, the name of that class should match the name of the file that holds the program. • Java is case-sensitive. Because capitalization of the filename matches the class name
- 30. Nov 26, 202530 Compiling the Program To compile the Example1 program, execute the compiler, javac, specifying the name of the source file on the command line, as shown here: C:>javac Example1.java When Java source code is compiled, each individual class is put into its own output file named after the class and using the .class extension. E.g the javac compiler creates a file called Example1.class that contains the bytecode version of the program. Java bytecode is the intermediate representation of your program that contains instructions the JVM will execute. Thus, the output of javac is not code that can be directly executed.
- 31. Nov 26, 202531 Run the Program To actually run the program, you must use the Java application launcher, called java. To do so, pass the class name Example1 as a command-line argument, as shown here: C:>java Example When the program is run, the following output is displayed: This is a simple Java program.
- 32. Nov 26, 202532 The First Sample Program-descriptions 1. /*This is a simple Java program. Call this file "Example.java". */ • This is a comment. • Java supports three styles of comments. • This type of comment must begin with /* and end with */. • Anything between these two comment symbols is ignored by the compiler. 2. class Example { • This line uses the keyword class to declare that a new class is being defined. • Example1 is an identifier that is the name of the class. • The entire class definition, including all of its members, will be between the opening curly brace ({) and the closing curly brace (}).
- 33. Nov 26, 202533 Con’ t… 3. // Your program begins with a call to main(). – This is the second type of comment supported by Java. – A single-line comment begins with a // and ends at the end of the line. – As a general rule, programmers use multiline comments for longer remarks and single-line comments for brief, line-by-line descriptions. 4. public static void main(String args[]) { This line begins the main( ) method. As the comment preceding it suggests, this is the line at which the program will begin executing. All Java applications begin execution by calling main( ). Let’s take a brief look at each part now at next slide
- 34. Nov 26, 202534 public keyword – The public keyword is an access specifier, • which allows the programmer to control the visibility of class members. – When a class member is preceded by public, then that member may be accessed by code outside the class in which it is declared. – The opposite of public is private, which prevents a member from being used by code defined outside of its class.) – In this case, main( ) must be declared as public, since it must be called by code outside of its class when the program is started. Con’ t…
- 35. Nov 26, 202535 Static keyword – If we declare any method as static, it is known as the static method. – The core advantage of the static method is that • there is no need to create an object to invoke the static method. – The main method is executed by the JVM, it doesn't require to create an object to invoke the main method. – So it saves memory. Void keyword – The keyword void simply tells the compiler that main( ) does not return a value. Con’ t…
- 36. Nov 26, 202536 main( ) – main( ) is the method called when a Java application begins. – Main is different from main. Because, Java is case-sensitive. – It is important to understand that the Java compiler will compile classes that do not contain a main( ) method. – But java has no way to run these classes. – So, if you had typed Main instead of main, the compiler would still compile your program. – However, java would report an error because it would be unable to find the main( ) method. Con’ t…
- 37. Nov 26, 202537 parentheses – Any information that you need to pass to a method is received by variables specified within the set of parentheses that follow the name of the method. – These variables are called parameters. – If there are no parameters required for a given method, you still need to include the empty parentheses. – In main( ), there is only one parameter – String args[ ] declares a parameter named args, which is an array of instances of the class String. (Arrays are collections of similar objects.) – Objects of type String store character strings. – In this case, args receives any command-line arguments present when the program is executed. Con’ t…
- 38. Nov 26, 202538 opening curly brace { and closing curly brace }. – All of the code that comprises a method will occur between the method’s opening curly brace { and its closing curly brace }. – One other point: main( ) is simply a starting place for your program. – A complex program will have dozens of classes, only one of which will need to have a main( ) method to get things started. – When you begin creating applets—Java programs that are embedded in web browsers—you won’t use main( ) at all, – since the web browser uses a different means of starting the execution of applets. Con’ t…
- 39. Nov 26, 202539 • Valid java main method signature – public static void main(String[] args) – public static void main(String []args) – public static void main(String args[]) – public static void main(String... args) – static public void main(String[] args) – public static final void main(String[] args) – final public static void main(String[] args) Invalid java main method signature public void main(String[] args) static void main(String[] args) public void static main(String[] args) abstract public static void main(Strin g[] args) Con’ t…
- 40. Nov 26, 202540 5. System.out.println("This is a simple Java program."); This line outputs the string “This is a simple Java program.” followed by a new line on the screen. Output is actually accomplished by the built-in println( ) method. In this case, println( ) displays the string which is passed to it. As you will see, println( ) can be used to display other types of information, too. The line begins with System.out. System is a predefined class that provides access to the system, and out is the output stream that is connected to the console. Notice that the println( ) statement ends with a semicolon. • All statements in Java end with a semicolon. Con’ t…
- 41. Nov 26, 202541 Concepts Covered • Basic Java structure (class, main method) • Printing output using System.out.println()
- 42. Nov 26, 202542 Atomic Elements of Java Java programs are a collection of whitespace, identifiers, literals, comments, operators, separators, and keywords. Whitespace: Java is a free-form language. This means that you do not need to follow any special indentation rules. In Java, whitespace is a space, tab, or newline. Identifiers: • Identifier is the name given to variable • Identifiers are used for class names, method names, and variable names. • An identifier may be any descriptive sequence of uppercase and lowercase letters, numbers, or the underscore and dollar-sign characters. • They must not begin with a number. e.g. valid identifier: AvgTemp, count, a4, $test, this_is_ok. • Invalid identifier: 2cout , high-temp, Not/Ok
- 43. Nov 26, 202543 Atomic Elements of Java(2) Literals: • Literals are number, text, or anything that represent a value. • In other words, Literals in Java are the constant values assigned to the variable. E.g. • Left to right, the first literal specifies an integer, floating-point value, ,character constant, and string respectively. • A literal can be used anywhere a value of its type is allowed. Comments: there are three types of comments defined by Java – single-line- begins with a // and ends at the end of the line. – Multiline- begin with /* and end with */. – documentation comment- begins with a /** and ends with a */. • This type of comment is used to produce an HTML file that documents your program.
- 44. Nov 26, 202544 Atomic Elements of Java(3) • Separators: In Java, there are a few characters that are used as separators. The most commonly used separator in Java is the semicolon.
- 45. Nov 26, 202545 The Java Keywords There are 50 keywords currently defined in the Java language (see Table ) These keywords, combined with the syntax of the operators and separators, form the foundation of the Java language. These keywords cannot be used as names for a variable, class, or method. The keywords const and goto are reserved but not used. Java reserves the following: true, false, and null. These are values defined by Java. But you may not use these words for the names of variables, classes, and so on.
- 46. Nov 26, 202546 Data Types, Variables, and Arrays Java supports several types of data to declare variables and to create arrays. Java is a statically-typed programming language. It means, all variables must be declared before its use. In java, every variable has a type, every expression has a type, and every type is strictly defined. all assignments, whether explicit or via parameter passing in method calls, are checked for type compatibility. There are no automatic conversions of conflicting types as in some languages. The Java compiler checks all expressions and parameters to ensure that the types are compatible. Any type mismatches are errors that must be corrected before the compiler will finish compiling the class.
- 47. Nov 26, 202547 Data Types in Java There are two types of data types in Java: i. Primitive data types & ii. Non-primitive data types. Data types specify the different sizes and values that can be stored in the variable.
- 48. Nov 26, 202548 The Primitive Types Primitive data types are used by programmers when creating variables in their program. Java defines eight primitive types of data: byte, short, int, long, char, float, double, and boolean. These can be put in four groups: – Integers: This group includes byte, short, int, and long, which are for whole-valued signed numbers. – Floating-point numbers: This group includes float and double, which represent numbers with fractional precision. – Characters: This group includes char, which represents symbols in a character set, like letters and numbers. – Boolean: This group includes boolean, which is a special type for representing true/false values.
- 49. Nov 26, 202549 Integers Java defines four integer types: byte, short, int, and long. All of these are signed, positive and negative values. Java does not support unsigned, positive-only integers. Many other computer languages support both signed and unsigned integers. The Java run-time environment is free to use whatever size it wants, as long as the types behave as The width and ranges of these integer types vary widely, as shown in this table:
- 50. Nov 26, 202550 Byte The smallest integer type is byte. It is useful in saving memory for large arrays, it is a signed two’s complement integer. It has a size of 8 bits with a range from -128 to 127. • Example // Java program to demonstrate byte data type in Java class byte{ public static void main(String args[]){ byte a = 126; System.out.println(a); } }
- 51. Nov 26, 202551 Short • Short is similar to byte and is used to save memory in large arrays. • It is also a two’s complement with a size of 16 bit and ranges from -32,768 to 32,767 (inclusive). • Examples of short variable declarations: // Java program to demonstrate short data type in Java class short{ public static void main(String args[]){ short a = 56; System.out.println(a); } }
- 52. Nov 26, 202552 int The most commonly used integer type is int. It is a signed 32-bit type that has a range from –2,147,483,648 to 2,147,483,647. Example- // Java program to demonstrate int data type in Java class int{ public static void main(String args[]) { int a = 56; System.out.println(a); } }
- 53. Nov 26, 202553 long • The range of a long is quite large • long is a signed 64-bit type and ranges from -2^64 to 2^63-1. • Is useful for those occasions where an int type is not large enough to hold the desired value. • Example: // Java program to demonstrate long data type in Java class long { public static void main(String args[]) { long a = 100000L; System.out.println(a); } }
- 54. Nov 26, 202554 long: Example#2 // Compute distance light travels using long variables. class Light { public static void main(String args[]) { int lightspeed; long days; long seconds; long distance; // approximate speed of light in miles per second lightspeed = 186000; days = 1000; // specify number of days here • seconds = days * 24 * 60 * 60; // convert to seconds distance = lightspeed * seconds; // compute distance System.out.print("In " + days); System.out.print(" days light will travel about "); System.out.println(distance + " miles."); } } . • This program generates the following output: • In 1000 days light will travel about 16070400000000 miles. • Clearly, the result could not have been held in an int variable
- 55. Nov 26, 202555 Floating-Point Types Floating-point numbers, also known as real numbers, are used when evaluating expressions that require fractional precision. For e.g. calculations such as square root, or transcendental such as sine and cosine, result in a value whose precision requires a floating-point type. There are two kinds of floating-point types, float and double, which represent single- and double-precision numbers, respectively. Their width and ranges are shown here:
- 56. Nov 26, 202556 float • The type float specifies a single-precision value that uses 32 bits of storage. • Variables of type float are useful when you need a fractional component, but don’t require a large degree of precision. • For example, a float can be useful when representing dollars and cents. • Example float variable declarations: – float hightemp, lowtemp; // Java program to demonstrate float data type in Java class float { public static void main(String args[]) { float a = 4.5541132f; System.out.println(a); } }
- 57. Nov 26, 202557 Double Double precision, as denoted by the double keyword, uses 64 bits to store a value. Used to manipulate large-valued numbers. Double precision is actually faster than single precision All transcendental math functions, such as sin( ), cos( ), and sqrt( ), return double values. Ex: double variables to compute the area of a circle: // Compute the area of a circle. class Area { public static void main(String args[]) { double pi, r, a; r = 10.8; // radius of circle pi = 3.1416; // pi, approximately a = pi * r * r; // compute area System.out.println("Area of circle is " + a); } }
- 58. Nov 26, 202558 Characters In Java, the data type used to store characters is char. char in Java is not the same as char in C or C++. In C/C++, char is 8 bits wide. This is not the case in Java. In Java char is a 16-bit type. Instead, Java uses Unicode to represent characters. The range of a char is 0 to 65,536. There are no negative chars. The standard set of characters known as ASCII still ranges from 0 to 127 .
- 59. Nov 26, 202559 Characters… • Here is a program that demonstrates char variables: – // Demonstrate char data type. class CharDemo { public static void main(String args[]) { char ch1, ch2; ch1 = 88; // code for X ch2 = 'Y'; System.out.print("ch1 and ch2: "); System.out.println(ch1 + " " + ch2); } } – This program displays the following output: ch1 and ch2: X Y • Notice that ch1 is assigned the value 88, which is the ASCII (and Unicode) value that corresponds to the letter X.
- 60. Nov 26, 202560 Booleans It can represent only one bit of information, i.e. true or false for logical values. This is the type returned by all relational operators, as in the case of a < b. boolean. They cannot be changed either explicitly or implicitly, but the programs for conversion can be easily written. • // A Java program to demonstrate boolean data type class boolean{ public static void main(String args[]) { boolean b = true; if (b == true) System.out.println("true"); } }
- 61. Nov 26, 202561 Non-primitive data types Non-primitive data types are created by programmers. They are not predefined in Java like primitive data types. When we define a variable of non-primitive data types, • it references a memory location where data is stored in the heap memory. • i.e, it references to a memory where an object is actually placed. Therefore, the variable of a non-primitive data type is also called reference data types or object reference variable. The stack holds a pointer to the object on the heap.
- 62. Nov 26, 202562 Non-primitive data types(2) In Java programming, all non-primitive data types are simply called objects which are created by instantiating a class. Key points: • The default value of any reference variable is null. • Whenever you will pass a non-primitive data type to a method, you are actually passing an address of that object where data is stored. Some types of non-primitive data types in Java as follows: Class, Array & String
- 63. Nov 26, 202563 Class When a class is defined, it can then be used as a data type. The variable declaration for a non-primitive data types is the same as for a primitive data type. In primitive data type, we declare like this: int p=100; // p is an int data type which can store the only integer value. In non-primitive data types, an object reference variable is declared just like we declare a primitive variable. School sc; In this example, • School is the name of a class & • "sc" is the name of a reference variable. No object has yet been created.
- 64. Nov 26, 202564 Class… We create an object of a class using the new keyword. Ex: the following statement creates an object of a class School and assigns it to the reference variable "sc". sc=new School() where School ➞ name of the class. sc ➞ Object reference. An object reference is a variable which stores the addresses of the objects in the computer's memory. An object represents an instance through which we can access member. School() ➞ Constructor of the class. The constructor of a class which is generally used to initialize an object. new ➞ is a special keyword that creates the memory in the java.
- 65. Nov 26, 202565 Class(3) Now an object of class School lives on the heap and the object reference variable "sc" refers to it. The declaration of an object reference variable, object creation, and initialization of reference variable can also be done in a single line statement like this: School sc=new School(); Let see Simple example program in the next slide, we will get address of the object as output which is stored in object reference variable on the stack memory.
- 66. Nov 26, 202566 Class- Example #1 public class School{ // Declaration of a primitive variable. String name="RSVM"; // Instance variable public static void main(String[] args){ // Creating an object of the class. School sc=new School(); // sc is Non-primitive data type i.e Object REFERENCE. // Print the address of the memory location of an Object. System.out.println(sc); // Now we cannot access instance variable directly. We call instance variable by using reference variable sc which is created above. System.out.println(sc.name); } } Output: School@1db9742 RSVM
- 67. Nov 26, 202567 Memory Allocation of Object & Object Reference Variable From e.g above. • In Java, a variable whose type is a class, does not actually hold an object. • Actually, it holds the memory location of an object. • The object itself is stored elsewhere. In the this figure, you can see the memory location of object and object reference variable of above program.
- 68. Nov 26, 202568 Memory Allocation of Object & Object Reference Variable… • As shown in the previous slide figure, – Object reference variable 'sc' contains the address '1db9742' which is the address of the memory location of the object on the heap. – On this address, data is stored inside the heap memory. – Creating an object means storing data in memory. – So, we can say that "sc" variable does not contain the object. – It refers to the object.
- 69. Nov 26, 202569 Array An array in java is an object which is used to store multiple variables of the same type. • i.e. a structure that can hold multiple values –but all the values must be of the same type. An array is declared by specifying the data type of the values it will hold, followed by [] to indicate that it is an array. That type can be a primitive data type or an object type. The example of declaring an array variable of primitive data type int is as follows: int [ ] scores; byte[] arrayOfBytes; //array of values of type byte byte[][] arrayOfArrayOfBytes ; //an array of arrays of byte[] type
- 70. Nov 26, 202570 Example #1: Array Customer[] arrayOfCustomers; //array of objects of the class Customer In the above Ex, we can say that byte[] and Customer[] are types. After an array has been declared, it must be created. Because an array is actually an object in Java, the new keyword must be used to create the array (new is used to create any object). The size of the array i.e. how many elements it can hold must be specified. For example, to declare an array called 'arrayOfBytes' that will hold 1024 bytes and to create it: byte[] arrayOfBytes = new byte[1024]; To declare an array of 50 strings: String[] lines = new String[50];
- 71. Nov 26, 202571 Assigning Values to Arrays When the array is created, each of the values in the array is initialized to the corresponding default value (i.e. array default value is null). The null literal can be used to indicate that an object that is of a reference data type does not yet exist i.e. to initialize an object to be empty or null. Ex: char[] password = null; • Literal values can also be used to specify the values of an array, • For Ex: String[] responses = new String[2]; responses[0] = "Yes"; responses[1] = "No"; //to read the elements System.out.println ("The answer should be " + responses[0] + " or " + responses[1] + "!");
- 72. Nov 26, 202572 Assigning Values to Arrays… An array can also be initialized by the following syntax • int[] someNumbers = {1, 2, 3, 4} **The element values are separated by commas. The new keyword is not used – but the object is implicitly created. The length of this array is now 4 The statement above could also be written as: int[] someNumbers = new int[4]; someNumbers[0] = 1; someNumbers[1] = 2; someNumbers[2] = 3; someNumbers[3] = 4;
- 73. Nov 26, 202573 Array of Objects Unlike traditional array which store values like string, integer, Boolean, etc. array of objects stores objects. The array elements store the location of reference variables of the object. Syntax: Class obj[]= new Class[array_length] For Ex, we use a class Student containing a single instance variable mark. class Student { int marks; }
- 74. Nov 26, 202574 Array of Objects… An array of objects is created just like an array of primitive type data items in the following way. Student[] studentArray = new Student[7]; The above statement: • creates the array which can hold references to seven Student objects. • It doesn't create the Student objects themselves. • They have to be created separately using the constructor of the Student class. • The studentArray contains seven memory spaces in which the address of seven Student objects may be stored. If we try to access the Student objects even before creating them, run time errors would occur. The Student objects have to be instantiated using the constructor of the Student class and their references should be assigned to the array elements in the following way. studentArray[0] = new Student();
- 75. Nov 26, 202575 String A string is a very important topic in the world of programming languages. For e.g. C, C++, Java, Python, or in any application whether it is a Java based or Python based, the most commonly used object is a string only. For example, • when you visit a bank to open an account then you are asked for information such as name, an address like house number, street, city, state, identification marks. The information you provided is in the form of an ordered sequence of characters and symbols. This ordered and sequence of characters and symbols is nothing but a string in java.
- 76. Nov 26, 202576 What is String in Java? Generally, String is a sequence of characters. But in Java, String is an object that represents a sequence of characters. For example, "Pencil" is a string of 6 characters. String class is used to create a string object. String class is an immutable class which is present in java.lang package. But in Java, all classes are also considered as a data type. So, you can also consider a string as a data type. Immutable means it cannot be changed.
- 77. Nov 26, 202577 What is String in Java?... Basically, memory in Java is divided into three parts such as : heap, stack, and String Pool. The string is so important in Java that it has dedicated memory location. What string pool does it? • Whenever a string gets repeated it does not allocate the new memory for that string. • It uses the same string by pointing a reference to it for saving memory
- 78. Nov 26, 202578 How to create a string object in Java? To handle the string data in Java, we need the objects of the string class. Basically, there are three ways to create a string object in Java. •By string literal •By new keyword •By converting character arrays into strings
- 79. Nov 26, 202579 String literal in Java String literal in Java is created by using double quotes. For example: String s ="Hello"; The string literal is always created in the string constant pool. In Java, String constant pool is a special area which is used for storing string objects. Whenever you create a string literal, the JVM checks the string constant pool first. • If the string already exists in the string constant pool, no new string object will be created in the string pool by the JVM. The JVM uses the same string object by pointing a reference to it to save memory. But if the string does not exist in the string pool, JVM creates a new string object and placed in the pool.
- 80. Nov 26, 202580 String literal in Java: Example String s1="Hello"; String s2="Hello"; They have been represented in the memory as below given figure. In the above example, when the JVM will execute the first statement, it will not find any string with the value "Hello" in the string constant pool. So, it will create an object in string pool and stores the string "Hello" in that object as shown in the figure. This object is referenced by the variable s1
- 81. Nov 26, 202581 String literal in Java: Example… When JVM will execute the second statement, it will first check the string constant pool to know whether the object with the same content is already available there or not. Since string with the value "Hello" is already available in the string pool. So, JVM will not create a new string object in the pool and address of the available object will assign to reference variable s2. i.e it will point a reference variable s2 to the old existing object as shown in the figure.
- 82. Nov 26, 202582 By new Keyword The second way of creating an object to string class is by using the new operator. It is just like creating an object of any class. It can be declared as follows: String s=new String("Hello"); Whenever we will create an object to the string class using the new operator, In this case, JVM will create two objects. • First, it will create an object in the heap area and stores the string "Hello" into the object and will point a reference variable s to the object in the heap. It can be seen in figure.
- 83. Nov 26, 202583 Summary: primitive vs Non- primitive data type Primitive Data Type predefined in Java variables can store only one value at a time All the data stored on the stack. Non- primitive data type created by programmers. i.e. They are not predefined in Java. we can store multiple values either the same type or different type or both. the stack holds a pointer to the object on the heap.
- 84. Nov 26, 202584 Java Variables The variable is the basic unit of storage in a Java program. A variable is a container which holds the value while the java program is executed. In other words, it is a name of memory location. It is a combination of "vary + able" that means its value can be changed. A variable is defined by the combination of an identifier, a type, and an optional initializer. In addition, all variables have a scope, which defines their visibility, and a lifetime.
- 85. Nov 26, 202585 Declaring a Variable In Java, all variables must be declared before they can be used. The basic form of a variable declaration is shown here: type identifier [ = value][, identifier [= value] ...] ; • The type is one of Java’s atomic types, or the name of a class or interface. • The identifier is the name of the variable. • You can initialize the variable by specifying an equal sign and a value. initialization expression must result in a value of the same (or compatible) type as that specified for the variable. To declare more than one variable of the specified type, use a comma separated list.
- 86. Nov 26, 202586 Example: Variable Declaration • Examples of variable declarations of various types. • Note that some include an initialization. – int a, b, c; // declares three ints, a, b, and c. int d = 3, e, f = 5; // declares three more ints, initializing // d and f. byte z = 22; // initializes z. double pi = 3.14159; // declares an approximation of pi. char x = 'x'; // the variable x has the value 'x'. – FirstJava myObject = new FirstJava (); – int sum = 0;
- 87. Nov 26, 202587 Rule of Variable Declaration A variable must be given an explicit name and data type. The name must be a legal identifier • A legal identifier begins with a letter and can consist of alpha-numeric characters (letters and digits) and can also include the underscore (_) and dollar ($) characters. Identifiers are case-sensitive and cannot have spaces in them. variable names begin with a lowercase letter while class names begin with an uppercase letter. • If a variable or class name has more than one word in it, the words are joined together and the first letter of each word after the first will begin with a capital letter. A variable must be initialized before it is used. E.g. int x=0;
- 88. Nov 26, 202588 Sample java code that uses a variable public class Sample { public static void main(String[] args) { int num = 10; System.out.println("The number is: "+ num); } } When we run this, we get the output: The number is: 10 int num = 10; • int is the type of the variable declared. • Integers are whole numbers (no decimal point) and can either be negative, positive, or zero. num is the name of the variable. = is the assignment operator. • It tells to store the value 10 to the variable num. • Hence, after the statement, num gets the value of 10.
- 89. Nov 26, 202589 Different variables refers to different data Consider this example: public class Sample { public static void main(String[] args) { int a = 50; int b = 75; System.out.println("The first number is: "+ a); System.out.println("The second number is: "+ b); } } The output of this is: • The first number is: 50 • The second number is: 75 a is a variable of type int and assigned a value of 50 b is another variable of type int and assigned a value of 75 a and b are different from each other because they have different names
- 90. Nov 26, 202590 Manipulating variables The value stored to a variable can be updated. Consider this example: public class Sample { public static void main(String[] args) { int num = 20; num = num + 5; System.out.println("The result is: "+ num); } } • The output of this is: The result is: 25 num is a variable of type int and assigned a value of 20 num's value is updated with the statement num = num + 5 num + 5 is evaluated first num is 20, by adding 5 the outcome is 25 25 is then assigned to num after the statement, num gets the value 25
- 91. Nov 26, 202591 A Second java Program This example shows how a variable is declared and how it is assigned a value. call this file /* Call this file "Example2.java". */ public class Example2 { public static void main(String args[]) { int num; // this declares a variable called num num = 100; // this assigns num the value 100 System.out.println("This is num: " + num); num = num * 2; System.out.print("The value of num * 2 is "); System.out.println(num); } } • When you run this program, you will see the following output • This is num: 100 • The value of num * 2 is 200
- 92. Nov 26, 202592 Let’s take a close look at why this output is generated. 1st . int num; // this declares a variable called num 2nd . num = 100; // this assigns num the value 100. 3rd . The code outputs the value of num preceded by the string “This is num:”. System.out.println("This is num: " + num); • In this statement, the plus sign causes the value of num to be appended to the string that precedes it, and then the resulting string is output. • (Actually, num is first converted from an integer into its string equivalent and then concatenated with the string that precedes it. • Using the + operator, you can join together as many items as you want within a single println( ) statement.
- 93. Nov 26, 202593 4th . assigns num the value of num times 2. * operator to indicate multiplication. After this line executes, num will contain the value 200. 5th . Here are the next two lines in the program: System.out.print("The value of num * 2 is "); System.out.println(num); Let’s take a close look at why this output is generated...
- 94. Nov 26, 202594 Several new things are occurring here. First, the built-in method print( ) is used to display the string “The value of num * 2 is ”. • This string is not followed by a newline. • This means that when the next output is generated, it will start on the same line. • The print( ) method is just like println( ), except that it does not output a newline character after each call. Now look at the call to println( ). Notice that num is used by itself. Both print( ) and println( ) can be used to output values of any of Java’s built-in types. Let’s take a close look at why this output is generated…
- 95. Nov 26, 202595 Types of variables in java There are three types of variables in java: local, instance and static. 1. Local Variable – Local variables are visible only within the declared method, constructor, or block. – Local variables are created when the method, constructor or block is entered and the variable will be destroyed once it exits the method, constructor, or block. – Access modifiers cannot be used for local variables. – Local variables are implemented at stack level internally. – There is no default value for local variables, so local variables should be declared and an initial value should be assigned before the first use.
- 96. Nov 26, 202596 Local Variable: Example #1 public class Test { public void pupAge() { int age = 0; age = age + 7; System.out.println("Puppy age is : " + age); } public static void main(String args[]) { Test test = new Test(); test.pupAge(); } } Here, age is a local variable. This is defined inside pupAge() method and its scope is limited to only this method. • This will produce the following result − • Output Puppy age is: 7
- 97. Nov 26, 202597 Local Variable: Example #2 • Following example uses age without initializing it, so it would give an error at the time of compilation. public class Test { public void pupAge() { int age; age = age + 7; System.out.println("Puppy age is : " + age); } public static void main(String args[]) { Test test = new Test(); test.pupAge(); } } • This will produce the following error while compiling it − – OutputTest.java:4:variable number might not have been initializedage = age + 7; ^1 error
- 98. Nov 26, 202598 2. Instance Variables An instance variable is a variable that's bound to the object itself. are declared in a class, but outside a method, or any block. Instance variables are available to any method bound to an object instance. Instance variables are created when an object is created with the use of the keyword 'new' and destroyed when the object is destroyed. Access modifiers can be given for instance variables. The instance variables are visible for all methods, constructors and block in the class. Normally, it is recommended to make these variables private (access level).
- 99. Nov 26, 202599 2. Instance Variables… Instance variables have default values. E.g. number, boolean & objet reference default value 0, false and null respectively. Values can be assigned during the declaration or within the constructor. Instance variables can be accessed directly by calling the variable name inside the class. However, within static methods (when instance variables are given accessibility), they should be called using the fully qualified name. ObjectReference.VariableName Example #1: Public class TestClass{ public String StudentName; public int age; }
- 100. Nov 26, 2025100 Instance Variables: Example#2 public class Employee { // this instance variable is visible for any child class. public String name; // salary variable is visible in Employee class only. private double salary; // The name variable is assigned in the constructor. public Employee (String empName) { name = empName; } // The salary variable is assigned a value. public void setSalary(double empSal) { salary = empSal; } // This method prints the employee details. public void printEmp() { System.out.println("name : " + name ); System.out.println("salary :" + salary); } public static void main(String args[]) { Employee empOne = new Employee("Abdi"); empOne.setSalary(1000); empOne.printEmp(); } }
- 101. Nov 26, 2025101 iii. Class/Static Variables Class variables also known as static variables are declared with the static keyword in a class, but outside a method, constructor or a block. There would only be one copy of each class variable per class, regardless of how many objects are created from it. If changes are made to that variable, all other instances will see the effect of the changes. Static variables are rarely used other than being declared as constants. Constants are variables that are declared as public/private, final, and static. Constant variables never change from their initial value. Static variables are stored in the static memory. Default values are same as instance variables.
- 102. Nov 26, 2025102 iii. Class/Static Variables… Values can be assigned during the declaration or within the constructor. Additionally, values can be assigned in special static initializer blocks. Static variables can be accessed by calling with the class name ClassName.VariableName. When declaring class variables as public static final, then variable names (constants) are all in upper case. If the static variables are not public and final, the naming syntax is the same as instance and local variables. Example#1 public class Product { public static int Barcode; }
- 103. Nov 26, 2025103 Class/Static Variable: Example#2 public class Employee { // salary variable is a private static variable private static double salary; // DEPARTMENT is a constant public static final String DEPARTMENT = "Development "; public static void main(String args[]) { salary = 1000; System.out.println(DEPARTMENT + "average salary:" + salary); } } • This will produce the following result − • Output • Development average salary:1000
- 104. Nov 26, 2025104 Variables Constants In Java, a variable declaration can begin with the final keyword. This means that once an initial value is specified for the variable, that value is never allowed to change. This is the equivalent of a constant in C++ or other languages. e.g. to declare a constant for the value of the maximum number of students allowed on a course: final int MAX_STUDENTS = 100; • The variable can be initialised after the declaration – but if the declaration includes the final modifier, the initial value is the last value that can be assigned. final int MAX_STUDENTS; MAX_STUDENTS = 100; • Note that the convention in Java programming is to use all uppercase letters for constant names, • Underscores are used to separate the words if there is more than one word in the constant's name.
- 105. Nov 26, 2025105 What is Java Packages? Java applications which users write are made up of classes. When the number of classes grows, it tends to be difficult to manage. To solve this, Java allows developers to organize the classes in Java applications using packages. A package in Java is used to group related classes. Think of it as a folder in a file directory. We use packages to avoid name conflicts, and to write a better maintainable code. To create a package simply includes a package command as the first statement in a Java source file. Any classes declared within that file will belong to the specified package. The package statement defines a name space in which classes are stored. If you omit the package statement, the class names are put into the default package, which has no name.
- 106. Nov 26, 2025106 How to create Java Packages(2) General form of the package statement: package pkg; Here, pkg is the name of the package. For example, the following statement creates a package called MyPackage. package MyPackage;
- 107. Nov 26, 2025107 Java uses file system directories to store packages. For example, the .class files for any classes you declare to be part of MyPackage must be stored in a directory called MyPackage. Remember that case-sensitive, and the directory name must match the package name exactly. Packages are divided into two categories: i. Built-in Packages (packages from the Java API) ii. User-defined Packages (create your own packages) How Java Store Package
- 108. Nov 26, 2025108 The Java API is a library of prewritten classes that are free to use, included in the Java Development Environment. The library contains components for managing input, database programming, and much much more. The library is divided into packages and classes. Meaning: – you can either import a single class (along with its methods and attributes), or – a whole package that contain all the classes that belong to the specified package. To use a class or a package from the library, you need to use the import keyword. i. Built-in Packages
- 109. Nov 26, 2025109 Import a Class Application developers use Java API classes when writing programs. To include these classes into programs, we use the import statement. The purpose of the import statement is : o to let the compiler know that the program is using a class that’s defined by the Java API. The import statements must appear at the beginning of the class file, before any class declarations. – This occurs immediately following the package statement (if it exists) and before any class definitions.
- 110. Nov 26, 2025110 You can include as many import statements as are necessary to import all the classes used by your program. • This is the general form of the import statement: import pkg1[.pkg2].classname; // Import a single class import pkg1[.pkg2].*; // Import the whole package • Here, – pkg1 is the name of a top-level package, and – pkg2 is the name of a subordinate package inside the outer package separated by a dot (.). Import a Class(2)
- 111. Nov 26, 2025111 Note: There is no practical limit on the depth of a package hierarchy, except that imposed by the file system. Finally, you specify either an explicit classname or a star (*). Star (*) means you can import all the classes in a particular package by listing the package name followed by an asterisk wildcard, like this: This code fragment shows both forms in use: import java.util.Scanner; import java.io.*; • Example: import java.util.Scanner; – In this e.g, java.util is a package, while Scanner is a class of the java.util package. Import a Class(3)
- 112. Nov 26, 2025112 Java User Input (Scanner) The Scanner class is used to get user input, and it is found in the java.util package. To use the Scanner class, create an object of the class and use any of the available methods found In the Scanner class documentation. For example, we will use the nextLine() method, which is used to read Strings:
- 113. Nov 26, 2025113 Example#1 import java.util.Scanner; // Import the Scanner class class MyClass { public static void main(String[] args) { // Create a Scanner object Scanner myObj = new Scanner(System.in); System.out.println("Enter username"); // Read user input String userName = myObj.nextLine(); // Output user input System.out.println("Username is: " + userName); } }
- 114. Nov 26, 2025114 Input Types In the e.g above, We used the nextLine() method, which is used to read Strings. To read other types, look at the table: Method Description nextBoolean() Reads a boolean value from the user nextByte() Reads a byte value from the user nextDouble() Reads a double value from the user nextFloat() Reads a float value from the user nextInt() Reads a int value from the user nextLine() Reads a String value from the user nextLong() Reads a long value from the user nextShort() Reads a short value from the user
- 115. Nov 26, 2025115 Ex #2: different methods to read data of various types: package inputuser; import java.util.Scanner; public class InputUser { public static void main(String[] args) { // TODO code application logic here Scanner sc=new Scanner(System.in); System.out.print("Enter your name:"); // String input String userName= sc.nextLine(); System.out.print("Enter your age:"); // Numerical input int age = sc.nextInt(); System.out.print("Enter salary:"); double salary = sc.nextDouble(); System.out.println("Your name is:"+ userName); System.out.println("Your age is:"+ age); System.out.println("Your salary:"+ salary); } }
- 116. Nov 26, 2025116 ii. User-defined Packages To create your own package, you need to understand that Java uses a file system directory to store them. Just like folders on your computer: Example └── root └── mypack └── MyPackageClass.java
- 117. Nov 26, 2025117 To create a package, use the package keyword: MyPackageClass.java package mypack; class MyPackageClass { public static void main(String[] args) { System.out.println("This is my package!"); } } Ex #1: Create package
- 118. Nov 26, 2025118 Run Example 1st . Save the file as MyPackageClass.java, and compile it: C:UsersYour Name>javac MyPackageClass.java 2nd . Then compile the package: C:UsersYour Name>javac -d . MyPackageClass.java • This forces the compiler to create the "mypack" package.
- 119. Nov 26, 2025119 Con’t… The -d keyword specifies the destination for where to save the class file. You can use any directory name, like c:/user (windows), or, if you want to keep the package within the same directory, you can use the dot sign ".", like in the example above. Note: The package name should be written in lower case to avoid conflict with class names. When we compiled the package in the example above, a new folder was created, called "mypack".
- 120. Nov 26, 2025120 Con’t… 3rd . To run the MyPackageClass.java file, write the following: C:UsersYour Name>java mypack.MyPackageClass • The output will be: This is my package!
- 121. Nov 26, 2025121 Type Conversion and Casting Sometimes, you need to convert numeric data of one type to another. For example, you might need to convert a double value to an integer, or vice versa. Some conversions can be done automatically. Others are done using a technique called casting.
- 122. Nov 26, 2025122 Casting A cast is simply an explicit type conversion. Casting is similar to conversion, but isn’t done automatically. Cast is used to create a conversion between two incompatible types. When you use casting, you run the risk of losing information. • For example, a double can hold larger numbers than an int. • But, an int can’t hold the fractional part of a double. • As a result, if you cast a double to an int, you run the risk of losing data or accuracy. • For example, 3.1415 become 3.
- 123. Nov 26, 2025123 Types of casting • In Java, there are two types of casting: i. Widening Casting (automatically) ii. Narrowing Casting (manually)
- 124. Nov 26, 2025124 i. Widening or Automatic Type Conversion Widening conversion takes place when two data types are automatically converted. This happens when: • The two data types are compatible. • When we assign value of a smaller data type to a bigger data type i.e. converting a smaller type to a larger type size byte -> short -> int -> long -> float -> double For Example ; the int type is always large enough to hold all valid byte values, so no explicit cast statement is required.
- 125. Nov 26, 2025125 i. Widening or Automatic Type Conversion… For widening conversions, • the numeric types, including integer and floating-point types, are compatible with each other. • But no automatic conversion is supported from numeric type to char or boolean. • Also, char and boolean are not compatible with each other.
- 126. Nov 26, 2025126 Example #1: Widening conversion (int to double) public class MyClass { public static void main(String[] args) { int a = 9; double d = a; // Automatic casting: int to double System.out.println(a); // Outputs 9 System.out.println(d) // Outputs 9.0 } }
- 127. Nov 26, 2025127 ii. Narrowing or Explicit Conversion converting a larger type to a smaller size type. This is useful for incompatible data types where automatic conversion cannot be done. In narrowing conversion, you use a cast operator, which is simply the name of a primitive type in parentheses placed before the value you want to cast. • The general syntax is: variable = (data-type) value • Here, data-type specifies the desired type to convert the specified value to.
- 128. Nov 26, 2025128 ii. Narrowing or Explicit Conversion… For e.g , the following fragment casts an int to a byte. If the integer’s value is larger than the range of a byte, it will be reduced modulo (the remainder of an integer division by the) byte’s range. – int a = 100; – byte b = (byte) a; A different type of conversion will occur when a floating-point value is assigned to an integer type: truncation. Thus, when a floating-point value is assigned to an integer type, the fractional component is lost. if the size of the whole number component is too large to fit into the target integer type, then that value will be reduced modulo the target type’s range.
- 129. Nov 26, 2025129 Narrowing or Explicit Conversion: Example#1 public class MyClass { public static void main(String[] args) { double d= 9.78; int a = (int) d; // Manual casting: double to int System.out.println(d); // Outputs 9.78 System.out.println(a); // Outputs 9 } }
- 130. Nov 26, 2025130 Narrowing or Explicit Conversion: Example#2 //Java program to illustrate explicit type conversion class Test { public static void main(String[] args) { double d = 100.04; //explicit type casting long l = (long)d; //explicit type casting int i = (int)l; System.out.println("Double value "+d); //fractional part lost System.out.println("Long value "+l); //fractional part lost System.out.println("Int value "+i); } } Output: Double value 100.04 Long value 100 Int value 100
- 131. Nov 26, 2025131 String to Number Converting a primitive value to a string value is pretty easy. But converting a string value to a primitive is a little more complex, because it doesn’t always work. For example, if a string contains the value 10, you can easily convert it to an integer. But if the string contains “thirty-two”, you can’t. • To convert a string to a primitive type, you use a parse method of the appropriate wrapper class (see next page table ).
- 132. Nov 26, 2025132 String to Number …. Wrapper class Parse Method Example Integer parseInt(String) int x = Integer.parseInt(“100”); Short parseShort(String) short x = Short.parseShort(“100”); Long parseLong(String) long x = Long.parseLong(“100”); Byte parseByte(String) byte x = Byte.parseByte(“100”); Float parseFloat(String) float x = Float.parseFloat (“19.95”); Double parseDouble(String) double x = Double.parseDouble(“19.95”); Boolean parseBoolean(String) boolean x = Boolean.parseBoolean(“true”);
- 133. Nov 26, 2025133 For example, to convert a string value to an integer • For example, to convert a string value to an integer, you use statements like this: String s = “10”; int x = Integer.parseInt(s);
- 134. Nov 26, 2025134 Operator An operator is a special symbol or keyword that’s used to designate a mathematical operation or some other type of operation that can be performed on one or more values, called operands. In all, Java has about 40 different operators. Most of its operators can be divided into the following groups: Unary, arithmetic, bitwise, relational, and Logical etc.
- 135. Nov 26, 2025135 Unary Operators The unary operators require only one operand; they perform various operations as shown in table below Operator Description + Unary plus operator; indicates positive value (numbers are positive without this still) - Unary minus operator; negates an expression ++ Increment operator; increments a value by 1 -- Decrement operator; decrements a value by 1 ! Logical complement operator; inverts the value of a boolean
- 136. Nov 26, 2025136 Unary Operators: Example public static void main(String[] args) { int result = +1; // result is now 1 result--; // result is now 0 result++; // result is now 1 result = -result; // result is now -1 boolean success = false; boolean tt = !success; // true }
- 137. Nov 26, 2025137 Arithmetic Operators Arithmetic operators are used in mathematical expressions in the same way that they are used in algebra. The following table lists the arithmetic operators:
- 138. Nov 26, 2025138 Basic Arithmetic Operators Java supports the standard arithmetic operators for all integer and floating-point numbers. These are: + (addition), - (subtraction), * (multiplication), / (division), % (modulo). All of these are binary operators i.e. they take two operands and the operator appears between the two operands (this is called infix notation), as follows: Operand1 operator operand2 • The operands of the arithmetic operators must be of a numeric type.
- 139. Nov 26, 2025139 Basic Arithmetic Operators(2) subtraction operator – used as a unary operator – when it is placed in front of a number e.g. –5. – When used in this way, it effectively multiplies the single operand by –1. addition operator • used to concatenate two strings. • If either one of the two operands is a string, then the other one is converted to a string and the strings are concatenated.
- 140. Nov 26, 2025140 Example: Additional operator the following code in a main method to see the addition operator operating on numbers and on strings. – System.out.println (3+4); //prints out 7 – System.out.println ("The value is: " + 4); //prints out 'The value is: 4' – System.out.println ("The value is: " + 3 + 4); //prints out 'The value is: 34', because there is at least one string operand – System.out.println ("The value is: " + (3+4)); //prints out 'The value is 7' – because the parentheses indicate that the sum of 3+4 is evaluated first, resulting in the value 7
- 141. Nov 26, 2025141 Basic Arithmetic Operators(3) Division operator divides the first operand by the second e.g. 12/4 evaluates to 3. If both operands are integers, the result is an integer and any remainder is lost. If you want to do division and get the remainder, at least one of the operands should be typed as a floating-point number – the result will then be a floating-point. When an integer and a floating-point number are used as operands to any arithmetic operator, the result is a floating-point number. This is because the integer is implicitly converted to a floating point value before the operation takes place.
- 142. Nov 26, 2025142 Simple example program demonstrates the arithmetic operators class BasicMath { public static void main(String args[]) { // arithmetic using integers System.out.println("Integer Arithmetic"); int a = 1 + 1; int b = a * 3; int c = b / 4; int d = c - a; int e = -d; System.out.println("a = " + a); System.out.println("b = " + b); System.out.println("c = " + c); System.out.println("d = " + d); System.out.println("e = " + e); Output: Integer Arithmetic a = 2 b = 6 c = 1 d = -1 e = 1
- 143. Nov 26, 2025143 Modulus Operator Modulus Operator – The modulus operator, %, returns the remainder of a division operation. – It can be applied to floating-point types as well as integer types. – Example: • // Demonstrate the % operator. class Modulus { public static void main(String args[]) { int x = 42; double y = 42.25; System.out.println("x mod 10 = " + x % 10); System.out.println("y mod 10 = " + y % 10); } } • When you run this program, you will get the following output: • x mod 10 = 2 y mod 10 = 2.25
- 144. Nov 26, 2025144 Arithmetic Compound Assignment Operators Java provides special operators that can be used to combine an arithmetic operation with an assignment. As you probably know, statements like the following are quite common in programming: a = a + 4; In Java, you can rewrite this statement as shown here: a += 4; This version uses the += compound assignment operator. Both statements perform the same action: they increase the value of a by 4.
- 145. Nov 26, 2025145 Arithmetic Compound Assignment Operators(2) Here is another example, a = a % 2; which can be expressed as a %= 2; In this case, the %= obtains the remainder of a/2 and puts that result back into a. • any statement of the form var = var op expression; can be rewritten as var op= expression;
- 146. Nov 26, 2025146 A sample program that shows several op= assignments // Demonstrate several assignment operators. class OpEquals { public static void main(String args[]) { int a = 1; int b = 2; int c = 3; a += 5; b *= 4; c += a * b; c %= 6; System.out.println("a = " + a); System.out.println("b = " + b); System.out.println("c = " + c); } } • The output of this program is shown here: a = 6 b = 8 c = 3
- 147. Nov 26, 2025147 Increment and Decrement The ++ and the – – are Java’s increment and decrement operators. What are the increments and decrement operators do. • The increment operator increases its operand by one. • The decrement operator decreases its operand by one. For example, this statement: x = x + 1 can be rewritten like this by use of the increment operator: x++; Similarly, this statement: x = x - 1; is equivalent to x--;
- 148. Nov 26, 2025148 Increment and Decrement(2) These operators are unique in that they can appear both in postfix form, where they follow the operand as just shown, and prefix form, where they precede the operand. In the foregoing examples, there is no difference between the prefix and postfix forms. However, when the increment and/or decrement operators are part of a larger expression, then a subtle, yet powerful, difference between these two forms appears. • In the prefix form, the operand is incremented or decremented before the value is obtained for use in the expression.
- 149. Nov 26, 2025149 Increment and Decrement(2) In postfix form, the previous value is obtained for use in the expression, and then the operand is modified. For example: x = 42; y = ++x; • In this case, y is set to 43 as you would expect, because the increment occurs before x is assigned to y. • Thus, the line y = ++x; is the equivalent of these two statements: • x = x + 1; y = x; • However, when written like this, x = 42; y = x++; the value of x is obtained before the increment operator is executed, so the value of y is 42. • Of course, in both cases x is set to 43. • Here, the line y = x++; is the equivalent of these two statements: y = x; x = x + 1;
- 150. Nov 26, 2025150 Example:Increment and Decrement The following program demonstrates the increment operator. // Demonstrate ++. class IncDec { public static void main(String args[]) { int a = 1, b = 2; int c, d; c = ++b; d = a++; c++; System.out.println("a = " + a); System.out.println("b = " + b); System.out.println("c = " + c); System.out.println("d = " + d); } } The output of this program follows: a = 2 b= 3 c = 4 d = 1
- 151. Nov 26, 2025151 Relational Operators The relational operators determine the relationship that one operand has to the other. Specifically, they determine equality and ordering. The relational operators are shown here:
- 152. Nov 26, 2025152 Relational Operators(2) The outcome of these operations is a boolean value. The relational operators are most frequently used in the expressions that control the if statement and the various loop statements. Any type in Java, including integers, floating-point numbers, characters, and Booleans can be compared using the equality test, ==, and the inequality test, !=. • For example, the following code fragment is perfectly valid: – int a = 4; int b = 1; boolean c = a < b; In this case, the result of a<b (which is false) is stored in c.
- 153. Nov 26, 2025153 Boolean Logical Operators The Boolean logical operators shown here operate only on boolean operands. All of the binary logical operators combine two boolean values to form a resultant boolean value.
- 154. Nov 26, 2025154 Boolean Logical Operators(2) The logical Boolean operators, &, |, and ^, operate on boolean values in the same way that they operate on the bits of an integer. The logical ! operator inverts the Boolean state: !true == false and !false == true. The following table shows the effect of each logical operation.
- 155. Nov 26, 2025155 Example: boolean logical operators. class BoolLogic { public static void main(String args[]) { boolean a = true, b = false; boolean c = a | b; boolean d = a & b; boolean e = a ^ b; boolean f = (!a & b) | (a & !b); boolean g = !a; System.out.println(" a = " + a); System.out.println(" b = " + b); System.out.println(" a|b = " + c); System.out.println(" a&b = " + d); System.out.println(" a^b = " + e); System.out.println("!a&b|a&!b = " + f); System.out.println(" !a = " + g); } } a = true b = false a|b = true a&b = false a^b = true a&b|a&!b = true !a = false
- 156. Nov 26, 2025156 Assignment Operator The assignment operator is the single equal sign, =. The assignment operator works in Java much as it does in any other computer language. It has this general form: var = expression; Here, the type of var must be compatible with the type of expression. For example, consider this fragment: int x, y, z; x = y = z = 100; // set x, y, and z to 100 This fragment sets the variables x, y, and z to 100 using a single statement. This works because the = is an operator that yields the value of the right-hand expression. Thus, the value of z = 100 is 100, which is then assigned to y, which in turn is assigned to x.
- 157. Nov 26, 2025157 Operator Precedence Operator precedence determines the order in which operators are performed. This can clearly affect the result of the operation. Parentheses raise the precedence of the operations that are inside them. his is often necessary to obtain the result you desire.
- 158. Nov 26, 2025158 Operator Precedence: Table Operators Associativity Type () [] . left to right highest ++ -- right to left unary postfix ++ -- + - ! (type) right to left Unary & prefix * / % left to right multiplicative + - left to right additive < <= > >= left to right relational == != left to right Equality & left to right boolean logical AND ^ left to right boolean logical exclusive OR | left to right boolean logical inclusive OR && left to right logical AND || left to right logical OR ?: right to left Conditional = += -= *= /= %= right to left Assignment
- 159. Nov 26, 2025159 Example: Evaluate the following expressions double x; x = 3 + 2 * 3; //9 x = (3 + 2) * 3; // 15 x = 3 + 2 * 3 * 3 + 5 % 2 / 2; // 21 x = –(2 * 3) + 6 / 2 / 3 + 9 % 4; //-4