What is-java

What is-java

• 1.
  Write once, Runanywhere Java Apps are platform independent; They can be run on any OS having JVM. If the OS does not have JVM then we can not run Java App.
• 2.
  Java class iswritten in Unicode characters. Java compiler convert these Unicode characters into Byte code. Java Byte code can only be understandable by JVM. JVM is native code and specific to OS
• 3.
  class file format Java bytecode is the instruction set of the Java virtual machine.
• 4.
  other languages canturn to the Java virtual machine as a delivery vehicle any language with functionality that can be expressed in terms of a valid class file can be hosted by the Java virtual machine.
• 5.
  Bytecode Outline pluginfor Eclipse Shows disassembled bytecode of current java editor or class file. The best way to learn JVM is to write a Java source file and then view Bytecode using this plugin.
• 6.
  Go to “Help-> Install new Software” http://andrei.gmxhome.de/eclipse/ Window -> Show View -> Other
• 7.
  Open Bytecode View
• 8.
  LDC "Hello World!" ● Open Bytecode Reference view ● Click “LDC” ldc : push single-word constant onto stack
• 9.
  Java allows youto play online games, chat with people around the world, calculate your mortgage interest, and view images in 3D, just to name a few. It’s also integral to the intranet applications and other e-business solutions that are the foundation of corporate computing.
• 10.
  Principles There werefive primary goals in the creation of the Java language : ● simple, object-oriented and familiar ● robust and secure ● architecture-neutral and portable ● execute with “high performance” ● interpreted, threaded, and dynamic
• 11.
  Java platform Javais a programming language and computing platform. Java is composed of a number of key components that, as a whole, create the Java platform. – The Java Virtual Machine – The Java Application Programming Interface (API) Java runs on more than 850 million personal computers worldwide, and on billions of devices worldwide, including mobile and TV devices.
• 12.
  Java API (RichStandard Library) The API is a large collection of ready-made software components that provide many useful capabilities. It is grouped into libraries of related classes and interfaces; these libraries are known as packages. Java includes a vast number of premade objects that can be used to perform such tasks as input/output, networking, and date manipulation.
• 13.
  java.lang – Providesclasses that are fundamental to the design of the Java programming language. java.io – Provides for system input and output through data streams, serialization and the file system. java.sql – Provides the API for accessing and processing data stored in a data source
• 14.
  Java Environment Javacomes in two flavors : ● JRE - Java Runtime Environment ● JDK – Java Development Kit You can download any of these two.
• 15.
  JRE JRE providescomponents to run applications written in the Java programming language : ● Java Virtual Machine ● Java API ● Tools to run Java Apps The JRE does not contain tools and utilities such as compilers or debuggers for developing applications.
• 16.
  Java Development Kit(JDK) JDK is a collection of tools for developing, packaging and distributing Java applications. JDK is a superset of the JRE, and contains everything that is in the JRE, plus tools such as the compilers and debuggers necessary for developing applications.
• 17.
  Java class loaders The Java Classloader is a part of the JRE that dynamically loads Java classes into the JVM. Usually classes are only loaded on demand. The Java run time system does not need to know about files and file systems because of classloaders.
• 18.
  Popular Java Editors ● Notepad++ ● Eclipse