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For Loop

The for loop is more complex, but it’s also the most commonly used loop.

for (begin; condition; step) {

    // execute the code statements
    // in the loop body

}

Here’s one where we go from 1 to 5.

for(int j = 1; j < 6;  j++){
    // loop body code
    System.out.println(j);
}

This loop will print out:

// print
1
2
3
4
5

Notice how there are THREE parts to the FOR loop’s mechanism.

  • begin: j = 1 // Executes once upon entering the loop.

  • condition: j < 6 // Checked before every loop iteration. If false, the loop stops.

  • loop step: j++ // Executes after the body on each iteration.

and

  • body: System.out.println() // Runs again and again while the condition is true.

Let’s show you another glimpse of the break statement.

for(int p = 1; p < 6; p++){
    if(p == 4){
        break;
    }
System.out.println("Loop " + p + " times");
}

Jumps out of the loop when p is equal to 4.

Exercise: Basic Loop Practice

  • Print from 10 to 1 with a for loop and a while loop (hint use decrement)

  • Write a loop that prints 1 - 5 but break out at 3

Stretch Goal: S/he who dares wins!

  • Go back to Arrays

  • Look at an array of donuts

  • Create an array of donuts

  • Loop through the array of donuts and print each donut string

You can do it, I know you can!

for(int x = 0; x < donuts.length; x++){
    System.out.println(donuts[x]);
}

If you had something like this, buy yourself a donut, you deserve it.

Chapter Exercises

Try these exercises in jshell to practice for loops:

Exercise 1: Basic For Loop

Practice counting and basic output:

// Count from 1 to 10
for (int i = 1; i <= 10; i++) {
    System.out.println("Count: " + i);
}

// Count backwards from 10 to 1
System.out.println("\nCountdown:");
for (int i = 10; i >= 1; i--) {
    System.out.println(i);
}
System.out.println("Blast off!");

// Count by 2s
System.out.println("\nEven numbers from 2 to 20:");
for (int i = 2; i <= 20; i += 2) {
    System.out.println(i);
}

Exercise 2: Mathematical Calculations

Use for loops for calculations:

// Calculate sum of numbers 1 to 100
int sum = 0;
for (int i = 1; i <= 100; i++) {
    sum += i;
}
System.out.println("Sum of 1 to 100: " + sum);

// Create a multiplication table
int number = 7;
System.out.println("\nMultiplication table for " + number + ":");
for (int i = 1; i <= 10; i++) {
    System.out.println(number + " × " + i + " = " + (number * i));
}

// Calculate factorial
int factorial = 1;
int n = 5;
for (int i = 1; i <= n; i++) {
    factorial *= i;
}
System.out.println(n + "! = " + factorial);

Exercise 3: Pattern Printing

Create visual patterns with loops:

// Print a triangle of stars
System.out.println("Triangle:");
for (int i = 1; i <= 5; i++) {
    for (int j = 1; j <= i; j++) {
        System.out.print("* ");
    }
    System.out.println();
}

// Print a square
System.out.println("\nSquare:");
for (int i = 1; i <= 4; i++) {
    for (int j = 1; j <= 4; j++) {
        System.out.print("# ");
    }
    System.out.println();
}

// Print numbers in a pattern
System.out.println("\nNumber pattern:");
for (int i = 1; i <= 4; i++) {
    for (int j = 1; j <= i; j++) {
        System.out.print(j + " ");
    }
    System.out.println();
}

Exercise 4: Working with Arrays

Combine for loops with arrays:

String[] names = {"Alice", "Bob", "Charlie", "Diana", "Eve"};

// Print all names with index
System.out.println("Student roster:");
for (int i = 0; i < names.length; i++) {
    System.out.println((i + 1) + ". " + names[i]);
}

// Find names that start with a specific letter
char searchLetter = 'A';
System.out.println("\nNames starting with '" + searchLetter + "':");
for (int i = 0; i < names.length; i++) {
    if (names[i].charAt(0) == searchLetter) {
        System.out.println("- " + names[i]);
    }
}

// Create a modified version
System.out.println("\nFormatted names:");
for (int i = 0; i < names.length; i++) {
    System.out.println("Hello, " + names[i] + "!");
}