Java for Loop

A for loop repeats steps a set number of times, like doing ten jumping jacks while counting. It keeps the start, the stopping rule and the counting all in one line.

In this page:

Basic for Loop
Decrementing for Loops
Iterating with Custom Steps
Iterating over Arrays
Nested for Loops

Syntax

java

for (initialization; condition; update) {
    // loop body
}

Basic for Loop

A for loop packs initialization, the continue condition, and the update step into a single header line, making it the natural choice whenever you know in advance roughly how many times you need to iterate.

Example: Basic for Loop

java

// Define the class Main
public class Main {
	// Program entry point: the JVM starts running here
	public static void main(String[] args) {
		// Loop: repeat while the condition holds
		for (int i = 0; i < 3; i++) {
			// Print a line to the console
			System.out.println(i);
		}
	}
}

Decrementing for Loops

Initializing the loop variable at a high value and using i-- as the update step walks the loop backward, which is handy for tasks like processing an array from its last element to its first.

Example: Decrementing for Loops

java

// Define the class Main
public class Main {
	// Program entry point: the JVM starts running here
	public static void main(String[] args) {
		// Loop: repeat while the condition holds
		for (int i = 5; i > 0; i--) {
			// Print a line to the console
			System.out.println(i);
		}
	}
}

Iterating with Custom Steps

The update expression isn't limited to i++ -- writing i += 2 steps by twos, letting you visit every other index or count by any custom increment your logic needs.

Example: Iterating with Custom Steps

java

// Define the class Main
public class Main {
	// Program entry point: the JVM starts running here
	public static void main(String[] args) {
		// Loop: repeat while the condition holds
		for (int i = 0; i < 10; i += 2) {
			// Print a line to the console
			System.out.println(i);
		}
	}
}

Iterating over Arrays

Because array indices run from 0 to length-1, a for loop like for (int i = 0; i < arr.length; i++) is the standard, idiomatic way to visit and process every element of an array in order.

Example: Iterating over Arrays

java

// Define the class Main
public class Main {
	// Program entry point: the JVM starts running here
	public static void main(String[] args) {
		// Declare arr and set it to {10, 20, 30}
		int[] arr = {10, 20, 30};
		// Loop: repeat while the condition holds
		for (int i = 0; i < arr.length; i++) {
			// Print a line to the console
			System.out.println(arr[i]);
		}
	}
}

Nested for Loops

An inner for loop runs to completion for every single iteration of its enclosing outer loop -- with two loops each running n times, that's n squared total iterations, the classic pattern behind processing 2D grids or comparing all pairs in a list.

Example: Nested for Loops

java

// Define the class Main
public class Main {
	// Program entry point: the JVM starts running here
	public static void main(String[] args) {
		// Loop: repeat while the condition holds
		for (int i = 0; i < 2; i++) {
			// Loop: repeat while the condition holds
			for (int j = 0; j < 2; j++) {
				// Print a line to the console
				System.out.println(i + "," + j);
			}
		}
	}
}

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Java for Loop

Basic for Loop

Decrementing for Loops

Iterating with Custom Steps

Iterating over Arrays

Nested for Loops

Chapter Quiz — Complete all 9 topics to unlock

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