Nested for Example in Java

Introduction

Nested For is a classic Java console program that demonstrates the concept with complete source code and sample output. Loops repeat work until a condition is met — essential for processing collections and numeric ranges.

This tutorial walks through the program line by line, explains how the logic works, and highlights best practices you can apply in your own code.

Definition

A nested loop is a loop within a loop, an inner loop within the body of an outer one. How this works is that the first pass of the outer loop triggers the inner loop, which executes to completion. Then the second pass of the outer loop triggers the inner loop again. This repeats until the outer loop finishes.

Syntax

for (initialization; condition ; increment) {
	for (initialization; condition ; increment) {
		//Do something
	}
}

Nested For Example Program

public class NestedForDemo{
	public static void main(String [] args){
		for (int i=1; i<=5; i++){
			System.out.println();
			for (int j=1; j<=i; j++){
				System.out.print(j);
			}
		}
		System.out.println();
	}
}

Sample Output

1
12
123
1234
12345

When to use

Use this nested for example when learning or revising core Java syntax.

How it works

1. Execution begins in the main method — the JVM calls this method when you run the class.

2. for (int i=1; i<=5; i++){ updates a variable used in the calculation or output.

3. A println / print call writes text to the console — part of the sample output below.

4. for (int j=1; j<=i; j++){ updates a variable used in the calculation or output.

5. A println / print call writes text to the console — part of the sample output below.

6. A println / print call writes text to the console — part of the sample output below.

7. Compare your console output with the sample output for Nested For to confirm the program behaves correctly.

Best Practices

• Use meaningful variable and class names that describe their purpose.
• Compile and run the program locally — modify values to see how output changes.
• Read compiler errors carefully; they usually point to the exact line to fix.

Common Mistakes

• Copying code without understanding each line — practice by changing one statement at a time.
• Mismatching the public class name and the .java filename.
• Forgetting semicolons at the end of statements.