Java - Understanding Nested Loops

Understanding Nested Loops in Java

Java - Nested Loops

Introduction

Loops are a fundamental concept in programming, allowing us to execute a block of code multiple times. Sometimes, we need a loop within another loop this is known as a nested loop. In this guide, we’ll explore nested loops in Java with examples to illustrate how they work.

What Are Nested Loops?

A nested loop is a loop inside the body of another loop. The inner loop executes completely for each iteration of the outer loop. This structure is useful in scenarios like working with multi-dimensional data structures, pattern printing, and complex iterations.

Example 1: Nested for Loop

class NestedForLoop {
    public static void main(String[] args) {
        for (int i = 0; i < 2; i++) {  // Outer loop
            System.out.println("Outer: " + i);
            for (int j = 0; j < 2; j++) {  // Inner loop
                System.out.println(" Inner: " + j);
            }
        }
        System.out.println("After nested for loops");
    }
}

Output:

Outer: 0
 Inner: 0
 Inner: 1
Outer: 1
 Inner: 0
 Inner: 1
After nested for loops

Here, the inner loop runs twice for every iteration of the outer loop. Once the outer loop reaches its condition (i = 2), the execution stops, and the statement after the loops is executed.

Example 2: while Loop Inside a for Loop

class NestedLoop {
    public static void main(String[] args) {
        for (int i = 0; i < 2; i++) {
            System.out.println("Outer For Loop: " + i);
            int counter = 0;
            
            while (counter < 2) {  // Inner while loop
                System.out.println(" Inner While Loop: " + counter);
                counter++;
            }
        }
    }
}

Output:

Outer For Loop: 0
 Inner While Loop: 0
 Inner While Loop: 1
Outer For Loop: 1
 Inner While Loop: 0
 Inner While Loop: 1

Example 3: do...while Loop Inside a while Loop

class NestedLoop {
    public static void main(String[] args) {
        int m = 0;
        while (m < 2) {  // Outer while loop
            System.out.println("Outer While Loop: " + m);
            int n = 0;
            
            do {  // Inner do-while loop
                System.out.println(" Inner Do-While Loop: " + n);
                n++;
            } while (n < 2);
            m++;
        }
    }
}

Output:

Outer While Loop: 0
 Inner Do-While Loop: 0
 Inner Do-While Loop: 1
Outer While Loop: 1
 Inner Do-While Loop: 0
 Inner Do-While Loop: 1

Example 4: for Loop Inside a for Loop

class NestedLoop {
    public static void main(String[] args) {
        for (int i = 1; i <= 3; i++) {  // Outer loop
            System.out.println("Outer For Loop: " + i);
            for (int j = 0; j < i; j++) {  // Inner loop
                System.out.println(" Inner For Loop: " + j);
            }
        }
    }
}

Output:

Outer For Loop: 1
 Inner For Loop: 0
Outer For Loop: 2
 Inner For Loop: 0
 Inner For Loop: 1
Outer For Loop: 3
 Inner For Loop: 0
 Inner For Loop: 1
 Inner For Loop: 2

Here, the inner loop runs incrementally based on the current value of i. The iterations are:

• i = 1 → Inner loop runs once.
• i = 2 → Inner loop runs twice.
• i = 3 → Inner loop runs three times.

Summary

• A nested loop is a loop inside another loop.
• The inner loop runs completely for each iteration of the outer loop.
• Loops can be nested in any combination (for, while, do...while).
• Nested loops are useful for handling multi-dimensional structures and complex iterations.

Related Posts :

        Java Introduction & Basics

         Sequence of Instructions in Java

         Java Data Types

         Java Input and Output Basics

         Java Type Conversions

         Java String Methods

         Java Logical Operators

         Conditional Statements in Java

         Java Ternary Operator

         Java Switch Statement

         Loops in Java

      Java String Method

          Chracters of Methods