Java Nested Loops with Examples

A Nested loop means a loop statement inside another loop statement. That is why nested loops are also called “loop inside loop“.

Nested For loop

for ( initialization; condition; increment ) {
for ( initialization; condition; increment ) {
// statement of inside loop
}

// statement of outer loop
}

Nested While loop

while(condition) {
while(condition) {
// statement of inside loop
}

// statement of outer loop
}

Nested Do-While loop

do{
do{
// statement of inside loop
}
while(condition);

// statement of outer loop
}
while(condition);

Note: There is no rule that a loop must be nested inside its own type. In fact, there can be any type of loop nested inside any type and to any level.

Hybrid Java Nested Loops

do{
while(condition) {
for ( initialization; condition; increment ) {
// statement of inside for loop
}

// statement of inside while loop

}

// statement of outer do-while loop
}while(condition);

Below are some examples to demonstrate the use of Nested Loops:

Examples of Java Nested Loops

Example 1: Below program uses a nested for loop to print a 2D matrix. 

Java

// Java program to print the elements of
// a 2 D array or matrix
import java.io.*;

// Driver Class
class GFG {
    public static void print2D(int mat[][])
    {
        // Loop through all rows
        for (int i = 0; i < mat.length; i++) {

            // Loop through all elements of current row
            for (int j = 0; j < mat[i].length; j++)
                System.out.print(mat[i][j] + " ");

            System.out.println();
        }
    }

      // main function
    public static void main(String args[]) throws IOException
    {
        int mat[][] = { { 1, 2, 3, 4 },
                        { 5, 6, 7, 8 },
                        { 9, 10, 11, 12 } };
        print2D(mat);
    }
}

Output

1 2 3 4 
5 6 7 8 
9 10 11 12

Example 2: Below program uses a nested for loop to print all prime factors of a number. 

Java

// Java program to print all prime factors
import java.io.*;
import java.lang.Math;

// Driver Class
class GFG {
    // A function to print all prime factors
    // of a given number n
    public static void primeFactors(int n)
    {
        // Print the number of 2s that divide n
        while (n % 2 == 0) {
            System.out.print(2 + " ");
            n /= 2;
        }

        // n must be odd at this point. So we can
        // skip one element (Note i = i +2)
        for (int i = 3; i <= Math.sqrt(n); i += 2) {
            // While i divides n, print i and divide n
            while (n % i == 0) {
                System.out.print(i + " ");
                n /= i;
            }
        }

        // This condition is to handle the case when
        // n is a prime number greater than 2
        if (n > 2)
            System.out.print(n);
    }

      // main function
    public static void main(String[] args)
    {
        int n = 315;
        primeFactors(n);
    }
}

Output

3 3 5 7