Java Program to Interchange the Diagonals

In this article, we will understand how to interchange the diagonal elements of a given matrix in Java. A matrix is a two-dimensional array made up of rows and columns. A matrix with m rows and n columns is called an m × n matrix.

Each element in the matrix is represented by a[i][j], which means that the particular element a is present in the i-th row and j-th column.

Problem Statement

Write a Java program to interchange the elements of the primary and secondary diagonals of a square matrix.

Example Scenario

Consider the following example scenario to understand the problem better:

Input: The matrix is defined as:
4 5 6
1 2 3
7 8 9

Output: The matrix after interchanging the elements:
6 5 4
1 2 3
9 8 7

Steps to Swap the Diagonal Elements of a Matrix

Following are the steps to achieve this:

• Define a square matrix with values.
• Iterate through each row from index 0 to matrix_size - 1.
• For each row i, check if it is not the middle row using the condition i != matrix_size / 2.
• If true, swap the primary diagonal element with the secondary diagonal element.
• Display the resulting matrix.

Example 1: Interchanging Diagonals

The following example demonstrates how to interchange the diagonal elements of a square matrix:

public class InterchangeDiagonals {
    public static int matrix_size = 3;
    public static void main (String[] args) {
        int input_matrix[][] = {
            {4, 5, 6},
            {1, 2, 3},
            {7, 8, 9}
        };
        System.out.println("The matrix is defined as: ");
        for (int i = 0; i < matrix_size; i++) {
            for (int j = 0; j < matrix_size; j++) {
                System.out.print(input_matrix[i][j] + " ");
            }
            System.out.println();
        }
        for (int i = 0; i < matrix_size; ++i)
            if (i != matrix_size / 2) {
                int temp = input_matrix[i][i];
                input_matrix[i][i] = input_matrix[i][matrix_size - i - 1];
                input_matrix[i][matrix_size - i - 1] = temp;
            }
        System.out.println("\nThe matrix after interchanging the elements: ");
        for (int i = 0; i < matrix_size; ++i) {
            for (int j = 0; j < matrix_size; ++j)
                System.out.print(input_matrix[i][j]+" ");
            System.out.println();
        }
    }
}

Output

The matrix is defined as:
4 5 6
1 2 3
7 8 9

The matrix after interchanging the elements:
6 5 4
1 2 3
9 8 7

Function-Based Approach

In this approach, we encapsulate the operations into a function, which also demonstrates the principles of object-oriented programming.

Example 2: Function-Based Implementation

The following example demonstrates how to interchange the diagonal elements of a square matrix using a separate method:

public class InterchangeDiagonals {
    public static int matrix_size = 3;
    static void interchange_diagonals(int input_matrix[][]) {
        for (int i = 0; i < matrix_size; ++i)
            if (i != matrix_size / 2) {
                int temp = input_matrix[i][i];
                input_matrix[i][i] = input_matrix[i][matrix_size - i - 1];
                input_matrix[i][matrix_size - i - 1] = temp;
            }
        System.out.println("\nThe matrix after interchanging the elements: ");
        for (int i = 0; i < matrix_size; ++i) {
            for (int j = 0; j < matrix_size; ++j)
                System.out.print(input_matrix[i][j]+" ");
            System.out.println();
        }
    }
    public static void main (String[] args) {
        int input_matrix[][] = {
            {4, 5, 6},
            {1, 2, 3},
            {7, 8, 9}
        };
        System.out.println("The matrix is defined as: ");
        for (int i = 0; i < matrix_size; i++) {
            for (int j = 0; j < matrix_size; j++) {
                System.out.print(input_matrix[i][j] + " ");
            }
            System.out.println();
        }
        interchange_diagonals(input_matrix);
    }
}

Output

The matrix is defined as:
4 5 6
1 2 3
7 8 9

The matrix after interchanging the elements:
6 5 4
1 2 3
9 8 7