Example: Matrix Multiplication in Java in Java

// Matrix Multiplication in Java
public class Main {

    // Method to multiply two matrices
    public static int[][] multiplyMatrices(int[][] matrixA, int[][] matrixB) {
        // Step 1: Get dimensions of the matrices
        int rowsA = matrixA.length;
        int colsA = matrixA[0].length;
        int rowsB = matrixB.length;
        int colsB = matrixB[0].length;

        // Step 2: Check for compatibility: colsA must be equal to rowsB
        if (colsA != rowsB) {
            System.out.println("Matrices dimensions are not compatible for multiplication.");
            return null; // Return null to indicate an error
        }

        // Step 3: Create a result matrix (rowsA x colsB)
        int[][] result = new int[rowsA][colsB];

        // Step 4: Perform multiplication using three nested loops
        for (int i = 0; i < rowsA; i++) { // Iterate through rows of matrixA
            for (int j = 0; j < colsB; j++) { // Iterate through columns of matrixB
                for (int k = 0; k < colsA; k++) { // Iterate through columns of matrixA (or rows of matrixB)
                    result[i][j] += matrixA[i][k] * matrixB[k][j];
                }
            }
        }
        return result;
    }

    // Method to print a matrix
    public static void printMatrix(int[][] matrix) {
        if (matrix == null) {
            System.out.println("Cannot print null matrix.");
            return;
        }
        for (int i = 0; i < matrix.length; i++) {
            for (int j = 0; j < matrix[0].length; j++) {
                System.out.print(matrix[i][j] + " ");
            }
            System.out.println();
        }
    }

    public static void main(String[] args) {
        // Step 1: Define two matrices for multiplication
        int[][] matrixA = {
            {1, 2},
            {3, 4}
        };

        int[][] matrixB = {
            {5, 6},
            {7, 8}
        };

        System.out.println("Matrix A:");
        printMatrix(matrixA);
        System.out.println("\nMatrix B:");
        printMatrix(matrixB);

        // Step 2: Perform matrix multiplication
        int[][] productMatrix = multiplyMatrices(matrixA, matrixB);

        // Step 3: Print the result
        if (productMatrix != null) {
            System.out.println("\nProduct of Matrix A and Matrix B:");
            printMatrix(productMatrix);
        }

        // Example with incompatible matrices
        System.out.println("\n--- Testing incompatible matrices ---");
        int[][] matrixC = {
            {1, 2, 3},
            {4, 5, 6}
        }; // 2x3

        int[][] matrixD = {
            {7, 8},
            {9, 10}
        }; // 2x2

        System.out.println("Matrix C:");
        printMatrix(matrixC);
        System.out.println("\nMatrix D:");
        printMatrix(matrixD);

        System.out.println("\nAttempting to multiply Matrix C (2x3) and Matrix D (2x2):");
        int[][] incompatibleProduct = multiplyMatrices(matrixC, matrixD);
        if (incompatibleProduct != null) {
            System.out.println("Product of Matrix C and Matrix D:");
            printMatrix(incompatibleProduct);
        }
    }
}