Java Program to Multiply two Matrices of any size

Given two matrices A and B of any size, the task to multiply them in Java. 
Examples:

Input: A[][] = {{1, 2}, 
                {3, 4}}
       B[][] = {{1, 1}, 
                {1, 1}}
Output: {{3, 3}, 
         {7, 7}}

Input: A[][] = {{2, 4}, 
                {3, 4}}
       B[][] = {{1, 2}, 
                {1, 3}}       
Output: {{6, 16}, 
         {7, 18}}

Approach:

• Take the two matrices to be multiplied
• Check if the two matrices are compatible to be multiplied 
  

• Create a new Matrix to store the product of the two matrices
• Traverse each element of the two matrices and multiply them. Store this product in the new matrix at the corresponding index.
• Print the final product matrix

Below is the implementation of the above approach:

Java

// Java program to multiply two square matrices.

import java.io.*;

class GFG {

    // Function to print Matrix
    static void printMatrix(int M[][],
                            int rowSize,
                            int colSize)
    {
        for (int i = 0; i < rowSize; i++) {
            for (int j = 0; j < colSize; j++)
                System.out.print(M[i][j] + " ");

            System.out.println();
        }
    }

    // Function to multiply
    // two matrices A[][] and B[][]
    static void multiplyMatrix(
        int row1, int col1, int A[][],
        int row2, int col2, int B[][])
    {
        int i, j, k;

        // Print the matrices A and B
        System.out.println("\nMatrix A:");
        printMatrix(A, row1, col1);
        System.out.println("\nMatrix B:");
        printMatrix(B, row2, col2);

        // Check if multiplication is Possible
        if (row2 != col1) {

            System.out.println(
                "\nMultiplication Not Possible");
            return;
        }

        // Matrix to store the result
        // The product matrix will
        // be of size row1 x col2
        int C[][] = new int[row1][col2];

        // Multiply the two matrices
        for (i = 0; i < row1; i++) {
            for (j = 0; j < col2; j++) {
                for (k = 0; k < row2; k++)
                    C[i][j] += A[i][k] * B[k][j];
            }
        }

        // Print the result
        System.out.println("\nResultant Matrix:");
        printMatrix(C, row1, col2);
    }

    // Driver code
    public static void main(String[] args)
    {

        int row1 = 4, col1 = 3, row2 = 3, col2 = 4;

        int A[][] = { { 1, 1, 1 },
                      { 2, 2, 2 },
                      { 3, 3, 3 },
                      { 4, 4, 4 } };

        int B[][] = { { 1, 1, 1, 1 },
                      { 2, 2, 2, 2 },
                      { 3, 3, 3, 3 } };

        multiplyMatrix(row1, col1, A,
                       row2, col2, B);
    }
}

Output:

Matrix A:
1 1 1 
2 2 2 
3 3 3 
4 4 4 

Matrix B:
1 1 1 1 
2 2 2 2 
3 3 3 3 

Resultant Matrix:
6 6 6 6 
12 12 12 12 
18 18 18 18 
24 24 24 24

Time Complexity: O(M²*N), as we are using a nested loop for traversing.

Auxiliary Space: O(M*N), as we are using extra space.