Java Program to Multiply Two Matrices

In the previous article, we have discussed Java Program to Subtract Two Matrices

In this article we are going to see how we can write a program to calculate the product of two matrices in JAVA language.

Java Program to Multiply Two Matrices

A 3*3 Matrix is having 3 rows and 3 columns where this 3*3 represents the dimension of the matrix. Means there are 3*3 i.e. total 9 elements in a 3*3 Matrix.

Let’s understand it in more simpler way.

                   | A00   A01   A02 |
Matrix A =  | A10   A11   A12 |
                   | A20   A21   A22 | 3*3
  • Matrix A represents a 3*3 matrix.
  • A‘ represents the matrix element
  • Aij‘ represents the matrix element at it’s matrix position/index.
  • i‘ represents the row index
  • j‘ represents the column index
  • Means A00=Aij  where i=0 and j=0A01=aij where i=0 and j=1 and like this.
  • Here we have started row value from 0 and column value from 0.

Let’s see different ways to multiply two matrices.

Method-1: Java Program to Multiply Two Matrices By Static Initialization of Array Elements

Approach:

  • Initialize and declare two arrays of size 3×3 with elements.
  • Use two for loops to iterate the rows and columns .
  • Inside the for loops set all the elements of the resultant matrix to 0, and there create another loop to multiply the elements and store them.
  • Print the resultant array.

Program:

import java.util.Scanner;
public class Matrix{
    public static void main(String args[])
    {
        //Scanner class to take input
        Scanner scan = new Scanner(System.in);

        // Initializing the 3X3 matrix i.e. 2D array
        int mat1[][] = {{19,25,32},{40,54,62},{70,20,60}};
        int mat2[][] =  {{50,15,10},{98,45,78},{23,73,50}};
        int res[][] = new int[3][3];
        int row, col ;
        // Printing the matrices using our user-defined function
        System.out.print("\nMatrix 1 : ");
        printMatrix(mat1);
        System.out.print("\nMatrix 2 : ");
        printMatrix(mat2);

        // Loops to find product of two matrices
        for(row=0;row<3;row++)
            for(col=0;col<3;col++)
            {   
                // Initializes the array element to zero first
                res[row][col] = 0;
                for(int i = 0;i<3;i++)
                    res[row][col]=mat1[row][i]*mat2[i][col];
            }
        System.out.print("\nAfter multiplication of both the matices : ");
        printMatrix(res);
    }

    // Function to print the matrix
    static void printMatrix(int arr[][])
    {
        int row, col;
        // Loop to print the elements
        for(row=0;row<3;row++)
        {
            // Used for formatting
            System.out.print("\n");
            for(col=0;col<3;col++)
            {
                System.out.print(arr[row][col]+" ");
            }
        }
        System.out.print("\n");
    }
}

Output:

Matrix 1 : 
19 25 32 
40 54 62 
70 20 60 

Matrix 2 : 
50 15 10 
98 45 78 
23 73 50 

After multiplication of both the matices : 
736   2336 1600 
1426 4526 3100 
1380 4380 3000

Method-2: Java Program to Multiply Two Matrices By Dynamic Initialization of Array Elements

Approach:

  • Initialize and declare two arrays of size 3×3.
  • Ask the user for input and store them in the arrays using two for loops.
  • Use two for loops to iterate the rows and columns.
  • Inside the for loops set all the elements of the resultant matrix to 0, and there create another loop to multiply the elements and store them.
  • Print the resultant array.

Program:

import java.util.Scanner;
public class Matrix{
    public static void main(String args[])
    {
        //Scanner class to take input
        Scanner scan = new Scanner(System.in);

        // Initializing the 3X3 matrix i.e. 2D array
        int mat1[][] = new int[3][3];
        int mat2[][] =  new int[3][3];
        int res[][] = new int[3][3];
        int row, col ;
        
        // Taking matrix1 input
        System.out.print("\nEnter the first matrix elements : ");
        for(row=0;row<3;row++)
            for(col=0;col<3;col++)
                mat1[row][col] = scan.nextInt();
            
        System.out.print("\nMatrix 1 :");
        //calling the printMatrix() method to print matrix 1    
        printMatrix(mat1);
        
        // Taking matrix2 input
        System.out.print("\nEnter the second matrix elements : ");
        for(row=0;row<3;row++)
            for(col=0;col<3;col++)
                mat2[row][col] = scan.nextInt();
        
         System.out.print("\nMatrix 2 :");
        //calling the printMatrix() method to print matrix 1    
        printMatrix(mat2);

        // Loops to find product of two matrices
        for(row=0;row<3;row++)
            for(col=0;col<3;col++)
            {   
                // Initializes the array element to zero first
                res[row][col] = 0;
                for(int i = 0;i<3;i++)
                    res[row][col]+=mat1[row][i]*mat2[i][col];
            }
        System.out.print("\nAfter multiplication of both the matrices : ");
        printMatrix(res);
    }

    // Function to print the matrix
    static void printMatrix(int arr[][])
    {
        int row, col;
        // Loop to print the elements
        for(row=0;row<3;row++)
        {
            // Used for formatting
            System.out.print("\n");
            for(col=0;col<3;col++)
            {
                System.out.print(arr[row][col]+" ");
            }
        }
        System.out.print("\n");
    }
}


Output:

Enter the first matrix elements : 1 2 3 4 5 6 7 8 9
Matrix 1 :
1 2 3 
4 5 6 
7 8 9

Enter the second matrix elements : 1 2 3 4 5 6 7 8 9
Matrix 2 :
1 2 3 
4 5 6 
7 8 9

After multiplication of both the matrices : 
30 36 42 
66 81 96 
102 126 150

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