BLUEJ PROGRAM ON MATRIX MULTIPLICATION

In this program we will do multiplication of two matrix.  In doing matrix multiplication, the condition is that rows in first matrix should match the number of columns in the second matrix.

import java.io.*;

class Arr

{

    int m1[][]=new int[10][10];

    int m2[][]=new int[10][10];

    int mult[][]=new int[10][10];

    int i,j,k,r1,c1,r2,c2;

    BufferedReader br=new BufferedReader(new InputStreamReader(System.in));

    public void show() throws IOException

    {

       System.out.println("Enter number of rows of first matrix (less than 10)\n");

        r1=Integer.parseInt(br.readLine());

        System.out.println("Enter number of columns of first matrix (less than 10)\n");

        c1=Integer.parseInt(br.readLine());

        System.out.println("Enter number of rows of second matrix (less than 10)\n");

        r2=Integer.parseInt(br.readLine());

        System.out.println("Enter number of columns of second matrix (less than 10)\n");

        c2=Integer.parseInt(br.readLine());

       

    if(r2==c1)

    {

      

        for(i=0;i< r1;i++)

        {

            for(j=0;j< c1;j++)

            {

                System.out.println("Value for 1st matrix:");

m1[i][j]=Integer.parseInt(br.readLine());

}

}

  for(i=0;i< r2;i++)

        {

            for(j=0;j< c2;j++)

            {

                System.out.println("Value for 2nd matrix:");

m2[i][j]=Integer.parseInt(br.readLine());

}

}

System.out.println("\n1st Matrix\n");

        for(i=0;i< r1;i++)

        {

            for(j=0;j< c1;j++)

                System.out.print(" "+m1[i][j]);

            System.out.println();

        }

        System.out.println("\n2nd Matrix\n");

        for(i=0;i< r2;i++)

        {

            for(j=0;j< c1;j++)

                System.out.print(" "+m2[i][j]);

            System.out.println();

        }

       for(i=0;i< r1;i++)

        {

            for(j=0;j< c2;j++)

            {

                mult[i][j]=0;

                for(k=0;k< r1;k++)

                {

                    mult[i][j]+=m1[i][k]*m2[k][j];

                }

            }

        }

    System.out.println("\nFinal Matrix\n");

        for(i=0;i< r1;i++)

        {

            for(j=0;j< c2;j++)

                System.out.print(" "+mult[i][j]);

            System.out.println();

        }

   }

}

}

Rule of matrix multiplication

If the first array is like: 

a  b

c  d

and the second array is like:

e  f

g  h

then the multiplication will be like:

ae + bg   af + bh

ce + dg   cf + dh