Addition Of Two Matrices

import java.io.*;
class Matrix
{
    int arr[][],m,n;
    void fillarray()throws IOException
    {
        BufferedReader x=new BufferedReader(new InputStreamReader(System.in));
        for(int i=0;i<m;i++)
        {
            for(int j=0;j<n;j++)
            {
                System.out.println("Enter number");
                arr[i][j]=Integer.parseInt(x.readLine());
            }
        }
    }
    Matrix(int a,int b)
    {
        m=a;n=b;arr=new int[m][n];
    }
    void display()
    {
        for(int i=0;i<m;i++)
        {
            for(int j=0;j<n;j++)
            {
                System.out.print(arr[i][j]+" ");
            }
            System.out.println();
        }
    }
    Matrix SubMat(Matrix A)throws IOException
    {
        Matrix B=new Matrix(m,n);
        for(int i=0;i<m;i++)
        {
            for(int j=0;j<n;j++)
            {
                B.arr[i][j]=A.arr[i][j]-arr[i][j];
            }
        }
        return B;
    }
    public static void main(String args[])throws IOException
    {
        BufferedReader x=new BufferedReader(new InputStreamReader(System.in));
        System.out.println("Enter rows");
        int a = Integer.parseInt(x.readLine());
        System.out.println("Enter columns");
        int b=Integer.parseInt(x.readLine());
        Matrix A=new Matrix(a,b);
        System.out.println("\nEnter Matrix A");
        A.fillarray();
        Matrix B=new Matrix(a,b);
        System.out.println("\nEnter Matrix B");
        B.fillarray();
        Matrix C=new Matrix(a,b);
        System.out.println("\nMatrix A");
        System.out.println("----------");
        A.display();
        System.out.println("\nMatrix B");
        System.out.println("----------");
        B.display();
        System.out.println("\nResultant Matrix");
        System.out.println("------------------");
        C=A.SubMat(B);
        C.display();
    }
}