The given code implements the Matrix class and show the addition of two matrices.

public class Matrix{
        int M;             
        int N;            
        int[][] data;

        public Matrix(int M, int N) {
            this.M = M;
            this.N = N;
            data = new int[M][N];
        }

        public Matrix(int[][] data) {
            M = data.length;
            N = data[0].length;
            this.data = new int[M][N];
            for (int i = 0; i < M; i++)
                for (int j = 0; j < N; j++)
                        this.data[i][j] = data[i][j];
        }
        Matrix(Matrix A) {
            this(A.data); 
        }

        public Matrix plus(Matrix B) {
            Matrix A = this;
            if (B.M != A.M || B.N != A.N)  throw new RuntimeException("Illegal matrix dimensions.");
            Matrix C = new Matrix(M, N);
            for (int i = 0; i < M; i++)
                for (int j = 0; j < N; j++)
                    C.data[i][j] = A.data[i][j] + B.data[i][j];
            return C;
        }

        public void show() {
            for (int i = 0; i < M; i++) {
                for (int j = 0; j < N; j++) {
                    System.out.print(data[i][j]+" ");
                }
                System.out.println();
            }
        }

        public static void main(String[] args) {
            int[][] arr1 = { { 1, 2, 3 }, { 4, 5, 6 }, { 9, 1, 3} };
            Matrix A = new Matrix(arr1);
            System.out.println("Matrix A: ");
            A.show();        
            System.out.println();

            int[][] arr2 = { { 2, 3, 4 }, { 1, 2, 3 }, { 4, 1, 2} };
            Matrix B = new Matrix(arr2);
            System.out.println("Matrix B: ");
            B.show(); 
            System.out.println();

            System.out.println("Sum of two matrices: ");
            A.plus(B).show();
            System.out.println();
           }
    }