为什么矩阵加法在这段代码中不起作用？

Question

Can anyone tell me why matrix addition is not working in this code? All other parts of the program are working except the addition part. It's just printing an empty array as output.

import java.util.*;

class matrix{
    int n1, n2 = 0;
    int[][] matrix1 = new int [n1][n2];
    int[][] matrix2 = new int [n1][n2];
    int[][] matrix3 = new int [n1][n2];
    Scanner sc = new Scanner(System.in);
     
    // get the dimensions of the matrix//
    void Matrix() {
        int n1, n2 = 0;
        System.out.println(" enter the dimension of the matrix");
        n1 = sc.nextInt();
        n2 = sc.nextInt();
        int[][] matrix1 = new int [n1][n2];
        int[][] matrix2 = new int [n1][n2]; 
    
     
        //get the values of the elements//
        System.out.println("Enter the elements of the matrix");
        for (int i = 0; i < n1; i++) {
            for (int j = 0; j < n2; j++) {
                matrix1[i][j] = sc.nextInt();
                matrix2[i][j] = matrix1[i][j];
            }
        }
        // print the arrays
        System.out.println("matrix1"+Arrays.deepToString(matrix1));
        System.out.println("matrix2"+Arrays.deepToString(matrix2));
    }

    void add() {
        int[][] matrix3 = new int[n1][n2];
        for (int i = 0; i < n1; i++) {
            for(int j=0; j < n2; j++) {
                matrix3[i][j] = matrix1[i][j] + matrix2[i][j];
            }
        }
        System.out.println("Addition of the elements" + Arrays.deepToString(matrix3));
    }
}

public class arrays2 {
    public static void main(String[] args) {
        matrix M1 = new matrix();
        M1.Matrix();
        M1.add();   
    }
}

Answer 1

You do not need to redeclare instance variables n1 , n2 , matrix1 , matrix2 inside method Matrix() if you are going to use them in other method:

// get the dimensions of the matrix//
    void Matrix() {
        System.out.println(" enter the dimension of the matrix");
        this.n1 = sc.nextInt();
        this.n2 = sc.nextInt();
        this.matrix1 = new int [n1][n2];
        this.matrix2 = new int [n1][n2]; 
     
        //get the values of the elements//
        System.out.println("Enter the elements of the matrix");
        for (int i = 0; i < n1; i++) {
            for (int j = 0; j < n2; j++) {
                matrix1[i][j] = sc.nextInt();
                matrix2[i][j] = matrix1[i][j];
            }
        }
        // print the arrays
        System.out.println("matrix1"+Arrays.deepToString(matrix1));
        System.out.println("matrix2"+Arrays.deepToString(matrix2));
    }

Answer 2

You already declared n1 , n2 , matrix1 and matrix2 at the beginning of your class, so you shouldn't redeclare them inside your method Matrix() because they'll be considered as local variables.

Your code should be something like This :

void Matrix() {
n1 = 0;
n2 = 0;
System.out.println(" enter the dimension of the matrix");
n1=sc.nextInt();
n2=sc.nextInt();
matrix1= new int [n1][n2];
matrix2= new int [n1][n2];
...  

Answer 3

    Scanner sc=new Scanner(System.in);
    System.out.println("enter the size of row:-");
    int r=sc.nextInt();
    System.out.println("enter the column of array:-");
    int c=sc.nextInt();
    int[][] arr1=new int[r][c];
    int[][] arr2=new int[r][c];
    int[][] arr3=new int[r][c];
    int i,j,k,l,m,n;
    System.out.println("first matrix:- ");
    for(i=0;i<r;i++)
    {
        for(j=0;j<c;j++)
        {
            arr1[i][j]=sc.nextInt();
        }
    }System.out.println("second matrix:");
    for(i=0;i<r;i++)
    {
        for(j=0;j<c;j++)
        {
            arr2[i][j]=sc.nextInt();
        }
    }System.out.println("third matrix:- ");
    for(i=0;i<r;i++)
    {
        for(j=0;j<c;j++)
        {
            arr3[i][j]=arr1[i][j]+arr2[i][j];
        }
    }System.out.println("adding is:- ");
    for(i=0;i<r;i++)
    {
        for(j=0;j<c;j++)
        {
            System.out.println(arr3[i][j]+" ");
        }
    }System.out.println("\n");
    
}

}