为什么矩阵加法在此代码中不起作用？答案

【问题标题】：Why is matrix addition not working in this code?为什么矩阵加法在此代码中不起作用？
【发布时间】：2021-01-12 00:17:37
【问题描述】：

谁能告诉我为什么矩阵加法在这段代码中不起作用？该程序的所有其他部分都在工作，除了添加部分。它只是打印一个空数组作为输出。

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();   
    }
}

【问题讨论】：

因为在方法Matrix() 的范围内有局部矩阵matrix1、matrix2。您不需要在方法中重新声明它们，只需分配即可。

标签： java arrays function matrix methods

【解决方案1】：

    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");
    
}

}

【讨论】：

【解决方案2】：

您已经在类的开头声明了n1、n2、matrix1 和matrix2，因此您不应在方法Matrix() 中重新声明它们，因为它们将被视为局部变量.

你的代码应该是这样的：

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];
...

【讨论】：

【解决方案3】：

如果您打算在其他方法中使用它们，则无需在方法Matrix() 中重新声明实例变量n1、n2、matrix1、matrix2：

// 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));
    }

【讨论】：