NoSuchElementException发生在简单的Java程序中以添加两个矩阵吗？

Question

Below is the program to add two matrices :

import java.util.Scanner;
//import java.io.BufferedReader;
//import java.io.InputStreamReader;
public class addmatrix {
    int row,col;
    int v[][]=new int[100][100];

    public addmatrix(int i, int j) {
        // TODO Auto-generated constructor stub
        row=i;
        col=j;
    }
    public void display(){
        for(int d=0;d<row;d++){
            for(int e=0;e<col;e++){
                System.out.print(v[d][e]);
            }
        System.out.println(" ");
        }
    }
    public void getmat(){   
        Scanner iny=new Scanner(System.in);
        for(int d=0;d<row;d++)
            for(int e=0;e<col;e++){
                System.out.println("Enter the element:");
                v[d][e]=iny.nextInt();
            }
        iny.close();
        }
    public addmatrix add(addmatrix m){
        addmatrix ans=new addmatrix(m.row,m.col);
        for(int d=0;d<m.row;d++)
            for(int e=0;e<m.col;e++){
                ans.v[d][e]=v[d][e]+m.v[d][e];
            }
        return ans;
    }

    /**
     * @param args
     */
    public static void main(String[] args)throws Exception {
        // TODO Auto-generated method stub
        System.out.println("Enter the no. of rows: ");
        Scanner inp=new Scanner(System.in);
        int i=0,j=0;
        i=inp.nextInt();
        System.out.println("Enter the no. of column: ");
        j=inp.nextInt();
        addmatrix m1=new addmatrix(i,j);
        m1.getmat();
        m1.display();
        addmatrix m2=new addmatrix(i,j);
        m2.getmat();
        System.out.print("+");
        m2.display();
        addmatrix m3=new addmatrix(i,j);
        m3=m1.add(m2);
        System.out.print("=");
        m3.display();
    }

}

There is no exception occuring when getmat() is called for the first time using m1, but when again I'm creating a object m2 and if I'm calling getmat() using m2 then it throws the exception.

Exception in thread "main" java.util.NoSuchElementException
    at java.util.Scanner.throwFor(Unknown Source)
    at java.util.Scanner.next(Unknown Source)
    at java.util.Scanner.nextInt(Unknown Source)
    at java.util.Scanner.nextInt(Unknown Source)
    at addmatrix.getmat(addmatrix.java:26)
    at addmatrix.main(addmatrix.java:54)

I don't understand why this exception is occuring.

Answer 1

In your getmat function you close the Scanner. This also closes the underlying source, which in your case is System.in. Because you closed System.in, you can no longer read from it.

I suggest you only create one Scanner and use it for all calls of getmat.

And also, please use camelcase!

You could do it this way:

import java.util.Scanner;

public class AddMatrix {
    int row, col;
    int values[][];

    public AddMatrix(int i, int j) {
        row = i;
        col = j;
        this.values = new int[i][j];
    }

    public void display() {
        for (int d = 0; d < row; d++) {
            for (int e = 0; e < col; e++) {
                System.out.print(values[d][e]);
            }
            System.out.println(" ");
        }
    }

    public void getMat(Scanner scanner) {
        for (int d = 0; d < row; d++)
            for (int e = 0; e < col; e++) {
                System.out.println("Enter the element:");
                values[d][e] = scanner.nextInt();
            }
    }

    public AddMatrix add(AddMatrix m) {
        AddMatrix ans = new AddMatrix(m.row, m.col);
        for (int d = 0; d < m.row; d++)
            for (int e = 0; e < m.col; e++) {
                ans.values[d][e] = values[d][e] + m.values[d][e];
            }
        return ans;
    }

    public static void main(String[] args) throws Exception {
        System.out.println("Enter the no. of rows: ");
        Scanner scanner = new Scanner(System.in);
        int i = 0, j = 0;
        i = scanner.nextInt();
        System.out.println("Enter the no. of column: ");
        j = scanner.nextInt();
        AddMatrix m1 = new AddMatrix(i, j);
        m1.getMat(scanner);
        m1.display();
        AddMatrix m2 = new AddMatrix(i, j);
        m2.getMat(scanner);
        System.out.print("+");
        m2.display();
        AddMatrix m3 = new AddMatrix(i, j);
        m3 = m1.add(m2);
        System.out.print("=");
        m3.display();
        scanner.close();
    }
}

Note: I also changed your array initialization to be exactly the entered size instead of 100x100.