关闭扫描器时出现java.util.NoSuChelementException错误

Question

public class a2 {

    public static int read() {
        Scanner sc = new Scanner(System.in);
        int num = sc.nextInt();
        sc.close();
        return num;
    }

    public static void out (int a, int b) {
        System.out.println("Sum: " + (a+b));
        System.out.println("Difference: " + (a-b));
        System.out.println("Product: " + (a*b));
        System.out.println("Quotient: " + ((double)a/(double)b));
        System.out.println("Remainder: " + (a%b));
    }

    public static void main(String[] args) {
        System.out.println("Please enter two integers!:");
        int a = read();
        int b = read();     
        out(a,b);
    } 
} 

我对我的代码有一点理解上的问题。每次运行代码时，在输入第一个整数后都会收到此错误消息。

在java.util.scanner.throwfor（未知源）在java.util.scanner.next（未知源）在java.util.scanner.nextint（未知源）在java.util.scanner.nextint（未知源）在java.util.scanner.nextint（未知源）在a2.read(A2.java:6)在a2.main(A2.java:22)

我发现，当我删除“sc.close（）；”行，或者当我将两个变量中的一个定义为常数时，它工作得非常好。有人能给我解释一下吗？

Answer 1

你不能这样做：

int a = read();
int b = read();     

因为read方法正在关闭扫描器，并在幕后关闭来自系统的输入流······

全局声明扫描器对象并读取所需的内容，最后关闭它

private static Scanner sc;

public static int read() {

    return sc.nextInt();
}

public static void out(final int a, final int b) {
    System.out.println("Sum: " + (a + b));
    System.out.println("Difference: " + (a - b));
    System.out.println("Product: " + a * b);
    System.out.println("Quotient: " + (double) a / (double) b);
    System.out.println("Remainder: " + a % b);
}

public static void main(final String[] args) {
    System.out.println("Please enter two integers!:");
    sc = new Scanner(System.in);
    int a = read();
    int b = read();
    sc.close();
    out(a, b);
}