java - 使用 Scanner.nextInt() 时如何处理无效输入

Question

我是一个初学者，我编写了一个java程序，允许您输入n个数字，并且仅在输入数字-5时才显示最大值、最小值和平均值，我的程序无法正确显示，我需要一些帮助。当输入字符串而不是整数时，我想使用 try/catch 来捕获错误。

        import java.util.Scanner;
public class Average{
public static void main(String[]args){

System.out.print("Enter any integer numbers or -5 to quit:");
        Scanner scan =new Scanner(System.in);
    double avg = 0.0;
    int number = -1;
    double avg = 0.0;
    double sum = 0;
    int count = 0; 
    int min = Integer.MAX_VALUE;
    int max = Integer.MIN_VALUE;

    try {
    while((scan.nextInt())!= -5)
       {
     if (count != 0) {
        avg = ((double) sum) / count;
    count++;
    }   
         if (number > max){
        max = number;
        }
        if(number < min){
       min = number;
        }
        catch (InputMismatchException e) {
      System.out.println("please enter only integer numbers");

    System.out.println("Average : " + avg); 
    System.out.println("maximum : " + max);
    System.out.println("minimum : " + min);
}
}
}
}
}

Answer 1

为了在循环中获取整数输入、响应“退出”值并防止无效输入，我将使用类似下面的模板的内容。

请注意，到目前为止，所有答案都没有提到的一个关键问题是，仅仅捕获 InputMismatchException 还不够好。您还必须调用扫描仪对象的 nextLine() 方法来清除其缓冲区中的错误输入。否则，错误的输入将在无限循环中重复触发相同的异常。根据具体情况，您可能需要使用 next() 来代替，但要知道像 this has paths 这样的输入会生成多个异常。

代码

package inputTest;

import java.util.Scanner;
import java.util.InputMismatchException;

public class InputTest {
    public static void main(String args[]) {
        Scanner reader = new Scanner(System.in);

        System.out.println("Enter integers or -5 to quit.");

        boolean done = false;
        while (!done) {
            System.out.print("Enter an integer: ");
            try {
                int n = reader.nextInt();
                if (n == -5) {
                    done = true;
                }
                else {
                    // The input was definitely an integer and was definitely 
                    // not the "quit" value.  Do what you need to do with it.
                    System.out.println("\tThe number entered was: " + n);
                }
            }
            catch (InputMismatchException e) {
                System.out.println("\tInvalid input type (must be an integer)");
                reader.nextLine();  // Clear invalid input from scanner buffer.
            }
        }
        System.out.println("Exiting...");
        reader.close();
    }
}

示例

Enter integers or -5 to quit.
Enter an integer: 12
    The number entered was: 12
Enter an integer: -56
    The number entered was: -56
Enter an integer: 4.2
    Invalid input type (must be an integer)
Enter an integer: but i hate integers
    Invalid input type (must be an integer)
Enter an integer: 3
    The number entered was: 3
Enter an integer: -5
Exiting...