Java Try-catch块，Catch块不会重新提示用户输入新值[重复]

Question

我是Java新手，想问你一个问题。

我编写了下面的代码，其中“numofthreads”应该由用户通过控制台分配一个有效的int值。

import java.util.Scanner;

public class Main {

    public static void main(String args[]){

        int numOfThreads;
        boolean promptUser = true;

        Scanner keyboard = new Scanner(System.in);

        while (promptUser)
        {
            try{
                numOfThreads = keyboard.nextInt();
                promptUser = false;
            }
            catch(Exception e){
                System.out.println("Entry is not correct and the following exception is returned: " + e);
                numOfThreads = keyboard.nextInt(); // DOES NOT SEEM TO BE ASKING FOR A NEW INPUT
            }
        }
    }
}

Answer 1

它不是因为NextInt试图使用最后一个令牌。当有一个无效的输入，它不能消耗它。因此，下面的NextInt调用也不能使用它。在numofthreads=keyboard.nextint()之前编写keyboard.nextline；就可以了。

catch(Exception e){
    System.out.println("Entry is not correct and the following exception is returned: " + e);
    // this consumes the invalid token now
    keyboard.nextLine();
    numOfThreads = keyboard.nextInt(); // It wasn´t able to get the next input as the previous was still invalid
    // I´d still rewrite it a little bit, as this keyboard.nextInt is now vulnerable to throw a direct exception to the main
}