如何停止while循环无限运行？

Question

不知道如何阻止这个while循环无限重复。我使用HasNextInt检查用户输入是否为int。如果没有输入int值，则循环将无限重复。

public static void validatingInput(){
    Scanner scan = new Scanner(System.in);

    boolean valid = false;
    int userNumber = 0;

    while(!valid) { 
    System.out.println("Enter number between 1 and 20: ");

    if (scan.hasNextInt()) {    
    userNumber = scan.nextInt();
    valid = true;   
    } else 
        System.out.print("Not an int. ");
    }

}

Answer 1

您需要使用来自扫描器的令牌，以便允许它读取下一个令牌：

while (!valid) { 
    System.out.println("Enter number between 1 and 20: ");

    if (scan.hasNextInt()) {    
        userNumber = scan.nextInt();
        valid = true;   
    } else 
        System.out.print("Not an int. ");
        scan.next(); // Skip a token
    }
}