如何阻止 while 循环无限运行？

不知道如何阻止这个 while 循环无限重复。我在用着hasNextInt检查用户输入是否为 int。如果未输入 int，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. ");
    }

}

您需要使用扫描仪中的令牌才能使其读取下一个令牌：

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
    }
}