java - 如何让用户重新输入一个值直到它有效

Question

我在网页设计上花了很多时间后最近开始学习 Java，但是当我尝试创建一个简单的猜谜游戏程序时遇到了一个问题。

        final int MAX = 15;
    int answer, guess;
    Scanner scan = new Scanner (System.in);

    Random generator = new Random();
    answer = generator.nextInt(MAX) + 1;

    System.out.println("I'm thinking of a number between 1 and " + MAX + ". Guess what is it: ");

    guess = scan.nextInt();

    if (guess > MAX)
        System.out.println("Please choose a number between 1 and 15.");
    if (guess == answer)
        System.out.println("You got it! Good guessing!");
    else
    {
        System.out.println("This isn't correct, sorry!");
        System.out.println("The number was " + answer);

我希望这样，如果用户输入的值大于 15，它会将用户发回以重新输入 1 到 15 之间的有效数字。

首先，如果我知道它尚未完成，因为这是我计划添加此功能的地方。

Answer 1

先看看 Control Flow Statements‌​ ，特别是 for-loop、while-loop 和 do-while-loop

部分

基本上，您需要某种循环，它将继续重复直到满足某些退出条件(即在您指定范围内的值)

有点像...

do {

    System.out.print("Please choose a number between 1 and " + max + ":");
    guess = scan.nextInt();

} while (guess < 1 || guess > 15);

这基本上会继续提示用户，直到他们输入一个介于 1 和 15 之间的值。

作为一个可运行的例子...

import java.util.Random;
import java.util.Scanner;

public class GuessMe {

    public static void main(String[] args) {

        int max = 15;

        int guess = 0;
        Random generator = new Random();
        int answer = generator.nextInt(max) + 1;
        Scanner scan = new Scanner(System.in);

        System.out.println("I'm thinking of a number between 1 and " + max + ". Guess what is it\n");
        do {

            do {

                System.out.print("Please choose a number between 1 and " + max + ":");
                guess = scan.nextInt();

            } while (guess < 1 || guess > 15);

            if (guess < answer) {
                System.out.println("Good guess, but mine is higher");
            } else if (guess > answer) {
                System.out.println("Good guess, but mine is low");
            }

        } while (guess != answer);

        System.out.println("Good guess, that's right!");

    }

}

已更新

严格来说，您不需要内部循环(在本例中)，但它确实展示了您如何能够重新提示用户输入单个给定值。

另一种方法可能是使用 if-else block ，而不是更直接地检查输入的结果。

import java.util.Random;
import java.util.Scanner;

public class GuessMe {

    public static void main(String[] args) {

        int max = 15;

        int guess = 0;
        Random generator = new Random();
        int answer = generator.nextInt(max) + 1;
        Scanner scan = new Scanner(System.in);

        System.out.println("I'm thinking of a number between 1 and " + max + ". Guess what is it\n");
        do {

            System.out.print("Please choose a number between 1 and " + max + ":");
            guess = scan.nextInt();

            if (guess < 1 || guess > 15) {
                System.out.println("You did't enter a valid number, please try again");
            } else if (guess < answer) {
                System.out.println("Good guess, but mine is higher");
            } else if (guess > answer) {
                System.out.println("Good guess, but mine is low");
            }

        } while (guess != answer);

        System.out.println("Good guess, that's right!");

    }

}