Question

我是java的新手，对使用循环很新，到目前为止，我一直在为我的班级制作一个程序，检查用户是否输入随机生成的正确数字的变体，但是它说一旦循环开始，就无法找到lotteryNumberString。关于如何修复它的任何提示？

    import java.util.Scanner;
    public class Lottery
    {
    public static void main(String[] args)
    {
    Scanner input = new Scanner(System.in);

    for(int i=0; i < 3; i++)
    {
        double lotto = Math.random();
        int lotteryNumberDigit = (int)(lotto*10);

        String lotteryNumberString = Integer.toString(lotteryNumberDigit);

        }



            String firstNumber = lotteryNumberString.substring(0,0);
            String secondNumber = lotteryNumberString.substring(1,1);
            String thirdNumber = lotteryNumberString.substring(2,2);

            String firstTwoWinner = firstNumber + secondNumber;
            String lastTwoWinner = secondNumber + thirdNumber;
            String allNumbersWinner = firstNumber + secondNumber + thirdNumber;

            System.out.println("Please enter your three numbers (e.g. 123): ");

            String userInput = input.next();

             if(userInput.substring(0,2).equals(firstTwoWinner))

        {
            System.out.println("Winner: " + allNumbersWinner );

            System.out.println("Congratulations, the front pair matched.");
        }

        else if (userInput.substring(1,3).equals(lastTwoWinner))
        {
             System.out.println("Winner: " + allNumbersWinner );

             System.out.println("Congratulations, the end pair matched.");
        }

        else if (userInput.equals(allNumbersWinner))
        {
             System.out.println("Winner: " + allNumbersWinner );

             System.out.println("Congratulations, both pairs matched.");
        }

        else
        {
             System.out.println("Winner: " + allNumbersWinner );

             System.out.println("Sorry, no matches. You only had one chance out of 100 to win anyway.");
        }



    }
}

Answer 1

看一下这篇文章：http://www.java-made-easy.com/variable-scope.html。您面临的问题与lotteryNumberString变量的范围（生命周期）有关。如果在循环内部声明，它不存在于循环外部。要解决此问题，请在for循环

之前声明lotteryNumberString

Answer 2

问题是编译问题..因为你的lotterNumberString只在for循环中作用域，所以它在外面不可见。你可能需要做这样的事情。

import java.util.Scanner;
public class Lottery
{
public static void main(String[] args)
{
Scanner input = new Scanner(System.in);
String lotteryNumberString = null;
for(int i=0; i < 3; i++)
{
    double lotto = Math.random();
    int lotteryNumberDigit = (int)(lotto*10);

    lotteryNumberString = Integer.toString(lotteryNumberDigit);

    }



        String firstNumber = lotteryNumberString.substring(0,0);
        String secondNumber = lotteryNumberString.substring(1,1);
        String thirdNumber = lotteryNumberString.substring(2,2);

        String firstTwoWinner = firstNumber + secondNumber;
        String lastTwoWinner = secondNumber + thirdNumber;
        String allNumbersWinner = firstNumber + secondNumber + thirdNumber;

        System.out.println("Please enter your three numbers (e.g. 123): ");

        String userInput = input.next();

         if(userInput.substring(0,2).equals(firstTwoWinner))

    {
        System.out.println("Winner: " + allNumbersWinner );

        System.out.println("Congratulations, the front pair matched.");
    }

    else if (userInput.substring(1,3).equals(lastTwoWinner))
    {
         System.out.println("Winner: " + allNumbersWinner );

         System.out.println("Congratulations, the end pair matched.");
    }

    else if (userInput.equals(allNumbersWinner))
    {
         System.out.println("Winner: " + allNumbersWinner );

         System.out.println("Congratulations, both pairs matched.");
    }

    else
    {
         System.out.println("Winner: " + allNumbersWinner );

         System.out.println("Sorry, no matches. You only had one chance out of 100 to win anyway.");
    }



}

如何使用'for'循环检查输入中的某些数字？

2 个答案: