Java字符串索引出界，CharAT问题

Question

我的代码抛出了一个错误“字符串索引超出界限：1”，下面是代码：

     package inlamningsuppgift2;
        import java.util.Random;
        import java.util.Scanner;
        import java.lang.Math;
        
        public class inlamningsuppgift2del2 {
    
        public static void main(String[] args) {
            System.out.println("Guess a number between 01-99");
            
            randomNumber();
            
            
            
        }
        
            public static void randomNumber () {
    
        Scanner scanner = new Scanner(System.in);
        Random random = new Random();
            
        int value = Integer.valueOf(scanner.nextLine());
    
        String str1 = Integer.toString(value);
        String sa = String.format("%02d", value);
    
    
            int randomNum = 10 * random.nextInt(9);
                int randomNum2 = 1 * random.nextInt(9) +1;
                int wholeNum = randomNum + randomNum2;
                String str2 = Integer.toString(randomNum + randomNum2);
                String s = String.format("%02d", randomNum + randomNum2);
    
    
    System.out.println("You guessed :" + sa);
    System.out.println("The correct number is : " + s);
        if (str2.charAt(0) == str1.charAt(0) && str2.charAt(1) == str1.charAt(1)) {
       System.out.println("Congratulations, you guessed the right number in the right order and won 1000$!");
    }
        
    else if (str1.charAt(0) == str2.charAt(1) && str1.charAt(1) == str2.charAt(0) ) {
    System.out.println("Congratulations, you guessed the right number but in the wrong order and won 500$ !");
    }
    else if (str2.charAt(0) == str1.charAt(0) && str2.charAt(1) != str1.charAt(1)
    || str2.charAt(0) != str1.charAt(0) && str2.charAt(1) == str1.charAt(1)
    || str1.charAt(1) == str2.charAt(0) && str1.charAt(0) != str2.charAt(1)
    || str1.charAt(0) == str2.charAt(1) && str1.charAt(1) != str2.charAt(0)) {
    System.out.println("Congratulations, you guessed one of the numbers right!");
    }
    
 else {
    System.out.println("Sorry you guessed wrong, try again");
    }
    }
    }

分配指令是：“彩票程序生成一个介于01-99之间的两位数。如果用户以正确的顺序猜对了数字，他们将赢得1000美元。如果用户以错误的顺序猜对了数字，例如16而不是61，他们将赢得500美元。如果用户猜对了其中一个数字，他们将赢得100美元。”

当用户输入和/或randomNum为10或以上时，代码工作正常。然而，当它低于10时，发生错误，因为该值被读取为1个字符而不是2，例如：09被读取为9，因此charAt（1）不存在。

我怎样才能解决这个问题？有没有一种方法可以使0计数为charAt（0），以便charAt（1）计数0之后的数字，或者我需要更改其他内容？

谢谢！

Answer 1

正如我在评论中提到的：您有String sa=String.format（"d"， value）；但您在主代码中使用str1。改用sa，即使数字小于10，它也会有2个字符。

另一个选项是不使用字符串。这是一个纯数学版本。

public static void randomNumber () {
{
    System.out.println("Guess a number between 01-99");
    Scanner scanner = new Scanner(System.in);
    Random random = new Random();
                
    int value = Integer.valueOf(scanner.nextLine());
    // TODO: add a check 1 <= value <= 99
    int randomNum = random.nextInt(98) + 1;
    
    System.out.printf("You guessed :%02d%n", value);
    System.out.printf("The correct number is : %02d%n", randomNum);
    
    // Check for exact match
    if (value == randomNum) {
        System.out.println("Congratulations, you guessed the right number in the right order and won 1000$!");
        return;
    }
    
    // Get the digits of the random number (works for single digit numbers, too)
    int randOnes = randomNum % 10;
    int randTens = randomNum / 10;

    // Check for reverse match
    if (value == (randOnes * 10 + randTens)) {
        System.out.println("Congratulations, you guessed the right number but in the wrong order and won 500$ !");
        return;
    }
    
    // Get user's digits
    int userOnes = value % 10;
    int userTens = value / 10;

    // Check for single digit match
    if (userOnes == randOnes || userOnes == randTens || userTens == randOnes || userTens == randTens) {
        System.out.println("Congratulations, you guessed one of the numbers right!");
        return;
    }
    System.out.println("Sorry you guessed wrong, try again");
}