Java字符串索引越界，CharAt問題

Question

我的代碼拋出錯誤“字符串索引越界：1”，這是代碼：

     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");
    }
    }
    }

分配說明是：“彩票程序生成一個介於 01-99 之間的兩位數。如果用戶以正確的順序猜對了數字，他們將贏得 1000$。如果用戶以錯誤的順序猜對了數字，示例 16 “他們贏了 500 美元，而不是 61。如果用戶猜對了其中一個數字，他們就贏了 100 美元。”

當用戶輸入和/或 randomNum 為 10 及以上時，代碼工作正常。 但是，當它低於 10 時，會發生錯誤，因為該值被讀取為 1 個字符而不是 2，例如： 09 讀取為 9 ，因此 charAt(1) 不存在。

我怎樣才能解決這個問題？ 有沒有辦法讓 0 算作 charAt(0) 以便 charAt(1) 計算 0 之后的數字，或者我需要更改其他內容嗎？

謝謝！

Answer 1

正如我在評論中提到的：你有String sa = String.format("%02d", value); 但是你在主代碼中使用了str1 。 使用sa代替，即使數字小於 10，它也會有 2 個字符。

另一種選擇是不使用字符串。 這是一個僅限數學的版本。

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");
}