本文旨在帮助Java初学者解决在掷骰子游戏中循环中断时遇到的异常问题。通过分析代码，找出导致异常的原因，并提供修改后的代码示例，确保游戏在玩家选择退出或资金不足时能够正常结束，并展示游戏结束时的信息。
在提供的代码中，主要问题集中在游戏循环的退出条件和System.out.printf的使用上。以下将详细解释并提供修改后的代码。
问题分析与修复
循环退出条件
原代码中，循环的退出条件是playAgain && total > 0。这意味着只有当playAgain为true且total大于0时，循环才会继续。虽然在循环内部有break语句用于处理total <= 9和again.equalsIgnoreCase("n")的情况，但逻辑上没有错误。问题在于，当输入无效字符时，again变量的值未被正确更新，导致可能进入死循环。
修改后的代码示例：
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while (playAgain && total > 0) { // ... (游戏逻辑) ... if (total <= 9) { break; } System.out.println("Keep playing (y/Y or n/N)? "); in.nextLine(); // Consume the newline character String again = in.nextLine(); if (again.equalsIgnoreCase("y")) { playAgain = true; } else if (again.equalsIgnoreCase("n")) { playAgain = false; // Set playAgain to false to exit the loop break; } else { System.out.println("Invalid character input, try again:"); // No need to read input again here. The loop will continue and ask again. }}
注意事项：
在读取字符串之前，使用in.nextLine()来消耗掉之前in.nextInt()留下的换行符，避免影响后续的输入。当玩家输入 “n” 时，将 playAgain 设置为 false，确保循环能够正常退出。当输入无效字符时，不需要再次读取输入。循环会自动回到开始，再次提示用户输入。
System.out.printf 异常
原始代码中使用System.out.printf(“Based on your play, the probability of winning is %.2%”, winPercent);，这可能会导致MissingFormatArgumentException异常，因为%.2%需要一个参数，而winPercent已经被用作格式化的数值。
正确的做法是使用System.out.println进行字符串拼接，或者使用String.format方法。
修改后的代码示例：
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// 方法一：使用 System.out.println 进行字符串拼接System.out.println("Based on your play, the probability of winning is " + String.format("%.2f", winPercent) + "%.");// 方法二：使用 String.format//System.out.printf("Based on your play, the probability of winning is %.2f%%", winPercent);
解释：
方法一使用 String.format(“%.2f”, winPercent) 将 winPercent 格式化为保留两位小数的浮点数，然后与字符串拼接。方法二使用 String.format 和 %% 来输出百分号。
完整修改后的代码
import java.util.Random;import java.util.Scanner;public class GameOfCrapsTester { static Scanner in = new Scanner(System.in); static Random rand = new Random(); public static void main(String[] args) { System.out.println("Welcome to the game of Craps"); System.out.println(" "); System.out.println("The house has given you a starting balance of $500"); System.out.println("On each round, you will make a whole number wager."); System.out.println("The minimum wager is $10, and the maximum wager is your remaining balance."); System.out.println(" "); System.out.println("You may keep playing until you decide to cash in, or"); System.out.println(" you can't cover the minimum wager."); System.out.println("Good Luck!"); boolean win; double wins = 0, numOfGames = 0; int total = 500; // Come out roll and set point value int pointValue = 0; boolean playAgain = true; while (playAgain && total > 0) { System.out.println(" "); System.out.println("Your balance is $" + total); System.out.println(" "); System.out.println("Place your bet: $"); // Get and check wager placed int bet = in.nextInt(); in.nextLine(); // Consume newline while (bet > total || bet < 10) { if (bet = 4 && num <= 10 && num != 7) || num == 0) { pointValue = num; System.out.println(" "); System.out.println("Your point value is " + pointValue); System.out.println(" "); win = rollWithPoint(pointValue); if (win) { total = wonGame(bet, total); wins++; numOfGames++; System.out.println("Wins: " + wins + " Number of games: " + numOfGames); } else if (!win) { total = lostGame(bet, total); numOfGames++; System.out.println("Wins: " + wins + " Number of games: " + numOfGames); } } else if (num == 7 || num == 11) { total = wonGame(bet, total); wins++; numOfGames++; System.out.println("Wins: " + wins + " Number of games: " + numOfGames); } else { total = lostGame(bet, total); numOfGames++; System.out.println("Wins: " + wins + " Number of games: " + numOfGames); } if (total <= 9) { break; } System.out.println("Keep playing (y/Y or n/N)? "); String again = in.nextLine(); if (again.equalsIgnoreCase("y")) { playAgain = true; } else if (again.equalsIgnoreCase("n")) { playAgain = false; break; } else { System.out.println("Invalid character input, try again:"); } }// end of loop gameOver(wins, numOfGames); } // END of main public static int rollDice() { int dice1, dice2, total; dice1 = rand.nextInt(6) + 1; dice2 = rand.nextInt(6) + 1; total = dice1 + dice2; System.out.print("Your roll: "); System.out.print("Dice1: " + dice1); System.out.print(", Dice2: " + dice2); System.out.println("; Roll Value: " + total); return total; } // END of rollDice public static boolean rollWithPoint(int point) { int total = rollDice(); boolean winner = false; while (total != 7 && winner == false) { total = rollDice(); if (total == point) { winner = true; } else { winner = false; } } return winner; } // END of rollWithPoint public static int lostGame(int bet, int total) { System.out.println("Oh, I'm sorry, you lost."); System.out.println(" "); total = total - bet; System.out.println("Your current balance: $" + total); System.out.println(" "); return total; } // END of lostGame public static int wonGame(int bet, int total) { System.out.println("A winner!"); System.out.println(" "); total = total + bet; System.out.println("Your current balance: $" + total); System.out.println(" "); return total; } // END of wonGame public static void gameOver(double win, double tot) { double winPercent = (win / tot) * 100; System.out.println(" "); System.out.println("Based on your play, the probability of winning is " + String.format("%.2f", winPercent) + "%."); System.out.println(" "); System.out.println("Seems you lost your shirt; better luck next time."); System.out.println("Have a nice day! Hope to see you soon!"); } // END of gameOver} // END of GameOfCraps
总结
通过以上修改，可以解决游戏循环中断时可能出现的异常，并确保游戏在玩家选择退出或资金不足时能够正常结束。同时，修正了概率输出的格式，使其更加清晰易懂。希望本文能够帮助Java初学者更好地理解和掌握循环控制和字符串格式化的相关知识。
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