Java掷骰子模拟程序无限循环问题定位求助

问题根源 #

• 外层哨兵循环的大括号范围错误：重置计数、询问用户是否继续执行的代码，被放在了while(runAgain == 0)的大括号外部。第一次完成10000次掷骰子后，runAgain永远保持初始值0，count也不会被重置，程序会反复输出上一次的运行结果，形成无限循环。
• 次要问题：count初始值设为-1不符合常规计数逻辑，虽不影响最终输出但可读性差，建议调整为0。

修复后的完整代码 #

import java.util.Random;   // Needed for the Random class
import java.util.Scanner;   // Needed for the Scanner class

/**
   This class simulates rolling a pair of dice 10,000 times
   and counts the number of times doubles of are rolled for
   each different pair of doubles.
*/
public class RollDice {
    public static void main(String[] args){

        final int NUMBER = 10000;  // Number of dice rolls

        // A random number generator used in
        // simulating the rolling of dice
        Random generator = new Random();

        int die1Value;       // Value of the first die
        int die2Value;       // Value of the second die
        int snakeEyes = 0;   // Number of snake eyes rolls
        int twos = 0;        // Number of double two rolls
        int threes = 0;      // Number of double three rolls
        int fours = 0;       // Number of double four rolls
        int fives = 0;       // Number of double five rolls
        int sixes = 0;       // Number of double six rolls
        int runAgain = 0;    // Sentinel variable

        Scanner keyboard = new Scanner(System.in); //Scanner Object

        while(runAgain == 0){ //This is a sentinel loop
            int count = 0;       // 每次运行重置计数，放在循环内部更合理
            // TASK #1 Enter your code for the algorithm here
            while(count < NUMBER)
            {
                // Roll both dice
                die1Value = generator.nextInt(6) + 1;
                die2Value = generator.nextInt(6) + 1;

                // Check to see if both dice are equal
                if(die1Value == die2Value)
                {
                    // Check dice values and update counts
                    if(die1Value == 1)
                        snakeEyes++;
                    else if(die1Value == 2)
                        twos++;
                    else if(die1Value == 3)
                        threes++;
                    else if(die1Value == 4)
                        fours++;
                    else if(die1Value == 5)
                        fives++;
                    else
                        sixes++;
                }
                count++;

            }
            // Display the results
            System.out.println ("You rolled snake eyes " +
                snakeEyes + " out of " +
                count + " rolls.");
            System.out.println ("You rolled double twos " +
                twos + " out of " + count +
                " rolls.");
            System.out.println ("You rolled double threes " +
                threes + " out of " + count +
                " rolls.");
            System.out.println ("You rolled double fours " +
                fours + " out of " + count +
                " rolls.");
            System.out.println ("You rolled double fives " +
                fives + " out of " + count +
                " rolls.");
            System.out.println ("You rolled double sixes " +
                sixes + " out of " + count +
                " rolls.");
            
            // 重置所有计数
            snakeEyes = 0;
            twos = 0;
            threes = 0;
            fours = 0;
            fives = 0;
            sixes = 0;

            // 询问用户是否重新运行
            System.out.println("Do you wish to run again?");
            System.out.println("Enter a 0 for yes or a -1 for no");
            // 读取用户的响应
            runAgain = keyboard.nextInt();
        }
        keyboard.close(); // 用完关闭扫描器避免资源泄漏
    }
}

修复说明 #

• 把变量重置、用户询问逻辑整体移入外层while(runAgain == 0)的大括号内部，每次完成一轮投掷后都会询问用户是否继续，更新runAgain的值，符合哨兵循环的逻辑
• 将count变量移到外层循环内部声明，每次运行自动重置，避免全局变量污染，可读性更强
• 新增Scanner的close调用，避免资源泄漏

内容的提问来源于stack exchange，提问作者Donovan Tuck