这两个类的逻辑区别是什么？

Question

我已经编写了一个Java类来解决教科书Javanotes 7中的一个问题，该教程要求提供一个程序，该程序显示与在掷骰子上获得给定值所需的掷骰数量相关的统计信息。我的班级没有给我正确的统计数据，但据我所知，这在教科书中给出的解决方案在逻辑上是相同的。显然不是。 这里是我的代码：

/** 
    This program rolls a pair of dice until they come up a certain value. It repeats this for a certain number of trials and then gives the user the average number of 
    rolls required to achieve the target value. It does this for each possible value of two six-sided dice. It also gives the standard deviation and the maximum 
    number of rolls. 
*/ 

public class DiceAverage{ 

    static final int SAMPLE_SIZE = 10000; 

    public static void main(String[] args){ 

     System.out.println("Total on Dice Average Number of Rolls Standard Deviation Maximum Number of Rolls"); 
     System.out.println("------------- ----------------------- ------------------ -----------------------"); 

     //each dice value iterator 
     for(int i = 2; i < 13; i ++){ 

      //for each value, create a Statcalc, and PairOfDice object 
      StatCalc dataset = new StatCalc(); 
      PairOfDice dice = new PairOfDice(); 

      //each trial iterator 
      for(int j = 0; j < SAMPLE_SIZE; j ++){ 

       int counter = 1;//counter for number of rolls. Initialized at 1 because dice object is rolled upon construction. 

       //get die1 and die2 
       while(dice.getDie1() + dice.getDie2() != i){ 

        dice.roll(); 
        counter ++; 

       } 

       dataset.enter(counter); 

      } 

      System.out.printf("  %-19d%-25.3f%-25.3f%1.3f%n", i, dataset.getMean(), dataset.getStandardDeviation(), dataset.getMax()); 

     } 

    } 

} 

这里是实际的解决方案：

/**This program performs the following type of experiment: 
* Given a desired total roll, such as 7, roll a pair of 
* dice until the given total comes up, and count how many 
* rolls are necessary. Now do the experiment over and over, 
* and find the average number of rolls. The number of times 
* the experiment is repeated is given by the constant, 
* NUMBER_OF_EXPERIMENTS. Several statistics are computed and 
* printed out for each possible roll = 2, 3, ..., 12: 
* the average number of rolls, the standard deviation, 
* and the maximum number of rolls. 
*/ 

public class DiceRollStats2 { 

    static final int NUMBER_OF_EXPERIMENTS = 10000; 

    private static PairOfDice dice = new PairOfDice(); 
      // A single pair of dice, which will be used for all 
      // the experiments. 


    public static void main(String[] args) { 

     System.out.println("Dice Total Avg # of Rolls Stand. Deviation Max # of Rolls"); 
     System.out.println("---------- -------------- ---------------- --------------"); 

     for (int total = 2; total <= 12; total++) { 
      StatCalc stats; // An object that will compute the statistics. 
      stats = new StatCalc(); 
      for (int i = 0; i < NUMBER_OF_EXPERIMENTS; i++) { 
       // Do the experiment of counting the number of rolls 
       // required to roll the desired total, and enter the 
       // number of rolls into stats' dataset. 
      stats.enter(rollFor(total)); 
      } 
      System.out.printf("%6d", total); 
      System.out.printf("%18.3f", stats.getMean()); 
      System.out.printf("%19.3f", stats.getStandardDeviation()); 
      System.out.printf("%14.3f", stats.getMax()); 
      System.out.println(); 
     } 

    } // end main 

    /** 
    * Roll the dice repeatedly until the total on the 
    * two dice comes up to be N. N MUST be one of the numbers 
    * 2, 3, ..., 12. (If not, this routine will go into an 
    * infinite loop!). The number of rolls is returned. 
    */ 
    static int rollFor(int N) { 
     int rollCt = 0; // Number of rolls made. 
     do { 
      dice.roll(); 
      rollCt++; 
     } while (dice.getDie1() + dice.getDie2() != N); 
     return rollCt; 
    } 


} // end class DiceRollStats2 

我看不到它们之间的逻辑差异。它是什么？

Answer 1

int rollCt = 0; // Number of rolls made. 
    do { 
     dice.roll(); 
     rollCt++; 
    } while (dice.getDie1() + dice.getDie2() != N); 
    return rollCt; 

这里的骰子在do ... while循环布尔测试之前推出初始化它计数加1卷。

int counter = 1;//counter for number of rolls. Initialized at 1 because dice object is rolled upon construction. 

      //get die1 and die2 
      while(dice.getDie1() + dice.getDie2() != i){ 

       dice.roll(); 
       counter ++; 

      } 

虽然这里的骰子在布尔测试后滚动。因此，如果骰子等于i，那么掷骰子值永远不会被roll（）改变 - 因为while循环被跳过了 - 并且您通过count == 1的for循环获得了一堆迭代。基本上，掷骰子是没有用这种方式正确模拟。

Answer 2

你被初始化int counter = 1;

尝试用0