為什么我在這里得到java.lang.StackOverflowError？

Question

_以下問題的以下程序給出了一系列異常Exception in thread "main" java.lang.StackOverflowError at testing_package.Compute.factorial(Compute.java:105)我不明白為什么會收到此錯誤。

問題 ：N個男孩和M個女孩正在從劇院學習表演技巧。 要表演戲劇，他們需要組成一組P演員，其中不少於4個男孩，且不少於1個女孩。 劇院要求您編寫一個程序，告訴他們組的形成方式的數量。 注意：合成應該是唯一的，而不是合成的順序。

import java.io.*;

class Compute {

private static int NFact;
private static int N_Minus_R_Fact;
private static int RFact;
private static int fact=0;

public static int readTheStrengthOfGroup() {
    int strengthOfGroup=0;
    try {
        System.out.println("Enter the strength of group : ");
        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
        String read = reader.readLine();
        strengthOfGroup = Integer.parseInt(read);
    } catch(Exception exc) {
        System.out.println(exc);
      }
      return strengthOfGroup;
}

public static int readTheNumberOfBoys() {
   int boysToParticipate=0;
   try {
    System.out.println("Enter the number of boys to participate in the play : ");
    BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
    String read = reader.readLine();
    boysToParticipate = Integer.parseInt(read);
   } catch(Exception exc) {
        System.out.println(exc);
     }
    return boysToParticipate;
}

public static int readTheNumberOfGirls() {
    int girlsToParticipate=0;
    try {
        System.out.println("Enter the number of girls to participate in the play : ");
        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
        String read = reader.readLine();
        girlsToParticipate = Integer.parseInt(read);
    } catch(Exception exc) {
        System.out.println(exc);
      }
    return girlsToParticipate;
}

public static int compute(int strengthOfGroup , int boysToParticipate , int girlsToParticipate) {
    if( boysToParticipate < 4 || girlsToParticipate < 1) {
        return 0;
    } else {
        /*  P >= 5 
         *  N : Boys
         *  M : Girls
         *  result = M+N C P - { (N C 0)(M C P)+(N C 1)(M C P-1)+(N C 2)(M C P-2)+(N C 3)(M C P-3)+(N C P)(M C 0) }
         */
         int resultP_2 = 0;
         int totalNumberOfParticipants = boysToParticipate + girlsToParticipate;
         int totalNumberOfParticipants_C_strengthOfGroup = computeFactorial(totalNumberOfParticipants , strengthOfGroup);
         for( int i = 0 ; i <= 4 ; i++ ) {
                          if( i == 4 ) {
                resultP_2 = resultP_2 + (computeFactorial(boysToParticipate,strengthOfGroup) * computeFactorial(girlsToParticipate,0)); 
            }else {
            resultP_2 = resultP_2 + (computeFactorial(boysToParticipate,i) * computeFactorial(girlsToParticipate,strengthOfGroup));
            strengthOfGroup--;}
         }
         int result = totalNumberOfParticipants_C_strengthOfGroup - resultP_2;
         return result;
      }
}

public static int computeFactorial(int N , int R) {
    if(R > N) {
        throw new RuntimeException("Invalid Parameters");
    } else {
        /* int NFact;
        int N_Minus_R_Fact;
        int RFact; */
        NFact = factorial(N);
        N_Minus_R_Fact = factorial(N-R);
        RFact = factorial(R);
        return( NFact / ( N_Minus_R_Fact-RFact ) );

      }
}

public static int factorial(int num) {
    if( num == 1 ) {
        return 1;
    } else {
        fact = num * factorial(num-1); // LINE 105
        return fact;
      }
}

public static void main(String args[]) {
    int strengthOfGroup = readTheStrengthOfGroup();
    int boysToParticipate = readTheNumberOfBoys();
    int girlsToParticipate = readTheNumberOfGirls();
    int result = compute(strengthOfGroup , boysToParticipate , girlsToParticipate);
    System.out.println("Number of groups that can be formed : " + result);
}

}

我已經評論了第105行。

Answer 1

computeFactorial避免在R > N調用factorial ，但是在所有其他情況下（ R == N ， R < N ）調用它，並傳入NR 。 如果R == N ，則NR為0 。 在factorial ，您要檢查num == 1並返回1 ，但是當num為0 ，將使用num - 1 （即-1進行factorial調用。 然后，它使用num - 1 （它是-2再次調用自己，依此類推，並使用越來越大的負數（ -1 ， -2 ，...），直到耗盡堆棧。

我沒有仔細閱讀代碼，但是至少當num == 0以及num == 1 （ 0! = 1 ）時，您需要有factorial返回1 。 如果您給它提供負數，我也會讓它拋出異常。