爲什麼我在這裏得到java.lang.StackOverflowError？

Question

_下面的問題的程序給出了一系列例外情況Exception in thread "main" java.lang.StackOverflowError at testing_package.Compute.factorial(Compute.java:105)我不明白爲什麼我會得到這個錯誤。

問題：N個男孩和M個女孩正在從劇院學習演技。要進行遊戲 ，他們需要組成一組包含不少於4個男孩和不少於1個女孩的P組演員。劇院要求你編寫一個程序，告訴他們可以組成團隊的方式數量。 注：組成應該是唯一的，而不是組成物的組成順序。

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); 
} 

}

我評論過線人數105

Answer 1

computeFactorial避免調用factorial如果R > N，但稱它在所有其他情況下（R == N，R < N），傳遞N-R。如果R == N，則N-R是0。在factorial中，您正在檢查是否num == 1和返回1，但是當num是0時，您有factorial調用本身與num - 1，這是-1。然後它會自動再次調用num - 1，這是-2等等，並且負數越來越大（-1，-2，...），直到您用完堆棧。

我還沒有仔細閱讀代碼，但最起碼​​，你需要有factorial回報1時num == 0以及何時num == 1（0! = 1）。如果你給它一個負數，我也會拋出異常。