使用類方法劃分總是爲零

Question

我的類方法之一的結果總是出現0。我知道這可能發生，因爲整數部門，我已經嘗試將所需的任何數字鑄造到double;但它保持0。問題在於底部的variance方法。這對我來說很奇怪，因爲Average方法似乎分得很好。

public class MyArray { 

    private int[] array; 
    private int count = 0; 
    public int length; 
    public double sum; 
    public double average; 
    public double sqSum; 
    public double variance; 

    //Constructor to instantiate a new array   
    public MyArray(int length) { 
     array = new int[length]; 
    } 

    public int length(){ 
     return array.length; 
    } 


    //getter for count 
    public int getCount(){ 
     return count; 
    } 

    //setter for count 
    public void setCount(int Count){ 
     this.count = Count; 
    } 

    //getter for integers 
    public int[] getInts(){ 
     return array; 
    } 

    //setter for integers 
    public void setInts(int counter, int input) { 
     array[counter] = input; 
    } 

    public int getArray(int position) { 
    return array[position]; 
    } 

    public void setArray(int counter, int element){ 
     array[counter] = element; 
    } 
    public int intAt(int index) { 
     return array[index]; 

    } 
    //Method to print Arrays 
    public void printArray() { 
     System.out.println("\nThe length of the array is "   
     + array.length); 

     for(int i=0; i<array.length; i++) 
      System.out.println("The array is:" + array[i]); 
    } 

//Method to check if array is sorted 
    public void isSortedArray() { 
     for(int i=0; i<array.length; i++) 
      System.out.println("The array is:" + array[i]); 
    } 

//method to calc sum 
    public double sum() { 
     for(int i=0; i<array.length;i++) 
      sum+= array[i]; 

     return (double)sum; 
    } 


    //method to calc Average 
    public double average() { 
     average =sum/array.length; 
      return (double)average; 
    } 

    //method to calc sqSum 
    public double sqSum() { 
     double sqSum = 0.0; 
     for(int i=0; i<array.length; i++) 

      sqSum = sqSum +array[i] * array[i]; 

     return (double)sqSum; 
    }  

    //method to calculate variance 
    public double variance() { 
      variance = (double)sqSum/array.length; 

      return (double)variance; 
    } 
} 

Answer 1

我在評論你的課程。可能問題在於調用方法的順序：調用sum（）之前調用average（）將返回零（因爲總和從未計算）。爲避免這種情況，最好避免將結果存儲在實例字段中，而是在需要時調用原始方法。防爆。 average = sum（）/ length。

要緩存結果（爲了提高性能），它比這更復雜一點。

這裏是你的類有一些變化：

public class MyArray { 

    private int[] array; 

    // Constructor to instantiate a new array 
    public MyArray(int length) { 
     array = new int[length]; 
    } 

    public int length() { 
     return array.length; 
    } 

    // getter for integers 
    public int getInts(int counter) { 
     return array[counter]; 
    } 

    // setter for integers 
    public void setInts(int counter, int input) { 
     array[counter] = input; 
    } 

    // getter for entire array 
    public int[] getArray() { 
     return array; 
    } 

    // setter for entire array 
    public void setArray(int[] newArray) { 
     this.array = newArray; 
    } 

    public int intAt(int index) { 
     return array[index]; 
    } 

    // Method to print Arrays 
    public void printArray() { 
     System.out.println("\nThe length of the array is " + array.length); 

     for (int i = 0; i < array.length; i++) 
      System.out.println("array[" + i + "] = " + array[i]); 
    } 

    // Method to check if array is sorted 
    public boolean isSortedArray() { 
     boolean isSorted = true; 
     for (int i = 1; i < array.length; i++) 
      if (array[i] > array[i-1]) { 
       isSorted = false; 
       break; 
      } 
     System.out.println("The array is " + (isSorted ? "sorted" : "not sorted")); 
     return isSorted; 
    } 

    // method to calc sum 
    public long sum() { 
     long sum = 0L; 
     for (int i = 0; i < array.length; i++) 
      sum += array[i]; 
     return sum; 
    } 

    // method to calc Average 
    public double average() { 
     return (double) sum()/array.length; 
    } 

    // method to calc sqSum 
    public long sqSum() { 
     long sqSum = 0L; 
     for (int i = 0; i < array.length; i++) 
      sqSum += array[i] * array[i]; 
     return sqSum; 
    } 

    // method to calculate variance 
    public double variance() { 
     return (double) sqSum()/array.length; 
    } 
} 

免責聲明：我沒有運行它，所以首先測試它:-)