ArrayStoreException

Question

我的問題是關於我得到的ArrayStoreException。正是在YaSort類的45線，我粘貼下面，在行：

result[m] = (Object) input[m]; 

很顯然，我試圖分配不兼容的類型，但我不明白這是如何發生的。

這裏是我的代碼：

（對不起，計算器不允許我發表兩個以上的鏈路，所以我不得不代碼在這裏複製粘貼

類DVD，一待比較：

// A single DVD. 

import java.text.NumberFormat; 

public class DVD implements Comparable { 
private String title, director; 
private int year; 
private double cost; 
private boolean bluray; 

public DVD(String title, String director, int year, double cost, 
     boolean bluray) { 
    this.title = title; 
    this.director = director; 
    this.year = year; 
    this.cost = cost; 
    this.bluray = bluray; 
} 


public String toString() { 
    NumberFormat myFormat = NumberFormat.getCurrencyInstance(); 

    String description = myFormat.format(cost) + "\t" + year + "\t" + 
      title + "\t" + director; 
    if (bluray) 
     description += "\t" + "Blu-ray"; 

    return description; 
} 


    public String getTitle() { 
     return title; 
    } 


    public int compareTo(Object input) { 
     return title.compareTo(((DVD)input).getTitle()); 
    } 


    public boolean equals(Object input) { 
     return title.equals(((DVD)input).getTitle()); 
    } 
} 

類YaSort，其包括兩個排序算法我使用的第二個，插入排序：

// implements various sorting algorithms for the Comparable interface 

import java.lang.reflect.Array; 

public class YaSort { 
public static Comparable[] selectionSort(Comparable[] input) { 
    int largestOne; 
    Comparable temp; 
    Comparable[] result; 
    result = input.clone(); 

    for (int k = 0; k < result.length - 1; k++) { 
     largestOne = k; 

     for (int j = k + 1; j < result.length; j++) { 
      if (result[largestOne].compareTo(result[j]) < 0) { 
       largestOne = j; 
      } 
     } 

     temp = result[k]; 
     result[k] = result[largestOne]; 
     result[largestOne] = temp; 
    } 

    return result; 
} 


public static Comparable[] insertionSort(Comparable[] input) { 

    // don't forget to remove empty references in the input 
    Object temp; 
    Object[] result; 
    int nonEmptyInput = 0; 

    for (int i = 0; i < input.length; i++) { 
     if (input[i] != null) 
      nonEmptyInput++; 
    } 

    result = (Object[]) Array.newInstance(input.getClass(), nonEmptyInput); 

    for (int m = 0; m < nonEmptyInput; m++) 
     result[m] = (Object) input[m]; 

    if (result.length > 1) { 
     for (int k = 1; k < result.length; k++) { 
      for (int j = 1; j <= k; j++) { 
       if (((Comparable)result[k - j]).compareTo(result[k - j + 1]) < 0) { 
        temp = ((Comparable)result[k - j + 1]); 
        result[k - j + 1] = result[k - j]; 
        result[k - j] = temp; 
       } 
      } 
     } 
    } 

    return (Comparable[]) result; 
} 
} 

類DVDCollection，它代表了DVD集合（DOH！）：

// Represents a collection of DVD movies. 

import java.text.NumberFormat; 

public class DVDCollection { 
private final int INITIAL_SIZE = 100; 
private DVD[] members; 
private int count; // really? 
private double totalCost; 

public DVDCollection() { 
    members = new DVD[INITIAL_SIZE]; 
    count = 0; 
    totalCost = 0.0; 
} 


public void addDVD(String title, String director, int year, double cost, 
     boolean bluray) { 
    if(count == members.length) 
     increaseSize(); 

    members[count] = new DVD(title, director, year, cost, bluray); 
    totalCost += cost; 
    count++; 

    members = (DVD[]) YaSort.insertionSort(members); 

//  Object members2 = new Object[members.length]; 
//  members2 = YaSort.insertionSort(members); 
//  for (int k = 0; k < members.length; k++) { 
//   System.out.println(members2[k].getClass()); 
//  } 
} 


private void increaseSize() { 
    DVD[] temp = new DVD[members.length * 2]; 

    for (int k = 0; k < members.length; k++) 
     temp[k] = members[k]; 

    members = temp; 
} 


public String toString() { 
    NumberFormat fmt = NumberFormat.getCurrencyInstance(); 

    String report = "*******************************************\n"; 
    report += "My DVD Collection\n\n"; 

    report += "Number of DVDs: " + count + "\n"; 
    report += "Total cost: " + fmt.format(totalCost) + "\n"; 
    report += "Average cost: " + fmt.format(totalCost/count); 

    report += "\n\nDVD List:\n\n"; 

    for (int nDvd = 0; nDvd < count; nDvd++) 
     report += members[nDvd].toString() + "\n"; 

    return report; 
} 
} 

類電影，這是存在於測試是否一切工作：

public class Movies { 
public static void main(String[] args) { 
DVDCollection movies = new DVDCollection(); 

movies.addDVD("The Godfather", "Francis Ford Coppola", 1972, 24.95, true); 
movies.addDVD("District 9", "Neill Blokamp", 2009, 19.95, false); 
movies.addDVD("Iron Man", "Jon Favreau", 2008, 15.95, false); 
movies.addDVD("All About Eve", "Joseph Mankiewicz", 1950, 17.50, false); 
movies.addDVD("The Matrix", "Andy & Lana Wachowski", 1999, 19.95, true); 

System.out.println(movies); 

movies.addDVD("Iron Man 2", "Jon Favreau", 2010, 22.99, false); 
movies.addDVD("Casablanca", "Michael Curtiz", 1942, 19.95, false); 

System.out.println(movies); 
} 
} 

順便說一句，我m知道，當數據的大小預計會發生變化時使用數組並沒有什麼意義，但是我試圖研究的這本書給出了這樣的例子。我也是ArrayLists的另一個版本，但它有不同的問題。

謝謝你的幫忙！

Answer 1

在java數組也是類。因此，對數組調用.getClass（）將返回數組類，而不是數組中包含的元素的類。

使用.getClass().getComponentType()來確定所包含的類並使用它通過newInstance創建一個數組。或者用Arrays.copyOf()創建一個精確的副本。

Answer 2

問題是這一行：

result = (Object[]) Array.newInstance(input.getClass(), nonEmptyInput); 

輸入類型是Comparible[]，但我認爲你是打算放Comparible類型。要做到這一點嘗試：

result = (Object[]) Array.newInstance(Comparable.class, nonEmptyInput);