使用泛型Object []的ClassCastException不能转换 [英] ClassCastException using Generics Object[] cannot be cast

问题描述

所以我试图创建一个类，它使用一个数组来实现一个堆来创建一个优先级列表。在我的构造函数中，我想创建一个Entry对象数组。这可能吗？之前我已经做过一些通用铸造，并且我已经尝试了所有通常适用于我的方法。我觉得它应该是可能的，但我无法弄清楚。

这是运行它时得到的异常：

[Ljava.lang.Object;无法转换为[Llab09.Entry;

 `public class ArrayHeap< K，V>实施PriorityQueue< K，V> {
`私人比较器< K>补偿; 
私人条目< K，V> []数据; 
 private int heapSize; 
 $ b @SuppressWarnings（{unchecked}）
 public ArrayHeap（int size，Comparator< K> c）{
 data =（Entry< K，V> []）新对象[size]; //类型转换数组
 heapSize = 0; 
 comp = c; 
} 
} 
  

另外，我会将嵌套的Entry类放入

 受保护的静态类AHEntry 实现Entry< K，V> {
 private K k; 
 private V v; 
 
 public AHEntry（K key，V value）{
 k = key; 
 v =价值; 
} 
 public K getKey（）{return k;} 
 public V getValue（）{return v;} 
 public void setKey（K key）{k = key;} 
 public void setValue（V value）{v = value;} 
} 
  

data =（Entry< K，V> []）new Object [size] 会导致类型转换错误因为 Object 数组不能转换为 Map.Entry 数组。以下代码使用您提供的自定义 AHEntry 类：

  public class ArrayHeap< K，V>实施PriorityQueue< K，V> {
私人比较器< K>补偿; 
私人条目< K，V> []数据; 
 private int heapSize; 
 $ b @SuppressWarnings（{unchecked}）
 public ArrayHeap（int size，Comparator< K> c）{
 data = new（AHEntry< K，V>）new AHEntry<？，？> [size]; 
 heapSize = 0; 
 comp = c; 
} 
} 
  

So I'm trying to create a class that implements a heap using an array in order to make a prioritized list. In my constructor I want to create an array of Entry objects. Is this possible to do? I have done some generic casting before and I have tried everything that usually works for me. I feel like It should be possible but i can't figure it out.

This is the exception I get when I run it:

[Ljava.lang.Object; cannot be cast to [Llab09.Entry;

`public class ArrayHeap<K,V> implements PriorityQueue<K,V> {
    `private Comparator<K> comp;
     private Entry<K,V>[] data;
     private int heapSize;

     @SuppressWarnings({"unchecked"})
     public ArrayHeap(int size, Comparator<K> c){
        data = (Entry<K,V>[]) new Object[size]; // type casting array
        heapSize = 0;
        comp = c;
    }
 }

Also I'll throw in my nested Entry class to look at aswell.

protected static class AHEntry<K,V> implements Entry<K,V> {
    private K k;
    private V v;

    public AHEntry(K key, V value){
        k = key;
        v = value;
    }
    public K getKey(){ return k;}
    public V getValue(){ return v;}
    public void setKey(K key){ k = key;}
    public void setValue(V value){ v = value;}
}

解决方案

The line data = (Entry<K,V>[]) new Object[size] is resulting in a type cast error because an Object array cannot be cast to a Map.Entry array. The following code makes use of the custom AHEntry class which you provided:

public class ArrayHeap<K,V> implements PriorityQueue<K,V> {
    private Comparator<K> comp;
    private Entry<K,V>[] data;
    private int heapSize;

    @SuppressWarnings({"unchecked"})
    public ArrayHeap(int size, Comparator<K> c){
        data = new (AHEntry<K, V>)new AHEntry<?, ?>[size];
        heapSize = 0;
        comp = c;
    }
}

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