铸造对象[] Java中的引用类型数组 [英] casting Object[] to a reference type array in java

问题描述

在实现一个通用的堆栈，下面的语句是用来和工作没有任何问题。

In implementation of a generic stack ,the following idiom is used and works without any problem

public class GenericStack<Item> {
    private int N;
    private Item[] data;    

    public GenericStack(int sz) {
        super();
        data = (Item[]) new Object[sz];

    }
        ...
}

然而，当我尝试以下方法，它会导致一个ClassCastException

However when I try the following ,it causes a ClassCastException

String[] stra = (String[]) new Object[4];

Exception in thread "main" java.lang.ClassCastException: [Ljava.lang.Object; cannot be cast to [Ljava.lang.String;

你怎么解释？

推荐答案

铸造一个新的对象[4] 到的String [] 不起作用，因为对象[] 不是的String [] ，就像一个对象不是字符串。

Casting a new Object[4] to a String[] doesn't work because an Object[] isn't a String[], just like an Object isn't a String.

第一个例子工程，因为类型擦除的。在运行时，类型参数项目已擦除对象。然而，如果你试图将数组分配给reifiable类型，它同样也会失败，例如，如果数据不是私人：

The first example works because of type erasure. At runtime, the type parameterItem has been erased to Object. However it would similarly fail if you tried to assign the array to a reifiable type, for example if data wasn't private:

String[] strings = new GenericStack<String>(42).data;

这同样也会抛出一个 ClassCastException异常，因为究竟是怎样一个对象[] 将转换为的String [] 。

This would similarly throw a ClassCastException, because what is actually an Object[] would be cast to String[].

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