为什么要编译？ [英] Why does this compile?

问题描述

我今天早些时候被调试一些代码，发现像下面的东西不会引发编译时异常：

I was taken aback earlier today when debugging some code to find that something like the following does not throw a compile-time exception:

 public Test () { 
     HashMap map = (HashMap) getList(); 
 }

 private List getList(){
     return new ArrayList();
 }

您可以想象， ClassCastException 在运行时抛出，但是有人可以解释为什么将 List 转换为 HashMap 因为可以想象 getList（）可能是在编译时合法的？

As you can imagine, a ClassCastException is thrown at runtime, but can someone explain why the casting of a List to a HashMap is considered legal at compile time?

推荐答案

返回 HashMap 的子类，它也实现了 List 。不太可能，是的，但可能的，因此可编译。

Because conceivably getList() could be returning a subclass of HashMap which also implements List. Unlikely, yes, but possible, and therefore compilable.

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