如何在签名中正确覆盖泛型的抽象方法 [英] How to properly override an abstract method with generics in the signature

问题描述

我以为我明白如何做到这一点，但我得到了一些意想不到的行为，所以显然我错过了一些东西。

基类：

  public abstract class Base< T> 
 {
 abstract public void foo（List< ;? extends T> l）; 
 
 
 
 $ b 
派生类：
 
 
  public class Derived< T>扩展Base 
 {
 @Override 
 public void foo（List< ;? extends T> l）{return; }基类遵守的很好，但是当我编译Derived类时，我得到了： 
 
 
 
 
 Derived.java:3：Derived不是抽象的，并且不会覆盖基本的抽象方法foo（java.util.List） / p> 
 
 
 public class Derived extends Base 
 
 ^ 
 
 Derived.java:5：方法不会覆盖或实现一个方法超类型 
 
 
  @Override 
 ^ 
  
 
 
 <2>错误 
 
参数 List的泛型<？延长T> 似乎是问题的原因。如果我用基本类型 int 替换这两个签名中的部分，它就会正常工作。
 
 
 
有人可以告诉我什么是在这里？ 
 
解决方案
您应该这样做
 
 pre>  public class Derived< T>延伸Base< T> 
  
您需要指定< T> 对于 Base ，否则您将不得不通过简单地声明 List 显示泛型
 
I thought I understood how to do this but I'm getting some unexpected behavior so apparently I'm missing something. Here's the problem boiled down.

Base Class:
public abstract class Base<T>
{
    abstract public void foo(List<? extends T> l);
}
Derived Class:
public class Derived<T> extends Base
{
    @Override
    public void foo(List<? extends T> l) { return; }
}
The Base class complies fine, but when I compile the Derived class I get:

  
Derived.java:3: Derived is not abstract and does not override abstract method foo(java.util.List) in Base 
  
  
public class Derived extends Base

         ^

  Derived.java:5: method does not override or implement a method from a supertype  
@Override  
^  
2 errors  
The generics of the parameter List<? extends T> appears to be the cause of the problem. If I replace that part in both signatures with the basic type int it comples fine.

Can anybody tell me what's going on here?
解决方案
You should do 
public class Derived<T> extends Base<T>
You need to specify <T> for Base otherwise you will have to override method by simply declaring List i.e.without generics

                        
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