如何获得“通知”泛型在Java中工作？ [英] How to get "circular" generics working in Java?

问题描述

我在编译涉及一些泛型的以下代码时遇到错误：

  public abstract class State< T extends HasAState< ;？扩展状态< T>>> {
 protected T parent; 
 
 public void setParent（）{//为了这个问题，它被简化了！ 
 parent.removeState（this）; //错误在这里！ 
 this.parent = parent; 
 parent.addState（this）; //错误在这里！ 
} 
} 
 
 public interface HasAState< T extends State< ;?扩展HasAState< T>>> {
 public void addState（T state）; 
 public void removeState（T state）; 
} 
  

错误是：方法removeState（capture＃ 1-of？extends State< T>）的类型HasAState<捕获＃1的？延伸状态< T>>不适用于参数（State< T>）

其实我想要的是类似于： class A implements HasAState 和 class B extends State< A> 其中 B 引用 A 并且可以调用 A.addState（B）（仅因为 B 扩展状态< A> ），其中 A 可以调用 B。 setParent（this）。

如何声明我的类以便我打算做的工作？

谢谢

解决方案

我同意Eran Zimmerman的评论。它接缝，你需要重新考虑你想要什么。

无论如何，我希望我已经理解这个问题，所以我改变了参数从一到两个，来描述 state 和 hasAState 分开。

  public abstract class State< S extends State< S，H>，H extends HasAState< S，H>> {
 protected H parent; 
 
 public void setParent（）{
 parent.removeState（this）; 
 this.parent = parent; // !!!这条线没有任何效果！ 
 parent.addState（this）; 
 
 
 
 public interface HasAState< S extends State< S，H>，H extends HasAState< S，H>> {
 public void addState（State< S，H> state）; 
 public void removeState（State< S，H>状态）; 
} 
  

此代码编译！ - 注意 setParent 中第二行的警告。

I am having an error while compiling the following code involving a few generics:

public abstract class State<T extends HasAState<? extends State<T>>>{
    protected T parent;

    public void setParent(){ // It's been simplified for the sake of the question!
        parent.removeState(this); // Error here!
        this.parent = parent;
        parent.addState(this);    // Error here!
    }
}

public interface HasAState<T extends State<? extends HasAState<T>>> {
    public void addState(T state);
    public void removeState(T state);
}

The errors are: The method removeState(capture#1-of ? extends State<T>) in the type HasAState<capture#1-of ? extends State<T>> is not applicable for the arguments (State<T>)

Actually what I would like to have is something like: class A implements HasAState and class B extends State<A> where B has a reference to A and can call A.addState(B) (only because B extends State<A>) and where A can call B.setParent(this).

How should I declare my classes so that what I intend to do work?

Thanks

解决方案

I agree with the comment of Eran Zimmerman. It seams that you need to rethink about what you want.

Anyway I hope I have understand the problem right, so I changed the Parameter from one to tow, to describe the state and the hasAState separately.

public abstract class State<S extends State<S, H>, H extends HasAState<S, H>>{
    protected H parent;

    public void setParent(){ 
        parent.removeState(this);
        this.parent = parent; //!!!this line has no effect!!!
        parent.addState(this);        
    }       
}

public interface HasAState<S extends State<S, H>, H extends HasAState<S, H>> {
    public void addState(State<S, H> state);
    public void removeState(State<S, H> state);
}

This code compiles! -- be aware of the warning for the second line in setParent.

这篇关于如何获得“通知”泛型在Java中工作？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！