我怎样才能引用一个接口在Java中实现的类类型？ [英] How can I refer to the class type a interface is implementing in Java?

问题描述

我遇到了一个我正在编写的程序中的接口问题。我想创建一个接口，它的方法之一是接收/返回对自己对象类型的引用。它是这样的：

  public interface I {
？ getSelf（）; 
} 
 
 public class A implements I {
 getSelf（）{
 return this; 
 
 
 
 public class B implements I {
 B getSelf（）{
 return this; 
 
 
  

我不能使用I一个？，因为我不想返回一个对接口的引用，而是类。我搜索了一下，发现在Java中没有办法自我引用，所以我不能用这个？替代。在自我关键字或类似的例子中。实际上，我想出了一个解决方案，就像

  public interface I< SELF> {
 SELF getSelf（）; 
} 
 
 public class A实现了I< A> {
 getSelf（）{
 return this; 
} 
} 
 
公共类B实现了I< B> {
 B getSelf（）{
 return this; 
} 
} 
  

但它看起来像是一种解决方法或类似的方法。有没有另外一种方法可以做到这一点？

解决方案

扩展接口时有一种强制使用自己的类作为参数的方法：

  interface I< SELF extends I< SELF>> {
 SELF getSelf（）; 
} 
 
 class A实现了I< A> {
 getSelf（）{
 return this; 
} 
} 
 
 class B实现了I< A> {//非法：绑定不匹配
 getSelf（）{
 return this; 
 
 
 
 
 
 
 
 这在编写泛型类时甚至可以工作。只有缺点：必须将这个转换为 SELF 。 
 
 
 
正如Andrey Makarov在不是可靠地工作。
  class A< SELF extends A< SELF>> {
 SELF getSelf（）{
 return（SELF）this; 
} 
} 
 class C extends A< B> {} //不会失败。 
 
 // C myC = new C（）; 
 // B myB = myC.getSelf（）; //<  -  ClassCastException 
  
 
I came to a problem with interfaces in a program I'm making. I want to create a interface which have one of its methods receiving/returning a reference to the type of the own object. It was something like:
public interface I {
    ? getSelf();
}

public class A implements I {
    A getSelf() {
        return this;
    }
}

public class B implements I {
    B getSelf() {
        return this;
    }
}
I can't use an "I" where it's a "?", because I don't want to return a reference to the interface, but the class. I searched and found that there are no way to "self-refer" in Java, so I can't just substitute that "?" in the example for a "self" keyword or something like this. Actually, I came up to a solution that goes like
public interface I<SELF> {
    SELF getSelf();
}

public class A implements I<A> {
    A getSelf() {
        return this;
    }
}

public class B implements I<B> {
    B getSelf() {
        return this;
    }
}
But it really seems like a workaround or something alike. Is there another way to do so?
解决方案
There is a way to enforce using ones own class as a parameter when extending an interface:
interface I<SELF extends I<SELF>> {
    SELF getSelf();
}

class A implements I<A> {
    A getSelf() {
        return this;
    }
}

class B implements I<A> { // illegal: Bound mismatch
    A getSelf() {
        return this;
    }
}
This even works when writing generic classes. Only drawback: one has to cast this to SELF.


As Andrey Makarov noted in a comment below this does not work reliably when writing generic classes.
class A<SELF extends A<SELF>> {
    SELF getSelf() {
        return (SELF)this;
    }
}
class C extends A<B> {} // Does not fail.

// C myC = new C();
// B myB = myC.getSelf(); // <-- ClassCastException


                        
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