复合继承：如何在子类构造函数中分配一个最终字段，该字段取决于'this'值（向后引用）？ [英] composite inheritance: how to assign a final field at sub-class constructor which depends on 'this' value (backward reference)?

问题描述

我使用复合类来对功能进行分组。

但是，A类（带有复合A1）由B继承（使用复合B1），并且A1中存在的行为将被调整在B1，但最终的a1必须是一个B1实例才能工作。

I use composite classes to group functionalities.
But, the class A (with composite A1), got inherited by B (with composite B1), and a behavior existent at A1 is going to be adapted at B1, but the final a1 must be a B1 instance for this to work.

Obs。：我有方法以确保复合实例化正确发生（仅由其复合伙伴）。

Obs.: I have ways to make sure the composite instantiation happens properly (only by its composite partner).

无法将B1对象分配给a1 final field：

Unable to assign a B1 object to a1 final field:

class finalFieldTestFails{
    class A1{
      A1(A a){}
    }

    class A{
      protected final A1 a1;
      A(){
        this.a1 = new A1(this);
      }

      A(A1 a1){
        this.a1 = a1;
      }
    }

    class B1 extends A1{
      B1(B b){
        super(b);
      }
    }

    class B extends A{
        //B(){ super.a1=new B1(this); } //FAIL: cant change final value
        //B(){super(new B1(this));} //FAIL: cant use 'this' or 'super'
    }
}

PS：如果可能，答案不应包含反射安全技巧。

PS.: the answer shall not involve reflection security tricks if possible.

推荐答案

这个小费，我发现这个回答我在下面输入了这段代码。

With this tip, given by @KevinHooke, I found this answer and I came with this code below.

但要注意我选择了这个选项可能会造成麻烦。

But be aware that this option I chose may cause trouble.

所以我最终使用重写方法来实例化1类型，让超级班负责任务。

So I ended up using an overriden method to instantiate the "1" kind, letting the super class take care of the assignment.

class finalFieldTestWorks{
    class A1{A1(A a){}}

    class A{
      protected final A1 a1;
      A(){
        this.a1=new1();
      }
      protected A1 new1(){return new A1(this);}
    }

    class B1 extends A1{B1(B b){super(b);}}

    class B extends A{
      B(){
        super();
      }
      @Override
      protected B1 new1(){return new B1(this);}
    }
}

PS。：其他提示/解决方法将不胜感激。

PS.: Other tips/workarounds will be appreciated.

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