多重继承没有多重继承，没有代码重复 [英] Multiple inheritance without multiple inheritance and without code duplication

问题描述

我有关于如何应对不允许多重继承的语言以下情形的理论问题。

I have a theoretical question concerning how to deal with the following scenario in a language which does not allow multiple inheritance.

想象一下，我有一个基类的美孚的，从中我希望创建三个子类：

Imagine I have a base class Foo and from it I am wishing to create three sub-classes:

• 类的栏的继承的富的和实现的功能A


• 类的巴兹的继承的富的并实现功能b


• 类的 Qux 的继承的富的并实现功能A和b

• Class Bar inherits Foo and implements functionality "A"
• Class Baz inherits Foo and implements functionality "B"
• Class Qux inherits Foo and implements functionalities "A" and "B"

想象一下代码来实现功能的A和b是永远不变的。有没有写A和B只有一次的代码，然后有相应的类应用（或继承）的方式呢？

Imagine that the code to implement functionalities "A" and "B" is always the same. Is there a way to write the code for "A" and "B" only once, and then have the appropriate classes apply (or "inherit") it?

推荐答案

好吧，我可以看到你在C＃中实现这一目标的唯一途径/ Java是由组成。试想一下：

Well the only way I can see you achieving this in C#/Java is by composition. Consider this:

class Foo {

}

interface A {
    public void a();
}

interface B {
    public void b();
}

class ImplA implements A {
    @Override
    public void a() {
        System.out.println("a");
    }
}

class ImplB implements B {
    @Override
    public void b() {
        System.out.println("b");
    }
}

class Bar extends Foo {
    A a = new ImplA();

    public void a() {
        a.a();
    }
}

class Baz extends Foo {
    B b = new ImplB();

    public void b() {
        b.b();
    }       
}

class Qux extends Foo {

    A a = new ImplA();
    B b = new ImplB();

    public void b() {
        b.b();
    }

    public void a() {
        a.a();          
    }       
}

现在 Qux 既有通过正常的继承富的功能，而且 A 和 b 。

Now Qux has both the functionality of Foo via normal inheritance but also the implementations of A and B by composition.

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