Question

我正在阅读一些关于设计模式的书籍，虽然有些人将抽象和实现之间的关系描述为一个组合，但有些人将其描述为聚合。现在我想知道：这取决于实施吗？关于语言？还是上下文？

Answer 1

术语“组合物”和“聚集”或多或少意味着相同的事物并且可以互换使用。在描述容器类（例如列表，动态数组，映射和队列，其中元素都是相同类型）时，可以更频繁地使用聚合;但是，可以找到这两个术语来描述根据其他类定义的类，无论这些类型是同质的（所有相同的类型）还是异类的（不同类型的对象）。

为了更清楚：

class Car {
    // ...
    private:
        Engine engine;
        Hood hood;
};

// The car is *composed* of an engine and a hood. Hence, composition. You are
// also bringing together (i.e. *aggregating*) an engine and hood into a car.

抽象和实现之间的关系通常意味着继承，而不是组合/聚合;通常，抽象是一个接口或虚拟基类，实现是一个实现给定接口的完全具体的类。但是，为了使事情变得混乱，组合/聚合可以是接口的一部分（例如，因为您可能需要设置/获取用作构建块的对象），它们也是实现的方法（因为您可以使用委托来为实现中的方法提供定义。

为了更清楚：

interface Car {
    public Engine getEngine();
    public Hood getHood();
    public void drive();
}
// In the above, the fact that a car has these building blocks
// is a part of its interface (the abstraction).

class HondaCivic2010 implements Car {
    public void drive(){ getEngine().drive(); }
    // ...
}
// In the above, composition/delegation is an implementation
// strategy for providing the drive functionality.

由于你已经标记了你的问题“桥”，我应该指出桥模式的定义是一种模式，你使用组合而不是继承来允许多个不同级别的变化。我在大学时学到的一个例子......使用继承你可能有类似的东西：

class GoodCharacter;
class BadCharacter;
class Mage;
class Rogue;
class GoodMage : public GoodCharacter, Mage;
class BadMage : public BadCharacter, Mage;
class GoodRogue : public GoodCharacter, Rogue;
class BadRogue : public BadCharacter, Rogue;

正如你所看到的，这种事情非常疯狂，而且你得到了一些荒谬的课程。桥梁模式也是如此：

 class Personality;
 class GoodPersonality : public Personality;
 class BadPersonality : public Personality;

 class CharacterClass;
 class Mage : public CharacterClass;
 class Rogue : public CharacterClass;

 class Character {
    public:
        // ...
    private:
        CharacterClass character_class;
        Personality personality;
 };
 // A character has both a character class and a personality.
 // This is a perfect example of the bridge pattern, and we've
 // reduced MxN classes into a mere M+N classes, and we've
 // arguably made the system even more flexible than before.

Answer 2

桥接模式必须使用委托（聚合/组合而不是继承）。来自四人帮书：

时使用Bridge模式

* you want to avoid a permanent binding between an abstraction and its implementation. This might be the case, for example, when the implementation must be selected or switched at run-time.

* both the abstractions and their implementations should be extensible by subclassing. In this case, the Bridge pattern lets you combine the different abstractions and implementations and extend them independently.

* changes in the implementation of an abstraction should have no impact on clients; that is, their code should not have to be recompiled.

* (C++) you want to hide the implementation of an abstraction completely from clients. In C++ the representation of a class is visible in the class interface.

* you have a proliferation of classes as shown earlier in the first Motivation diagram. Such a class hierarchy indicates the need for splitting an object into two parts. Rumbaugh uses the term "nested generalizations" [RBP+91] to refer to such class hierarchies.

* you want to share an implementation among multiple objects (perhaps using reference counting), and this fact should be hidden from the client. A simple example is Coplien's String class [Cop92], in which multiple objects can share the same string representation (StringRep).

Answer 3

Bridge模式的标准UML清除混乱周围的所有空气。下面是一个简短示例的解释，以清除周围的空气。

为这个冗长的代码道歉，最好的方法是将此代码复制到Visual Studio以轻松理解它。

仔细阅读代码末尾的解释

interface ISpeak
{
    void Speak();
}

class DogSpeak : ISpeak
{
    public void Speak()
    {
        Console.WriteLine("Dog Barks");
    }
}
class CatSpeak : ISpeak
{
    public void Speak()
    {
        Console.WriteLine("Cat Meows");
    }
}

abstract class AnimalBridge
{
    protected ISpeak Speech;

    protected AnimalBridge(ISpeak speech)
    {
        this.Speech = speech;
    }

    public abstract void Speak();
}
class Dog : AnimalBridge
{
    public Dog(ISpeak dogSpeak)
        : base(dogSpeak)
    {

    }
    public override void Speak()
    {
        Speech.Speak();
    }
}

class Cat : AnimalBridge
{
    public Cat(ISpeak catSpeak)
        : base(catSpeak)
    {

    }
    public override void Speak()
    {
        Speech.Speak();
    }
}

- ISpeak是狗和猫必须实施的抽象 - 通过引入由ISpeak组成的桥梁“动物”来解耦狗和猫类 - Dog和Cat类扩展了Animal类，因此与ISpeak分离。

希望这澄清

桥模式 - 组合还是聚合？

3 个答案:

仔细阅读代码末尾的解释