oop – 桥模式 – 组合还是聚合？

术语“组合物”和“聚集”意味着或多或少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;然而,可以发现这两个术语都描述了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为您的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.

既然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.桥梁模式也是这样,看起来像：

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.