11. 合成与继承的选择 | Hexo

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合成与继承的选择

• 要点： “属于”关系是用继承来表达的，而 “包含”关系是用合成来表达的。

合成的使用场景举例:

package com.isflee.c06_4_1_car;

//: reusing/Car.java
// Composition with public objects.
//到底选择合成还是继承(合成和继承的应用场景)
//以下例子时合成的应用场景， 对于一辆车， 它 "包含" 了引擎，车轮， 窗户， 车门等部件。
class Engine {
    public void start() {
    }

    public void rev() {
    }

    public void stop() {
    }
}

class Wheel {
    public void inflate(int psi) {
    }
}

class Window {
    public void rollup() {
    }

    public void rolldown() {
    }
}

class Door {
    public Window window = new Window();

    public void open() {
    }

    public void close() {
    }
}

public class Car {
    public Engine engine = new Engine();
    public Wheel[] wheel = new Wheel[4];
    public Door
            left = new Door(),
            right = new Door(); // 2-door

    public Car() {
        for (int i = 0; i < 4; i++)
            wheel[i] = new Wheel();
    }

    public static void main(String[] args) {
        Car car = new Car();
        car.left.window.rollup();
        car.wheel[0].inflate(72);
    }
} ///:~