依赖倒转原则

public class  TestLight{//测试类
    public static void main(String[] args) {
        Bulb redbulb = new RedBulb();//创建一个红灯泡对象
        Bulb yellowbulb = new YellowBulb();//创建一个黄灯泡对象
        Light light = new Light();//创建一个台灯对象
        light.setLight(redbulb);//将红灯泡放进台灯里面
        light.bulbPower();//打开台灯开关
        light.setLight(yellowbulb);//将黄灯泡放进台灯里面
        light.bulbPower();//打开台灯开关
    }
    
}
class Light{//台灯
    private Bulb bulb;//灯泡属性
    public Light(){}//构造方法
    public Bulb setLight(Bulb bulb){//修改灯泡的方法
        this.bulb = bulb;
        return bulb;
    }
    public void bulbPower(){//台灯开灯方法
        bulb.shine();//调用灯泡发光
    }
}
abstract class Bulb{//灯泡抽象类
    public abstract void shine();//抽象发光方法
}
class RedBulb extends Bulb{//红灯泡继承灯泡类
    public void shine(){//实现灯泡发光方法
        System.out.println("红灯发红光");
    }
}
class YellowBulb extends Bulb{
    public void shine(){
        System.out.println("黄灯发黄光");
    }
}