设计模式之装饰者模式

设计模式 Java About 2,169 words

作用

动态的将新功能附加到对象上。在对象功能扩展方面,它比继承更有弹性,装饰者模式也体现了开闭原则(OCP)。

原理

打包快递。

主体-被装饰者:陶瓷、衣服

包装-装饰者:纸板、塑料袋

案例

装饰者继承被装饰者,并且聚合被装饰者。

被装饰者

public abstract class Drink {

    private String desc;

    private float price;

    public abstract float cost();

    public String getDesc() {
        return desc;
    }

    public void setDesc(String desc) {
        this.desc = desc;
    }

    public float getPrice() {
        return price;
    }

    public void setPrice(float price) {
        this.price = price;
    }
}

装饰者

public class Decorator extends Drink {

    private Drink drink;

    public Decorator(Drink drink) {
        this.drink = drink;
    }

    @Override
    public float cost() {
        return getPrice() + drink.cost();
    }
}

被装饰者缓冲层

public class Coffee extends Drink {

    @Override
    public float cost() {
        return getPrice();
    }

}

具体被装饰者

浓咖啡

public class Espresso extends Coffee {

    public Espresso() {
        setDesc("浓咖啡");
        setPrice(6f);
    }
}

美式咖啡

public class LongBlack extends Coffee {

    public LongBlack() {
        setDesc("美式咖啡");
        setPrice(4f);
    }
}

具体装饰者

牛奶

public class Milk extends Decorator {
    public Milk(Drink drink) {
        super(drink);
        setDesc("牛奶");
        setPrice(2f);
    }
}

豆浆

public class Soy extends Decorator {

    public Soy(Drink drink) {
        super(drink);
        setDesc("豆浆");
        setPrice(1.5f);
    }
}

使用

public class CoffeeBar {

    public static void main(String[] args) {
        Drink order = new Espresso();
        System.out.println(order.cost());

        Drink order2 = new Milk(new Espresso());
        System.out.println(order2.cost());

        Drink order3 = new Soy(new Milk(new Milk(new Espresso())));
        System.out.println(order3.cost());
    }

}

源码

关系

pic.png

分析

  1. InputStream是抽象类,类似案例中的Drink。
  2. FileInputStream是InputStream的子类,类似案例中的Espresso、LongBlack。
  3. FilterInputStream是InputStream的子类且聚合了被装饰者InputStream(protected volatile InputStream in;),类似案例中的Decorator。
  4. BufferedInputStream是FilterInputStream的子类,类似案例中的Milk、Soy。

应用

BufferedInputStream br = new BufferedInputStream(new FileInputStream("README.md"));
System.out.println(br.read());
br.close();
Views: 2,488 · Posted: 2019-12-18

————        END        ————

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