2020-03-14

Design Patterns(七) Decorator

Decorator pattern allows a user to add new functionality to an existing object without altering its structure. This type of design pattern comes under structural pattern as this pattern acts as a wrapper to existing class.

前言

装饰者模式（Decorator Pattern）允许向一个现有的对象添加新的功能，同时又不改变其结构。这种类型的设计模式属于结构型模式，它是作为现有的类的一个包装。这种模式创建了一个装饰类，用来包装原有的类，并在保持类方法签名完整性的前提下，提供了额外的功能。

装饰者模式

装饰者模式原理：

1) 装饰者模式就像打包一个快递：
主体：比如：陶瓷、衣服 (Component) // 被装饰者；
包装：比如：报纸填充、塑料泡沫、纸板、木板(Decorator)。
2) Component：
主体：比如类似前面的Drink。
3) ConcreteComponent和Decorator：
ConcreteComponent：具体的主体，比如前面的各个单品咖啡；
Decorator: 装饰者，比如各调料。
4) 在Component 与ConcreteComponent 之间，如果ConcreteComponent类很多,还可以设计一个缓冲层，将共有的部分提取出来，抽象层一个类。

装饰者模式-UML图：

装饰者模式-案例图：

代码：

/**
 * @Auther: Arsenal
 * @Date: 2020-03-14 17:32
 * @Description: 装饰者模式
 */
public class Decorator {
    public static void main(String[] args) {

        /*System.out.println("==========Bayonet==========");
        Weapon weapon1 = new Bayonet(new Pistol());
        weapon1.aimAndFire();
        Weapon weapon2 = new Bayonet(new AK47());
        weapon2.aimAndFire();
        Weapon weapon3 = new Bayonet(new AWP());
        weapon3.aimAndFire();
        System.out.println("==========Sniperscope==========");
        Weapon weapon4 = new Sniperscope(new Pistol());
        weapon4.aimAndFire();
        Weapon weapon5 = new Sniperscope(new AK47());
        weapon5.aimAndFire();
        Weapon weapon6 = new Sniperscope(new AWP());
        weapon6.aimAndFire();
        System.out.println("==========Cartridge==========");
        Weapon weapon7 = new Cartridge(new Pistol());
        weapon7.aimAndFire();
        Weapon weapon8 = new Cartridge(new AK47());
        weapon8.aimAndFire();
        Weapon weapon9 = new Cartridge(new AWP());
        weapon9.aimAndFire();*/


       System.out.println("====================Pistol====================");
        Weapon weapon1 = new Pistol();
        weapon1 = new Bayonet(weapon1);
        weapon1 = new Sniperscope(weapon1);
        weapon1 = new Cartridge(weapon1);
        weapon1.aimAndFire();
        System.out.println("====================AK47====================");
        Weapon weapon2 = new AK47();
        weapon2 = new Cartridge(weapon2);
        weapon2 = new Bayonet(weapon2);
        weapon2 = new Sniperscope(weapon2);
        weapon2.aimAndFire();
        System.out.println("====================AWP====================");
        Weapon weapon3 = new AWP();
        weapon3 = new Sniperscope(weapon3);
        weapon3 = new Cartridge(weapon3);
        weapon3 = new Bayonet(weapon3);
        weapon3.aimAndFire();
    }
}

/**
 * 被装饰者
 */
interface Weapon {
    void aimAndFire();
}

/**
 * base weapon
 */
class Pistol implements Weapon {

    @Override
    public void aimAndFire() {
        System.out.println("手枪瞄准射击");
    }
}

/**
 * base weapon
 */
class AK47 implements Weapon {

    @Override
    public void aimAndFire() {
        System.out.println("冲锋枪瞄准射击");
    }
}

/**
 * base weapon
 */
class AWP implements Weapon {

    @Override
    public void aimAndFire() {
        System.out.println("狙击枪瞄准射击");
    }
}

/**
 * 装饰者
 */
abstract class WeaponDecorator implements Weapon {

    Weapon weapon;

    WeaponDecorator(Weapon weapon) {
        this.weapon = weapon;
    }

    @Override
    public void aimAndFire() {
        weapon.aimAndFire();
    }
}

/**
 * weapon accessory
 */
class Bayonet extends WeaponDecorator {

    Bayonet(Weapon weapon) {
        super(weapon);
    }

    @Override
    public void aimAndFire() {
        addBayonet();
        super.aimAndFire();
    }

    void addBayonet() {
        System.out.print("加刺刀的-");
    }
}

/**
 * weapon accessory
 */
class Sniperscope extends WeaponDecorator {

    Sniperscope(Weapon weapon) {
        super(weapon);
    }

    @Override
    public void aimAndFire() {
        addSniperscope();
        super.aimAndFire();
    }

    void addSniperscope() {
        System.out.print("加瞄准镜的-");
    }
}

/**
 * weapon accessory
 */
class Cartridge extends WeaponDecorator {

    Cartridge(Weapon weapon) {
        super(weapon);
    }

    @Override
    public void aimAndFire() {
        addCartridge();
        super.aimAndFire();
    }

    void addCartridge() {
        System.out.print("加弹夹的-");
    }
}