装饰模式 Decorator Pattern

Attach additional responsibilities to an object dynamically keeping the same interface.Decorators provide a flexible alternative to subclassing for extending functionality.

动态地给一个对象添加一些额外的职责。就增加功能来说，装饰模式比生成子类更为灵活。

抽象构建角色（Component）：该角色用于规范需要装饰的对象（原始对象）。

package com.DesignPattern.Structural.Decorator;

public interface Component {
    public void operation();
}

具体构件角色（Concrete Component）：该角色实现抽象构件接口，定义一个需要装饰的原始类。

package com.DesignPattern.Structural.Decorator;

public class ConcreteComponent implements Component {
    @Override
    public void operation() {
        // 业务代码
        System.out.println("concreteComponent opration");
    }
}

装饰角色（Decorator）：该角色持有一个构件对象的实例，并定义一个与抽象构件接口一致的接口。

package com.DesignPattern.Structural.Decorator;

public abstract class Decorator implements Component {

    private Component component=null;
    public Decorator(Component component){
        this.component=component;
    }
    @Override
    public void operation() {
        this.component.operation();
    }
}

具体修饰角色（Concrete Decorator）：该角色负责对构件对象进行装饰。

package com.DesignPattern.Structural.Decorator;

public class ConcreteDecorator extends Decorator {

    public ConcreteDecorator(Component component) {
        super(component);
    }
    //自己定义的方法
    private void method(){
        System.out.println("add decorator method");
    }
    //重写operation方法
    public void operation(){
        this.method();
        super.operation();
    }
}

Client.java

package com.DesignPattern.Structural.Decorator;

public class Client {

    public static void main(String[] args){
        Component component=new ConcreteComponent();
        //进行装饰
        component=new ConcreteDecorator(component);
        component.operation();
    }
}

装饰模式的实例

Car.java

package com.DesignPattern.Structural.Decorator;

//汽车接口
public interface Car {
    // 车的装配
    public void show();
}

Benz.java

package com.DesignPattern.Structural.Decorator;

//奔驰车（裸车，需要装饰）
public class Benz implements Car {
    @Override
    public void show() {
        System.out.println("Benz default color is black");
    }
}

CarDecorator.java

package com.DesignPattern.Structural.Decorator;

//汽车装饰（抽象装饰）
public abstract class CarDecorator implements Car {
    private Car car = null;

    public CarDecorator(Car car) {
        this.car = car;
    }

    @Override
    public void show() {
        this.car.show();
    }
}

ConcreteCarDecorator.java

package com.DesignPattern.Structural.Decorator;

//具体汽车修饰
public class ConcreteCarDecorator extends CarDecorator {
    public ConcreteCarDecorator(Car car) {
        super(car);
    }

    // 给车彩绘
    private void print() {
        System.out.println("print on car");
    }

    // 给车安装GPS
    private void setGps() {
        System.out.println("install GPS");
    }

    // 重写show()方法
    public void show() {
        super.show();
        this.print();
        this.setGps();
    }
}

ClientDemo.java

package com.DesignPattern.Structural.Decorator;

public class ClientDemo {
    public static void main(String[] args) {
        Car car = new Benz();
        // 对奔驰车进行装饰
        CarDecorator cd = new ConcreteCarDecorator(car);
        cd.show();
    }
}