Java设计模式：装饰者模式（Decorator Pattern）

装饰者模式，涉及的重要设计原则：类应该对扩展开放，对修改关闭。

装饰者模式定义：

装饰者模式动态地将责任附加到对象上。若要扩展功能，装饰者提供了比继承更有弹性的替代方案。

UML类图：

装饰者模式事例：

咖啡店

咖啡种类：

1）深焙咖啡（DarkRoast）

2）家庭混合咖啡（HouseBlend）

3）浓咖啡（Espresso）

4）低咖啡因咖啡（Decaf）

5）其它咖啡。。。

咖啡调料：

1）摩卡（Mocha）

2）牛奶（Milk）

3）豆浆（Soy）

4）奶泡（Whip）

5）其它调料。。。

点单：

要一份加了摩卡和奶泡的深焙咖啡...等等

UML类图

代码实现：

Beverage.java

package com.jing.decorator;

/**
 * 所有饮料的抽象超类
 * @author LiuJing
 *
 */
public abstract class Beverage {

  /**
   * 饮料的名字
   */
  String description = "Unknow Beverage";
  
  /*
   * 获取饮料的名字
   */
  public String getDescription(){
    return description;
  }
  
  
  /***
   * 获取饮料的价格
   * @return 返回计算后的总价
   */
  public abstract double cost();
  
}

DarkRoast.java

package com.jing.decorator;

import java.text.DecimalFormat;

/***
 * 深烤咖啡
 * @author LiuJing
 *
 */
public class DarkRoast extends Beverage {

  /***
   * 构造时确定名字
   */
  public DarkRoast(){
    description = "DarkRoast";
  }
  
  /***
   * 价格
   */
  public double cost() {
    double cost = 10.0;
    
    // 用于保存2位小数
    DecimalFormat df = new DecimalFormat("#.00");
    return Double.valueOf(df.format(cost));
  }
}

Decaf.java

package com.jing.decorator;

import java.text.DecimalFormat;

/***
 * 低咖啡因咖啡
 * @author LiuJing
 *
 */
public class Decaf extends Beverage {

  /***
   * 构造时确定名字
   */
  public Decaf() {
    description = "Decaf";
  }
  
  /***
   * 价格
   */
  public double cost() {
    double cost = 11.0;

    DecimalFormat df = new DecimalFormat("#.00");
    return Double.valueOf(df.format(cost));
  }
}

Espresso.java

package com.jing.decorator;

import java.text.DecimalFormat;

/***
 * 浓咖啡
 * @author LiuJing
 *
 */
public class Espresso extends Beverage {

  /***
   *  构造时确定其名字
   */
  public Espresso(){
    description = "Espresso";
  }
  
  /***
   * 方法返回 该饮料的价格
   */
  public double cost() {
    double cost = 12.0;
    
    DecimalFormat df = new DecimalFormat("#.00");
    return Double.valueOf(df.format(cost));
  }
}

HouseBlend.java

package com.jing.decorator;

import java.text.DecimalFormat;

/***
 * 家庭混合咖啡
 * @author LiuJing
 *
 */
public class HouseBlend extends Beverage {

  /***
   * 构造时确定其名字
   */
  public HouseBlend(){
    description = "HouseBlend";
  }
  
  /***
   * 返回该咖啡的价格
   */
  public double cost() {
    double cost = 13.0;
    
    DecimalFormat df = new DecimalFormat("#.00");
    return Double.valueOf(df.format(cost));
  }

}

CondimentDecorator.java

package com.jing.decorator;

/***
 * 调料装饰者抽象超类，继承至 Beverage,便于类型的统一，能彼此替换。
 * @author LiuJing
 *
 */
public abstract class CondimentDecorator extends Beverage {
  
  /***
   * 用于保存要装饰的咖啡对象
   */
  Beverage beverage;
  
  /***
   * 所有子类都必须重新实现 getDescription()方法
   */
  public abstract String getDescription();

}

Milk.java

package com.jing.decorator;

import java.text.DecimalFormat;

/***
 * 咖啡调料 牛奶  Milk >> CondimentDecorator >> Beverage
 * @author LiuJing
 *
 */
public class Milk extends CondimentDecorator {

  
  /**
   * 构造时确定要加给谁
   * @param beverage
   */
  public Milk(Beverage beverage){
    this.beverage = beverage;
  }
  
  
  /***
   * 不仅显示当前名，还说明被装饰的名字 
   */
  @Override
  public String getDescription() {
    // TODO Auto-generated method stub
    return beverage.getDescription() + ", Milk";
  }

  /***
   * 获取本身的价格和咖啡的价格
   */
  @Override
  public double cost() {
    // TODO Auto-generated method stub
    double cost = beverage.cost();
    cost += 0.1;
    
    DecimalFormat df = new DecimalFormat("#.00");
    return Double.valueOf(df.format(cost));
  }

}

Mocha.java

package com.jing.decorator;

import java.text.DecimalFormat;

/***
 * 咖啡调料 摩卡 Mocha >> CondimentDecorator >> Beverage
 * 
 * @author LiuJing
 * 
 */
public class Mocha extends CondimentDecorator {


  /**
   * 构造时确定要加给谁
   * 
   * @param beverage
   */
  public Mocha(Beverage beverage) {
    this.beverage = beverage;
  }

  /***
   * 不仅显示当前名，还说明被装饰的名字
   */
  @Override
  public String getDescription() {
    // TODO Auto-generated method stub
    return beverage.getDescription() + ", Mocha";
  }

  /***
   * 获取本身的价格和咖啡的价格
   */
  @Override
  public double cost() {
    // TODO Auto-generated method stub
    double cost = beverage.cost();
    cost += 0.1;

    DecimalFormat df = new DecimalFormat("#.00");
    return Double.valueOf(df.format(cost));
  }

}

Soy.java

package com.jing.decorator;

import java.text.DecimalFormat;

/***
 * 咖啡调料 豆浆 Soy >> CondimentDecorator >> Beverage
 * 
 * @author LiuJing
 * 
 */
public class Soy extends CondimentDecorator {


  /**
   * 构造时确定要加给谁
   * 
   * @param beverage
   */
  public Soy(Beverage beverage) {
    this.beverage = beverage;
  }

  /***
   * 不仅显示当前名，还说明被装饰的名字
   */
  @Override
  public String getDescription() {
    // TODO Auto-generated method stub
    return beverage.getDescription() + ", Soy";
  }

  /***
   * 获取本身的价格和咖啡的价格
   */
  @Override
  public double cost() {
    // TODO Auto-generated method stub
    double cost = beverage.cost();
    cost += 0.1;

    DecimalFormat df = new DecimalFormat("#.00");
    return Double.valueOf(df.format(cost));
  }

}

Whip.java

package com.jing.decorator;

import java.text.DecimalFormat;

/***
 * 咖啡调料 奶泡 Whip >> CondimentDecorator >> Beverage
 * 
 * @author LiuJing
 * 
 */
public class Whip extends CondimentDecorator {


  /**
   * 构造时确定要加给谁
   * 
   * @param beverage
   */
  public Whip(Beverage beverage) {
    this.beverage = beverage;
  }

  /***
   * 不仅显示当前名，还说明被装饰的名字
   */
  @Override
  public String getDescription() {
    // TODO Auto-generated method stub
    return beverage.getDescription() + ", Whip";
  }

  /***
   * 获取本身的价格和咖啡的价格
   */
  @Override
  public double cost() {
    // TODO Auto-generated method stub
    double cost = beverage.cost();
    cost += 0.1;

    DecimalFormat df = new DecimalFormat("#.00");
    return Double.valueOf(df.format(cost));
  }

}

测试类

Test.java

package com.jing.decorator;

public class Test {

  /**
   * @param args
   */
  public static void main(String[] args) {
    // TODO Auto-generated method stub

    
    // 点了一份浓咖啡
    Beverage beverage = new Espresso();
    System.out.println(
        beverage.getDescription() + ": $ " + beverage.cost());

    // 点了一份深烤
    Beverage beverage2 = new DarkRoast();
    beverage2 = new Mocha(beverage2);    // 加 摩卡装饰
    beverage2 = new Mocha(beverage2);    // 再加 摩卡装饰
    beverage2 = new Whip(beverage2);     // 再加 奶泡装饰
    System.out.println(
        beverage2.getDescription() + ": $ " + beverage2.cost());

    // 点了一份家庭混合
    Beverage beverage3 = new HouseBlend();
    beverage3 = new Soy(beverage3);   // 加 豆浆装饰
    beverage3 = new Mocha(beverage3); // 再加 摩卡装饰
    beverage3 = new Whip(beverage3);  // 再加 奶泡装饰
    System.out.println(
        beverage3.getDescription() + ": $ " + beverage3.cost());

    // 用 工厂模式 和 生成器模式，可以更好的建立被 装饰者对象
  }

}

输出：

Espresso: $ 12.0
DarkRoast, Mocha, Mocha, Whip: $ 10.3
HouseBlend, Soy, Mocha, Whip: $ 13.3

扩展：

现在咖啡要有区分大，中，小杯的价格；

同理,

调料因为杯的大小也要区分不同的价格；

Beverage.java

package com.jing.decorator.size;

/**
 * 所有饮料的抽象超类
 * @author LiuJing
 *
 */
public abstract class Beverage {
  
  /**
   * 杯子的容量类型
   */
  public final static int TALL = 1;
  public final static int GRANDE = 2;
  public final static int VENTI = 3;
  
  /**
   * 杯子的容量
   */
  private int volume = 2; // 默认为中杯
  
  public int getSize() {
    return volume;
  }

  public void setSize(int valume) {
    this.volume = valume;
  }
  
  public String getSizeDescription() {
    
    String type = "未知杯的大小 ";
    switch(volume){
    case TALL:
      type = "小杯";
      break;
    case GRANDE:
      type = "中杯";
      break;
    case VENTI:
      type = "大杯";
      break;
    }

    return type;
  }

  /**
   * 饮料的名字
   */
  String description = "Unknow Beverage";
  

  
  /*
   * 获取饮料的名字
   */
  public String getDescription(){
    return description;
  }
  
  
  /***
   * 获取饮料的价格
   * @return 返回计算后的总价
   */
  public abstract double cost();
  
}

DarkRoast.java

package com.jing.decorator.size;

import java.text.DecimalFormat;

/***
 * 深烤咖啡
 * @author LiuJing
 *
 */
public class DarkRoast extends Beverage {

  /***
   * 构造时确定名字
   */
  public DarkRoast(){
    description = "DarkRoast";
  }
  
  public DarkRoast(int volume){
    setSize(volume);
    description = "DarkRoast";
  }
  
  /***
   * 价格
   */
  public double cost() {
    double cost = 0.0;
    if (getSize() == Beverage.TALL) {
      cost = 10.0;
    }else if (getSize() == Beverage.GRANDE){
      cost = 15.0;
    }else if (getSize() == Beverage.VENTI){
      cost = 20.0;
    }
    
    DecimalFormat df = new DecimalFormat("#.00");
    return Double.valueOf(df.format(cost));
  }

}

Decaf.java

package com.jing.decorator.size;

import java.text.DecimalFormat;

/***
 * 低咖啡因咖啡
 * @author LiuJing
 *
 */
public class Decaf extends Beverage {

  /***
   * 构造时确定名字
   */
  public Decaf() {
    description = "Decaf";
  }
  public Decaf(int volume){
    setSize(volume);
    description = "Decaf";
  }
  
  /***
   * 价格
   */
  public double cost() {
    double cost = 0.0;
    if (getSize() == Beverage.TALL) {
      cost = 11.0;
    }else if (getSize() == Beverage.GRANDE){
      cost = 16.0;
    }else if (getSize() == Beverage.VENTI){
      cost = 21.0;
    }
    
    DecimalFormat df = new DecimalFormat("#.00");
    return Double.valueOf(df.format(cost));
  }

}

Espresso.java

package com.jing.decorator.size;

import java.text.DecimalFormat;

/***
 * 浓咖啡
 * @author LiuJing
 *
 */
public class Espresso extends Beverage {

  /***
   *  构造时确定其名字
   */
  public Espresso(){
    description = "Espresso";
  }
  
  public Espresso(int volume){
    setSize(volume);
    description = "Espresso";
  }
  
  /***
   * 方法返回 该饮料的价格
   */
  public double cost() {
    double cost = 0.0;
    if (getSize() == Beverage.TALL) {
      cost = 12.0;
    }else if (getSize() == Beverage.GRANDE){
      cost = 17.0;
    }else if (getSize() == Beverage.VENTI){
      cost = 22.0;
    }
    
    DecimalFormat df = new DecimalFormat("#.00");
    return Double.valueOf(df.format(cost));
  }
}

HouseBlend.java

package com.jing.decorator.size;

import java.text.DecimalFormat;

/***
 * 家庭混合咖啡
 * @author LiuJing
 *
 */
public class HouseBlend extends Beverage {

  /***
   * 构造时确定其名字
   */
  public HouseBlend(){
    description = "HouseBlend";
  }
  
  public HouseBlend(int volume){
    setSize(volume);
    description = "HouseBlend";
  }
  
  /***
   * 返回该咖啡的价格
   */
  public double cost() {
    double cost = 0.0;
    if (getSize() == Beverage.TALL) {
      cost = 13.0;
    }else if (getSize() == Beverage.GRANDE){
      cost = 18.0;
    }else if (getSize() == Beverage.VENTI){
      cost = 23.0;
    }
    
    DecimalFormat df = new DecimalFormat("#.00");
    return Double.valueOf(df.format(cost));
  }

}

CondimentDecorator.java

package com.jing.decorator.size;

/***
 * 调料装饰者抽象超类，继承至 Beverage,便于类型的统一，能彼此替换。
 * @author LiuJing
 *
 */
public abstract class CondimentDecorator extends Beverage {
  
  /***
   * 要装饰的咖啡对象
   */
  Beverage beverage;
  
  
  /***
   * 所有子类都必须重新实现 getDescription()方法
   */
  public abstract String getDescription();

}

Milk.java

package com.jing.decorator.size;

import java.text.DecimalFormat;

/***
 * 咖啡调料 牛奶  Milk >> CondimentDecorator >> Beverage
 * @author LiuJing
 *
 */
public class Milk extends CondimentDecorator {


  /**
   * 构造时确定要加给谁
   * @param beverage
   */
  public Milk(Beverage beverage){
    this.beverage = beverage;
    setSize(beverage.getSize());
  }
  
  public int getSize(){
    return beverage.getSize();
  }
  
  /***
   * 不仅显示当前名，还说明被装饰的名字 
   */
  @Override
  public String getDescription() {
    // TODO Auto-generated method stub
    return beverage.getDescription() + ", Milk";
  }

  /***
   * 获取本身的价格和咖啡的价格
   */
  @Override
  public double cost() {
    // TODO Auto-generated method stub
    double cost = beverage.cost();
    if (getSize() == Beverage.TALL){
      cost += 0.1;
    } else if (getSize() == Beverage.GRANDE){
      cost += 0.2;
    } else if (getSize() == Beverage.VENTI){
      cost += 0.3;
    }
    
    DecimalFormat df = new DecimalFormat("#.00");
    return Double.valueOf(df.format(cost));
  }

}

Mocha.java

package com.jing.decorator.size;

import java.text.DecimalFormat;

/***
 * 咖啡调料 摩卡 Mocha >> CondimentDecorator >> Beverage
 * @author LiuJing
 *
 */
public class Mocha extends CondimentDecorator {

  
  /**
   * 构造时确定要加给谁
   * @param beverage
   */
  public Mocha(Beverage beverage){
    this.beverage = beverage;
    setSize(beverage.getSize());
  }
  
  public int getSize(){
    return beverage.getSize();
  }
  
  /***
   * 不仅显示当前名，还说明被装饰的名字 
   */
  @Override
  public String getDescription() {
    // TODO Auto-generated method stub
    return beverage.getDescription() + ", Mocha";
  }

  /***
   * 获取本身的价格和咖啡的价格
   */
  @Override
  public double cost() {
    // TODO Auto-generated method stub
    double cost = beverage.cost();
    if (getSize() == Beverage.TALL){
      cost += 0.1;
    } else if (getSize() == Beverage.GRANDE){
      cost += 0.2;
    } else if (getSize() == Beverage.VENTI){
      cost += 0.3;
    }
    
    DecimalFormat df = new DecimalFormat("#.00");
    return Double.valueOf(df.format(cost));
  }

}

Soy.java

package com.jing.decorator.size;

import java.text.DecimalFormat;

/***
 * 咖啡调料 豆浆  Soy >> CondimentDecorator >> Beverage
 * @author LiuJing
 *
 */
public class Soy extends CondimentDecorator {

  
  /**
   * 构造时确定要加给谁
   * @param beverage
   */
  public Soy(Beverage beverage){
    this.beverage = beverage;
    setSize(beverage.getSize());
  }
  
  public int getSize(){
    return beverage.getSize();
  }
  
  /***
   * 不仅显示当前名，还说明被装饰的名字 
   */
  @Override
  public String getDescription() {
    // TODO Auto-generated method stub
    return beverage.getDescription() + ", Soy";
  }

  /***
   * 获取本身的价格和咖啡的价格
   */
  @Override
  public double cost() {
    // TODO Auto-generated method stub
    double cost = beverage.cost();
    if (getSize() == Beverage.TALL){
      cost += 0.1;
    } else if (getSize() == Beverage.GRANDE){
      cost += 0.2;
    } else if (getSize() == Beverage.VENTI){
      cost += 0.3;
    }
    
    DecimalFormat df = new DecimalFormat("#.00");
    return Double.valueOf(df.format(cost));
  }

}

Whip.java

package com.jing.decorator.size;

import java.text.DecimalFormat;

/***
 * 咖啡调料 奶泡  Whip >> CondimentDecorator >> Beverage
 * @author LiuJing
 *
 */
public class Whip extends CondimentDecorator {


  /**
   * 构造时确定要加给谁
   * @param beverage
   */
  public Whip(Beverage beverage){
    this.beverage = beverage;
    setSize(beverage.getSize());
  }
  
  public int getSize(){
    return beverage.getSize();
  }
  
  /***
   * 不仅显示当前名，还说明被装饰的名字 
   */
  @Override
  public String getDescription() {
    // TODO Auto-generated method stub
    return beverage.getDescription() + ", Whip";
  }

  /***
   * 获取本身的价格和咖啡的价格
   */
  @Override
  public double cost() {
    // TODO Auto-generated method stub
    double cost = beverage.cost();
    if (getSize() == Beverage.TALL){
      cost += 0.1;
    } else if (getSize() == Beverage.GRANDE){
      cost += 0.2;
    } else if (getSize() == Beverage.VENTI){
      cost += 0.3;
    }
    
    DecimalFormat df = new DecimalFormat("#.00");
    return Double.valueOf(df.format(cost));
  }

}

Test.java

package com.jing.decorator.size;

public class Test {

  /**
   * @param args
   */
  public static void main(String[] args) {
    // TODO Auto-generated method stub

    
    // 点了一份浓咖啡
    Beverage beverage = new Espresso(); // 使用默认中杯
    System.out.println(beverage.getSizeDescription()
        + beverage.getDescription() + ": $ " + beverage.cost());

    // 点了一份深烤
    Beverage beverage2 = new DarkRoast();// 默认为中号
    beverage2.setSize(Beverage.TALL);    // 重新设置杯号为小号
    beverage2 = new Mocha(beverage2);    // 加 摩卡装饰
    beverage2 = new Mocha(beverage2);    // 再加 摩卡装饰
    beverage2 = new Whip(beverage2);     // 再加 奶泡装饰
    System.out.println(beverage2.getSizeDescription()
        + beverage2.getDescription() + ": $ " + beverage2.cost());

    // 点了一份家庭混合
    Beverage beverage3 = new HouseBlend(Beverage.VENTI); // 构造初始时就设为大号
    beverage3 = new Soy(beverage3);   // 加 豆浆装饰
    beverage3 = new Mocha(beverage3); // 再加 摩卡装饰
    beverage3 = new Whip(beverage3);  // 再加 奶泡装饰
    System.out.println(beverage3.getSizeDescription()
        + beverage3.getDescription()
        + ": $ " + beverage3.cost());

    // 用 工厂模式 和 生成器模式，可以更好的建立被 装饰者对象
  }

}

中杯Espresso: $ 17.0
小杯DarkRoast, Mocha, Mocha, Whip: $ 10.3
大杯HouseBlend, Soy, Mocha, Whip: $ 23.9

Java设计模式：装饰者模式（Decorator Pattern）

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