一、定义
指在不改变现有对象结构的情况下,动态地给该对象增加一些职责(即增加其额外功能)的模式。 我们先来看一个快餐店的例子。快餐店有炒面、炒饭这些快餐,可以额外附加鸡蛋、火腿、培根这些配菜,当然加配菜需要额外加钱,每个配菜的价钱通常不太一样,那么计算总价就会显得比较麻烦。如果使用继承的方式存在的问题:扩展性不好如果要再加一种配料(火腿肠),我们就会发现需要给FriedRiceFriedNoodles分别定义一个子类。如果要新增一个快餐品类(炒河粉)的话,就需要定义更多的子类。产生过多的子类 所以我们使用装饰者模式 进行修饰
二、代理模式和装饰模式的区别
相同点 都要实现与目标类相同的业务接口 在两个类中都要声明目标对象 都可以在不修改目标类的前提下增强目标方法 不同点 目的不同 装饰者是为了增强目标对象 静态代理是为了保护和隐藏目标对象 获取目标对象构建的地方不同 装饰者是由外界传递进来,可以通过构造方法传递 静态代理 是在代理类内部创建,以此来隐藏目标对象
public abstract class FastFood { private float price; private String desc; public FastFood ( ) { } public FastFood ( float price, String desc) { this . price = price; this . desc = desc; } public void setPrice ( float price) { this . price = price; } public float getPrice ( ) { return price; } public String getDesc ( ) { return desc; } public void setDesc ( String desc) { this . desc = desc; } public abstract float cost ( ) ; }
}
public class FriedRice extends FastFood { public FriedRice ( ) { super ( 10 , "炒饭" ) ; } public float cost ( ) { return getPrice ( ) ; }
}
public class FriedNoodles extends FastFood { public FriedNoodles ( ) { super ( 12 , "炒面" ) ; } public float cost ( ) { return getPrice ( ) ; }
}
public abstract class Garnish extends FastFood { private FastFood fastFood; public FastFood getFastFood ( ) { return fastFood; } public void setFastFood ( FastFood fastFood) { this . fastFood = fastFood; } public Garnish ( FastFood fastFood, float price, String desc) { super ( price, desc) ; this . fastFood = fastFood; }
}
public class Egg extends Garnish { public Egg ( FastFood fastFood) { super ( fastFood, 1 , "鸡蛋" ) ; } public float cost ( ) { return getPrice ( ) + getFastFood ( ) . getPrice ( ) ; } @Override public String getDesc ( ) { return super . getDesc ( ) + getFastFood ( ) . getDesc ( ) ; }
}
public class Bacon extends Garnish { public Bacon ( FastFood fastFood) { super ( fastFood, 2 , "培根" ) ; } @Override public float cost ( ) { return getPrice ( ) + getFastFood ( ) . getPrice ( ) ; } @Override public String getDesc ( ) { return super . getDesc ( ) + getFastFood ( ) . getDesc ( ) ; }
}
public class Client { public static void main ( String [ ] args) { FastFood food = new FriedRice ( ) ; System . out. println ( food. getDesc ( ) + " " + food. cost ( ) + "元" ) ; System . out. println ( "========" ) ; FastFood food1 = new FriedRice ( ) ; food1 = new Egg ( food1) ; System . out. println ( food1. getDesc ( ) + " " + food1. cost ( ) + "元" ) ; System . out. println ( "========" ) ; FastFood food2 = new FriedNoodles ( ) ; food2 = new Bacon ( food2) ; System . out. println ( food2. getDesc ( ) + " " + food2. cost ( ) + "元" ) ; }
}