设计模式-装饰器模式(Decorator Pattern)

青旅半醒 2022-05-11 07:42 256阅读 0赞

装饰器模式是什么？

动态的给一个对象添加一些额外的功能，同事又不改变对象的结构。

装饰器模式的要素

1.  被装饰对象（Bread）
2.  装饰对象
3.  装饰器（Decorator）
4.  公共接口或者抽象类

![70][] 装饰器模式示意图

# 简单例子 #

package myDesignPatternsTest.decoratorPattern;
    
    /**
     * 这是一个他们的公共父类(一般为抽象类或者接口)
     */
    public abstract class Ingredient {
    public abstract String getDescription();
    public  abstract Double getCost();
    public  void printDescription(){
        System.out.println("Name:"+this.getDescription());
        System.out.println("this value is :"+this.getCost());
    
    }
    }

package myDesignPatternsTest.decoratorPattern;
    //被配饰对象
    public class Bread extends Ingredient {
        private String desc;
    
        public Bread(String desc) {
            this.desc = desc;
        }
    
        public String getDescription() {
            return desc;
        }
    
    
        public Double getCost() {
            return 26.8;
        }
    }

package myDesignPatternsTest.decoratorPattern;
    
    /**
     * 抽象装饰器是所有具体装饰器的的父亲
     * 1.必须有一个他自己的父类（Ingreditne）作为自己的成员变量
     * 2.必须继承公共父类
     */
    public abstract class Decorator extends  Ingredient {
        Ingredient ingredient;
    
        public Decorator(Ingredient ingredient) {
            this.ingredient = ingredient;
        }
        public abstract String getDescription();
        public  abstract Double getCost();
    }

package myDesignPatternsTest.decoratorPattern;
    
    /**
     * 具体配适器
     * 1.对被配饰对象进行了加强
     */
    public class Mutton extends Decorator {
        public Mutton(Ingredient ingredient) {
            super(ingredient);
        }
    
        public String getDescription() {
            String base=ingredient.getDescription();
            return base+"....."+"Decrocated is Mutton";
        }
    
        @Override
        public Double getCost() {
            Double base=ingredient.getCost();
            double porkvalue=27.3;
            return base+porkvalue;
        }
    }

package myDesignPatternsTest.decoratorPattern;
    
    /**
     * 具体配适器
     */
    public class Pork extends Decorator {
        public Pork(Ingredient ingredient) {
            super(ingredient);
        }
    
        public String getDescription() {
            String base=ingredient.getDescription();
            return base+"....."+"Decrocated is Pork";
        }
    
        @Override
        public Double getCost() {
            Double base=ingredient.getCost();
            double porkvalue=26.3;
            return base+porkvalue;
        }
    }

package myDesignPatternsTest.decoratorPattern;
    
    /**
     * 具体配适器
     */
    public class Celery extends Decorator {
        public Celery(Ingredient ingredient) {
            super(ingredient);
        }
    
        public String getDescription() {
            String base=ingredient.getDescription();
            return base+"....."+"Decrocated is Celery";
        }
    
        @Override
        public Double getCost() {
            Double base=ingredient.getCost();
            double porkvalue=27.3;
            return base+porkvalue;
        }
    }

package myDesignPatternsTest.decoratorPattern;
    
    import java.util.Scanner;
    
    public class Client {
        public static void main(String[] args) {
            Ingredient a=new Mutton(new Bread("mutoon"));
            a.printDescription();
            Ingredient b=new Pork(new Bread("pork"));
            b.printDescription();
        }
    
    }
    Name:mutoon.....Decrocated is Mutton
    this value is :54.1
    Name:pork.....Decrocated is Pork
    this value is :53.1

装饰器模式的优缺点

**优点：**装饰类和被装饰类可以独立发展，不会相互耦合，装饰模式是继承的一个替代模式，装饰模式可以动态扩展一个实现类的功能。

**缺点：**多层装饰比较复杂。

[70]: /images/20220511/b9a681059fac4e7c9077418f9830bca4.png