不同的穿衣打扮可以让一个人显示出不同的气质,这就好比我们编程中的装饰设计模式一样,进行不同的装饰后可以出现不同的产品对象,下来就让我们看看装饰模式到底是怎么用的吧。
首先介绍一下装饰模式到底是什么吧,其实装饰模式就是在不必改变原类文件和使用继承的情况下,动态地扩展一个对象的功能。它是通过创建一个包装对象,也就是装饰来包裹真实的对象,这正好遵循了我们程序设计的开闭原则。
先说这样一个需求吧,假设咖啡馆需要你编写程序计算咖啡的价格,这样的要求看似是很简单的,可是一细想你会发现咖啡中可以加入这样活那样的料,这样就需要在原有的价格上进行累加,可是这样一来,如果有多种料需要进行不同的搭配,如果采用普通的方法进行累加求和,那是一件让人很崩溃的事。恰恰装饰者模式就是在这种情况下发挥着巨大的作用了,我们来看看吧!
首先我们需要先定义一个所有咖啡的抽象类Beverage
public abstract class Beverage { String description = "unknow Beverage"; public String getDescription() { return description; } public abstract double cost(); }
public abstract class CondimentDecorator extends Beverage { public abstract String getDescription(); }好了基本的都写好了,我们来写几个具体的咖啡实现类吧
public class Espresso extends Beverage { @Override public double cost() { return 1.99; } public Espresso() { description = "Espresso"; } }
public class HouseBlend extends Beverage { @Override public double cost() { return .89; } public HouseBlend() { description = "House Blend Coffee"; } }
public class Mocha extends CondimentDecorator { Beverage beverage; public Mocha(Beverage beverage) { this.beverage = beverage; } @Override public String getDescription() { return this.beverage.getDescription() + ", Mocha"; } @Override public double cost() { return .20 + this.beverage.cost(); } }
public class Soy extends CondimentDecorator { Beverage beverage; public Soy(Beverage beverage) { this.beverage = beverage; } @Override public String getDescription() { return this.beverage.getDescription() + ", Soy"; } @Override public double cost() { return .10 + this.beverage.cost(); } }
public class Whip extends CondimentDecorator { Beverage beverage; public Whip(Beverage beverage) { this.beverage = beverage; } @Override public String getDescription() { return this.beverage.getDescription() + ", Whip"; } @Override public double cost() { return .30 + this.beverage.cost(); } }
public class Test { public static void main(String[] args) { //定义Espresso,不加调料,打印描述价格 Beverage beverage = new Espresso(); System.out.println(beverage.getDescription() + ", $" + beverage.cost()); //定义House Blend,两份摩卡,一份Soy和Whip Beverage beverage2 = new HouseBlend(); beverage2 = new Mocha(beverage2); beverage2 = new Mocha(beverage2); beverage2 = new Soy(beverage2); beverage2 = new Whip(beverage2); System.out.println(beverage2.getDescription() + ", $" + beverage2.cost()); } }运行看看结果吧:
Espresso, $1.99 House Blend Coffee, Mocha, Mocha, Soy, Whip, $1.69
这样以后随便加入调料,我们直接扩展就行了,很方便吧,这就是我们的装饰者模式。
其实jdk自带的最常用的装饰者就是I/O,输入输出流进行各种装饰,比如:DataInputStream in = new DataInputStream(new BufferedInputStream(new FileInputStream("FileTest.Java"))); InputStream is = new BufferedInputStream(new FileInputStream(new File(""))); InputStream isis = new BufferedInputStream(new GZIPInputStream(new FileInputStream("")));