开发者模式------装饰模式

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2013-05-28 17:29
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装饰模式定义：装饰模式动态的将责任附加到对象上，若要扩展功能，装饰模式提供了比继承更有弹性的替代方案
看下下面的例子，总共有两种咖啡：Decaf、Espresso，另有两种调味品：Mocha、Whip（3种设计的主要差别在于抽象方式不同）
设计一：
<img src="http://img.blog.csdn.net/20150724154701506?watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQv/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/Center" alt="">
即使添加在多的调味品，咖啡依然是咖啡，在抽象的过程中并没有考虑咖啡和调味品之间的关系
当咖啡和调味品的种类很多时，将会产生大量的类，如果一种咖啡的价格发生变动，需要找到所有相关的类逐一修改
设计二：
<img src="http://img.blog.csdn.net/20150724160235303?watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQv/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/Center" alt="">
将调味品作为Coffee类的属性，比起设计一，类的数量大大减少，相应的，程序结构也更加清晰
<div class="dp-highlighter bg_java"><div class="bar"><div class="tools">[java] <a href="#" class="ViewSource" title="view plain" onclick="dp.sh.Toolbar.Command('ViewSource',this);return false;" target="_blank">view plain</a> <a href="#" class="CopyToClipboard" title="copy" onclick="dp.sh.Toolbar.Command('CopyToClipboard',this);return false;" target="_blank">copy</a><div style="position: absolute; left: 839px; top: 1330px; width: 18px; height: 18px; z-index: 99;"><embed id="ZeroClipboardMovie_1" src="http://static.blog.csdn.net/scripts/ZeroClipboard/ZeroClipboard.swf" loop="false" menu="false" quality="best" bgcolor="#ffffff" width="18" height="18" name="ZeroClipboardMovie_1" align="middle" allowscriptaccess="always" allowfullscreen="false" type="application/x-shockwave-flash" pluginspage="http://www.macromedia.com/go/getflashplayer" flashvars="id=1&width=18&height=18" wmode="transparent"></div> <a href="#" class="PrintSource" title="print" onclick="dp.sh.Toolbar.Command('PrintSource',this);return false;" target="_blank">print</a><a href="#" class="About" title="?" onclick="dp.sh.Toolbar.Command('About',this);return false;" target="_blank">?</a></div></div><ol start="1" class="dp-j"><li class="alt">public class Coffee {  </li><li class="">    private boolean mocha;  </li><li class="alt">    private boolean whip;  </li><li class="">      </li><li class="alt">    public double cost(){  </li><li class="">        double price = 0d;  </li><li class="alt">        if(mocha){  </li><li class="">            price += 0.5;  </li><li class="alt">        }  </li><li class="">        if(whip){  </li><li class="alt">            price += 0.1;  </li><li class="">        }  </li><li class="alt">        return price;  </li><li class="">    }  </li><li class="alt">      </li><li class="">    public void addMocha(){  </li><li class="alt">        this.mocha = true;  </li><li class="">    }  </li><li class="alt">      </li><li class="">    public void addWhip(){  </li><li class="alt">        this.whip = true;  </li><li class="">    }  </li><li class="alt">}  </li></ol></div><pre name="code" class="java" style="display: none;">public class Coffee {
private boolean mocha;
private boolean whip;

public double cost(){
double price = 0d;
if(mocha){
price += 0.5;
}
if(whip){
price += 0.1;
}
return price;
}

public void addMocha(){
this.mocha = true;
}

public void addWhip(){
this.whip = true;
}
}
</pre><div class="dp-highlighter bg_java"><div class="bar"><div class="tools">[java] <a href="#" class="ViewSource" title="view plain" onclick="dp.sh.Toolbar.Command('ViewSource',this);return false;" target="_blank">view plain</a> <a href="#" class="CopyToClipboard" title="copy" onclick="dp.sh.Toolbar.Command('CopyToClipboard',this);return false;" target="_blank">copy</a><div style="position: absolute; left: 839px; top: 1812px; width: 18px; height: 18px; z-index: 99;"><embed id="ZeroClipboardMovie_2" src="http://static.blog.csdn.net/scripts/ZeroClipboard/ZeroClipboard.swf" loop="false" menu="false" quality="best" bgcolor="#ffffff" width="18" height="18" name="ZeroClipboardMovie_2" align="middle" allowscriptaccess="always" allowfullscreen="false" type="application/x-shockwave-flash" pluginspage="http://www.macromedia.com/go/getflashplayer" flashvars="id=2&width=18&height=18" wmode="transparent"></div> <a href="#" class="PrintSource" title="print" onclick="dp.sh.Toolbar.Command('PrintSource',this);return false;" target="_blank">print</a><a href="#" class="About" title="?" onclick="dp.sh.Toolbar.Command('About',this);return false;" target="_blank">?</a></div></div><ol start="1" class="dp-j"><li class="alt">public class Decaf extends Coffee{  </li><li class="">    public double cost(){  </li><li class="alt">        double price = super.cost();  </li><li class="">        price += 2.0;  </li><li class="alt">        return price;  </li><li class="">    }  </li><li class="alt">}  </li></ol></div><pre name="code" class="java" style="display: none;">public class Decaf extends Coffee{
public double cost(){
double price = super.cost();
price += 2.0;
return price;
}
}</pre><div class="dp-highlighter bg_java"><div class="bar"><div class="tools">[java] <a href="#" class="ViewSource" title="view plain" onclick="dp.sh.Toolbar.Command('ViewSource',this);return false;" target="_blank">view plain</a> <a href="#" class="CopyToClipboard" title="copy" onclick="dp.sh.Toolbar.Command('CopyToClipboard',this);return false;" target="_blank">copy</a><div style="position: absolute; left: 839px; top: 2006px; width: 18px; height: 18px; z-index: 99;"><embed id="ZeroClipboardMovie_3" src="http://static.blog.csdn.net/scripts/ZeroClipboard/ZeroClipboard.swf" loop="false" menu="false" quality="best" bgcolor="#ffffff" width="18" height="18" name="ZeroClipboardMovie_3" align="middle" allowscriptaccess="always" allowfullscreen="false" type="application/x-shockwave-flash" pluginspage="http://www.macromedia.com/go/getflashplayer" flashvars="id=3&width=18&height=18" wmode="transparent"></div> <a href="#" class="PrintSource" title="print" onclick="dp.sh.Toolbar.Command('PrintSource',this);return false;" target="_blank">print</a><a href="#" class="About" title="?" onclick="dp.sh.Toolbar.Command('About',this);return false;" target="_blank">?</a></div></div><ol start="1" class="dp-j"><li class="alt">public class Espresso extends Coffee {  </li><li class="">    public double cost(){  </li><li class="alt">        double price = super.cost();  </li><li class="">        price += 2.5;  </li><li class="alt">        return price;  </li><li class="">    }  </li><li class="alt">}  </li></ol></div><pre name="code" class="java" style="display: none;">public class Espresso extends Coffee {
public double cost(){
double price = super.cost();
price += 2.5;
return price;
}
}</pre>
<a href="http://lib.csdn.net/base/softwaretest" class="replace_word" title="软件测试知识库" target="_blank" style="color:#df3434; font-weight:bold;">测试</a>一下：
<div class="dp-highlighter bg_java"><div class="bar"><div class="tools">[java] <a href="#" class="ViewSource" title="view plain" onclick="dp.sh.Toolbar.Command('ViewSource',this);return false;" target="_blank">view plain</a> <a href="#" class="CopyToClipboard" title="copy" onclick="dp.sh.Toolbar.Command('CopyToClipboard',this);return false;" target="_blank">copy</a><div style="position: absolute; left: 839px; top: 2244px; width: 18px; height: 18px; z-index: 99;"><embed id="ZeroClipboardMovie_4" src="http://static.blog.csdn.net/scripts/ZeroClipboard/ZeroClipboard.swf" loop="false" menu="false" quality="best" bgcolor="#ffffff" width="18" height="18" name="ZeroClipboardMovie_4" align="middle" allowscriptaccess="always" allowfullscreen="false" type="application/x-shockwave-flash" pluginspage="http://www.macromedia.com/go/getflashplayer" flashvars="id=4&width=18&height=18" wmode="transparent"></div> <a href="#" class="PrintSource" title="print" onclick="dp.sh.Toolbar.Command('PrintSource',this);return false;" target="_blank">print</a><a href="#" class="About" title="?" onclick="dp.sh.Toolbar.Command('About',this);return false;" target="_blank">?</a></div></div><ol start="1" class="dp-j"><li class="alt">public class Test {  </li><li class="">    public static void main(String[] args) {  </li><li class="alt">        Coffee coffee = new Decaf();  </li><li class="">        coffee.addMocha();  </li><li class="alt">        coffee.addWhip();  </li><li class="">        //2.6  </li><li class="alt">        System.out.println(coffee.cost());  </li><li class="">    }  </li><li class="alt">}  </li></ol></div><pre name="code" class="java" style="display: none;">public class Test {
public static void main(String[] args) {
Coffee coffee = new Decaf();
coffee.addMocha();
coffee.addWhip();
//2.6
System.out.println(coffee.cost());
}
}</pre>
考虑到下面几个问题，设计二有明显的不足：
1，如果调味品的种类较多，Coffee类将会变得相当庞大，难以维护
2，无法处理顾客希望添加双倍的Mocha的场景
3，添加一种新的咖啡IceCoffee，从逻辑上来说IceCoffee是不能加Mocha的，但是由于IceCoffee类继承自Coffee类，IceCoffee类依然从父类继承了addMocha()方法，这就需要在IceCoffee类中重写一个空的addMocha()方法，并且当使用IceCoffee类时，不能够面向Coffee类编程，以避免错误的调用父类方法
设计三--装饰器模式：
<img src="http://img.blog.csdn.net/20150724163818712?watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQv/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/Center" alt="">
装饰模式分为3个部分：
1，抽象组件 -- 对应Coffee类
2，具体组件 -- 对应具体的咖啡，如：Decaf，Espresso
3，装饰者 -- 对应调味品，如：Mocha，Whip
装饰模式有3个特点：
1，具体组件和装饰者都继承自抽象组件(Decaf、Espresson、Mocha和Whip都继承自Coffee)，并且装饰者持有抽象组件的引用
2，可以使用装饰者组合具体组件创造出新的类(Mocha组合Decaf创造出MochaDecaf)
3，过程2可以重复，直到创造出需要的类
使用装饰模式，想要获得一个WhipDoubleMochaEspresso是很容易的：
<img src="http://img.blog.csdn.net/20150724174118284?watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQv/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/Center" alt=""><div class="dp-highlighter bg_java"><div class="bar"><div class="tools">[java] <a href="#" class="ViewSource" title="view plain" onclick="dp.sh.Toolbar.Command('ViewSource',this);return false;" target="_blank">view plain</a> <a href="#" class="CopyToClipboard" title="copy" onclick="dp.sh.Toolbar.Command('CopyToClipboard',this);return false;" target="_blank">copy</a><div style="position: absolute; left: 839px; top: 3666px; width: 18px; height: 18px; z-index: 99;"><embed id="ZeroClipboardMovie_5" src="http://static.blog.csdn.net/scripts/ZeroClipboard/ZeroClipboard.swf" loop="false" menu="false" quality="best" bgcolor="#ffffff" width="18" height="18" name="ZeroClipboardMovie_5" align="middle" allowscriptaccess="always" allowfullscreen="false" type="application/x-shockwave-flash" pluginspage="http://www.macromedia.com/go/getflashplayer" flashvars="id=5&width=18&height=18" wmode="transparent"></div> <a href="#" class="PrintSource" title="print" onclick="dp.sh.Toolbar.Command('PrintSource',this);return false;" target="_blank">print</a><a href="#" class="About" title="?" onclick="dp.sh.Toolbar.Command('About',this);return false;" target="_blank">?</a></div></div><ol start="1" class="dp-j"><li class="alt">public interface Coffee {  </li><li class="">    public double cost();  </li><li class="alt">}  </li></ol></div><pre name="code" class="java" style="display: none;">public interface Coffee {
public double cost();
}</pre><div class="dp-highlighter bg_java"><div class="bar"><div class="tools">[java] <a href="#" class="ViewSource" title="view plain" onclick="dp.sh.Toolbar.Command('ViewSource',this);return false;" target="_blank">view plain</a> <a href="#" class="CopyToClipboard" title="copy" onclick="dp.sh.Toolbar.Command('CopyToClipboard',this);return false;" target="_blank">copy</a><div style="position: absolute; left: 839px; top: 3788px; width: 18px; height: 18px; z-index: 99;"><embed id="ZeroClipboardMovie_6" src="http://static.blog.csdn.net/scripts/ZeroClipboard/ZeroClipboard.swf" loop="false" menu="false" quality="best" bgcolor="#ffffff" width="18" height="18" name="ZeroClipboardMovie_6" align="middle" allowscriptaccess="always" allowfullscreen="false" type="application/x-shockwave-flash" pluginspage="http://www.macromedia.com/go/getflashplayer" flashvars="id=6&width=18&height=18" wmode="transparent"></div> <a href="#" class="PrintSource" title="print" onclick="dp.sh.Toolbar.Command('PrintSource',this);return false;" target="_blank">print</a><a href="#" class="About" title="?" onclick="dp.sh.Toolbar.Command('About',this);return false;" target="_blank">?</a></div></div><ol start="1" class="dp-j"><li class="alt">public class Espresso implements Coffee {  </li><li class="">    public double cost(){  </li><li class="alt">        return 2.5;  </li><li class="">    }  </li><li class="alt">}  </li></ol></div><pre name="code" class="java" style="display: none;">public class Espresso implements Coffee {
public double cost(){
return 2.5;
}
}</pre><div class="dp-highlighter bg_java"><div class="bar"><div class="tools">[java] <a href="#" class="ViewSource" title="view plain" onclick="dp.sh.Toolbar.Command('ViewSource',this);return false;" target="_blank">view plain</a> <a href="#" class="CopyToClipboard" title="copy" onclick="dp.sh.Toolbar.Command('CopyToClipboard',this);return false;" target="_blank">copy</a><div style="position: absolute; left: 839px; top: 3946px; width: 18px; height: 18px; z-index: 99;"><embed id="ZeroClipboardMovie_7" src="http://static.blog.csdn.net/scripts/ZeroClipboard/ZeroClipboard.swf" loop="false" menu="false" quality="best" bgcolor="#ffffff" width="18" height="18" name="ZeroClipboardMovie_7" align="middle" allowscriptaccess="always" allowfullscreen="false" type="application/x-shockwave-flash" pluginspage="http://www.macromedia.com/go/getflashplayer" flashvars="id=7&width=18&height=18" wmode="transparent"></div> <a href="#" class="PrintSource" title="print" onclick="dp.sh.Toolbar.Command('PrintSource',this);return false;" target="_blank">print</a><a href="#" class="About" title="?" onclick="dp.sh.Toolbar.Command('About',this);return false;" target="_blank">?</a></div></div><ol start="1" class="dp-j"><li class="alt">public class Dressing implements Coffee {  </li><li class="">    private Coffee coffee;  </li><li class="alt">      </li><li class="">    public Dressing(Coffee coffee){  </li><li class="alt">        this.coffee = coffee;  </li><li class="">    }  </li><li class="alt">      </li><li class="">    public double cost(){  </li><li class="alt">        return coffee.cost();  </li><li class="">    }  </li><li class="alt">}  </li></ol></div><pre name="code" class="java" style="display: none;">public class Dressing implements Coffee {
private Coffee coffee;

public Dressing(Coffee coffee){
this.coffee = coffee;
}

public double cost(){
return coffee.cost();
}
}</pre><div class="dp-highlighter bg_java"><div class="bar"><div class="tools">[java] <a href="#" class="ViewSource" title="view plain" onclick="dp.sh.Toolbar.Command('ViewSource',this);return false;" target="_blank">view plain</a> <a href="#" class="CopyToClipboard" title="copy" onclick="dp.sh.Toolbar.Command('CopyToClipboard',this);return false;" target="_blank">copy</a><div style="position: absolute; left: 839px; top: 4212px; width: 18px; height: 18px; z-index: 99;"><embed id="ZeroClipboardMovie_8" src="http://static.blog.csdn.net/scripts/ZeroClipboard/ZeroClipboard.swf" loop="false" menu="false" quality="best" bgcolor="#ffffff" width="18" height="18" name="ZeroClipboardMovie_8" align="middle" allowscriptaccess="always" allowfullscreen="false" type="application/x-shockwave-flash" pluginspage="http://www.macromedia.com/go/getflashplayer" flashvars="id=8&width=18&height=18" wmode="transparent"></div> <a href="#" class="PrintSource" title="print" onclick="dp.sh.Toolbar.Command('PrintSource',this);return false;" target="_blank">print</a><a href="#" class="About" title="?" onclick="dp.sh.Toolbar.Command('About',this);return false;" target="_blank">?</a></div></div><ol start="1" class="dp-j"><li class="alt">public class Whip extends Dressing {  </li><li class="">    public Whip(Coffee coffee){  </li><li class="alt">        super(coffee);  </li><li class="">    }  </li><li class="alt">      </li><li class="">    public double cost(){  </li><li class="alt">        return super.cost() + 0.1;  </li><li class="">    }  </li><li class="alt">}  </li></ol></div><pre name="code" class="java" style="display: none;">public class Whip extends Dressing {
public Whip(Coffee coffee){
super(coffee);
}

public double cost(){
return super.cost() + 0.1;
}
}</pre><div class="dp-highlighter bg_java"><div class="bar"><div class="tools">[java] <a href="#" class="ViewSource" title="view plain" onclick="dp.sh.Toolbar.Command('ViewSource',this);return false;" target="_blank">view plain</a> <a href="#" class="CopyToClipboard" title="copy" onclick="dp.sh.Toolbar.Command('CopyToClipboard',this);return false;" target="_blank">copy</a><div style="position: absolute; left: 839px; top: 4442px; width: 18px; height: 18px; z-index: 99;"><embed id="ZeroClipboardMovie_9" src="http://static.blog.csdn.net/scripts/ZeroClipboard/ZeroClipboard.swf" loop="false" menu="false" quality="best" bgcolor="#ffffff" width="18" height="18" name="ZeroClipboardMovie_9" align="middle" allowscriptaccess="always" allowfullscreen="false" type="application/x-shockwave-flash" pluginspage="http://www.macromedia.com/go/getflashplayer" flashvars="id=9&width=18&height=18" wmode="transparent"></div> <a href="#" class="PrintSource" title="print" onclick="dp.sh.Toolbar.Command('PrintSource',this);return false;" target="_blank">print</a><a href="#" class="About" title="?" onclick="dp.sh.Toolbar.Command('About',this);return false;" target="_blank">?</a></div></div><ol start="1" class="dp-j"><li class="alt">public class Mocha extends Dressing {  </li><li class="">    public Mocha(Coffee coffee){  </li><li class="alt">        super(coffee);  </li><li class="">    }  </li><li class="alt">      </li><li class="">    public double cost(){  </li><li class="alt">        return super.cost() + 0.5;  </li><li class="">    }  </li><li class="alt">}  </li></ol></div><pre name="code" class="java" style="display: none;">public class Mocha extends Dressing {
public Mocha(Coffee coffee){
super(coffee);
}

public double cost(){
return super.cost() + 0.5;
}
}</pre>
测试一下：
<div class="dp-highlighter bg_java"><div class="bar"><div class="tools">[java] <a href="#" class="ViewSource" title="view plain" onclick="dp.sh.Toolbar.Command('ViewSource',this);return false;" target="_blank">view plain</a> <a href="#" class="CopyToClipboard" title="copy" onclick="dp.sh.Toolbar.Command('CopyToClipboard',this);return false;" target="_blank">copy</a><div style="position: absolute; left: 839px; top: 4716px; width: 18px; height: 18px; z-index: 99;"><embed id="ZeroClipboardMovie_10" src="http://static.blog.csdn.net/scripts/ZeroClipboard/ZeroClipboard.swf" loop="false" menu="false" quality="best" bgcolor="#ffffff" width="18" height="18" name="ZeroClipboardMovie_10" align="middle" allowscriptaccess="always" allowfullscreen="false" type="application/x-shockwave-flash" pluginspage="http://www.macromedia.com/go/getflashplayer" flashvars="id=10&width=18&height=18" wmode="transparent"></div> <a href="#" class="PrintSource" title="print" onclick="dp.sh.Toolbar.Command('PrintSource',this);return false;" target="_blank">print</a><a href="#" class="About" title="?" onclick="dp.sh.Toolbar.Command('About',this);return false;" target="_blank">?</a></div></div><ol start="1" class="dp-j"><li class="alt">public class Test {  </li><li class="">    public static void main(String[] args) {  </li><li class="alt">        Coffee coffee = new Espresso();  </li><li class="">        coffee = new Mocha(coffee);  </li><li class="alt">        coffee = new Mocha(coffee);  </li><li class="">        coffee = new Whip(coffee);  </li><li class="alt">        //3.6(2.5 + 0.5 + 0.5 + 0.1)  </li><li class="">        System.out.println(coffee.cost());  </li><li class="alt">    }  </li><li class="">}  </li></ol></div><pre name="code" class="java" style="display: none;">public class Test {
public static void main(String[] args) {
Coffee coffee = new Espresso();
coffee = new Mocha(coffee);
coffee = new Mocha(coffee);
coffee = new Whip(coffee);
//3.6(2.5 + 0.5 + 0.5 + 0.1)
System.out.println(coffee.cost());
}
}</pre>
当然Decorator类中可以重写父类的方法，也可以扩展自己需要的方法
 
装饰模式的缺点：
1，装饰模式虽然扩展性较高，但是没有设计二简洁，类的数量略多（但肯定比设计一少很多），如何取舍可扩展性和简洁性是个问题，有所选择就要有所牺牲
2，很难搞清楚一个类究竟被装饰了多少层，可能是1层，也可能是100层

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