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<title> 设计模式之Strategy 策略模式</title>
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<h3 align="center">设计模式之Strategy(策略)</h3>
<p align="center"><a href="http://www.jdon.com/aboutme.htm">板桥里人</a> http://www.jdon.com 2002/03/30</p>
<p align="center"><a href="../mybook/index.htm" target="_blank"><strong>模式实战书籍《Java实用系统开发指南》</strong></a></p>
<p>Strategy策略模式是属于设计模式中 对象行为型模式,主要是定义一系列的算法,把这些算法一个个封装成单独的类.</p>
<p>Stratrgy应用比较广泛,比如, 公司经营业务变化图, 可能有两种实现方式,一个是线条曲线,一个是框图(bar),这是两种算法,可以使用Strategy实现.</p>
<p>这里以字符串替代为例, 有一个文件,我们需要读取后,希望替代其中相应的变量,然后输出.关于替代其中变量的方法可能有多种方法,这取决于用户的要求,所以我们要准备几套变量字符替代方案.</p>
<p><img src="images/Strategy.jpg" width="443" height="323"></p>
<p> </p>
<p>首先,我们建立一个抽象类RepTempRule 定义一些公用变量和方法:</p>
<table width="80%" border="0" cellspacing="3" cellpadding="3" bordercolor="#CCCCCC">
<tr>
<td bgcolor="#CCCCCC">public abstract class RepTempRule{<br>
<br>
protected String oldString="";<br>
public void setOldString(String oldString){<br>
this.oldString=oldString; <br>
}<br> <br>
protected String newString="";<br>
public String getNewString(){<br>
return newString;<br>
}<br> <br> <br> <br>
public abstract void replace() throws Exception;<br> <br>
<br>
}</td>
</tr>
</table>
<p>在RepTempRule中 有一个抽象方法abstract需要继承明确,这个replace里其实是替代的具体方法.<br>
我们现在有两个字符替代方案,<br>
1.将文本中aaa替代成bbb;<br>
2.将文本中aaa替代成ccc;<br>
<br>
对应的类分别是RepTempRuleOne RepTempRuleTwo</p>
<table width="80%" border="0" cellspacing="3" cellpadding="3">
<tr>
<td bgcolor="#CCCCCC"> <p>public class RepTempRuleOne extends
RepTempRule{<br>
<br>
<br>
public void replace() throws Exception{ <br>
<br>
//replaceFirst是jdk1.4新特性 <br>
newString=oldString.replaceFirst("aaa",
"bbbb") <br>
System.out.println("this is replace one");<br>
<br>
}<br>
<br>
<br>
}</p></td>
</tr>
</table>
<table width="80%" border="0" cellspacing="3" cellpadding="3">
<tr>
<td bgcolor="#CCCCCC">public class RepTempRuleTwo extends
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