HashMap中的对象根据成员进行自定义排序
<p >HashMap中的对象根据成员进行自定义排序 <BR><BR> Map是Java中最常用的存储对象的集合类之一，存储在HashMap中的对象在取出时是无序的，下文以示例介绍了如果对HashMap中存储的对象根据成员进行自定义排序。<BR><BR>应用说明：计算缓存对象的点击次数按次数排序输出。<BR><BR>1. 定义CacheObj类<BR><BR>定义了一个简单的对象，这个对象将存储在一个HashMap中，希望根据CacheObj中的整型成员变量cachedCounter进行排序输出。<BR><BR><BR>/*<BR> * Created on 2003-3-5<BR> */<BR>package com.cache;<BR>/*** @author Weidong **/<BR>public class CacheObj {<BR>int cachedCounter;<BR>Object cacheObj = null;<BR>/**<BR> * @return Returns the cacheObj.<BR> */<BR>public Object getCacheObj() {<BR> return cacheObj;<BR>}<BR>/**<BR> * @param cacheObj<BR> * The cacheObj to set.<BR> */<BR>public void setCacheObj(Object cacheObj) {<BR> this.cacheObj = cacheObj;<BR>}<BR>/**<BR> * @return Returns the cachedCounter.<BR> */<BR>public int getCachedCounter() {<BR> return cachedCounter;<BR>}<BR>/**<BR> * @param cachedCounter<BR> * The cachedCounter to set.<BR> */<BR>public void setCachedCounter(int cachedCounter) {<BR> this.cachedCounter = cachedCounter;<BR>}<BR>}<BR><BR><BR><BR><BR>2. 自定义HotItemComparator <BR><BR>HotItemComparator实现了Comparator 接口， 实现的方法非常简单就是根据cachedCounter进行比较返回比较结果<BR><BR>正序：return obj1.getCachedCounter() - obj2.getCachedCounter();<BR><BR>倒序：return obj2.getCachedCounter() - obj1.getCachedCounter();<BR><BR><BR>package com.cache;<BR>import java.util.Comparator;<BR>/**<BR> * @author Weidong <BR> */<BR>public final class HotItemComparator implements Comparator {<BR> /*<BR> * @see java.util.Comparator#compare(java.lang.Object, java.lang.Object)<BR> */<BR> public int compare(Object arg0, Object arg1) {<BR> CacheObj obj1 = (CacheObj) arg0;<BR> CacheObj obj2 = (CacheObj) arg1;<BR> return obj1.getCachedCounter() - obj2.getCachedCounter();<BR> }<BR>}<BR><BR><BR>3. 测试用例<BR><BR>定义变量：public static final Comparator HOT_ITEM = new HotItemComparator(); <BR>将HashMap追加到List对象sortList中：sortList.addAll(caches.values()); <BR>对sorList应用HOT_ITEM排序：Collections.sort(sortList, HOT_ITEM);<BR><BR>package com.cache;<BR>import java.util.ArrayList;<BR>import java.util.Collections;<BR>import java.util.HashMap;<BR>import java.util.Iterator;<BR>import java.util.List;<BR>import java.util.Map;<BR>/**<BR> * @author Weidong<BR> */<BR>public class TestBean {<BR> public static final Comparator HOT_ITEM = new HotItemComparator();<BR><BR> public static void sortMap() {<BR> Map caches = new HashMap();<BR> CacheObj s1 = new CacheObj();<BR> s1.setCachedCounter(2);<BR> CacheObj s2 = new CacheObj();<BR> s2.setCachedCounter(3);<BR> CacheObj s3 = new CacheObj();<BR> s3.setCachedCounter(1);<BR> caches.put("1", s1);<BR> caches.put("2", s2);<BR> caches.put("3", s3);<BR><BR> List sortList = new ArrayList();<BR> sortList.addAll(caches.values());<BR> Collections.sort(sortList, HOT_ITEM);<BR> Iterator iter = sortList.iterator();<BR> while (iter.hasNext()) {<BR> CacheObj s = (CacheObj) iter.next();<BR> System.out.println("counter is "+s.getCachedCounter());<BR> }<BR> }<BR> public static void main(String[] args) {<BR> sortMap();<BR> }<BR>}<BR><BR>输出：文中用正序<BR><BR>counter is 1<BR>counter is 2<BR>counter is 3 <BR><FONT face="Times New Roman">（责任编辑：董建伟）</FONT><p align="center"></p></p>
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