……天天向上

          好的想法總是無窮無盡

          統計

          留言簿(1)

          閱讀排行榜

          評論排行榜

          2012年9月5日 #

          calendar獲取當前日期及時間的用例

          1. import Java.util.*;
          2.   public class ShowDate {
          3.   public static void main(String[] args) {
          4.   Calendar calendar = new GregorianCalendar();
          5.   Date trialTime = new Date();
          6.   calendar.setTime(trialTime);
          7.   // print out a bunch of interesting things
          8.   System.out.println("ERA: " + calendar.get(Calendar.ERA));
          9.   System.out.println("YEAR: " + calendar.get(Calendar.YEAR));
          10.   System.out.println("MONTH: " + calendar.get(Calendar.MONTH));
          11.   System.out.println("WEEK_OF_YEAR: " + calendar.get(Calendar.WEEK_OF_YEAR));
          12.   System.out.println("WEEK_OF_MONTH: " + calendar.get(Calendar.WEEK_OF_MONTH));
          13.   System.out.println("DATE: " + calendar.get(Calendar.DATE));
          14.   System.out.println("DAY_OF_MONTH: " + calendar.get(Calendar.DAY_OF_MONTH));
          15.   System.out.println("DAY_OF_YEAR: " + calendar.get(Calendar.DAY_OF_YEAR));
          16.   System.out.println("DAY_OF_WEEK: " + calendar.get(Calendar.DAY_OF_WEEK));
          17.   System.out.println("DAY_OF_WEEK_IN_MONTH: " + calendar.get(Calendar.DAY_OF_WEEK_IN_MONTH));
          18.   System.out.println("AM_PM: " + calendar.get(Calendar.AM_PM));
          19.   System.out.println("HOUR: " + calendar.get(Calendar.HOUR));
          20.   System.out.println("HOUR_OF_DAY: " + calendar.get(Calendar.HOUR_OF_DAY));
          21.   System.out.println("MINUTE: " + calendar.get(Calendar.MINUTE));
          22.   System.out.println("SECOND: " + calendar.get(Calendar.SECOND));
          23.   System.out.println("MILLISECOND: " + calendar.get(Calendar.MILLISECOND));
          24.   System.out.println("ZONE_OFFSET: " + (calendar.get(Calendar.ZONE_OFFSET)/(60*60*1000)));
          25.   System.out.println("DST_OFFSET: " + (calendar.get(Calendar.DST_OFFSET)/(60*60*1000)));
          26.   System.out.println("Current Time, with hour reset to 3");
          27.   calendar.clear(Calendar.HOUR_OF_DAY); // so doesn't override
          28.   calendar.set(Calendar.HOUR, 3);
          29.   System.out.println("ERA: " + calendar.get(Calendar.ERA));
          30.   System.out.println("YEAR: " + calendar.get(Calendar.YEAR));
          31.   System.out.println("MONTH: " + calendar.get(Calendar.MONTH));
          32.   System.out.println("WEEK_OF_YEAR: " + calendar.get(Calendar.WEEK_OF_YEAR));
          33.   System.out.println("WEEK_OF_MONTH: " + calendar.get(Calendar.WEEK_OF_MONTH));
          34.   System.out.println("DATE: " + calendar.get(Calendar.DATE));
          35.   System.out.println("DAY_OF_MONTH: " + calendar.get(Calendar.DAY_OF_MONTH));
          36.   System.out.println("DAY_OF_YEAR: " + calendar.get(Calendar.DAY_OF_YEAR));
          37.   System.out.println("DAY_OF_WEEK: " + calendar.get(Calendar.DAY_OF_WEEK));
          38.   System.out.println("DAY_OF_WEEK_IN_MONTH: " + calendar.get(Calendar.DAY_OF_WEEK_IN_MONTH));

          posted @ 2012-09-19 09:51 japper 閱讀(6354) | 評論 (0)編輯 收藏

          Android SDK下載和更新失敗的解決方法


          Android SDK下載和更新失敗的解決方法

           

          最近剛換了電腦,開始搭建Android開發環境的時候,下載SDK總是會出現如下錯誤:
           
          1.Failed to fetch URL http://dl-ssl.google.com/Android/repository/addons_list-1.xml
          據說dl-ssl.google.com在大陸被強了,偉大的天朝真是不讓人活了,解決方法就是修改C:\Windows\System32\drivers\etc\hosts文件。添加一行:
           
          1.74.125.237.1       dl-ssl.google.com 
          這里需要注意的是hosts文件是只讀的,我們沒有權限修改,需要我們將hosts文件復制到桌面或者其他地方,然后修改,代碼如下:
          1.# Copyright (c) 1993-2009 Microsoft Corp. 
          2.# 
          3.# This is a sample HOSTS file used by Microsoft TCP/IP for Windows. 
          4.# 
          5.# This file contains the mappings of IP addresses to host names. Each 
          6.# entry should be kept on an individual line. The IP address should 
          7.# be placed in the first column followed by the corresponding host name. 
          8.# The IP address and the host name should be separated by at least one 
          9.# space. 
          10.# 
          11.# Additionally, comments (such as these) may be inserted on individual 
          12.# lines or following the machine name denoted by a '#' symbol. 
          13.# 
          14.# For example: 
          15.# 
          16.#      102.54.94.97     rhino.acme.com          # source server 
          17.#       38.25.63.10     x.acme.com              # x client host 
          18. 
          19.# localhost name resolution is handled within DNS itself. 
          20.#   127.0.0.1       localhost 
          21.#   ::1             localhost 
          22.//親,就是增加這一句哦  
          23.74.125.237.1       dl-ssl.google.com 
          然后保存,復制修改后的hosts文件到C:\Windows\System32\drivers\etc 目錄,替換文件就好!!!我們再次下載SDK的時候就會成功啦,如下圖:
           


          嘿嘿,大功告成啦!!!
           
          PS:補充下,在mac或Linux中,hosts文件所在位置為/etc/hosts,可以使用sudo vim /etc/hosts來編輯。

          posted @ 2012-09-10 11:18 japper 閱讀(349) | 評論 (0)編輯 收藏

          免安裝版Tomcat 6.0.35碰到的問題 :打開tomcat管理界面時,用戶名和密碼錯誤的設置方法

          Tomcat 6.0.35 的功能有些不同于Tomcat 6.0.20。我下載的Tomcat 6.0.35是免安裝的,而以前使用的Tomcat 6.0.20是需要安裝的,而且Tomcat 6.0.20 的安裝密碼,即進入Tomcat Manager 這個地方的密碼是在安裝的時候指定的,但是呢,Tomcat 6.0.35 由于是免安裝的,所以就沒有地方去指定密碼了,當我們訪問Tomcat 6.0.35 的Tomcat Manager的時候 ,輸入以前默認的用戶名:admin 密碼為空,會發現出現了403 錯誤,即access deny 。調試了好久,最后終于找出原因了。根據403頁面的提示,需要在tomcat的配置文件中(即conf/tomcat-users.xml)加入

          <role rolename="manager-gui"/>

          <user username="admin" password="" roles="manager-gui"/>

          有一點必須注意,其中的rolename 必須是“manager-gui” ,更改成admin 或者 admin-gui,都不好用,而下面的username  password是可以任意的,但是后面的roles 必須和上面role 中的rolename相同。

          posted @ 2012-09-05 14:22 japper 閱讀(3835) | 評論 (0)編輯 收藏

          通過 jconsole查看tomcat運行情況的配置方法

          通過 jconsole查看tomcat運行情況的配置方法

          ——基于JDK1.5LinuxRedhat5.5)、Tomcat6

          由于項目的原因,需要使用jconsoletomcat進行遠程監控,結合網上的資料對配置方法進行了總結。

          第一步、配置tomcat

          打開%TOMCAT_HOME%/bin下的文件catalina.sh搜索“JAVA_OPTS”找到下面這行:

          if [ -z "$LOGGING_MANAGER" ]; then

            JAVA_OPTS="$JAVA_OPTS -Djava.util.logging.manager=org.apache.juli.ClassLoaderLogManager"

          else

            JAVA_OPTS="$JAVA_OPTS $LOGGING_MANAGER"

          fi 

          在每個“JAVA_OPTS”后邊都添加以下標黃代碼段,且在一行顯示

          if [ -z "$LOGGING_MANAGER" ]; then

            JAVA_OPTS="$JAVA_OPTS -Djava.util.logging.manager=org.apache.juli.ClassLoaderLogManager -Djava.rmi.server.hostname=192.9.100.48  -Dcom.sun.management.jmxremote -Dcom.sun.management.jmxremote.port="9004" -Dcom.sun.management.jmxremote.authenticate="false" -Dcom.sun.management.jmxremote.ssl="false""

          else 

            JAVA_OPTS="$JAVA_OPTS $LOGGING_MANAGER -Djava.rmi.server.hostname=192.9.100.48  -Dcom.sun.management.jmxremote -Dcom.sun.management.jmxremote.port="9004" -Dcom.sun.management.jmxremote.authenticate="false" -Dcom.sun.management.jmxremote.ssl="false""

          fi

          其中-Djava.rmi.server.hostname項必須設置,否則遠程連接會因為解析到127.0.0.1失敗,該項的值就是你在windows客戶端連接linux時的ip地址

          -Dcom.sun.management.jmxremote.port="9004"項設置遠程連接端口,不要與其他應用沖突

          sslauthenticate設置為false,如果需要安全,請不要false

          、重啟tomcat

          使用root身份登錄系統,進入%TOMCAT_HOME%/bin目錄下:

          [root@test ~]#ps ef |grep tomcat -輸入命令查看是否存在tomcat進程

          [root@test ~]#./shutdown.sh--停止tomcat服務,如果無效使用kill命令殺掉進程

          [root@test ~]#./startup.sh  --啟動tomcat服務

          、運行jconsole

          進入JDK安裝目錄%JDK_HOME%/bin下,找到“jconsole.exe”,點擊運行并選擇【遠程】選項卡:

          在【主機名或ip】輸入要遠程監控的tomcat服務器地址

          在【端口】輸入上文設置的端口號:9004

          【用戶名、口令】為空,點擊【連接】進入監控界面。

          posted @ 2012-09-05 14:16 japper 閱讀(3959) | 評論 (0)編輯 收藏

          TOMCAT獲取信息:JMXServiceURL 、JMXConnector 和MBeanServerConnection

          1. import java.lang.management.MemoryUsage;
          2. import java.text.SimpleDateFormat;
          3. import java.util.Date;
          4. import java.util.Formatter;
          5. import java.util.HashMap;
          6. import java.util.Iterator;
          7. import java.util.Map;
          8. import java.util.Set;
          9. import javax.management.MBeanAttributeInfo;
          10. import javax.management.MBeanInfo;
          11. import javax.management.MBeanServerConnection;
          12. import javax.management.ObjectInstance;
          13. import javax.management.ObjectName;
          14. import javax.management.openmbean.CompositeDataSupport;
          15. import javax.management.remote.JMXConnector;
          16. import javax.management.remote.JMXConnectorFactory;
          17. import javax.management.remote.JMXServiceURL;
          18. public class test {
          19. /**
          20. * @param args
          21. */
          22. public static void main(String[] args) {
          23. try {
          24. String jmxURL = "service:jmx:rmi:///jndi/rmi://192.168.1.126:10090/jmxrmi";//tomcat jmx url
          25. JMXServiceURL serviceURL = new JMXServiceURL(jmxURL);
          26. Map map = new HashMap();
          27. String[] credentials = new String[] { "monitorRole", "QED" };
          28. map.put("jmx.remote.credentials", credentials);
          29. JMXConnector connector = JMXConnectorFactory.connect(serviceURL, map);
          30. MBeanServerConnection mbsc = connector.getMBeanServerConnection();
          31. //端口最好是動態取得
          32. ObjectName threadObjName = new ObjectName("Catalina:type=ThreadPool,name=http-8089");
          33. MBeanInfo mbInfo = mbsc.getMBeanInfo(threadObjName);
          34. String attrName = "currentThreadCount";//tomcat的線程數對應的屬性值
          35. MBeanAttributeInfo[] mbAttributes = mbInfo.getAttributes();
          36. System.out.println("currentThreadCount:" + mbsc.getAttribute(threadObjName, attrName));
          37. //heap
          38. for (int j = 0; j < mbsc.getDomains().length; j++) {
          39. System.out.println("###########" + mbsc.getDomains()[j]);
          40. }
          41. Set MBeanset = mbsc.queryMBeans(null, null);
          42. System.out.println("MBeanset.size() : " + MBeanset.size());
          43. Iterator MBeansetIterator = MBeanset.iterator();
          44. while (MBeansetIterator.hasNext()) {
          45. ObjectInstance objectInstance = (ObjectInstance) MBeansetIterator.next();
          46. ObjectName objectName = objectInstance.getObjectName();
          47. String canonicalName = objectName.getCanonicalName();
          48. System.out.println("canonicalName : " + canonicalName);
          49. if (canonicalName.equals("Catalina:host=localhost,type=Cluster")) {
          50. // Get details of cluster MBeans
          51. System.out.println("Cluster MBeans Details:");
          52. System.out.println("=========================================");
          53. //getMBeansDetails(canonicalName);
          54. String canonicalKeyPropList = objectName.getCanonicalKeyPropertyListString();
          55. }
          56. }
          57. //------------------------- system ----------------------
          58. ObjectName runtimeObjName = new ObjectName("java.lang:type=Runtime");
          59. System.out.println("廠商:" + (String) mbsc.getAttribute(runtimeObjName, "VmVendor"));
          60. System.out.println("程序:" + (String) mbsc.getAttribute(runtimeObjName, "VmName"));
          61. System.out.println("版本:" + (String) mbsc.getAttribute(runtimeObjName, "VmVersion"));
          62. Date starttime = new Date((Long) mbsc.getAttribute(runtimeObjName, "StartTime"));
          63. SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
          64. System.out.println("啟動時間:" + df.format(starttime));
          65. Long timespan = (Long) mbsc.getAttribute(runtimeObjName, "Uptime");
          66. System.out.println("連續工作時間:" + test.formatTimeSpan(timespan));
          67. //------------------------ JVM -------------------------
          68. //堆使用率
          69. ObjectName heapObjName = new ObjectName("java.lang:type=Memory");
          70. MemoryUsage heapMemoryUsage = MemoryUsage.from((CompositeDataSupport) mbsc.getAttribute(heapObjName,
          71. "HeapMemoryUsage"));
          72. long maxMemory = heapMemoryUsage.getMax();//堆最大
          73. long commitMemory = heapMemoryUsage.getCommitted();//堆當前分配
          74. long usedMemory = heapMemoryUsage.getUsed();
          75. System.out.println("heap:" + (double) usedMemory * 100 / commitMemory + "%");//堆使用率
          76. MemoryUsage nonheapMemoryUsage = MemoryUsage.from((CompositeDataSupport) mbsc.getAttribute(heapObjName,
          77. "NonHeapMemoryUsage"));
          78. long noncommitMemory = nonheapMemoryUsage.getCommitted();
          79. long nonusedMemory = heapMemoryUsage.getUsed();
          80. System.out.println("nonheap:" + (double) nonusedMemory * 100 / noncommitMemory + "%");
          81. ObjectName permObjName = new ObjectName("java.lang:type=MemoryPool,name=Perm Gen");
          82. MemoryUsage permGenUsage = MemoryUsage.from((CompositeDataSupport) mbsc.getAttribute(permObjName, "Usage"));
          83. long committed = permGenUsage.getCommitted();//持久堆大小
          84. long used = heapMemoryUsage.getUsed();//
          85. System.out.println("perm gen:" + (double) used * 100 / committed + "%");//持久堆使用率
          86. //-------------------- Session ---------------
          87. ObjectName managerObjName = new ObjectName("Catalina:type=Manager,*");
          88. Set<ObjectName> s = mbsc.queryNames(managerObjName, null);
          89. for (ObjectName obj : s) {
          90. System.out.println("應用名:" + obj.getKeyProperty("path"));
          91. ObjectName objname = new ObjectName(obj.getCanonicalName());
          92. System.out.println("最大會話數:" + mbsc.getAttribute(objname, "maxActiveSessions"));
          93. System.out.println("會話數:" + mbsc.getAttribute(objname, "activeSessions"));
          94. System.out.println("活動會話數:" + mbsc.getAttribute(objname, "sessionCounter"));
          95. }
          96. //----------------- Thread Pool ----------------
          97. ObjectName threadpoolObjName = new ObjectName("Catalina:type=ThreadPool,*");
          98. Set<ObjectName> s2 = mbsc.queryNames(threadpoolObjName, null);
          99. for (ObjectName obj : s2) {
          100. System.out.println("端口名:" + obj.getKeyProperty("name"));
          101. ObjectName objname = new ObjectName(obj.getCanonicalName());
          102. System.out.println("最大線程數:" + mbsc.getAttribute(objname, "maxThreads"));
          103. System.out.println("當前線程數:" + mbsc.getAttribute(objname, "currentThreadCount"));
          104. System.out.println("繁忙線程數:" + mbsc.getAttribute(objname, "currentThreadsBusy"));
          105. }
          106. } catch (Exception e) {
          107. e.printStackTrace();
          108. }
          109. }
          110. public static String formatTimeSpan(long span) {
          111. long minseconds = span % 1000;
          112. span = span / 1000;
          113. long seconds = span % 60;
          114. span = span / 60;
          115. long mins = span % 60;
          116. span = span / 60;
          117. long hours = span % 24;
          118. span = span / 24;
          119. long days = span;
          120. return (new Formatter()).format("%1$d天 %2$02d:%3$02d:%4$02d.%5$03d", days, hours, mins, seconds, minseconds)
          121. .toString();
          122. }
          123. }

          1. import java.util.Iterator;
          2. import java.util.Set;
          3. import javax.management.Attribute;
          4. import javax.management.MBeanInfo;
          5. import javax.management.MBeanServerConnection;
          6. import javax.management.MBeanServerInvocationHandler;
          7. import javax.management.ObjectInstance;
          8. import javax.management.ObjectName;
          9. import javax.management.remote.JMXConnector;
          10. import javax.management.remote.JMXConnectorFactory;
          11. import javax.management.remote.JMXServiceURL;
          12. public class Client {
          13. public static void main(String[] args) throws Exception {
          14. JMXServiceURL url = new JMXServiceURL("service:jmx:rmi:///jndi/rmi://localhost:9999/server");
          15. JMXConnector jmxc = JMXConnectorFactory.connect(url, null);
          16. MBeanServerConnection mbsc = jmxc.getMBeanServerConnection();
          17. ObjectName mbeanName = new ObjectName("chengang:name=HelloWorld");
          18. // 把所有Domain都打印出來
          19. System.out.println("Domains:---------------");
          20. String domains[] = mbsc.getDomains();
          21. for (int i = 0; i < domains.length; i++) {
          22. System.out.println("\tDomain[" + i + "] = " + domains[i]);
          23. }
          24. // MBean的總數
          25. System.out.println("MBean count = " + mbsc.getMBeanCount());
          26. // 對name屬性的操作(屬性名的第一個字母要大寫)
          27. mbsc.setAttribute(mbeanName, new Attribute("Name", "PANDA"));// 設值
          28. System.out.println("Name = " + mbsc.getAttribute(mbeanName, "Name"));// 取值
          29. // 得到proxy代理后直接調用的方式
          30. HelloMBean proxy = (HelloMBean) MBeanServerInvocationHandler.newProxyInstance(mbsc, mbeanName, HelloMBean.class, false);
          31. proxy.printHello();
          32. proxy.printHello("Raymend");
          33. // 遠程調用的方式
          34. mbsc.invoke(mbeanName, "printHello", null, null);
          35. mbsc.invoke(mbeanName, "printHello", new Object[] { "熊貓燒香" }, new String[] { String.class.getName() });
          36. // 得mbean的信息
          37. MBeanInfo info = mbsc.getMBeanInfo(mbeanName);
          38. System.out.println("Hello Class: " + info.getClassName());
          39. System.out.println("Hello Attriber:" + info.getAttributes()[0].getName());
          40. System.out.println("Hello Operation:" + info.getOperations()[0].getName());
          41. // 得到所有的MBean的ObjectName
          42. System.out.println("all ObjectName:---------------");
          43. Set set = mbsc.queryMBeans(null, null);
          44. for (Iterator it = set.iterator(); it.hasNext();) {
          45. ObjectInstance oi = (ObjectInstance) it.next();
          46. System.out.println("\t" + oi.getObjectName());
          47. }
          48. // 關閉MBeanServer連接
          49. jmxc.close();
          50. }
          51. }

          posted @ 2012-09-05 14:14 japper 閱讀(4994) | 評論 (0)編輯 收藏

          LinkedHashMap和HashMap的比較使用

          由于現在項目中用到了LinkedHashMap,并不是太熟悉就到網上搜了一下。







          import
          java.util.HashMap;

          import
          java.util.Iterator;

          import
          java.util.LinkedHashMap;

          import
          java.util.Map;

          public
          class TestLinkedHashMap {


            public static
          void main(String
          args[])

            {

             System.out.println("*************************LinkedHashMap*************");

             Map<Integer,String> map = new LinkedHashMap<Integer,String>();

             map.put(6, "apple");

             map.put(3, "banana");

             map.put(2,"pear");

            

             for (Iterator it =  map.keySet().iterator();it.hasNext();)

             {

              Object key = it.next();

              System.out.println(
          key+
          "="+
          map.get(key));

             }

            

             System.out.println("*************************HashMap*************");

             Map<Integer,String>
          map1 =
          new  HashMap<Integer,String>();

             map1.put(6, "apple");

             map1.put(3, "banana");

             map1.put(2,"pear");

            

             for (Iterator it = map1.keySet().iterator();it.hasNext();)

             {

              Object key = it.next();

              System.out.println(
          key+
          "="+
          map1.get(key));

             }

            }

          }


          運行結果如下:


          *************************LinkedHashMap*************
          6=apple
          3=banana
          2=pear
          *************************HashMap**************************
          2=pear
          6=apple
          3=banana


          分析:LinkedHashmap 的特點是put進去的對象位置未發生變化,而HashMap會發生變化.


          再普及下:




          java為數據結構中的映射定義了一個接口java.util.Map;它有四個實現類,分別是HashMap
          Hashtable LinkedHashMap 和TreeMap
          .


          Map主要用于存儲健值對,根據鍵得到值,因此不允許鍵重復(重復了覆蓋了),但允許值重復。
          Hashmap
          是一個最常用的Map,它根據鍵的HashCode值存儲數據,根據鍵可以直接獲取它的值,具有很快的訪問速度,遍歷時,取得數據的順序是完全隨機的。
          HashMap最多只允許一條記錄的鍵為Null;允許多條記錄的值為
          Null;HashMap不支持線程的同步,即任一時刻可以有多個線程同時寫HashMap;可能會導致數據的不一致。如果需要同步,可以用
          Collections的synchronizedMap方法使HashMap具有同步的能力,或者使用ConcurrentHashMap。


          Hashtable與
          HashMap類似,它繼承自Dictionary類,不同的是:它不允許記錄的鍵或者值為空;它支持線程的同步,即任一時刻只有一個線程能寫Hashtable,因此也導致了
          Hashtable在寫入時會比較慢。


          LinkedHashMap
          是HashMap的一個子類,保存了記錄的插入順序,在用Iterator遍歷LinkedHashMap時,先得到的記錄肯定是先插入的.也可以在構造時用帶參數,按照應用次數排序。在遍歷的時候會比HashMap慢,不過有種情況例外,當HashMap容量很大,實際數據較少時,遍歷起來可能會比
          LinkedHashMap慢,因為LinkedHashMap的遍歷速度只和實際數據有關,和容量無關,而HashMap的遍歷速度和他的容量有關。


          TreeMap實現SortMap接口,能夠把它保存的記錄根據鍵排序,默認是按鍵值的升序排序,也可以指定排序的比較器,當用Iterator
          遍歷TreeMap時,得到的記錄是排過序的。


          一般情況下,我們用的最多的是HashMap,在Map 中插入、刪除和定位元素,HashMap
          是最好的選擇。但如果您要按自然順序或自定義順序遍歷鍵,那么TreeMap會更好。如果需要輸出的順序和輸入的相同,那么用LinkedHashMap
          可以實現,它還可以按讀取順序來排列.


          HashMap是一個最常用的Map,它根據鍵的hashCode值存儲數據,根據鍵可以直接獲取它的值,具有很快的訪問速度。HashMap最多只允許一條記錄的鍵為NULL,允許多條記錄的值為NULL。


          HashMap不支持線程同步,即任一時刻可以有多個線程同時寫HashMap,可能會導致數據的不一致性。如果需要同步,可以用Collections的synchronizedMap方法使HashMap具有同步的能力。


          Hashtable與HashMap類似,不同的是:它不允許記錄的鍵或者值為空;它支持線程的同步,即任一時刻只有一個線程能寫Hashtable,因此也導致了Hashtable在寫入時會比較慢。


          LinkedHashMap保存了記錄的插入順序,在用Iterator遍歷LinkedHashMap時,先得到的記錄肯定是先插入的。


          在遍歷的時候會比HashMap慢TreeMap能夠把它保存的記錄根據鍵排序,默認是按升序排序,也可以指定排序的比較器。當用Iterator遍歷TreeMap時,得到的記錄是排過序的。

          posted @ 2012-09-05 14:12 japper 閱讀(16471) | 評論 (5)編輯 收藏

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