Java Hashtable遍历与方法使用

超、凢脫俗 2021-11-01 09:40 310阅读 0赞

## 参考文档 ##

我参考了[Java 集合系列11之 Hashtable详细介绍(源码解析)和使用示例][Java _11_ Hashtable]，阅读了jdk 1.8的源码

## Hashtable的继承关系 ##

Hashtable继承了Dictionary类，实现了Map、Cloneable、Serializable接口

public class Hashtable<K,V> extends Dictionary<K,V> implements Map<K,V>, Cloneable, java.io.Serializable

## Hashtable数据结构 ##

依赖的数组和链表，跟HashMap不一样的

## Hashtable是线程安全的 ##

共有方法就是线程安全的方法

## Hashtable遍历方法 ##

通过entrySet()去遍历，效率高
    通过keySet()去遍历key，效率低
    通过values遍历
    通过Enumeration keys遍历
    通过Enumeration elements遍历

## 使用例子 ##

import lombok.extern.slf4j.Slf4j; import java.io.ObjectStreamException; import java.util.Collection; import java.util.Enumeration; import java.util.Hashtable; import java.util.Iterator; import java.util.Map; import java.util.Random; import java.util.Set; @Slf4j public class HashtableTest { public static void main(String[] args) { Hashtable hashtable = new Hashtable(); Random ran = new Random(); for (int i = 0; i < 5; i++) { int tmp=ran.nextInt(1000); hashtable.put(Integer.valueOf(i),String.valueOf(tmp)); } //测试遍历 iteratorEntrySet(hashtable); iteratorKeySet(hashtable); iteratorValues(hashtable); enumerationKeys(hashtable); enumerationElements(hashtable); //打印table log.info("table :{}",hashtable); //键值对个数 log.info("table size {}",hashtable.size()); //包含键 log.info("contans key 1 :{}",hashtable.containsKey(Integer.valueOf(1))); //包含values //remove key log.info("remove key :{}",hashtable.remove(Integer.valueOf(1))); log.info("after remove ,table size {}",hashtable.size()); //clear log.info("clear table "); hashtable.clear(); //is empety log.info("is empty: {}", hashtable.isEmpty()); } //entrySet()去遍历 public static void iteratorEntrySet(Hashtable hashtable) { Set entry = hashtable.entrySet(); Iterator<Map.Entry> it = entry.iterator(); log.info("iteratorEntrySet:"); while (it.hasNext()) { Map.Entry entry1=it.next(); log.info("key :{}, value :{}", entry1.getKey(), entry1.getValue()); //下面的逻辑是错误的，it.next()执行了两次，可能为空 //log.info("key :{}, value :{}", it.next().getKey(), it.next().getValue()); } } //keySet()去遍历key public static void iteratorKeySet(Hashtable hashtable){ Set set =hashtable.keySet(); log.info("iteratorKeySet"); Iterator it =set.iterator(); while(it.hasNext()){ Object key =it.next(); log.info("key :{}, value :{}",key,hashtable.get(key)); } } //values遍历 public static void iteratorValues(Hashtable hashtable){ Collection values=hashtable.values(); log.info("iteratorValues"); Iterator it =values.iterator(); while(it.hasNext()){ log.info("value :{}",it.next()); } } //Enumeration keys遍历 //内部类实现接口Enumeration，通过TYPE实现hasMoreElements() nextElement()方法 public static void enumerationKeys(Hashtable hashtable){ Enumeration keys = hashtable.keys(); log.info("enumerationKeys"); while(keys.hasMoreElements()){ Object key =keys.nextElement(); log.info("key :{}, value :{}",key,hashtable.get(key)); } } //Enumeration elements遍历 public static void enumerationElements(Hashtable hashtable){ Enumeration values =hashtable.elements(); log.info("enumerationElements"); while(values.hasMoreElements()) { Object value =values.nextElement(); log.info("value : {}",value); } } }

## 运行结果 ##

D:\zxems\work\OpenJdk\8\bin\java.exe "-javaagent:D:\Program Files\JetBrains\IntelliJ IDEA 2019.1.1\lib\idea_rt.jar=52315:D:\Program Files\JetBrains\IntelliJ IDEA 2019.1.1\bin" -Dfile.encoding=GB2312 -classpath D:\zxems\work\OpenJdk\8\jre\lib\charsets.jar;D:\zxems\work\OpenJdk\8\jre\lib\ext\access-bridge-64.jar;D:\zxems\work\OpenJdk\8\jre\lib\ext\cldrdata.jar;D:\zxems\work\OpenJdk\8\jre\lib\ext\dnsns.jar;D:\zxems\work\OpenJdk\8\jre\lib\ext\jaccess.jar;D:\zxems\work\OpenJdk\8\jre\lib\ext\localedata.jar;D:\zxems\work\OpenJdk\8\jre\lib\ext\nashorn.jar;D:\zxems\work\OpenJdk\8\jre\lib\ext\sunec.jar;D:\zxems\work\OpenJdk\8\jre\lib\ext\sunjce_provider.jar;D:\zxems\work\OpenJdk\8\jre\lib\ext\sunmscapi.jar;D:\zxems\work\OpenJdk\8\jre\lib\ext\sunpkcs11.jar;D:\zxems\work\OpenJdk\8\jre\lib\ext\zipfs.jar;D:\zxems\work\OpenJdk\8\jre\lib\jce.jar;D:\zxems\work\OpenJdk\8\jre\lib\jsse.jar;D:\zxems\work\OpenJdk\8\jre\lib\management-agent.jar;D:\zxems\work\OpenJdk\8\jre\lib\resources.jar;D:\zxems\work\OpenJdk\8\jre\lib\rt.jar;D:\My\code\javalearn\java-learn\target\classes;D:\My\tools\maven\repo\org\slf4j\slf4j-log4j12\1.7.2\slf4j-log4j12-1.7.2.jar;D:\My\tools\maven\repo\org\slf4j\slf4j-api\1.7.2\slf4j-api-1.7.2.jar;D:\My\tools\maven\repo\log4j\log4j\1.2.17\log4j-1.2.17.jar java.javabase.map.HashtableTest
    2019-07-15 16:57:21,254   [main] INFO  java.javabase.map.HashtableTest  - iteratorEntrySet:
    2019-07-15 16:57:21,254   [main] INFO  java.javabase.map.HashtableTest  - key :4, value :771
    2019-07-15 16:57:21,254   [main] INFO  java.javabase.map.HashtableTest  - key :3, value :567
    2019-07-15 16:57:21,254   [main] INFO  java.javabase.map.HashtableTest  - key :2, value :933
    2019-07-15 16:57:21,254   [main] INFO  java.javabase.map.HashtableTest  - key :1, value :421
    2019-07-15 16:57:21,254   [main] INFO  java.javabase.map.HashtableTest  - key :0, value :304
    2019-07-15 16:57:21,254   [main] INFO  java.javabase.map.HashtableTest  - iteratorKeySet
    2019-07-15 16:57:21,254   [main] INFO  java.javabase.map.HashtableTest  - key :4, value :771
    2019-07-15 16:57:21,254   [main] INFO  java.javabase.map.HashtableTest  - key :3, value :567
    2019-07-15 16:57:21,254   [main] INFO  java.javabase.map.HashtableTest  - key :2, value :933
    2019-07-15 16:57:21,254   [main] INFO  java.javabase.map.HashtableTest  - key :1, value :421
    2019-07-15 16:57:21,254   [main] INFO  java.javabase.map.HashtableTest  - key :0, value :304
    2019-07-15 16:57:21,254   [main] INFO  java.javabase.map.HashtableTest  - iteratorValues
    2019-07-15 16:57:21,254   [main] INFO  java.javabase.map.HashtableTest  - value :771
    2019-07-15 16:57:21,254   [main] INFO  java.javabase.map.HashtableTest  - value :567
    2019-07-15 16:57:21,254   [main] INFO  java.javabase.map.HashtableTest  - value :933
    2019-07-15 16:57:21,254   [main] INFO  java.javabase.map.HashtableTest  - value :421
    2019-07-15 16:57:21,254   [main] INFO  java.javabase.map.HashtableTest  - value :304
    2019-07-15 16:57:21,254   [main] INFO  java.javabase.map.HashtableTest  - enumerationKeys
    2019-07-15 16:57:21,254   [main] INFO  java.javabase.map.HashtableTest  - key :4, value :771
    2019-07-15 16:57:21,254   [main] INFO  java.javabase.map.HashtableTest  - key :3, value :567
    2019-07-15 16:57:21,254   [main] INFO  java.javabase.map.HashtableTest  - key :2, value :933
    2019-07-15 16:57:21,254   [main] INFO  java.javabase.map.HashtableTest  - key :1, value :421
    2019-07-15 16:57:21,254   [main] INFO  java.javabase.map.HashtableTest  - key :0, value :304
    2019-07-15 16:57:21,254   [main] INFO  java.javabase.map.HashtableTest  - enumerationElements
    2019-07-15 16:57:21,254   [main] INFO  java.javabase.map.HashtableTest  - value : 771
    2019-07-15 16:57:21,269   [main] INFO  java.javabase.map.HashtableTest  - value : 567
    2019-07-15 16:57:21,269   [main] INFO  java.javabase.map.HashtableTest  - value : 933
    2019-07-15 16:57:21,269   [main] INFO  java.javabase.map.HashtableTest  - value : 421
    2019-07-15 16:57:21,269   [main] INFO  java.javabase.map.HashtableTest  - value : 304
    2019-07-15 16:57:21,269   [main] INFO  java.javabase.map.HashtableTest  - table :{4=771, 3=567, 2=933, 1=421, 0=304}
    2019-07-15 16:57:21,269   [main] INFO  java.javabase.map.HashtableTest  - table size 5
    2019-07-15 16:57:21,269   [main] INFO  java.javabase.map.HashtableTest  - contans key 1 :true
    2019-07-15 16:57:21,269   [main] INFO  java.javabase.map.HashtableTest  - remove key :421
    2019-07-15 16:57:21,269   [main] INFO  java.javabase.map.HashtableTest  - after remove ,table size 4
    2019-07-15 16:57:21,269   [main] INFO  java.javabase.map.HashtableTest  - clear table 
    2019-07-15 16:57:21,269   [main] INFO  java.javabase.map.HashtableTest  - is empty: true
    
    Process finished with exit code 0

转载于:https://www.cnblogs.com/JuncaiF/p/11191344.html

[Java _11_ Hashtable]: https://www.cnblogs.com/skywang12345/p/3310887.html