Java Multithreaded Series six--map implementation class

Resources:

https://crunchify.com/hashmap-vs-concurrenthashmap-vs-synchronizedmap-how-a-hashmap-can-be-synchronized-in-java/

Https://stackoverflow.com/questions/35534906/java-hashmap-getobject-infinite-loop

Some implementation classes of map and their characteristics

class	thread safe	attribute
Hashtable	Yes	key cannot be null
HashMap	no	Read-write efficiency is highest, but improper use in Java6 multithreaded environments can lead to a dead loop, which in turn leads to high CPU usage (see the principle: http://coolshell.cn/articles/ 9606.html)
collections.synchronizedmap	is	Collections.synchronizedmap locks on all methods of map, efficiency is equivalent to Hashtable
Concurr Enthashmap	Yes	takes a segmented lock, get is generally unlocked, put fragment lock, key/value cannot be null, Efficiency second only to HashMap

The following code tests the reading and writing efficiency of various

Importjava.util.Collections;ImportJava.util.HashMap;Importjava.util.Hashtable;ImportJava.util.Map;ImportJava.util.concurrent.ConcurrentHashMap;ImportJava.util.concurrent.ExecutorService;Importjava.util.concurrent.Executors;ImportJava.util.concurrent.TimeUnit;/*** @Description: Test Map*/ Public classThreadmaptest { Public Static voidMain (string[] args)throwsinterruptedexception {Map<integer, integer> hashtable =NewHashtable<>(); Map<integer, integer> HashMap =NewHashmap<>(); Map<integer, integer> synchronizedhashmap = Collections.synchronizedmap (NewHashmap<>()); Map<integer, integer> concurrenthashmap =NewConcurrenthashmap<>();        Test (Hashtable);        Test (HASHMAP);        Test (SYNCHRONIZEDHASHMAP);    Test (CONCURRENTHASHMAP); }    Private Static voidTest (Map<integer, integer> Map)throwsinterruptedexception {intTesttimes = 5; LongTotaltimemillis = 0;  for(intk = 0; K < Testtimes; k++) {Totaltimemillis+=costtimemillis (map); } System.out.println ("Test" + map.getclass () + "Average Time" + (Totaltimemillis/testtimes)); }    Private Static LongCosttimemillis (Map<integer, integer> Map)throwsinterruptedexception {intCount = 5; Executorservice Executorservice=Executors.newfixedthreadpool (count); LongStartmillis =System.currenttimemillis ();  for(inti = 0; I < count; i++) {Executorservice.execute (NewRunnable () {@Override Public voidrun () { for(intj = 0; J < 500000; J + +) {Map.put (0, 0); Map.get (0);        }                }            });        } executorservice.shutdown ();        Executorservice.awaittermination (Long.max_value, timeunit.days); returnSystem.currenttimemillis ()-Startmillis; }}

The output results are as follows:

class java.util.Hashtable Average Time 267class Java.util.HashMap average  time class Java.util.collections$synchronizedmap average Time 262class Java.util.concurrent.ConcurrentHashMap Average Time 167

Java Multithreaded Series six--map implementation class