Here you can find the source of getConcurrentHashMap()
public static <K, V> Map<K, V> getConcurrentHashMap()
//package com.java2s; import java.util.Collections; import java.util.Map; import java.util.concurrent.ConcurrentHashMap; public class Main { public static <K, V> Map<K, V> getConcurrentHashMap() { return Collections.synchronizedMap(new ConcurrentHashMap<K, V>()); }/*from ww w . ja v a2 s .c om*/ }