concurrenthashmap(Java的ConcurrentHashMap如何使用)

說明

1、ConcurentHashMap結合了HashMap和Hashtable的優點。HashMap不考慮同步,Hashtable考慮同步。但是Hashtable每次同步都要鎖定整個結構。

2、ConcurentHashMap鎖的方式是稍微細粒度的。ConcurentHashMap將hash表分成16桶(默認值),如get、put、remove等常用操作只鎖定目前需要的桶。

實例

/***Createsanew,emptymapwiththedefaultinitialtablesize(16).*/publicConcurrentHashMap(){}/***Createsanew,emptymapwithaninitialtablesize*accommodatingthespecifiednumberofelementswithouttheneed*todynamicallyresize.**@paraminitialCapacityTheimplementationperformsinternal*sizingtoaccommodatethismanyelements.*@throwsIllegalArgumentExceptioniftheinitialcapacityof*elementsisnegative*/publicConcurrentHashMap(intinitialCapacity){if(initialCapacity<0)thrownewIllegalArgumentException();intcap=((initialCapacity>=(MAXIMUM_CAPACITY>>>1))?MAXIMUM_CAPACITY:tableSizeFor(initialCapacity+(initialCapacity>>>1)+1));this.sizeCtl=cap;}/***Createsanewmapwiththesamemappingsasthegivenmap.**@parammthemap*/publicConcurrentHashMap(Map<?extendsK,?extendsV>m){this.sizeCtl=DEFAULT_CAPACITY;putAll(m);}