java - synchrozie get method from map? -

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in order synchrozie map method use 

myobj = mymap.get("aaa");   if (myobj==null)     synchronize (someobject){         myobj = mymap.get("aaa");           if (myobj==null){             myobj = createnew();             mymap.put(myobj);      }  } return myobj;

is besdt way. asking null condition twice?

synchronizing get isn't useful. get not change state of map. have synchronize put (with same object monitor). , can use collections.synchronizedmap(..) or concurrenthashmap that

update: get & put can use concurrenthashmap.putifabsent(..)


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