HashMap to concurrentHashMap

Question

I have a getHashMap method that returns HashMap . I need to populate a ConcurrentHashMap (in setConcurrentHashMap ) with the HashMap .

Is there a way to do it?

Sample code:

//getHashMap return a HashMap<String, String>
Map<String, String> myMap = getHashMap();
TestClass.getSingleton().setConcurrentHashMap(ConcurrentHashMap<String, String> concurrentHashMap)

Answer 1

A quick look at the javadoc shows that ConcurrentHashMap has a copy constructor that takes a Map as a parameter:

Map<String, String> myMap = getHashMap();
ConcurrentMap<String, String> concurrentMap = new ConcurrentHashMap<> (myMap);

Answer 2

You have the Collections#synchronizedXXX that works fine for these kind of tasks.

In your case, you'll use the Collections#synchronizedMap(Map) map.

TestClass.getSingleton()
         .setConcurrentHashMap(Collections.synchronizedMap(myMap));

Answer 3

ConcurrentHashMap class provides a constructor to create a ConcurrentHashMap from a given Map .

Map<String, String> myMap = getHashMap();
TestClass.getSingleton()
    .setConcurrentHashMap(new ConcurrentHashMap<String, String>(myMap));