I’m currently diving in the implementation of java 11 Properties class. In java 11 source code, Properties class stores its data in a ConcurrentHashMap field called ‘map’. When you call the method setProperty of Properties, under the hood it makes a put method call of its internal ConcurrentHashMap. I understand that ConcurrentHashMap is a thread-safe collection, so i don’t really get why the setProperty method has to be synchronized if ConcurrentHashMap already is. The synchronization of setProperty method isn’t killing the point of using a ConcurrentHashMap. By this i mean that users of Properties class will have to wait to lock for setProperty method that already uses a concurrent collection with its own synchronization.