title: Performance ConcurrentHashmap vs HashMap
body: <p>How is the performance of ConcurrentHashMap compared to HashMap, especially .get() operation (I'm especially interested for the case of only few items, in the range between maybe 0-5000)?</p>
  
  <p>Is there any reason not to use ConcurrentHashMap instead of HashMap?</p>
  
  <p>(I know that null values aren't allowed)</p>
  
  <p><strong>Update</strong></p>
  
  <p>just to clarify, obviously the performance in case of actual concurrent access will suffer, but how compares the performance in case of no concurrent access?</p>