:D

Cool, correct synchronizatoin

In totalVisits long volatile is excess. Because

synchronized provide below

• limiting one thread
• correct value visibility aka memory publication

volatile provide only

• correct value visibility aka memory publication

when you sync access to variable, you can do not write volatile.

Also sync access to concurrent hash map is excess.

Your hash map have race condition.

T1: get value from hash map for username "Steve"
T2: get value from hash map for username "Steve" too
T1: set counter value for "Steve" to 1
T2: set counter value for "Steve" to 1

But this should be 2 and addings atomic long here not solve this problem. You should sync access to hash map or use concurrent hash map with atomic operations like 'compute'

This is incorrect synchornization.

totalVisits also must be synchronized on same monitor that visit method, also this rule must be applied to visitsBy method

Explain