Java HashMap<String, String> containsKey() fails

Question

I have a Java HashMap<String, String> . Firstly I populate this map with 100 known string keys. Next I use multiple callables to add random string keys, two thousand keys in total. I also use multiple callables to call HashMap.containsKey() for the 100 known keys. I execute these callables all concurrently, Why do I see many of these containsKey() calls fail? Surely String implements the hashCode() and equals() methods "properly".

What do I need to do to ensure my 100 known keys are always found within the map?

Answer 1

我所有的问题都可以通过简单地将HashMap（）更改为ConcurrentHashMap（）来解决。