java - Hashmap and hashtable in multithreaded environment

Question

I am really confused on how these 2 collections behave in multithreaded environment.

Hash table is synchronized that means no 2 threads will be updating its value simultaneously right?

Answer 1

Look at ConcurrentHashMaps for Thread safe Maps.

They offer all the features of HashTable with a performance very close to a HashMap.

Performance is gained by instead of using a map wide lock, the collection maintains a list of 16 locks by default, each of which is used to lock a single bucket of the map. You can even configure the number of buckets :) Tweaking this can help performance depending on your data.

I can't recommend enough Java Concurrency in Practice by Brian Goetz http://jcip.net/

I still learn something new every time I read it.