我应该使用ConcurrentHashMap或Hashmap还是SynchronizedMap？

Question

I have created a hashmap outside my mutithreading code. There are going to be no changes in this hasmap later.

After this, I am starting two threads which will both be reading from this hashmap(yes, only read operations). If thread1 is reading from my hashmap object , can thread 2 also read at the same time? Or do I need a Concurrenthashmap or any other version of Map?

Answer 1

No you don't need concurrent Hash maps..but only since you don not do any modifications. You can read the same without any problem.

Answer 2

If thread1 is reading from my hashmap object, can thread 2 also read at the same time?

If you are sure that there are no write operations then you need not use Synchronization options at all, Go for a normal version of Map.

You can also use Immutable Map

A Map whose contents will never change, with many other important properties detailed at ImmutableCollection

Answer 3

如果只需要读操作，则无需使用同步。如果创建后未进行任何写操作，则使其不可变，因此没有主体可以更改它。不需要同步。