Question

I have a static method like follows

 public static void foo(){
     final ClassA a = new ClassA();
 } 

I have two hash maps inside classA.

Are those hash map thread safe…?

Answer 1

It is not clear whether you mean to access the hash maps inside the object a with multiple threads or call the method foo with multiple threads.

In the first case thread safety of a collection has nothing to do with the outer context i.e. it was created in a static context or not. So no, if you try to access the hash maps from the object a with multiple threads, it will cause unexpected behavior. You need to regulate access to them with synchronized blocks.

In the second case, each thread will have a different copy of foo on its stack and allocate different instance of ClassA. Therefore, they will not collide because they will have different HashMaps to work with.

Please clarify which of there cases you are working with.