communication between threads in threadpool

Question

Assume I have one threadpool and each thread is running following method:

void runMe(HashMap myHash){
   ...
   myHash.remove(keyToBeRemoved);
   ...
}

My question is; should not myHash be the same in all threads at the beginning? Because my second thread does not have the key keyToBeRemoved . I was wondering why.

Answer 1

The myHash reference may be the same for all threads, but when the first thread executes

myHash.remove(keyToBeRemoved);

then the hash map (which all references refer to) will no longer have that mapping.

Answer 2

HashMap hm => Depends on your program. If you are using it shared among threads, it will be modified by each thread simultaneously and you have provide concurrency.

keyToBeRemoved => same as above