Can We Use Hashmap in Multithreaded Environment?

What's wrong using HashMap in multithreaded environment? ... It is a problem if multiple threads are adding to the same HashMap instance without it being synchronized . Even if just 1 thread is modifying a HashMap and other threads are reading from that same map without synchronization, you will run into problems.

Can you use an HashMap in a multithreaded environment?

You must make sure: All of the updates to the HashMap are completed before the threads are instantiated and the thread that creates the map also forks the threads. The threads are only using the HashMap in read-only mode – either get() or iteration without remove. There are no threads updating the map.

Why HashMap should not be used in multithreaded environment can it cause an infinite loop as well?

The default capacity of HashMap is 16 and Load factor is 0.75, which means HashMap will double its capacity when 12th Key-Value pair enters in the map (16 * 0.75 = 12). When 2 thread tries to access HashMap simultaneously, then you may encounter infinite loop. Thread 1 and Thread 2 tries to put 12th key-value pair.