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06 Feb 2019

Difference between Blocked and Waiting state in Java?

There are six thread states in java. They are NEW, RUNNABLE, BLOCKED, WAITING, TIMED_WAITING and TERMINATED. At any point of time, a thread will be in any one of these six states. In these six states, BLOCKED and WAITING states are closely related. In this post, we will discuss the differences between BLOCKED Vs WAITING states in java.

BLOCKED And WAITING States In Java :

A thread enters into WAITING state when it calls wait() or join() method on an object. Before entering into WAITING state, thread releases the lock of the object it holds. It will remain in WAITING state until any other thread calls either notify() or notifyAll() on the same object.

Once the other thread calls notify() or notifyAll() on the same object, one or all the threads which are WAITING for lock of that object will be notified. All the notified threads will not get the object lock immediately. They will get the object lock on a priority basis once the current thread releases the lock. Until that they will be in BLOCKED state.

In simple terms, a thread will be in WAITING state if it is waiting for notification from other threads. A thread will be in BLOCKED state if it is waiting for other thread to release the lock it wants.

Look at the below diagram for more clarity.