What are different concurrent Queues and when they are used ?

BlockingQueue

• FIFO queue used in designing Producer - Consumer scenarios.
• provides blocking put and take methods.
• If the queue is full, put blocks until space becomes available.
• If queue is empty, take blocks until an element is available.

LinkedBlockingQueue and ArrayBlockingQueue

• FIFO queues (similar to LinkedList and ArrayList) provides concurrency and better performance than synchronized list.

PriorityBlockingQueue

• Priority-ordered queue but not FIFO
• useful when you want to process elements in an order other than FIFO
• can compare elements according to their natural order using Comparable / Comparartor

SynchronousQueue

• Not a real queue
• maintains no space for queued elements; maintains a list of queued threads waiting to queue / dequeue the elements
• Example
• In Dish washing producer - consumer scenario, with no dish rack and produce dishes directly to consumer