You can use wait, notify, and notifyAll methods to communicate between threads in Java. For example, if you have two threads running in your programs like Producer and Consumer then the producer thread can communicate to the consumer that it can start consuming now because there are items to consume in the queue. Similarly, a consumer thread can tell the producer that it can also start putting items now because there is some space in the queue, which is created as a result of consumption. A thread can use the wait() method to pause and do nothing depending upon some condition. For example, in the producer-consumer problem, the producer thread should wait if the queue is full and the consumer thread should wait if the queue is empty.
