what is CountDownLatch ,

it makes the thread communication and synchronization more sophisticated than traditional

if u want all threads to be started after one thread completed


or


if u want one thread to be started , after all threads completed


or


if u want one thread to be started , after some task completed by certain number of times


in all the above cases we can use CountdownLatch

in all the above cases we have Thread Communications and Synchronizations


lets see how we can use this CountDownLatch , finally a class under the java api from 1.5 version like below

java.lang.Object
  java.util.concurrent.CountDownLatch

lets consider a case where one main thread has to complete one task , then only remaining thread can start there execution.

u can consider the producer and consumer problem

here producer who writes some data into the variable and

consumers will all are waiting for that variable to be filled by the producer, in such case this CountDownlatch will be very useful