Exchanger is a class in Java's java.util.concurrent package that provides a way for two threads to exchange data between each other. The Exchanger class provides a synchronization point where two threads can exchange objects in a thread-safe manner.

An Exchanger object is constructed without any arguments. Two threads can exchange objects using the exchange() method, which blocks until both threads have called the method. The exchange() method takes an object as an argument and returns an object, which represents the object exchanged by the other thread.

When one thread calls exchange(), it is blocked until the other thread calls the method. Once both threads have called exchange(), the objects are exchanged, and the method returns the object provided by the other thread. If one thread completes before the other calls exchange(), the first thread is blocked until the second thread completes.

Exchanger is useful in scenarios where two threads need to communicate and exchange data in a thread-safe manner. Examples include a game where two players need to exchange moves or a simulation where two threads need to exchange data between each other to perform a complex calculation.

It's worth noting that the Exchanger class provides a simple and lightweight mechanism for exchanging data between two threads. However, it is not suitable for scenarios where more than two threads need to communicate, or where a more complex protocol is required to ensure safe communication between threads.