Explain Exchanger in Java thread.

Exchanger is a synchronization point at which threads can pair and swap elements between the pair. Each thread presents some object on entry to the exchange method, matches with a partner thread, and receives its partner's object on return.

An Exchanger may be viewed as a bidirectional form of a SynchronousQueue. Exchangers may be useful in applications such as genetic algorithms and pipeline designs.

package main.java.tags;

import java.util.concurrent.*;
import java.util.*;

public class ExchangerExample {

	public static void main(String[] args) {

		Exchanger<Integer> exchanger = new Exchanger<Integer>();

		Thread t1 = new MyThread(exchanger, new Integer(5));
		Thread t2 = new MyThread(exchanger, new Integer(10));
		t1.start();
		t2.start();
	}
}

class MyThread extends Thread {

	Exchanger<Integer> exchanger;
	Integer numberToExchange;

	MyThread(Exchanger<Integer> exchanger, Integer message) {
		this.exchanger = exchanger;
		this.numberToExchange = message;
	}

	public void run() {
		try {
			System.out.println(this.getName() + " has value: " + numberToExchange);

			// exchange messages
			numberToExchange = exchanger.exchange(numberToExchange);

			System.out.println("After exchange " + this.getName() + " has value: " + numberToExchange);
		} catch (Exception e) {
		}
	}
}

The above example exchanges Integer objects between a pair of threads. The below is the output.

Thread-0 has value: 5
Thread-1 has value: 10
After exchange Thread-0 has value: 10
After exchange Thread-1 has value: 5

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