pekko/akka-docs/rst/java/code/jdocs/io/japi/Watcher.java

package jdocs.io.japi;

import java.util.concurrent.CountDownLatch;

import akka.actor.ActorRef;
import akka.actor.Terminated;
import akka.actor.AbstractActor;

public class Watcher extends AbstractActor {
  
  static public class Watch {
    final ActorRef target;
    public Watch(ActorRef target) {
      this.target = target;
    }
  }
  
  final CountDownLatch latch;

  public Watcher(CountDownLatch latch) {
    this.latch = latch;
  }

  @Override
  public Receive createReceive() {
    return receiveBuilder()
      .match(Watch.class, msg -> {
        getContext().watch(msg.target);
      })
      .match(Terminated.class, msg -> {
        latch.countDown();
        if (latch.getCount() == 0) getContext().stop(getSelf());
      })
      .build();
  }

}