CleanerTest.java

import sun.misc.Cleaner;
import java.util.concurrent.atomic.AtomicBoolean;

class Resource {
  private AtomicBoolean cleaned;
  public Resource(AtomicBoolean b) {
    this.cleaned = b;
  }

  public void clean() {
    this.cleaned.set(true);
  }
}

class Closer implements Runnable {
  private Resource resource;
  public Closer(Resource resource) {
    this.resource = resource;
  }

  @Override
  public void run() {
    this.resource.clean();
  }
}

class Wrapper {
  Resource wrapped;
}

class CleanerTest {
  public static void unwrapped(AtomicBoolean cleaned) {
    Resource resource = new Resource(cleaned);
    Closer closer = new Closer(resource);
    Cleaner.create(resource, closer);
  }

  public static void wrapped(AtomicBoolean cleaned) {
    Resource resource = new Resource(cleaned);
    Closer closer = new Closer(resource);

    Wrapper wrapper = new Wrapper();
    wrapper.wrapped = resource;

    Cleaner.create(wrapper, closer);
  }

  public static void main(String[] args) {
    {
      AtomicBoolean cleaned = new AtomicBoolean(false);
      wrapped(cleaned);
      while (!cleaned.get()) {
        System.gc();
      }
      System.out.println("Cleaner ran wrapped");
    }

    {
      AtomicBoolean cleaned = new AtomicBoolean(false);
      unwrapped(cleaned);
      while (!cleaned.get()) {
        System.gc();
      }
      System.out.println("Cleaner ran unwrapped");
    }
  }
}