Code to show that multiple calls to Weakreference.get() might return null.

WeakReferenceCaller.java

// GC is a background thread and JVM doesn't have a spec for it to be daemon or not.
// https://stackoverflow.com/questions/5553783/java-garbage-collection-thread-priority

public class WeakReferenceCaller {
  public static void main(String[] args) throws InterruptedException {
   MyObject myObject = new MyObject();
   Thread thread = new Thread(new WeakReferenceRunnable(myObject));
   thread.start();
   myObject = null;
   System.out.println(myObject);
   System.gc();

   while (true) {
     Thread.sleep(200);
   }
  }

  static class MyObject { }
}

WeakReferenceRunnable.java

public class WeakReferenceRunnable implements Runnable {
  private final WeakReference<Caller.MyObject> weakReference;

  public WeakReferenceRunnable(Caller.MyObject input) {
    this.weakReference = new WeakReference<Caller.MyObject>(input);
  }

  @Override public void run() {
    while (weakReference.get() != null) {
      try {
        Thread.sleep(1000);
      } catch (InterruptedException e) {
        e.printStackTrace();
      }
    }
    System.out.println("I am here"); // This will be printed.
  }
}