from-java-to-javascript-callback-and-promise-0.java

interface ISomeEventListener {
  void someEvent();
}

class SynchronousExample {
  private ISomeEventListener someEventListener;

  public void setSomeEventListener(ISomeEventListener someEventListener) {
    this.someEventListener = someEventListener;
  }

  public void doSomeHeavyCalculation(final long howLongInMs) {
    System.out.println("Doing some heavy work..."); 

    // some heavy work...
    try {
      Thread.sleep(howLongInMs);
    } catch (InterruptedException e) {
      e.printStackTrace();
    }

    if (this.someEventListener != null) {
      someEventListener.someEvent();
    }
  }

  public static void main(String[] args) {
    final SynchronousExample example = new SynchronousExample();

    example.setSomeEventListener(() -> {
      System.out.println("Received some event!");
    });

    example.doSomeHeavyCalculation(1000);
  }
}