from-java-to-javascript-callback-and-promise-2.java

class AsynchronousExample {
  private ISomeEventListener someEventListener;

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

  public void doSomeHeavyCalculation(final long howLongInMs) {
    // some heavy work...
    new Thread(() -> {
      try {
        System.out.println("Doing some heavy work...");
        Thread.sleep(howLongInMs);
      } catch (InterruptedException e) {
        e.printStackTrace();
      }

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

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

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

    example.doSomeHeavyCalculation(1000);
  }
}