JavaFX .Join() Keyword Causes to Freeze the App for a While

Question

I have few line of cords that need to be executed upon the running Thread completion. So i used thread.join() keyword right before the cords that i want to execute later.

When i run the program with join() keywords, My App interface get stuck until thread execution completed. How do i overcome this issue..?

Actually what my program doing is, once i press button it will execute method call Pass_data_from_java_to_report(); and while it's running, a separate view or Stage will appear to notify the user that program is still working. once above method finish execution waiting Stage will be closed by calling stage.close() . Those operations are working fine but the freezing with join keyword.

This is my first approach.

if(event.getSource() == btnAdd){

   Stage stage     = Waiting();   // Returns Waiting Message
   Task <Void> task = new Task<Void>() {

       @Override
       protected Void call() throws Exception {           
       Pass_data_from_java_to_report();         // My Method     
       return null;
           }

      };
            // Displaying Waiting Message
            task.setOnRunning(eve -> {
                stage.show();
            });

            // Closing Waiting Message
            task.setOnSucceeded(e -> {
                stage.close();
            });

            // Thread for executing task
            Thread t1 = new Thread(() -> {
                task.run();
            });

            t1.start();
            t1.join();   // if i remove this buddy, there is no freezing 

           // below from here i want to execute upon thread completion
            System.out.println("Finish "); 

        }

Second Approach

if(event.getSource() == btnAdd){

    Stage stage = Waiting();

    Thread t1 = new Thread(() -> {
      Platform.runLater(() -> {
        stage.show();
       });
    });

   Thread t2 = new Thread(() -> {
     Pass_data_from_java_to_report();  // My Method
       Platform.runLater(() -> {
    // Closing the Stage running on another thread upon Above Method Completion
          stage.close();           
         });
     });

        t1.start();
        t2.start();

        t1.join();   // These are the Problems
        t2.join();   // this one too

      System.out.println("Finish ");

        }

Here is the Method

     public void Pass_query_to_report(){    
        try {
              // Since method is not time consuming,  
                          // i added 3 sec sleep   before the Execution
             Thread.sleep(3000);
               /*
                    Some cord

               */
            } catch (Exception e) {
                e.printStackTrace();
            }

        }

1. How can i overcome the issue..?
   
2. Which Approach is best to use..? is it Approach one or Approach two
3. Is it safe to close the Stage started in another thread, the way i was done it..? will it automatically close the thread belongs to it..?

(Note - i also tried to use CountDownLatch but no luck)

Answer 1

Thread.join() blocks the current thread until the specified thread completes. Since you're calling it on the FX Application Thread, which is responsible for rendering the UI and processing user events, it blocks that thread, making the UI unresponsive.

Just move the code that needs to be executed after the task completes to the onSucceeded handler:

if(event.getSource() == btnAdd){

   Stage stage     = Waiting();   // Returns Waiting Message
   Task <Void> task = new Task<Void>() {

       @Override
       protected Void call() throws Exception {           
           Pass_data_from_java_to_report();         // My Method     
           return null;

       }

  };

    // Displaying Waiting Message
    task.setOnRunning(eve -> {
        stage.show();
    });

    // Closing Waiting Message
    task.setOnSucceeded(e -> {
        stage.close();

        // below from here i want to execute upon thread completion
        System.out.println("Finish "); 

    });

    // Thread for executing task
    Thread t1 = new Thread(task);

    t1.start();


}