JTextArea real time output

Question

Hi I have created a waiting queue simulation with loops and also I have made the GUI what the problem is when the user clicks the run button nothing shows up for couples of seco

Answer 1

One way you can do this is using the model-view type of program design. Basically, you have 2 threads: one that handles the GUI (view/controller), and a second thread that manipulates the data (model). When an action is performed in the GUI, you start the second thread and tell it to go muck with the data. Then, as the data model thread starts changing values, it tells the GUI thread to go update the GUI by sending an event of some sort.

For more about the Model-View-Controller design, see http://en.wikipedia.org/wiki/Model%E2%80%93view%E2%80%93controller

In pseudo code, here's how this would work:

GUI Thread

Initialize UI
While program is running
    Wait for event (like action performed, or ready to update event)
    If button was pressed
        Add task to data model's work queue
    Else // Was not a button event, so therefore the data model must 
         // have sent an update
        Set values in GUI components using the updated data
        Repaint GUI

Data Model Thread (usually has a work queue that the GUI thread can use to tell it what to do)

While model has work to do
    Work on next task // and manipulate data
    Send update event to GUI

As you can see, this is easier to implement if you incorporate this idea from the start.

Another way to "fix" this issue is to plant this call whenever you want the UI to update instantly:

frame.paint(frame.getGraphics());

HOWEVER, this is a hack, as JFrame.paint and JFrame.getGraphics are both internal Swing methods, and so this should not be used unless you have no other choice. If you call this too frequently, it does create a nasty flickering effect/screen tearing, as you are updating the pixel data at the exact same time as the computer is sending that pixel data to the monitor for display. (Most computers do this about 30-60 times per second.)

Answer 2

Swing is a single threaded framework. That is, all interactions with the UI are intended to performed from within the context of the Event Dispatching Thread.

One of the responsibilities of the EDT is to process repaint requests.

Any process that blocks this thread will prevent it from updating the UI.

In your actionPerformed method, you are running a time consuming process within the EDT which is why it takes time before you see the results

Yu could start a second thread and process the data there, allowing the EDT to continue responding to update requests. The problem is, Swing also requires that any modifications to the UI be executed from within the EDT as well.

Luckily for you, there is a simple solution.

The best option is to use a SwingWorker. It has a doInBackground method, which allows you to do processing off the EDT, a publish method to allow you to send results back to the EDT, a process method to process what's being published, which is executed in the EDT and a done method which is called within the context of the EDT when the doInBackground method exists

Take a look at Concurrency in Swing for more details