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 seconds like 10-15sec then the whole output shows in the JTextArea. How do I output everything that is being appending to the jtextarea like in the console. I looked up something called SwingWorker. But have not idea how to use it. any help please.

package Windows;
import java.awt.Container;
import java.awt.Dimension;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Calendar;
import java.util.LinkedList;
import java.util.Queue;
import java.util.Random;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;


public class Station implements  ActionListener 
{
    private JTextArea userinput, useroutput;
    private JScrollPane sbr_userinput, sbr_useroutput;
    private JButton runButton, clearButton, homeButton;

    //LinkedList Customer Queue created here.
    public static Queue<String> line = new  LinkedList<String> ();
    private static String time;   //time variable.
    private static DateFormat dateFormat = new SimpleDateFormat("HH:mm:ss");   //DateFormat variable.

    private int intervals;
    private int cashiers;
    private int processing_time;

    public static void main(String[] args) 
    {
        new Station();
    }

    public Station()
    {
        JFrame frame = new JFrame("[=] Train Station Simulation [=]");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(800, 400);

        frame.setContentPane(GUI());

        frame.setVisible(true);
    }

    public Container GUI() 
    {
        JPanel totalGUI = new JPanel();
        totalGUI.setLayout(new GridLayout(1, 2, 3, 3));

        JPanel lPanel = new JPanel();
        lPanel.setLayout(new GridLayout(2, 1, 3 , 3));
        totalGUI.add(lPanel);

        JPanel rPanel = new JPanel(new GridLayout(3, 1, 3 , 3));
        totalGUI.add(rPanel);

        userinput = new JTextArea("Welcome to Train Station Queue Simulation!!!" + "\n" + 
        "Enter the number of cashiers available HERE!!!!:" + "\n");
        userinput.setEditable(true);
        userinput.setLineWrap(true);
        userinput.setWrapStyleWord(true);
        lPanel.add(userinput);

        useroutput = new JTextArea();
        useroutput.setEditable(false);
        useroutput.setLineWrap(true);
        useroutput.setWrapStyleWord(true);
        lPanel.add(useroutput);

        sbr_userinput = new JScrollPane(userinput, JScrollPane.VERTICAL_SCROLLBAR_AS_NEEDED, 
                JScrollPane.HORIZONTAL_SCROLLBAR_AS_NEEDED);
        sbr_userinput.setPreferredSize(new Dimension(300, 300));
        lPanel.add(sbr_userinput);

        sbr_useroutput = new JScrollPane(useroutput, JScrollPane.VERTICAL_SCROLLBAR_AS_NEEDED, 
                JScrollPane.HORIZONTAL_SCROLLBAR_AS_NEEDED);
        sbr_useroutput.setPreferredSize(new Dimension(300, 300));
        lPanel.add(sbr_useroutput);

        runButton = new JButton("RUN");
        runButton.addActionListener(this);
        rPanel.add(runButton);

        clearButton = new JButton("CLEAR");
        clearButton.addActionListener(new ActionListener()
        {
            public void actionPerformed(ActionEvent e)
            {
                userinput.setText("");
                useroutput.setText("");
                System.out.println("cleared");
            }
        });
        rPanel.add(clearButton);

        homeButton = new JButton("HOME");
        rPanel.add(homeButton);

        totalGUI.setOpaque(true);
        return totalGUI;
    }

    public void actionPerformed(ActionEvent e)
    {
        cashiers = Integer.parseInt(userinput.getText());
        if (e.getSource() == this.runButton)
        {
            useroutput.append("CUSTOMERS ARE COMING !!!! !!!!" + "\n" + "\n");;

            //Array of all the customer that will enter the queue.
            String list[] = {"Naqi", "Monty", "Mohin", "Yasmin", "Maighjoo", "Ashish", "Paal", "Kevin", "Ruhail", "Tony"};
            //2nd ArrayList which customer are added to and removed later on so no duplicates arise.
            ArrayList<String> customer = new ArrayList<String>(Arrays.asList(list));

            int array_customer_list = list.length; //Recording the number of customers in the array.

            //While statement containing for loop add customers to the empty LinkedList object.
            while (line.isEmpty())
            {
                for (int x = 0; x < array_customer_list; x++ )
                {
                    try
                    {
                        Thread.sleep(ran_interval() * 1000);   //Sleep method to hold the arrival time by 1-2 seconds. 
                        int cus = (int) (Math.random() * customer.size());   //Random customer is picked here. 
                        String new_cus = customer.get(cus);   //New customer object is created ere.
                        line.add(new_cus);   //Customer objects are added to the empty LinkedList queue.
                        customer.remove(cus);

                        //For loop statement to outputting the queue.
                        for (String s : line)
                        {
                            useroutput.append("[" + s.toString() + " " + "]" + "\n");; //Outputting each customer and using the ".name" method so customers are readable.
                        }
                        //Outputting the whole queue and stating who has joined the queue.
                        useroutput.append("\n" + "The queue has " + line.size() + " customers so far" + "\n" + 
                        new_cus.toString() + " Has Joined the Queue " + " <=== WAITING" + "\n" + "\n");
                    }
                    catch(Exception a)   //ERROR handler for sleep method.
                    {
                        System.out.println("Intervals error: " + e);   //Outputting the ERROR message.
                        System.exit(0);   //If ERROR found exit system.
                    }

                }
            }

            userinput.append("\n");
            useroutput.append("CUSTOMERS ARE WAITING !!!! !!!!" + "\n" + "\n");
            useroutput.append("Processing START !!!!" + "\n" + "\n");

            while (!line.isEmpty())   //While statement with for loop to remove each customer from LinkedList queue.
            {
                try 
                {
                    String cus = line.remove(); //Method to remove customer from LinkedList queue.
                    String time = getTime();
                    Thread.sleep((processing_time() * 1000) / cashiers); //Sleep method to hold the processing by 1-3 seconds.
                    for (String s : line)
                    {
                        useroutput.append("[" + s.toString() + " " + "]" + "\n"); //Outputting each customer and using the ".name" method so customers are readable.
                    }
                    //Outputting the whole queue and stating who has joined the queue.
                    useroutput.append("\n" + "The queue has " + line.size() + " customers left" + "\n" + 
                    cus.toString()+ " waited for " + time + " <=== SERVED" + "\n" + "\n");
                }
                catch(Exception a)   //ERROR handler for sleep method.
                {
                    System.out.println("Cashiers_wait error: " + e);   //Outputting the ERROR message.
                    System.exit(0);   //If ERROR found exit system.
                }
            }
        }

        useroutput.append("Processing FINISHED !!!!" + "\n");
        System.out.println("working");
    }

    static String getTime()   //Time Constructor
    {
       Calendar cal = Calendar.getInstance();
       time = dateFormat.format(cal.getTime());   //Getting the current system time.
       return time;   //Return time.
    }

    public int ran_interval()
     {
         Random rand = new Random(); //Random object created here.
         int interval = this.intervals = rand.nextInt(2) + 1; //Random number between 1-2 is generated for customer arrival here.

         return interval;
     }

    public int processing_time()
     {
         Random ran = new Random();    //Random object created here.
         int time = this.processing_time = ran.nextInt(4) + 1;  //Random number between 1-3 is generated for customer arrival here.

         return time;
     }
}

Answer 1

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

Answer 2

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.)