Encountering problems with Thread.sleep in Swing

Question

This program was written to count from 0 to 1000 but it just goes straight to 1000 without displaying the counting process. I have written similar code using a progress bar and Thread.sleep() method and it works perfectly.

import javax.swing.JFrame;
import javax.swing.JButton;
import javax.swing.JTextField;
import javax.swing.JPanel;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

public class project extends JFrame implements ActionListener {

    JButton CountUpButton = new JButton("Count up");
    JButton CountDownButton = new JButton("Count Down");
    JButton ResetButton = new JButton("Reset");
    JTextField NumberField = new JTextField();
    int count = 0;

    public project(){
        setLayout(new GridLayout(1, 4));
        setSize(500, 300);
        add(NumberField);
        add(CountUpButton);
        add(CountDownButton);
        add(ResetButton);
        CountUpButton.addActionListener(this);
        CountDownButton.addActionListener(this);
        ResetButton.addActionListener(this);
        NumberField.setText("0");
        setVisible(true);
        setDefaultCloseOperation(EXIT_ON_CLOSE);

    }

    @Override
    public void actionPerformed(ActionEvent a){
        if(CountUpButton.hasFocus()){        
            count = Integer.parseInt(NumberField.getText());
            try{
            while(count < 1000){
                count = count + 1;
                NumberField.setText(Integer.toString(count));
                Thread.sleep(100);                
            }
            }catch(InterruptedException r){
                r.printStackTrace();
            }
        }
        if(CountDownButton.hasFocus()){
            count = Integer.parseInt(NumberField.getText());
            try{
                while(count > 0){
                    count -= 1;
                    NumberField.setText(Integer.toBinaryString(count));
                    Thread.sleep(100);                    
                }
            }catch(InterruptedException r){
                r.printStackTrace();
            }
        }
        if(ResetButton.hasFocus()){
            NumberField.setText("0");
        }
    }

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

Answer 1

Any long-running task should be run in a separate thread. Your use of Thread.sleep certainly qualifies as long-running.

By running in the Swing user-interface thread, no updates can be rendered in that user-interface until your code completes. Instead your counting should be spawned in another thread. That other thread should periodically update the user interface in a thread-safe manner using the SwingWorker.

Study up on launching threads, executors such as a ScheduledExecutorService, the Swing event-dispatch thread (EDT), and SwingWorker.

Swing Timer

A simpler approach might be the Swing Timer class (Tutorial), not to be confused with java.util.Timer. It will do much of the thread-handling work for you. But I have no experience with it.