How do I implement the codes which works as a timer app using awt,swing,Thread while satisfying some conditions?

I have to make the timer codes of Java using awt,swing,Thread.

The overview of the eventual app has below 4 features.

1. The app has just one button.

2. Firstly the button display the "START"on the button itself.

3. Dynamic time is displayed on the button as the button is pressed.

4. As the button pressed while counting the time,the button stop the counting and display "START".

I've written the code such as below.

boolean isCounting = false;

int cnt = 0;

void counter() {
	while (isCounting == true) {
		btn.setText(Integer.toString(++cnt));
		try {
			Thread.sleep(1000);
		} catch (InterruptedException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}
}

public void actionPerformed(ActionEvent e) {
	if (isCounting == true) {
		isCounting = false;
	} else {
		isCounting = true;
		counter();
	}

}

Of course this code doesn't satisfy the conditions because once the button is pressed then
the button is no more able to be pressed again and the counter never works.

In this code,once the button is pressed then the function "counter" is called but the value on the button never changes until the button is unpressed.

I have to make the codes satisfying the above conditions.

How do I implement it?

If I understood your question correctly, then this snippet I quickly put together should work for you.

import java.awt.Dimension;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.SwingUtilities;
import javax.swing.Timer;

public class Testing {

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {

            @Override
            public void run() {
                Testing t = new Testing();
            }
        });
    }

    private Timer timer;
    private JFrame frame;
    private JButton btn;
    private int timePassed;

    public Testing() {

        frame = new JFrame();
        timer = new Timer(1000, new ActionListener() {

            @Override
            public void actionPerformed(ActionEvent e) {
                timePassed++;
                updateTimeOnButton();
            }
        });
        btn = new JButton("START");

        btn.addActionListener(new ActionListener() {

            @Override
            public void actionPerformed(ActionEvent e) {
                if (timer.isRunning()) {
                    timer.stop();
                    btn.setText("START");
                } else {
                    timePassed = 0;
                    timer.start();
                    updateTimeOnButton();
                }
            }
        });
        frame.getContentPane().add(btn);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setVisible(true);
        frame.setSize(new Dimension(300, 300));
    }

    private void updateTimeOnButton() {
        btn.setText(timePassed + " seconds");
    }
}