[hardwired]

The start and interrupt methods are in the Thread class api. (One of) The Thread constructor(s) takes a Runnable as an argument. The Runnable interface has a single method: run. We don't call run directly but start up a Thread which does the work of calling the run method which runs until completion/the method returns or ends.
Here is an example of how you can put these together to make a timer.

Code:

import java.awt.event.*;
import javax.swing.*;

public class ConcurrencyExample implements Runnable,
                                           ActionListener {
    JLabel label;
    Thread thread;
    boolean running;
    long delay = 1000;
    int count = 0;

    public void run() {
        while(running) {
            try {
                Thread.sleep(delay);
            } catch(InterruptedException e) {
                System.out.println("interrupted");
                stop();
            }
            label.setText("count = " + count++);
        }
    }

    private void start() {
        if(!running) {
            running = true;
            thread = new Thread(this);
            thread.setPriority(Thread.NORM_PRIORITY);
            thread.start();
        }
    }

    public void stop() {
        running = false;
        if(thread != null)
            thread.interrupt();  // wake up
        thread = null;
    }

    public void actionPerformed(ActionEvent e) {
        String ac = e.getActionCommand();
        if(ac.equals("START"))
            start();
        if(ac.equals("STOP"))
            stop();
    }

    private JLabel getCenter() {
        label = new JLabel("", JLabel.CENTER);
        return label;
    }

    private JPanel getControls() {
        String[] ids = { "start", "stop" };
        JPanel panel = new JPanel();
        for(int j = 0; j < ids.length; j++) {
            JButton button = new JButton(ids[j]);
            button.setActionCommand(ids[j].toUpperCase());
            button.addActionListener(this);
            panel.add(button);
        }
        return panel;
    }

    public static void main(String[] args) {
        ConcurrencyExample test = new ConcurrencyExample();
        JFrame f = new JFrame();
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.getContentPane().add(test.getCenter());
        f.getContentPane().add(test.getControls(), "Last");
        f.setSize(300,160);
        f.setLocation(200,200);
        f.setVisible(true);
    }
}

For background and discussion see the basic lesson on threads in java Lesson: Concurrency and the more specialized Lesson: Concurrency in Swing which deals with the event dispatch thread/single thread issues in swing.