Action em JButton

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

import javax.swing.GroupLayout;
import javax.swing.GroupLayout.Alignment;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTextArea;
import javax.swing.border.EmptyBorder;


public class TelaTrabalho extends JFrame implements ActionListener{

	private JPanel contentPane;

	/**
	 * Launch the application.
	 */
	public static void main(String[] args) {
		EventQueue.invokeLater(new Runnable() {
			public void run() {
				try {
					TelaTrabalho frame = new TelaTrabalho();
					frame.setVisible(true);
				} catch (Exception e) {
					e.printStackTrace();
				}
			}
		});
	}

	/**
	 * Create the frame.
	 */
	public TelaTrabalho() {
		setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		setBounds(100, 100, 450, 300);
		contentPane = new JPanel();
		contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
		setContentPane(contentPane);

		JButton btn = new JButton("Ok");
           btn.addActionListener(verificaArquivo.start());

import java.io.BufferedReader;
	import java.io.File;
	import java.io.FileInputStream;
	import java.io.IOException;
	import java.io.InputStream;
	import java.io.InputStreamReader;

	public class Codigo extends Thread {	

		public void run(){
			while(true)
				leArquivo();
			
		}
		Thread verificaArquivo = new Thread();
		 
		public  void leArquivo() {
long tamanhoArquivo;
			
			File diretorio = new File("C:\\Teste");
			
					
			
			File arquivo = new File(diretorio, "Nomes.txt");
			
			try {
				
				
				
				InputStream is = new FileInputStream(arquivo);
				InputStreamReader isr = new InputStreamReader(is);
				BufferedReader br = new BufferedReader(isr);
tamanhoArquivo=arquivo.length();
				String s = br.readLine(); // primeira linha
				while (s != null) {
					System.out.println(s);
					s = br.readLine();
				}
				br.close();

			} catch (IOException e) {
				
				e.printStackTrace();
			}

		}

	}