Inability to draw simple graphics in Java properly (threads and JFrame)

Question

I am trying to use a thread to continually draw randomly positioned and randomly sized squares in the middle of a JFrame window. I have got 'something' working with the following code, however when run, the actual window doesn't come up properly. If I resize the window it does, and I get the result I wanted, but when the window is first opened it does not fully draw itself on screen. Can anybody help here? I am a bit of a novice when it comes to Java
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.util.*;
public class TestDraw extends JFrame implements Runnable {
//DECLARE VARIABLES
     private JLabel lblText;
     private JButton btnBegin;
     private JPanel contentPane;
     private int CoordX, CoordY,SizeX, SizeY, Colour;     // Co'ords for drawing the squares
     Random random = new Random();                              // Random numbers (for square dimensions and colours)
     int n_1 = 450, n_2 = 130, n_3 = 100, n_4 = 4;          // The different ranges of randoms I require
     Thread squares = new Thread(this);                         // Implements a new thread
//END OF DECLARE VARIABLES
// CALLS INITIAL PROCEDURE, SETS VISIBLE ETC
     public TestDraw() {
          super();
          initializeComponent();
          this.setVisible(true);
// INITIALISATION PROCEDURE CALL
     private void initializeComponent() {
          lblText = new JLabel();
          btnBegin = new JButton();
          contentPane = (JPanel)this.getContentPane();
          // lblText
          lblText.setText("This should draw squares on screen...");
          // btnBegin
          btnBegin.setText("Start");
          btnBegin.addActionListener(new ActionListener() {
               public void actionPerformed(ActionEvent e) {
                    btnBegin_actionPerformed(e);
          // contentPane
          contentPane.setLayout(null);
          addComponent(contentPane, lblText, 10,300,364,18);
          addComponent(contentPane, btnBegin, 144,10,101,28);
          // TestDraw
          this.setTitle("TestDraw Program for CM0246");
          this.setLocation(new Point(0, 0));
          this.setSize(new Dimension(390, 350));
// POSITION COMPONENTS ON SCREEN
     private void addComponent(Container container,Component c,int x,int y,int width,int height)     {
          c.setBounds(x,y,width,height);
          container.add(c);
// EVENT HANDLING PROCEDURES
     private void btnBegin_actionPerformed(ActionEvent e) {
          System.out.println("\nAction Event from btnBegin called...");
          squares.start(); //STARTS THE SQUARES DRAWING THREAD (Draws random squares on screen)
// THE MAIN METHOD (STARTS THE PROGRAM)
     public static void main(String[] args) {
          TestDraw bobdole = new TestDraw();
// THE SQUARE DRAWINGS THREAD (SHOULD DRAW RANDOM SIZED AND COLOURED SQUARES IN RANDOM PLACES)
     public void run() {
          System.out.println("Thread running if this prints");
               while(true) {
                    int int_1 = random.nextInt(n_1);     // chooses random int for X co'ord
                    int int_2 = random.nextInt(n_2)+70;     // chooses random int for Y co'ord
                    int int_3 = random.nextInt(n_3)+10;     // chooses random int for X dimension
                    int int_4 = random.nextInt(n_3)+10;     // chooses random int for Y dimension
                    CoordX = int_1;
                    CoordY = int_2;
                    SizeX  = int_3;
                    SizeY  = int_4;
                    repaint();
                    try {
                         squares.sleep(500);
                    catch (InterruptedException e) {
                         System.out.println(e);
// THE PAINT METHOD ATTATCHED TO THE SQUARES THREAD
     public void paint( Graphics g ) {
          System.out.print("Colour" + Colour);
          g.setColor(Color.blue);
          g.fillRect(CoordX, CoordY, SizeX, SizeY);
// END OF PROGRAM

Answer 1

I don't see any problem when I run the program but.. In general you shouldn't paint directly on a frame by overloading the paint method. You should rather create a custom component on which you draw.
But if you do overload paint, make sure you call super.paint before doing anything else.
More information in this tutorial: http://java.sun.com/docs/books/tutorial/uiswing/painting/index.html