Why my JInternalFrame show two times?

Question

/* I want to Draw a cycle on JPanel in JInternalFrame, but it Draw two times, and when I klick the JInternalFrame, it will show right.
There are two Class, one ist TestDrawingJPanel, another ist DrawingJPanel.
import java.awt.*;
public class TestDrawingJPanel extends javax.swing.JFrame {
/** Creates new form TestDrawingJPanel */
public TestDrawingJPanel() {
initComponents();
DrawingJPanel drawingJPanel=new DrawingJPanel();
jInternalFrame1.getContentPane().add(drawingJPanel,java.awt.BorderLayout.CENTER);
drawingJPanel.start();
/** This method is called from within the constructor to
* initialize the form.
* WARNING: Do NOT modify this code. The content of this method is
* always regenerated by the Form Editor.
private void initComponents() {
jInternalFrame1 = new javax.swing.JInternalFrame();
addWindowListener(new java.awt.event.WindowAdapter() {
public void windowClosing(java.awt.event.WindowEvent evt) {
exitForm(evt);
jInternalFrame1.setBackground(java.awt.Color.white);
jInternalFrame1.setPreferredSize(new java.awt.Dimension(300, 260));
try {
jInternalFrame1.setSelected(true);
} catch (java.beans.PropertyVetoException e1) {
e1.printStackTrace();
jInternalFrame1.setVisible(true);
getContentPane().add(jInternalFrame1, java.awt.BorderLayout.CENTER);
pack();
/** Exit the Application */
private void exitForm(java.awt.event.WindowEvent evt) {
System.exit(0);
* @param args the command line arguments
public static void main(String args[]) {
new TestDrawingJPanel().show();
// Variables declaration - do not modify
private javax.swing.JInternalFrame jInternalFrame1;
// End of variables declaration
import java.awt.*;
public class DrawingJPanel extends javax.swing.JPanel implements Runnable {
/** Creates a new instance of DrawingJPanel */
Graphics g;
Thread thisThread;
public void start(){
thisThread=new Thread(this);
thisThread.start();
public void paint(Graphics g){
g.setColor(Color.black);
g.drawArc((this.getWidth()/2)-100,(this.getHeight()/2)-100,200,200,0,360);
public void run() {
try{
thisThread.sleep(100);
}catch(Exception e){};
repaint();

Answer 1

Q1
2 internalframes
ANS
remove any one of these
jInternalFrame1.setVisible(true);
new TestDrawingJPanel().show();