How to draw rectanlge in the panel, clear, repaint?

Question

when i was taking my coding, i found a problem which i could not solve.So, i hope someone can help. Thank you.
the question :
1. how to draw Rectangle in the Panel?
2. how to clear?
3. how to repaint?
The following is my coding.
import javax.swing.*;
import java.awt.*;
public class DrawScreen extends JFrame {
Color rectColor=Color.white;
int hight=100;
Panel Button_panel = new Panel();
Button button1 = new Button();
Button button2 = new Button();
Button button3 = new Button();
Panel Draw_Panel = new Panel();
public DrawScreen(String title) {
     super(title);
     try {
     Init();
     catch(Exception e) {
     e.printStackTrace();
private void Init() throws Exception {
setResizable(false);
setFont(new Font("Serif",Font.ITALIC,12));
     this.getContentPane().setLayout(null);
     Button_panel.setBackground(SystemColor.control);
     Button_panel.setLocale(java.util.Locale.getDefault());
     Button_panel.setBounds(new Rectangle(14, 17, 118, 259));
     Button_panel.setLayout(null);
     button1.setLabel("Draw Square");
     button1.setBounds(new Rectangle(0, 69, 115, 22));
     button2.setLabel("Colour Red");
     button2.setBounds(new Rectangle(0, 111, 115, 22));
     button3.setLabel("Clear Screen");
     button3.setBounds(new Rectangle(2, 152, 115, 22));
     Draw_Panel.setBackground(Color.white);
     Draw_Panel.setBounds(new Rectangle(138, 15, 254, 266));
//     System.out.println(Draw_Panel.getBounds());
     this.getContentPane().setBackground(Color.white);
     this.getContentPane().add(Button_panel, "East");
     Button_panel.add(button3, null);
     Button_panel.add(button2, null);
     Button_panel.add(button1, null);
     this.getContentPane().add(Draw_Panel, "West");
     addWindowListener(new java.awt.event.WindowAdapter(){
          public void windowClosing(java.awt.event.WindowEvent e){
               System.exit(0);
button1.addActionListener(new java.awt.event.ActionListener() {
public void actionPerformed(java.awt.event.ActionEvent evt) {
button1ActionPerformed(evt);
button2.addActionListener(new java.awt.event.ActionListener() {
public void actionPerformed(java.awt.event.ActionEvent evt) {
button2ActionPerformed(evt);
button3.addActionListener(new java.awt.event.ActionListener() {
public void actionPerformed(java.awt.event.ActionEvent evt) {
button3ActionPerformed(evt);
pack();
private void button1ActionPerformed(java.awt.event.ActionEvent evt) {
     hight=(int)(Math.random()*100);
     rectColor=Color.black;
repaint();
private void button2ActionPerformed(java.awt.event.ActionEvent evt) {
     rectColor=Color.red;
repaint();
private void button3ActionPerformed(java.awt.event.ActionEvent evt) {
rectColor=Color.white;
repaint();
public void paint(Graphics g){
     g.setColor(rectColor);
     g.drawRect(50, 50,hight,hight);
public static void main(String[] args) {
DrawScreen ds=new DrawScreen("Square Plotter");
     ds.setSize(600,350);
     ds.setVisible(true);

Answer 1

Few changes and it works:
import javax.swing.*;
import java.awt.*;
public class DrawScreen extends JFrame
     Color  rectColor    = Color.white;
     int    hight        = 100;
     Panel  Button_panel = new Panel();
     Button button1      = new Button();
     Button button2      = new Button();
     Button button3      = new Button();
     DPanel Draw_Panel   = new DPanel();
public DrawScreen(String title)
     super(title);
     setResizable(false);
//     setFont(new Font("Serif",Font.ITALIC,12));
//     this.getContentPane().setLayout(null);
     Button_panel.setBackground(SystemColor.control);
     Button_panel.setLocale(java.util.Locale.getDefault());
     Button_panel.setBounds(new Rectangle(14, 17, 118, 259));
     Button_panel.setLayout(null);
     button1.setLabel("Draw Square");
     button1.setBounds(new Rectangle(0, 69, 115, 22));
     button2.setLabel("Colour Red");
     button2.setBounds(new Rectangle(0, 111, 115, 22));
     button3.setLabel("Clear Screen");
     button3.setBounds(new Rectangle(2, 152, 115, 22));
     Draw_Panel.setBackground(Color.white);
     Draw_Panel.setBounds(new Rectangle(138, 15, 254, 266));
//  System.out.println(Draw_Panel.getBounds());
//     this.getContentPane().setBackground(Color.white);
     this.getContentPane().add(Button_panel, "East");
     Button_panel.add(button3);
     Button_panel.add(button2);
     Button_panel.add(button1);
     this.getContentPane().add(Draw_Panel, "Center");
     addWindowListener(new java.awt.event.WindowAdapter()
          public void windowClosing(java.awt.event.WindowEvent e)
               System.exit(0);
     button1.addActionListener(new java.awt.event.ActionListener()
          public void actionPerformed(java.awt.event.ActionEvent evt)
               button1ActionPerformed(evt);
     button2.addActionListener(new java.awt.event.ActionListener()
          public void actionPerformed(java.awt.event.ActionEvent evt)
          button2ActionPerformed(evt);
     button3.addActionListener(new java.awt.event.ActionListener()
          public void actionPerformed(java.awt.event.ActionEvent evt)
               button3ActionPerformed(evt);
//     pack();
private void button1ActionPerformed(java.awt.event.ActionEvent evt)
     hight=(int)(Math.random()*100);
     rectColor=Color.black;
     repaint();
private void button2ActionPerformed(java.awt.event.ActionEvent evt)
     rectColor=Color.red;
     repaint();
private void button3ActionPerformed(java.awt.event.ActionEvent evt)
     rectColor=Color.white;
     repaint();
public class DPanel extends JPanel
public DPanel()
public void paintComponent(Graphics g)
     super.paintComponent(g);
     g.setColor(rectColor);
     g.drawRect(50, 50,hight,hight);
public static void main(String[] args)
     DrawScreen ds=new DrawScreen("Square Plotter");
     ds.setSize(600,350);
     ds.setVisible(true);
}Noah