List Demo in Java

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class ListDemonstration extends Frame implements ActionListener{
private Label l = new Label("Enter Data");
private Button b1 = new Button("Add");
private TextField txt = new TextField(10);
private Button b2 = new Button("Close");
private List l1 = new List();
private List l2 = new List();
private Panel p = new Panel();
private Panel p1 = new Panel();
public ListDemonstration(String title){
super(title);
setSize(400, 400);
Dimension screen = Toolkit.getDefaultToolkit().getScreenSize();
Dimension fr = getSize();

int xpos = screen.width/2 - fr.width/2;
int ypos = screen.height/2 - fr.height/2;
setLocation(xpos,ypos);
setResizable(false);
setVisible(true);
init();
start();
}
public void start(){
b1.addActionListener(this);
b2.addActionListener(this);
txt.setFocusable(true);
l1.addMouseListener(new MouseAdapter() {
public void mouseClicked(MouseEvent e){
list1Click(e);
}
});
l2.addMouseListener(new MouseAdapter() {
public void mouseClicked(MouseEvent e){
list2Click(e);
}
});
WindowListener window =new WindowAdapter() {
public void windowClosing(WindowEvent evt){
System.exit(0);
}
};
addWindowListener(window);
}
public void init(){
this.setLayout(new BorderLayout());
p.setLayout(new GridLayout(1,4));
p.add(l);
p.add(txt);
p.add(b1);
p.add(b2);
this.add(BorderLayout.NORTH,p);
p1.setLayout(new GridLayout(1,2));
p1.add(l1);
p1.add(l2);
this.add(BorderLayout.CENTER,p1);
}
public void actionPerformed(ActionEvent e) {
if(e.getSource()== b1){
if(txt.getText().equals("")||txt.getText().equals(null)){
JOptionPane.showMessageDialog(this, "Your have to input "
+ "data into textfield!!!!",
"Confirm", JOptionPane.CANCEL_OPTION);
txt.setFocusable(true);
}else{
l1.add(txt.getText());
txt.setText("");
txt.setFocusable(true);
}
}if(e.getSource()== b2){
System.exit(0);
}
}
public void list1Click(MouseEvent e){
if(l1.getItemCount()==0)
return;
if(e.getClickCount()==2){
l2.add(l1.getSelectedItem().toString());
l1.remove(l1.getSelectedItem());
}
}
public void list2Click(MouseEvent e){
if(e.getClickCount()==2){
l1.add(l2.getSelectedItem().toString());
l2.remove(l2.getSelectedItem());
}
}
public static void main(String[] args) {
new ListDemonstration("List Demo");
}
}