Java Assignment#4

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package javaassignment4;

import java.awt.BorderLayout;
import java.awt.Container;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.Vector;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JList;
import javax.swing.JPanel;
import javax.swing.JSeparator;
import javax.swing.JTextField;
import javax.swing.event.ListSelectionEvent;
import javax.swing.event.ListSelectionListener;

/**
 *
 * @author youssefgamil
 */
class Project4 extends JFrame implements ActionListener,ListSelectionListener
{
    private JList a,b;
    private JButton copy,clear;
    private JTextField tf;
    private Vector<String> data;
    public Project4()
    {
        super("d");
        Container c=getContentPane();
        c.setLayout(new BorderLayout());

        JPanel jp=new JPanel(new GridLayout(1,3));
            tf=new JTextField();
            tf.setHorizontalAlignment(JTextField.CENTER);
            jp.add(tf);
            copy=new JButton("Copy");
            copy.addActionListener(this);
            copy.setEnabled(false);
            copy.setHorizontalAlignment(JButton.CENTER);
            jp.add(copy);
            clear=new JButton("Clear");
            clear.setHorizontalAlignment(JButton.CENTER);
            clear.addActionListener(this);
            clear.setEnabled(false);
            jp.add(clear);
        c.add(jp,BorderLayout.NORTH);

        JPanel jp2=new JPanel(new GridLayout(1,3));
            a=new JList(new String[]{"Hossam Hassen","Abu Trika","Essam Elhadry","Ahmed Hssen","Hassen Shehata","Hossam Elbadry","Shikabala"});
            a.addListSelectionListener(this);
            jp2.add(a);
            jp2.add(new JSeparator());
            data=new Vector<String>();
            b=new JList();
            jp2.add(b);
        c.add(jp2,BorderLayout.CENTER);
        setSize(300,300);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setVisible(true);
    }

    @Override
    public void actionPerformed(ActionEvent ae) {
        if(ae.getSource()==copy)
        {
            clear.setEnabled(true);
            data.add(tf.getText());
        }
        if(ae.getSource()==clear)
        {
            copy.setEnabled(false);
            clear.setEnabled(false);
            data=new Vector<String>();
        }
        b.setListData(data);
    }

    @Override
    public void valueChanged(ListSelectionEvent lse) {
        tf.setText( (String)a.getSelectedValue() );
        copy.setEnabled(true);
    }
}
public class JavaAssignment4 {
    public static void main(String[] args) {
        new Project4();
    }
}