import java.awt.BorderLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.ArrayList;

import javax.swing.DefaultListModel;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JList;
import javax.swing.JScrollPane;

public class TryJlist extends JFrame {
    public ArrayList<String> list;
    public JList jlist;

    public TryJlist() {
        list = new ArrayList<String>();
        list.add("item1");
        list.add("item2");
        list.add("itme3");
        jlist = new JList(new MyModel());
        JScrollPane panel = new JScrollPane(jlist);
        JButton button = new JButton("change");
        button.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                // TODO Auto-generated method stub
                list.add("additem");
                System.out.println(list.size());
                jlist.setModel(new MyModel());
                //jlist.repaint();
            }
        });
        add(panel, BorderLayout.CENTER);
        add(button, BorderLayout.NORTH);
        setSize(400, 300);
        setVisible(true);
    }

    public static void main(String[] args) {
        new TryJlist();
    }
    class MyModel extends DefaultListModel {

        public Object getElementAt(int index) {
            // TODO Auto-generated method stub

            return list.get(index);
            // return super.getElementAt(index);
        }

        public int getSize() {
            // TODO Auto-generated method stub
            System.out.println(list.size());
            return list.size();
            // return super.getSize();
        }
    }
}