Inserir valor selecionado em um combo em um lista

package combo;

import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.ArrayList;
import javax.swing.JButton;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.WindowConstants;

public class Combo extends JFrame implements ActionListener {

	private JComboBox combo1, combo2;
	private JButton btAdd;
	private ArrayList<String> itens;

	public Combo() {
		super("Combo");
		super.setResizable(false);
		this.itens = new ArrayList<String>();

		this.combo1 = new JComboBox();
		combo1.addItem("String 0");
		combo1.addItem("String 1");
		combo1.addItem("String 2");

		this.btAdd = new JButton("Add!");
		btAdd.addActionListener(this);

		combo2 = new JComboBox();

		super.setLayout(new GridLayout(3, 1));
		super.add(combo1);
		super.add(btAdd);
		super.add(combo2);

		super.pack();
		super.setVisible(true);
		super.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
	}

	@Override
	public void actionPerformed(ActionEvent e) {
		String selected = (String) combo1.getSelectedItem();
		itens.add(selected);
		combo2.addItem(selected);
	}

	public static void main(String[] args) {
		Combo combo = new Combo();
	}

}