Add value to JComboBox in Java

// ww  w.  ja v a 2s.  com
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;

import javax.swing.JComboBox;
import javax.swing.JFrame;

public class Main extends JFrame {
  JComboBox combo = new JComboBox();

  public Main() {
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    combo.addItem("A");
    combo.addItem("H");
    combo.addItem("P");


    getContentPane().add(combo);
    setLayout(new java.awt.FlowLayout());
    pack();
    setVisible(true);
  }

  public static void main(String arg[]) {
    new Main();
  }
}