Simple Java GUI example (ComboBox & ListBox)

Combo.java

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.util.*;

class Combo extends JFrame{
	private JLabel lbl1 = new JLabel("Bilangan : ");	
	private JTextField tBil   = new JTextField();	
	private JButton btnTambah  = new JButton("Tambah");
	private DefaultComboBoxModel ganjil = new DefaultComboBoxModel();
	private JComboBox cmb = new JComboBox(ganjil);

	private DefaultListModel genap = new DefaultListModel();
	private JList list = new JList(genap);

	private JButton btnTutup = new JButton("Tutup");

	public Combo(){
		setTitle("ComboBox & ListBox");
		setSize(350,300);
		setLocation(new Point(250,250));
		setLayout(null);    
		setResizable(false);

		initComponent();
		initEvent();
	}

	private void initComponent(){
		lbl1.setBounds(20,20,60,20); 
		tBil.setBounds(90,20,80,20);
		btnTambah.setBounds(180,20,50,20);
		cmb.setBounds(20,60,150,20);
		list.setBounds(180,60,140,150);
		btnTutup.setBounds(250,220,70,20);

		add(lbl1);
		add(tBil);
		add(btnTambah);
		add(cmb);
		add(list);
		add(btnTutup);
	}

	private void initEvent(){
		this.addWindowListener(new WindowAdapter() {
			public void windowClosing(WindowEvent e){
			System.exit(1);
			}
		});

		btnTambah.addActionListener(new ActionListener() {
			public void actionPerformed(ActionEvent e) {
			btnTambahClick(e);
			}
		});

		btnTutup.addActionListener(new ActionListener() {
			public void actionPerformed(ActionEvent e) {
			btnTutupClick(e);
			}
		});
	}

	private void btnTambahClick(ActionEvent evt){
		Integer p;
		try
		{
			p = Integer.parseInt(tBil.getText());
			if (p % 2 == 0)
			{
				genap.insertElementAt(p.toString(),0);
			}else{
				ganjil.insertElementAt(p.toString(),0);
			}
		}
		catch (Exception e)
		{
			System.out.println(e);
			JOptionPane.showMessageDialog(null, 
                                    e.toString(),
                                    "Error", 
                                    JOptionPane.ERROR_MESSAGE);
		}
	}
	
	private void btnTutupClick(ActionEvent evt){
		System.exit(0);
	}
}

frmCombo.java

class frmCombo {

  public static void main(String[] args) 
  {
    Combo f = new Combo();
    f.setVisible(true);
  }
}