[ Belajar Java ] - Membuat Data Mahasiswa

import javax.swing.JFrame;
import javax.swing.JButton;
import javax.swing.JLabel;
import javax.swing.JTextField;
import javax.swing.JComboBox;
import javax.swing.JMenuItem;
import javax.swing.JMenu;
import javax.swing.JMenuBar;
import javax.swing.BoxLayout;
import java.awt.Container;
import java.awt.Insets;
import java.awt.Dimension;
import java.awt.event.WindowEvent;
import java.awt.event.WindowAdapter;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;

class Data_Mahasiswa extends JFrame implements ActionListener
{
    String[] items = { " Teknik Informatika "," Teknik Komputer ",
            " Teknik Elektro "," Teknik Sipil "," Manajemen Informatika ",
            " Desain Komunkisai Visual "," Akutansi "," Sastra "," Hukum" };

    private JButton button;
    private JLabel label;
    private JTextField a;
    private JComboBox cb;

    private void dframe()
    {
        Dimension size;

        JMenuBar menuBar = new JMenuBar();
        JMenu fileMenu = new JMenu("file");
        JMenu About = new JMenu("About");
        menuBar.add(fileMenu);
        menuBar.add(About);
        JMenuItem exitMenuItem = new JMenuItem("Exit");
        exitMenuItem.addActionListener(this);
        fileMenu.add(exitMenuItem);
        setJMenuBar(menuBar);


        Container pane = getContentPane();
        pane.setLayout(null);

        Insets insets = pane.getInsets();

        label = new JLabel("DATA MAHASIWA");
        size = label.getPreferredSize();
        label.setBounds(10 + insets.left,8 + 
        insets.top,size.width,size.height);
        pane.add(label);

        label = new JLabel("NAMA");
        size = label.getPreferredSize();
        label.setBounds(10 + insets.left,45 + 
        insets.top,size.width,size.height);
        pane.add(label);

        label = new JLabel("NIM");
        size = label.getPreferredSize();
        label.setBounds(10 + insets.left,70 + 
        insets.top,size.width,size.height);
        pane.add(label);

        label = new JLabel("JURUSAN");
        size = label.getPreferredSize();
        label.setBounds(10 + insets.left,95 + 
        insets.top,size.width,size.height);
        pane.add(label);

        a = new JTextField(16);
        size = a.getPreferredSize();
        a.setBounds(100 + insets.left,45 + 
        insets.top,size.width,size.height);
        pane.add(a);

        a = new JTextField(16);
        size = a.getPreferredSize();
        a.setBounds(100 + insets.left,70 + 
        insets.top,size.width,size.height);
        pane.add(a);

        cb = new JComboBox(items);
        size = cb.getPreferredSize();
        cb.setBounds(100 + insets.left,95 + 
        insets.top,size.width,size.height);
        pane.add(cb);

        button = new JButton("OK");
        size = button.getPreferredSize();
        button.setBounds(100 + insets.left,135 +
        insets.top,size.width+35,size.height);
        button.addActionListener(this);
        pane.add(button);

        button = new JButton("CANCEL");
        size = button.getPreferredSize();
        button.setBounds(200 + insets.left,135 + 
        insets.top,size.width,size.height);
        button.addActionListener(this);
        pane.add(button);

        int width = 300 + insets.left + insets.right;
        int height = 225 + insets.top + insets.bottom;
            setSize(width,height);
    }

    public void actionPerformed(ActionEvent e)
    {
        String selection = e.getActionCommand();
             if(selection.equals("Exit"))
             {
                   System.exit(0);
             }
    }

    public static void main(String args[])
    {
        new Data_Mahasiswa();
    }

    public Data_Mahasiswa()
    {
        super("Membuat Nama dan Nim");
        addWindowListener(new WindowAdapter()
        {
            public void windowClosing(WindowEvent e)
            {
                System.exit(0);
            }
        });

        dframe();
        setLocation(250,150);
        setVisible(true);
    }
}