Code of simple Swing Java Applications

//package swing;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class Converter implements ActionListener {

JFrame frame;
JPanel panel;
JTextField tempCel;
JLabel celLabel, fahLabel, resultFah;
JButton changeTemp;

public Converter() {
	//Create and set up the window.
	frame = new JFrame("Change Celsius to Fahrenheit");
	frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
	frame.setSize(new Dimension(180, 80));

	//Create and set up the panel.
	panel = new JPanel(new GridLayout(3, 2));
	panel.setBorder(BorderFactory.createEmptyBorder(60, //top
	60, //left
	20, //bottom
	60) //right	
	);
	//Add the items.
	addItems();

	//Set the default button.
	frame.getRootPane().setDefaultButton(changeTemp);

	//Add the panel to the frame.
	frame.getContentPane().add(panel, BorderLayout.CENTER);
	//Display the window.
	frame.pack();
	frame.setVisible(true);
}
private void addItems() {
	//Create items.
	tempCel = new JTextField(2);
	celLabel = new JLabel("Celsius", SwingConstants.LEFT);
	resultFah = new JLabel("", SwingConstants.LEFT);
	fahLabel = new JLabel("Fahrenheit", SwingConstants.LEFT);
	changeTemp = new JButton("Convert");

	//Listen to events from the Convert button.
	changeTemp.addActionListener(this);
	//Add the items to the container.
	panel.add(tempCel);
	panel.add(celLabel);
	panel.add(resultFah);
	panel.add(fahLabel);
	panel.add(changeTemp);

	celLabel.setBorder(BorderFactory.createEmptyBorder(5, 5, 5, 5));
	fahLabel.setBorder(BorderFactory.createEmptyBorder(5, 5, 5, 5));
}
public void actionPerformed(ActionEvent event) {
	//Parse degrees Celsius as a double and convert to Fahrenheit.
	int tempFahr =
     (int) ((Double.parseDouble(tempCel.getText())) * 1.8 + 32);
	resultFah.setText(tempFahr + "");
}
	
private static void createAndShowGUI() {
	//Make sure we have nice window decorations.
	JFrame.setDefaultLookAndFeelDecorated(true);

	Converter converter = new Converter();
}
public static void main(String[] args) {
	javax.swing.SwingUtilities.invokeLater(new Runnable() {
		public void run() {
			createAndShowGUI();
		}
	});
}
}

More...