Simplified Introduction to Swing and Java GUI programming

We'll start with Java apps.

There are four things to know before you begin:

Swing containers
The layout
The components and how to link them to their event handlers
The Swing timer

Containers

Each Swing GUI program contains one top-level Swing container: JFrame (app), JApplet(applet) or JDialog.

A JFrame implements a window with standard decorations (border, title, ...).

The top-level container (e.g.,JFrame) has a default content panel. Often when you refer to the toplevel container, you are also referring to the default content panel, and vice versa.

You can specify zero or more JPanels that are contained within the content panel. The JPanels are used to organize the GUI into logical sense.

Layout Managers

Layout managers specify how components are positions in a container. Commonly used layout managers

BorderLayout (center, north south east west)
BoxLayout (either horizontally or vertically)
FlowLayout (left to right, each line centered)
GridLayout (rectangular grid, specifying number of columns and number of rows, equal sized boxes)

All content panes (the main container in JFrame and Japplet) have default BorderLayout.

All JPanel objects have default FlowLayout.

Components

Each GUI component can be (must be) contained in exactly one container. There is a containment hierarchy that has the top-level container as its root.

Commonly used components

JButton
Jlabel
JTextField
JTextPane
JCheckBox
JComboBox
JRadioButton
JSlider
JColorChooser
JFileChooser

To include a component on a GUI: (1) instantiate it, (2) create the event handler for it, (3) add it to the proper container.

Event handlers

Listener	event
ActionListener	click a button
WindowListener	close the main window
MouseListener	click mouse button
MouseMotionListener	move mouse
ListSelectionListener	list selection changes

The code for an event handler will have three pieces; Example for ActionListener class:

Either implement a listener interface
or extend a class that implements a listener interface public class EventClass implements ActionListener { ...
Connect the event handler instance to one or more components: button1.addActionListener(new EventClass());
Implement actionPerformed code in the ActionListener public void actionPerformed(ActionEvent e) { ... // do stuff to handle event }

Events cause the event-handling code to be placed on a single thread called the event-dispatching thread. Each event handler will finish before the next one starts. Event handler code must be quick to avoid freezing up the GUI.

Swing timer

The Swing timer is the easiest way to implement animation. Like a Javascript interval timer, it fires an event after the interval time has elapse.

Here is the API for the Swing Timer: http://download.oracle.com/javase/1.4.2/docs/api/javax/swing/Timer.html The methods of greatest importance to us are: start(), stop(), isRunning(), setDelay().

The API for the ActionListener interface is here: http://download.oracle.com/javase/1.4.2/docs/api/java/awt/event/ActionListener.html We must implement actionPerformed(), which is the code that is executed when a timer "goes off."

The Swing Timer is a nifty class that lets us set up timers. We can start and stop each timer. We can set a delay time for the timer. When the timer "goes off" the specified "listener" code will be executed. Warning, there is a Timer class in java.util.Timer. We don't want to use that one. We want to use javax.swing.Timer.