CS1054: Lecture 21

- Graphical User Interface

Graphical User Interfaces vs. Text User Interface

Three steps to GUI Programming

What kind of elements can we show on screen? Components

How do we arrange those elements? Layout

How do we react to user input? Event Handlers

AWT vs SWING

Java has two GUI libraries – AWT and Swing

Swing later and much improved than AWT

Equivalent classes in Swing can be identified by a J at the start of class name.

Top level Window

In control of Operating System’s window management

Java word – Frames Swing calls - JFrame

JFrame Windows

Title bar

Menu bar

Content pane

Adding Simple Components

JLabel

frame.pack( );frame.setVisible (true);

Adding Menus

JMenuBar JMenu JMenuItem

Creating Menubars – 3 stepsJMenuBar menubar = new JMenuBar ( );frame.setJMenuBar ( menubar );

JMenu fileMenu = new JMenu ( “File”);menubar.add (fileMenu);

JMenuItem openItem = new JMenuItem (“Open”);fileMenu.add (openItem);

JMenuItem quitItem = new JMenuItem (“Quit”);fileMenu.add (quitItem);

Event Handling

ActionEvent MouseEvent WindowEvent

To receive events

1. import java.awt.event.*;2. To class header ActionListener interface3. public void actionPerformed

(ActionEvent event)4. The objects must call addActionListener

( ) to register as a listener

Add ActionListener

public class ImageViewer implements ActionListener public void actionPerformed (ActionEvent event) {

System.out.println ("Item: " + event.getActionCommand ( )); }

openItem.addActionListener( this); quitItem.addActionListener( this);

Layout Managers

- Arrange components on a screen.- Each container has a Layout

Manager associated with it.- The Layout Manager takes care of

arranging components within that container

Layout Managers

http://java.sun.com/docs/books/tutorial/uiswing/layout/visual.html- FlowLayout- BorderLayout- GridLayout

MouseListener Demo

http://java.sun.com/j2se/1.4.2/docs/api/java/awt/event/MouseListener.html