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AWT and Swing
Most GUI class libraries in C++ are platform specific
Different hardware capabilities
Subtle differences between the "look-and-feel" of various
Windowing operating systems
Abstract Window Toolkit (AWT) is cross-platform
Swing can observe various OS look-and-feel conventions
Common functionality/specific implementation approach
Toolkit -------------------------------------------------- AWT
Button List JVM
| | Native GUI
Button Peer List Peer (Windows, Mac, X)
AWT GUI classes are platform-independent elements
Each AWT platform-specific toolkit comes with peer class
implementing platform-specific behavior of its AWT class
Combining platform-independent AWT class with
platform-specific peer class transforms generic, abstract windows
behavior into specific, particular behavior
JDK 1.0 (circa 1996)
JDK 1.0 went a long way to implementing
platform-independent GUI library
Bruce Eckel: it "produced a GUI that looks
equally mediocre on all systems."
Just 4 fonts
Couldn‟t access GUI of native OS
Didn‟t separate model and UI code cleanly
JDK 1.1 (circa 1998)
JDK 1.1 makes AWT more robust and extensible
Delegation-based event model separates user
interface from problem domain
Avoids cascaded if statements testing for object type
required by first AWT
Designates "listeners" of events triggered by problem
domain objects
Listeners implement the Observer design pattern
Other enhancements: button tool tips, cut/paste
to the clipboard, popup menus, printing, etc.
Adds supports for JavaBeans
Graphical Components
button menus title bar menu bar combo box
scroll bars
AWT class hierarchy
Checkbox, Choice, Label, List, Scrollbar,ScrollPane, TextArea, TextField
Window and Frame classes
A Window is a top-level window with no borders and no menubar
It can generate a WindowOpened or a WindowClosed event,
to which a WindowListener or WindowAdapter can respond
A Frame is a top-level window with a title and a border
Because it has more features, it can generate more events:
WindowOpened, WindowClosing, WindowClosed,
WindowIconified, WindowDeiconified,
WindowActivated, WindowDeactivated
Respond to these events with a WindowListener
Once a subclass of Container has been constructed, it can add
(attach) any AWT component within it, such as a Button, Label,
TextField, or another Frame or Panel
A simple example
//Demonstrates construction of a Container and a Button
import java.awt.*;
class Gui extends Frame
{ public Gui(String s) //constructor { super(s); //construct Frame part of Gui setBackground(Color.yellow); setLayout(new FlowLayout()); Button pushButton = new Button("press me"); add(pushButton); }
} //class Gui
class Ex_1 //Creates an instance of class Gui
{ public static void main(String[] args)
{ Gui screen = new Gui("Example 1"); screen.setSize(500,100); screen.setVisible(true); }
} //class Ex_
Superclass does not most of the work
of creating an instance of Gui. Modify properties of Gui.
Create a button and attach it to Gui.
Construct a Gui, set its size
and make it visible.
What does this program not do?docsity.com
Responding to events, continued
Uses event delegation model of JDK 1.
When an event occurs, it generates an ActionEvent object
ActionListener interface listens for a particular ActionEvent Responds in its actionPerformed method
WindowListener interface observes events triggered by
Window object, such as closing it, and responds in
corresponding methods
Program now has a live Button: actionPerformed method
rings a bell
Also a live close window button, which performs System.exit(0)
Most Components in the AWT have corresponding Listeners
Adapter Classes
Time consuming to define all interface methods
WindowListener has seven methods
- What if we only want to use one?
- Required to define all methods in interface
Adapter class implements an interface
- Does anyone recognize a design pattern here?
- Default implementation ({ }, empty body) for all
methods
You then extend adapter class,
- overriding methods for events you care about, such as
windowClosing.
Has "is a" relationship with interface
- WindowAdapter is a WindowListener
- MouseAdapter is a MouseListener
Layout managers
JDK provides a set of genericSketchpad uses hard-coded layout, which depends on a 800x600 screen layout manager classes
- Arrange Component objects within a Container object in predictable ways
FlowLayout (the default) add components one after another in rows:
setLayout(new FlowLayout(FlowLayout.LEFT,10,10); for (int counter=1; counter <= 6; counter++) add(new Button(String.valueOf(counter)));
GridLayout places components in cells of a grid:
setLayout(new GridLayout(3,2,5,5); //3 rows, 2 columns, 5 pixel gaps for (int counter=1; counter <= 6; counter++) add(new Button(String.valueOf(counter)));
BorderLayout arranges components using along four sides (North, South, East West) and Center positions
Swing overview
Defined in package javax.swing
Original GUI components from AWT in java.awt
Heavyweight components - rely on local platform's
windowing system for look and feel
Swing components are lightweight
Not weighed down by GUI capabilities of platform
More portable than heavyweight components
Swing components allow programmer to specify look and feel
Can change depending on platform
Can be same across all platforms
Jcomponent features
Pluggable look and feel
Can look like different platforms, at run-time
Shortcut keys (mnemonics)
Direct access to components through keyboard
Common event handling
If several components perform same actions
Tool tips
Describe component when mouse rolls over it
Menus
Menu Bar
JMenuBar()
add( JMenu )
Menu
JMenu( String )
add( JMenuItem )
JMenuBar mb = new JMenuBar(); //create a menu bar JMenu fileMenu = new JMenu (“File”); //create a menu mb.add( fileMenu ); //add menu to menu bar setMenuBar( mb ); // add a menu bar to frame fileMenu.setMnemonic( KeyEvent.VK_F ); // add a hotkey to menu
JMenuItem miOpen = new JMenuItem( “Open...”, KeyEvent.VK_O ); JMenuItem miExit = new JMenuItem( “Exit” );
fileMenu.add( miOpen ); // add a menu item fileMenu.addSeparator(); // add a menu separator fileMenu.add( miExit );
JMenuItem( String )
JMenuItem( String,int )
