Transcript Document
CS110 Lecture 26
Thursday, May 6, 2004
• This lecture not delivered from slides
• Announcements
– final exam Thursday, May 20, 8:00 AM
McCormack, Floor 01, Room 0608
– wise1 due next Tuesday
• Agenda
– Questions (WISE and otherwise)
– GUI programming
– Interfaces
Lecture 26
1
GUI Programming
• Fun
– some introductory courses start here
– requires hardware support (PCs)
– maybe more in CS110 in time
• GUI syntax: what windows look like containers and components
• GUI semantics: how windows behave –
event driven programming
• System does lots of work for you
• Learn the APIs, use software tools
Lecture 26
2
10/joi
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GUI Syntax
(what windows look like)
• AWT (Abstract Windowing Toolkit)
• Abstract class Container
– subclasses: Panel, Window, Frame
– methods: add, setLayout
• Abstract class Component
– subclasses: Button, Checkbox, Textfield,
• Up to date Java GUI programmers use swing:
– classes: JButton, JTextfield,…
• or they use GUI builders
Lecture 26
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Building window look and feel
• class JOIPanel extends Applet extends Panel
• init method creates a button and adds it to
this Panel, sets font:
38
39
40
button = new Button( "Press Me" );
this.add( button );
font = new Font("Garamond",
Font.BOLD, 48);
Lecture 26
5
Building window behavior
• Add a listener to the button
43
button.addActionListener(
new JOIButtonListener( this ) );
• When button is pressed, system sends an
actionPerformed message to the listener
• To see what happens, look at method
actionPerformed in class
JOIButtonListener
Lecture 26
6
JOIButtonListener
// constructor remembers the Panel
27 public JOIButtonListener
( JOIPanel panel )
28 {
29
this.panel = panel;
30 }
// send panel a changeMessage message now!
41 public void actionPerformed
( ActionEvent e )
42 {
43
panel.changeMessage();
44 }
Lecture 26
7
Changing the message
• In JOIPanel: change the message and ask
the system to repaint:
51 public void changeMessage()
52 {
53
currentMessage =
54
currentMessage.equals(MESSAGE1) ?
MESSAGE2 : MESSAGE1;
55
this.repaint();
56 }
Lecture 26
8
Changing the message
•
•
repaint( ) (which is really super.repaint( ))
invokes paint( )
A Graphics object is like a programmable
pen or paintbrush
67 public void paint(Graphics g)
68 {
69
g.setColor(Color.black);
70
g.setFont(font);
71
g.drawString(currentMessage, 40, 75);
72 }
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Running the program
• as an application
• > java JOIPanel
public static void main( String[] args )
{
Terminal t
= new Terminal();
Frame frame
= new Frame();
JOIPanel panel = new JOIPanel();
panel.init();
frame.add(panel);
frame.setSize(400,120);
frame.show();
t.readLine("return to close window ");
System.exit(0);
}
Lecture 26
10
Running the program
• as an applet from a browser: file joi.html
<html>
This file is written in html
(“hypertext markup language”),
<body>
not Java. Browsers understand html.
<applet code="JOIPanel.class"
height=100 width=400>
</applet>
main method
never runs.
Execution starts with init.
</body>
</html>
Lecture 26
11
Interfaces
• An interface is like a very abstract class
– no fields
– only abstract methods
• A class that implements an interface
promises to implement its abstract methods
public class JOIButtonListener
implements ActionListener
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All together now
public class JOIApplet extends Applet
implements ActionListener
{ ...
public void actionPerformed
( ActionEvent e )
{
currentMessage =
currentMessage.equals(MESSAGE1) ?
MESSAGE2 : MESSAGE1;
this.repaint();
}
Lecture 26
14
Interfaces in Collection framework
• Inheritance hierarchy (classes)
java.lang.Object
java.util.AbstractMap
java.util.TreeMap
• TreeMap implements interfaces:
– Cloneable, Map, Serializable, SortedMap
• AbstractMap implements Map
• Map foo = new TreeMap( ) // legal
Lecture 26
15
Juno 10 has a GUI
• Juno CLI prompts for input when it wants it
=> the program is in control
• Juno GUI sits waiting for user input from
anywhere mouse can go, then takes action
=> the user is in control (event driven)
• > java Juno –g
.
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java Juno -e -g
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