Applets and Course Evaluation

Transcript Applets and Course Evaluation

Applets and Course Evaluation
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Applet Example - Sailing
Applet UML Diagrams
Applet Web Page Encoding (HTML)
Applet Java Coding – Hello World
Course Evaluation
Reading for this lecture: L&L 2.7-2.9, App G
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Applet Use Case Diagram
Browser
(Firefox)
Scenario:
Run Applet
Server
Via
Internet
Applet
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Applet Class Diagram
JApplet
+ init( ) : void
+ start( ) : void
+ stop( ) : void
+ destroy( ) : void
AppletName
(Override parent methods)
+ paint(screen : Graphics) : void
Graphics
+ clearRect( … ) : void
+ setColor( … ) : void
+ drawString( … ) : void
+ drawRect( … ) : void
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Applet Sequence Diagram
User
Browser
Server
Open Page
Obtain HTML file and Applet class file
Display Page
JApplet app = new JApplet();
app.init ( )
app.start ( )
app.paint (Graphics screen)
Applet Display via calls to Graphics methods
Close Page
app.stop ( )
app.destroy ( )
app = null;
(Garbage)
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JApplet Class
• JApplet is a class in javax.swing package
• It is a top level GUI container like a JFrame
• Differences:
– Not a standalone application – no main method
– It is instantiated by an Internet browser
– Browser calls the constructor: JApplet( )
– Browser controls the screen display
– No JFrame methods such as:
setSize()
setVisible()
setDefaultCloseOperation()
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Applet Web Page Coding (HTML)
<HTML>
<HEAD>
<TITLE>Applet Name</TITLE>
</HEAD>
<BODY>
<APPLET code=“AppletName" width=700
height=350>
<PARAM NAME="Author" VALUE="Bob Wilson">
</APPLET>
</BODY>
</HTML>
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Applet Java Source Code
import javax.swing.*;
public class AppletName extends JApplet
{
public void init() // override
{
// called when browser loads Applet
}
public void start() // override
{
// called when Applet started/restarted
}
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Applet Java Source Code
public void stop()
// override
{
// called when Applet is stopped
}
public void destroy()
// override
{
// called when browser (tab) is closed
}
public paint(Graphics screen)
// override
{
// called to paint/repaint the screen
// e.g., when part of screen is uncovered
}
}
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Paint Method for “Hello World”
public void paint (Graphics screen)
{
// look up/study the Graphics class methods
// clear the Applet screen area
screen.clearRect(0,0,this.getWidth(),
this.getHeight());
// pick up a red pen for drawing
screen.setColor(new Color(255,0,0));
// Ubiquitous “Hello World” in upper left
screen.drawString(“Hello World!”, 0, 10);
// and surround it with a rectangle
screen.drawRect(0, 0, 100, 10);
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}
Graphics Methods
• Look carefully at the reference point for
drawing something with each graphics
method or you can have a problem
Example: drawString(“Hello World”, 0, 0)
• If drawn at 0,0: The text box will be above
the visible area of the screen display
Hello World!
Reference point is
at lower left corner
Visible Area of screen display (looks blank)
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Graphics Methods
• Use drawString (“Hello World!”, 0, 10)
• But to surround the text with a rectangle,
use drawRect(0, 0, … )
• If drawn at 0,10: The rectangle will be
below the text – not around it.
Hello World!
Reference point is
at upper left corner
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Applets in Local Files
• You don’t need files stored on a server
• You can store the HTML file and applet
.class file on any local disk and the browser
can open the file as a web page
– The applet operates normally in the page
• You can also run it in DrJava AppletViewer
menu: Tools -> Run Document as Applet
– The applet runs in an otherwise empty frame
• Try it yourself in Lab 10
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Course Evaluation
• Need a student volunteer to collect evaluations
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Applets and Course Evaluation

Transcript Applets and Course Evaluation

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