Applets

1
Applets

• Robert Salkin
• CSI 205 OOP using Java
• Summer 2005, 6W1

2
Quick Review

• Swing Components usually are lightweight and
  start with J.
• GUI Components are put into Containers.
• A Container is also a Component, so a Container
  can be put (add) into another Container.

3
Quick Review

• Graphics objects handle the graphics context, in
  which shapes can be drawn.
• Methods starting with fill draw filled shapes,
  while draw methods draw unfilled shapes, or
  outlines of shapes.
• paintComponent is the method that should be
  overridden, while repaint should be called when a
  repaint of the screen should be done.

4
Applets

• Applets are compiled classes that extend JApplet.
• An HTML page with APPLET tags is required to view
  an applet online via a browser or appletviewer.
• ltAPPLET CODEMyClassName.class WIDTHw
  HEIGHThgtlt/APPLETgt

5
Methods

• There are 5 methods that may be overridden in an
  applet a main method is irrelevant.
• public void init()
• Called once after applet is loaded.
• public void start()
• Called after init and when the user browses back
  to the applet.
• public void paint(Graphics g)
• Called after start and after the window is
  uncovered.
• public void stop()
• Called before destroy and when the user browses
  away from the applet.
• public void destroy()
• Called when the browser is quit entirely.

6
Application to Applet

• Not much needs to be done to convert an
  application to an applet.
• main logic needs to be moved into start and/or
  paint.
• The main method isnt useful to the applet.
• Constructor operations should be moved into init.
• Most GUI operation stays the same.
• The class is instantiated by the mechanism that
  runs the applet, so do not instantiate yourself.

7
Security

• Applets are generally not allowed to interact
  with the local systems resources or do risky
  things.
• Cant save/load files.
• Cant connect to other IPs.
• A signed applet may be allowed to access the
  local disks and do other risky things.

8
Final Exam

• Longer than the Midterm.
• Open book/notes.
• Computers may be used ONLY for checking files on
  the class website.
• NO compiling/googling/etc.
• Visiting other websites will result in a failure
  for the exam.
• Answers will be written on an answer sheet.
• Less emphasis on graphics/applets, but at
  minimum, you will need to write an applet, with
  HTML, to draw a fairly simple object on the
  screen worth 15 pts of the exam.
• There will be multiple choice, short answer,
  whats wrong with the code, and writing your own
  code.

9
Review

• May be heavily emphasized
• If/else
• Switch
• Loops
• Methods
• Classes/objects
• Inheritance
• Polymorphism
• GUI
• Arrays
• Searching/sorting/randomizing
• May be on the test, but with less emphasis
• Files
• Graphics
• Applets