Applications vs. Applets

1
Applications vs. Applets

• Applets run inside a browser.
• Applets almost always do something graphical
  (e.g. a stock ticker)
• The security in place does not allow applet to
• Write files
• Contact servers (other than the one that sent it)
• Applications run outside a browser.
• Applications typically are more full featured
  programs (e.g. word processors, IDEs (JBuilder is
  written in Java))
• There are no security restrictions for
  applications.

2
Skeleton of an Application

• package appvsapplet
• public class MyLameApp
• public static void main(String args)
• System.out.println("Hello world!")

3
Skeleton of an Applet

• package appvsapplet
• import java.awt.
• import java.applet.
• public class MyLameApplet extends Applet
• public void paint(Graphics g)
• g.drawString("Hello world!", 20, 20)

4
Life cycle methods for an applet

• init put code here that should be executed only
  once in the applets lifetime this method is
  called when the applet is first encountered
• start put code here to start your applet
  called right after init or when user revisits
  page
• stop put code here to stop your applet called
  when user leaves page containing applet
• destroy put code here to relinquish resources
  many dont even use this method

5
Examples of life cycle code

• init load images
• start start an animation (usually with separate
  thread)
• stop stop animation (by stopping the thread)
• destroy close network connections

6
Life cycle methods (continued)

• Browser calls these methods for you at
  appropriate times you just need to define what
  it does at those times
• appvsapplet.MyLameApplet inherits from
  java.applet.Applet using the extends reserved
  word
• Question Why doesnt MyLameApplet need to
  define init, start, stop, and destroy?

7
Applet Inheritance

• MyLameApplet is not required to define life cycle
  methods since it INHERITS the implementation of
  those methods from java.applet.Applet
• java.applet.Applets implementations of those
  methods do nothing!
• So if you want them to do something, you must
  override those methods (more on this later)

8
Program 1

• There are no objects explicitly instantiated in
  this program
• Use only primitives (e.g. float) for this program
• Find on the Internet how to convert Celsius value
  to Fahrenheit (you may hardcode the input (45)
  but not the output)
• Youll need one more thing to finish

9
Methods of the String class

• String.valueOf(myAnswer)
• valueOf is a static method why?
• valueOf can convert floats, ints, and others into
  String objects
• Why do we care about this method?
• Your calculated answer will be a float.
• But there is no drawFloat method!
• There is only a drawString method!