Keywords


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Lesson:
Main Points:
  1. The Java language specifies 50 keywords and other reserved words.
  2. The words goto and const are reserved even though they aren't used for anything.
  3. An identifier is a word used by the programmer to name a variable, method, class, or label.
  4. Identifiers may begin with a letter, a dollar sign, or an underscore.

Java Keywords: 
abstract   const      final     instanceof   private     synchronized 
boolean    continue   finally   int          protected   this
break      default    float     interface    public      throw
byte       do         for       long         return      throws
case       double     goto      native       short       transient
catch      else       if        new          static      true
char       extends    null      super        try         implements
class      false      import    package      switch      void
volatile   while

Identifiers:
An identifier must begin with a letter, a dollar sign ($), or an underscore (_); subsequent characters may be letters, dollar signs, underscores, or digits. Here are some examples:

  1. foobar (legal)
  2. BIGfloat (legal: embedded keywords OK)
  3. $income (legal)
  4. 4square (illegal: starts with digit)
  5. !more (illegal: must start with letter, $, or _)

NOTE: Identifiers are case sensitive. This means that the identifiers circle and Circle are two distinct identifiers. The same goes for circle and cIrcle. This can be confusing and so it's not a great idea to have two identifier names with the only difference between them being letter case.

EXAMPLE:

import java.awt.*; import java.applet.*; public class ex2 extends Applet{ // class name: ex2 (matches file name) int dogs; // variable name int cats; // variable name String message; //varialbe name Color $xxx = new Color(0, 255, 255); //variable name beginning with $ Color _xxx = new Color(255,255,0); //variable name beginning with _ public void init(){ setBackground($xxx); message="Good Morning Trona High!"; makePets(); // call to method } public void makePets(){ dogs=12; cats=15; } public void paint(Graphics g){ g.setColor(_xxx); g.drawString(message, 10, 20); g.drawString("DOGS: "+dogs, 10, 40); g.drawString("CATS: "+cats, 10, 60); } }

Study this example. It shows several names used for class, methods, and varibles.
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Assignment:
You will make a simple applet in which you create one method and six variables. Show that you can use a variety of interesting names which are all legal. (If you use an illegal name the compiler will let you know.) Your applet can be VERY simple as long as it has the elements described, BUT all variable values must be displayed in your applet.

Present your code along with your applet on a web page.
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