Notes on HelloWorld.java
P. Conrad 01/02/2006

(1) The file must be named the same as the class.

(2) Execution starts in the main.  

     
(3) To compile use:

    javac HelloWorld.java
  
    This produces HelloWorld.class

(4) To run, use

    java HelloWorld





Common mistakes:
==============

 (1) Having a class named HelloWorld but calling the file hello.java
     The class name and the filename must match.

 (2) Trying to compile with
       javac HelloWorld

 (3) Trying to run with one of the following
       java HelloWorld.java
       java HelloWorld.class


If javac or java produce "command not found"
============================================

You need to add the Java Development Kit (JDK) to your path.

For information on how to do that:

 * for strauss.udel.edu, check the directory topics/java/compilingOnStrauss


Basic Java Concepts: Source vs. object, bytecodes, JVM, public static void
==========================================================================

(This is stuff you should already know from CISC370; 
 I provide it as a reminder in case CISC370 was "a while ago",
 and you need some prompting to get back in the Java game.)


The HelloWorld.java file is the source file
The HelloWorld.class file is the result of compling into bytecodes

Bytecodes are like "machine independent instructions"

Bytecodes are interpreted (executed) by the Java Virtual Machine (JVM)
  when you type "java classname".

The three keywords
    in front of main have these meanings:

     public  the function must be public, or can't access it outside the class
     static  the function isn't tied to a specific instance of the class
     void    the function doesn't return anything to the caller