# Java Notes

# Compiling a Java program

Turning a Java source program into an object program takes a couple of steps. Assuming that you are using the popular, but awkward, JDK (Java Development Kit) by Sun Microsystems, do the following:

1. Create the source program with a text editor (eg, jEdit, TextPad, ...). Save it in a file with the same name as the public class adding the extension ".java" (eg, Greeting.java). A common error is to use a different name for the file and the class. The name before the "." must be the same as the class name, including upper- or lowercase. Many programmers save their source file every 10 minutes or so -- it's quick and saves the aggravation of having to type it again if there is a system crash.
2. Open a DOS command window and `cd` to the directory containing the source file. This is easy if you've used short directory names without spaces.
3. Compile the source program (Greeting.java in this example) with the following DOS command:

       javac Greeting.java

This produces one or more ".class" files, which are the object (Java byte code) form of Java programs. You can produce a ".exe" file from this, but that isn't normally done.
4. Run it with:

       java Greeting

   This loads the Greeting.class file and all necessary classes. Execution starts with the `main` method in the Greeting class.

Continue in this cycle until the program works.