.class vs .java

A .class file is a compiled .java file.

.java is all text and is human readable.
.class is binary (usually).

You compile a java file into a class file by going to the command line, navigating to the .java file, and running

javac "c:\the\path\to\your\file\yourFileName.java"

You must have a java SDK installed on your computer (get it from Oracle), and make sure the javac.exe file is locatable in your computer's PATH environment variable.

Also, check out Java's Lesson 1: Compiling & Running a Simple Program

If any of this is unclear, please comment on this response and I can help out :)

• .class -> compiled (for JVM)
• .java -> source (for humans)

A .java file contains your Java source code while a .class file contains the Java bytecode produced by the Java compiler. It is your .class files that run on the JVM to execute a Java application.

It is the .class files you will use when you deploy your applet.