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Lesson 4 The Java compiler
Objective Java compiler used to compile Java

Java Compiler

Use the Java compiler to compile Java programs.
The Java compiler[1] is probably the most important tool in the Java 2 SDK because it is responsible for compiling Java source code into executable Java programs. The Java compiler creates executable program code in a special format known as bytecode.
Most compilers for other programming languages generate native executable code, which is code that is created to run solely on a specific type of computer platform. The Java compiler takes a very different approach by generating bytecode that can be executed on any platform that supports Java.

Compiling a Java applet

The file that ships with the Java SDK contains the source code for a demonstration Java applet that allows you to play Tic-Tac-Toe against the computer.
To compile this source code file into an executable applet with the Java compiler, you would issue the following command at a command-line prompt (which you will do in this lesson's exercise):
  1. The name of the Java compiler
  2. The source code file to be compiled

Java is a case-sensitive programming language. This especially applies to the Java API, which consists of classes, methods, and variables that are all given case-sensitive names. Even the names of applets are case-sensitive, which means the name of the applet in the source code (DateTime) must match the name of the source code file (

After issuing the javac command, the file TicTacToe.class will be created, which is the executable applet class file that is ready to be embedded in a Web page. Executable Java programs are stored in files with a .class file extension because they are comprised of classes .

A class defines data and methods and is a unit of organization in a Java program.
A class is an object-oriented programming construct that attempts to make the modeling of real-world objects in software much more intuitive.
The Web page TicTacToe.html contains the embedded applet, and must be opened in a Web browser in order to run the applet.

Compiling Java Applet - Exercise

Click the Exercise link below to compile a Java applet using the Java compiler.
Compiling Java Applet - Exercise
[1] Class: A class is a template that defines the implementation of an object, effectively acting as a blueprint for the object.