So you have a great looking program. Perhaps you typed out the source code for the hello world tutorial. Now, you need to transfer that source code into a computer language. You do that through a process called compiling. In our case, Java is compiled into Java Bytecode.
Compiling a Java file produces a new file. If the old file is called HelloWorld.java, the compiled version of the file will be HelloWorld.class. This is how you can tell the difference between a compiled class and the original human readable format.
Where do I get a compiler?
Fortunately for potential Java programmers, the Java compiler (called the Java SDK) is free. The most generic solution is to go to the Sun Microsystems Java 2 SE download page and get the latest compiler version.
However, there are other options. One thing that I would recommend is to install an Integrated Development Environment, such as Netbeans. The Netbeans installer can also install the Java SDK. You will find a link to the Netbeans installer on the same Java SE download page. There is also a special “learning edition” of Netbeans that is called the BlueJ edition. It can be found here. It is specially designed to help students of java to learn the basics, and get familiar with an integrated development environment.