Compiling the Program into a Class File
Before you can run a Java program, you must compile it. When you compile a program, the instructions given to the computer in the program are converted into a form the computer can better understand.
The Java compiler speaks up only when there’s an error to complain about. If you compile a program successfully without any errors, nothing happens in response. This is a little anticlimactic. When I was starting out as a Java programmer, I was hoping successful compilation would be met with a grand flourish of celebratory horns.
NetBeans compiles programs automatically as they are saved. If you typed everything as shown in Listing 2.2, the program compiles successfully.
A compiled version of the program, a new file called Saluton.class, is created. All Java programs are compiled into class files, which are given the .class file extension. A Java program can be made up of several classes that work together, but in a simple program such as Saluton only one class is needed.