You can compile and run a program at any time while you are developing the program. A Java compiler reads Java source files and produces the Java program in the form of .class files. These files contain the bytecodes that can be executed by the Java Virtual Machine (JVM). The JVM locates the classes that your program uses using the class path.
For help with compiling and running programs, see:
Compiling Java Programs
Setting Compiler Options
Running Java Programs
Setting Run Arguments
Setting Executor Options