Compile multiple source files

Question

sorry, this is maybe a newbie question.
but iI have a problem compiling an application that use multiple sources files
for exemple
the class A is in the file 1
the class B is in the file 2
class A uses an instance of the class B
class B uses an instance of the class A
so i'm unable to compile these files coz each one tells me he doesn't know about the other
Is there a way to define prototypes of class or fonctions before their use like in C/C++?
Or is there another way i didn"t pay attention
thanks all

Answer 1

This is a minimal explanation of packages. For a full explanation of packages and how to compile and run Java programs, see this page:
http://java.sun.com/j2se/1.4.2/docs/tooldocs/tools.html
and read the Setting the Classpath and the How Classes are Found topics.
Assume that your programs are part of a package named myapp, which is specified by this first line in each source file:
package myapp;
Also assume that directory (C:\java\work\) is listed in the CLASSPATH list of directories.
Also assume that all your source files reside in this directory structure: C:\java\work\myapp\
Then a statement to compile your source file named aProgram.java is:
C:\java\work\>javac myapp\aProgram.java
And a statement to run the program is:
java myapp.aProgram
(This can be issued from any directory, as Java will search for the program, starting the search from the classpath directories.)
Explanation:
Compiling
A class is in a package if there is a package statement at the top of the class.
The source file needs to be in a subdirectory structure. The subdirectory structure must match the package statement. The top subdirectory must be in the classpath directory.
So, you generate a directory structure C:\java\work\myapp\ which is the [classpath directory + the package subdirectory structure], and place aProgram.java in it.
Then from the classpath directory (C:\java\work\) use the command: javac myapp\aProgram.java
Running
Compiling creates a file, aProgram.class in the myapp directory.
(The following is where people tend to get lost.)
The correct name now, as far as java is concerned, is the combination of package name and class name: myapp.aProgram (note I omit the .class) If you don't use this name, java will complain that it can't find the class.
To run a class that's NOT part of a package, you use the command: java SomeFile (assuming that SomeFile.class is in a directory that's listed in the classpath)
To run a class that IS part of a package, you use the command java myapp.aProgram (Note that this is analogous to the command for a class not in a package, you just use the fully qualified name)