Help with packages and classpath

Question

Heya,
first off, i use textpad to compile my java, i don't do it via the command line.
my problem is faily simple, i think. i've got a main class and i'd like it to import a custom class from a subdir.
Main class is in
C:\Documents and Settings\David\Desktop\java\test_gen.java
I would like it to import
C:\Documents and Settings\David\Desktop\java\obj_data\objects.java
I understand that I have to declare objects.java to be a part of a package, so i head the code with: package obj_data; as i understand it, the directory in which the package to be imported resides in will be named the same as the package.
When i import my package into test_gen.java, i import obj_data as follows:
import obj_data.*;
this should import objects.class and any other classes in the same directory. also import obj_data.objects.*; could be used.
Anyway, thats my understanding of how you set up the class and package; i also understand that when the java file compiles the compiler looks at the directoy(s) indicated in the class path for the classes to import. that in mind i tried to add:
C:\Documents and Settings\David\Desktop\java\obj_data\
to my classpath. i did this via dos, javac -classpath "C:\Documents and Settings\David\Desktop\java\obj_data\"
i got no error messages, so i assume it worked. however when i try to compile the main java (test_gen) i get-
package packages does not exist
import packages.*;
^
1 error
Tool completed with exit code 1
can anyone give me some help please?

Answer 1

This is a minimal explanation of packages.
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
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)