I cant access my custom library. "error:Package X does not exist".

Question

First of all, there is nothing wrong with my sourcecode. I've checked it and it runs fine when my client class and the rest of the classes is thrown into the same directory together.
Thing is, I have a lot of reusable code,which works, and I have to my best ability followed guidelines on the net how to put them into a liberary and use the import statement in the client to make use of that liberary. My client class still cant find the library, and yes it has the proper import statement. It just tells me that the package does not exist. I've tried to compress the library to a jarfile:
jar cf mittBibliotek.jar *
, and I've tried treating it as it is(a directory with java files, each one containing the proper package statement).
First I tried to setup my library using the Netbeans IDE 5.0.
(Right click the libraries node in the project iew->properties>-Libraries->Add Jar/Folder) Source code still cant find any of the classes contained in the jar file.
The netbeans interface can be a bit involved, so I switched to BlueJ just to see if my client class was able to find anything (Tools->preferences->Libraries->add).
I've tried multiple variations trying to explain to the the source code where the liberary is located. Should the files in the library be compiled before it can be used as a jar? Have I set up my classpath correctly? I'm using windows XP, and I've placed the classpath by going to system properties-advanced tab->envirornment variables and typing it under the system variables.Is
this wrong? Should it be someplace else? Haven't BlueJ or netbeans their own setup for classpaths? And why the need to type anything else in the classpath, when the dot in CLASSPATH=.;c:\Java;c:\suff;c:\andSoOn; actually means everything? Would it not be the same to just
write CLASSPATH=.;?
I seem to be getting off topic here, sorry about that. All I want is to be able to use my class library with my source code.
PS: I've used the terms "source code" and "client class" arbitrarely. They are both the same.
Message was edited by:
javabra

Answer 1

Have I set up my classpath
correctly? I'm using windows XP, and I've placed the
classpath by going to system properties-advanced
tab->envirornment variables and typing it under the
system variables.Is
this wrong? That can work, but changing the CLASSPATH environment variable every time you want to run a program isn't recommended. Instead, you should you use the -classpath option of the javac command to compile your programs. Here is the syntax
C:> javac -classpath C:\folder1;C:\folder2\subfolder1 MyClass.java
Tip: construct your command in a text editor, so if it doesn't work, you can modify it and then copy and paste it into your DOS window. That will save you from having to retype the whole command in the DOS window.
And
why the need to type anything else in the classpath,
when the dot in
CLASSPATH=.;c:\Java;c:\suff;c:\andSoOn; actually
means everything? Would it not be the same to just
write CLASSPATH=.;? No. The dot means to look in the current directory. Suppose you have a DOS window open and you change directories to an existing directory on your computer called C:\folder1\subfolder1:
something here>cd C:\folder1\subfolder1
C:\folder1\subfolder1>Now, let's say you want to compile the MyClass.java file and it's in subfolder1. Also, suppose MyClass.java imports a class in folder1. If you use this command to compile:
C:\folder1\subfolder1>
javac -classpath . MyClass.java
the current directory is C:\folder1\subfolder1 (note: I put the javac command on a different line for clarity). The -classpath is the dot, which instructs javac to look in the current directory for the classes referred to in the program MyClass.java. Since by assumption the class referred to by MyClass.java is not in subfolder1, the program won't compile. Also, the current directory does not include files in subdirectories of the current directory.
Unfortunately, one of the biggest barriers to learning java is learning how to compile and execute programs. I still have trouble, and I constantly revise the rules I follow to take into account some new thing I stumbled on. Here are the current rules I follow:
=================================
EXAMPLE DIRECTORY STRUCTURE:
D:\javaStuff\aFolder\TryPackage.java
TryPackage.java is in the aFolder package and references the Line and Point classes. Line.java and Point.java are in the Geometry package, and they reside in the Geometry folder like this:
C:\moreJava\Packages\Geometry\Line.java
====================================
COMPILING: Use cd to change the DOS prompt to the current directory of the FILE you are trying to compile. In the -classpath option, include the classpaths to packages of all CLASSES referenced in your program whether they are in an import statement or not. If the file you want to compile is in the current directory, the compiler can find your FILE--it uses "." for the default location. To compile TryPackage.java above use this command:
D:\javaStuff\aFolder>
javac -classpath C:\moreJava\Packages filename
where filename = TryPackage.java. If your FILE is not in the current directory, then you need to use the full path name of the FILE like this: filename = d:\javaStuff\aFolder\TryPackage.java
RUNNING: In -classpath, include all paths to all packages of the classes USED in the program, which includes the path to the package of the .class file you are trying to run. If the .class file you are trying to run is not in a named package, then it is part of the default package, and the -classpath for that package must be included. For the default package, the -classpath equals the path to the directory that contains the file. If TryPackage.java did not have a package statement, the -classpath to the default package would be D:\javaStuff\aFolder. In addition, you need tack on the package name to the beginning of the .class file you compiled. Here is how you would run the TryPackage program:
D:\javaStuff\aFolder>
java -classpath C:\moreJava\Packages;D:\javaStuff filename
where filename = aFolder.TryPackage. It does not matter if the .class file you are trying to run is in the current directory or not. The preceding command will work from any directory.
ADDITIONAL RULES: You don't necessarily have to specify the full path name to the file when you are at a prompt other than the directory which contains the file. Instead, you can just complete the path to the file from the current directory, i.e. the prompt. For instance, if this is the directory structure:
C:
----javaPrograms
-----------Pack1
-----------------DemoA.java
and you are at the prompt:
C:\javaPrograms>
You can compile DemoA.java with this command:
javac Pack1\DemoA.java
Note that if you add the prompt directory to the path specified for the file, you get:
C:\javaPrograms + Pack1\DemoA.java = C:\javaPrograms\Pack1\DemoA.java
which results in the full path name to the file. So, javac can use the prompt directory as the starting point for path to the file you are compiling.
The same thing works for the java command when you execute your program. Assume you are at the C:\ prompt:
C:\>
You can compile the program using:
javac javaPrograms\Pack1\DemoA.java
(Note: I've only completed the path to the file from the current directory). I can execute the program using:
java -classpath javaPrograms Pack1.DemoA
The java command completes the path to package. The prompt directory added to the -classpath is:
C:\ + javaPrograms = C:\javaPrograms
which is the full path to the parent directory of the package.