Setting Path and Classpath Variable’s For Java in Win NT

For beginners in java, setting these two variables causes a lot of confusion. Here is my attempt to make life a bit simpler for them. Any suggestion for improving this page is most welcome.

PATH : This variable simply tells the SYSTEM where to find javac.exe & java.exe to execute. ie when you say
C:\> javac myClass.java   OR
C:\>java myClass

How does the system know where is the executable javac or java stored ?
So all you have to do is to inform the system where your javac.exe and java.exe are kept(In fact all executable files that come with jdk, like javah, javadoc, jar, appletviewer, rmic etc). In case of jdk packages they are always stored in the bin folder, so if jdk was installed in C drive, in folder jdk1.3 then the PATH variable must point to C:\jdk1.3\bin
ie you must have
PATH=C:\jdk1.3\bin
How to set them will be shown in a little while, I am just dealing with the definitions first.   

CLASSPATH : So now the system knows where the executables are, but all execuatble files in bin folder like javac.exe and java.exe too depend on a few files to compile and run your codes.Primarily it needs tools.jar.  This jar stores all predefined classes made by sun to compile  and execute your code. Just as all executables for jdk are stored in bin folders, similarly all helping jars are stored in lib folder at the same level as the bin folder.
So CLASSPATH must point to C:\jdk1.3\lib;
ie you must have
CLASSPATH=C:\jdk1.3\lib;
Just by including lib folder tools.jar is automatically included, however if you add other jars like mail.jar or activation.jar(which will be needed in your experiments with JAVAMail API)  in the lib folder you have to explicitly set them in the CLASSPATH.
ie now the CLASSPATH will be
CLASSPATH=C:\jdk1.3\lib;C:\jdk1.3\lib\mail.jar; C:\jdk1.3\lib\activation.jar;

And for packages if we want to include all child folders, append just one more thing ”.;” at the end of CLASSPATH as shown in red color below.

CLASSPATH=C:\jdk1.3\lib;C:\jdk1.3\lib\mail.jar; C:\jdk1.3\lib\activation.jar;.;

Now having understood the two variables lets see how do we set them.

There are several methods to do this,

  1. Set for the current DOS PROMPT.         Temporary

  2. Set through batch file.                        Temporary  

  3. Set for System in Environment.             Permanent.

 
1)Set for current DOS PROMPT Temporary Setting.

When you open a command prompt from START->PROGRAMS->Command Prompt you get a screen as shown below :

 
If I have my jdk1.3 installed in C drive, in folder named jdk1.3
Now type these lines to set path and classpath

C:\> set PATH=C:\jdk1.3\bin;   PRESS ENTER.
And
C:\> set CLASSPATH=C:\jdk1.3\lib;   PRESS ENTER.

So now you will have this

 
However this will cause all previous PATH and CLASSPATH settings to be erased for the CURRENT DOS PROMPT WINDOW ONLY.  And when this window will be closed you will have to again set path and classpath , next time you want to compile or run your codes. Hence this is a temporary setting method for path and classpath. 
If you want to retain the original(system default settings) Environment PATH and CLASSPATH values ie assuming your system has already these settings,
PATH=C:\Oracle\Ora81\bin;
CLASSPATH=C:\Oracle\Ora81\lib;c:\mysql\xyz.jar;
And you want to add (append to already existing values) your jdk PATH and CLASSPATH
For windows set it as
PATH=%PATH%;C:\jdk1.3\bin;
CLASSPATH=%CLASSPATH%;C:\jdk1.3\lib;
Here,
%PATH% is a variable name that stores the value C:\Oracle\Ora81\bin;
And
 %CLASSPATH% is a variable name that stores the value C:\Oracle\Ora81\lib;c:\mysql\xyz.jar;

So when you check what is the path value for the current DOS PROMPT window just type
C:\>PATH and press enter,
       the console will show something like this
PATH= C:\Oracle\Ora81\bin;C:\jdk1.3\bin;
And to check classpath issue the next command
C:\>echo %classpath% and press enter,
this time console will show
CLASSPATH=C:\Oracle\Ora81\lib;c:\mysql\xyz.jar;C:\jdk1.3\lib;

This done you can begin to compile and excute your codes now.

2) SET THROUGH BATCH FILE (Temporary Action)

So you are a lazy bum who is not interested to type set Path and set Classpath every time you open a command prompt,  and still not ready to make changes in System Environment Settings What you can do is to make a simple batch file which will set path and classpath for you. Open a notepad and type the same lines as I have shown above for setting path and classpath, save the file as setMyClasspath.bat (or whatever name you fancy… as long as it has a .bat extension)

The batch file will look as shown here :


@echo Off
echo Setting PATH AND CLASSPATH               
echo *******************************************
SET PATH=%PATH%;C:\jdk1.3\bin;
SET CLASSPATH=%CLASSPATH%;C:\jdk1.3\lib;
echo Setting PATH AND CLASSPATH DONE
echo *******************************************
echo Current Settings ARE
echo ...........................................
Path
echo -------------------------------------------
echo CLASSPATH= %classpath%
echo -------------------------------------------
echo start compiling or running your code now..... :-)

In this batch file you can remove all the echo statements ( I put them for checking whats happening where and when ……)

SET PATH=%PATH%;C:\jdk1.3\bin;
SET CLASSPATH=%CLASSPATH%;C:\jdk1.3\lib;
So batch file has been made, now all you got to do is , open a Dos Prompt and type
C:\> setMyClasspath
(if the batch file is stored in C drive or change to whichever directory you created it in)

This time your PATH and CLASSPATH have been set, once again they are temporary ie, once you close the Command Prompt Window, the extra settings are gone. And next time you wish to use it open a new window and blah blah blah….. as before.  

Sample Batch File I created
 

 
Simple isnt it !!!
I recommend it too because you are not fiddling with the System Environment Variables and these settings do not clash with other programs , However if you are so lazy that you don’t want to create even a batch file ……. See next method .

3)Setting In System Environment (Permanent Setting…. Till system crash and reformat)  

There are many ways to reach the system environment, One way is to right click on my Computer at desktop and click on properties. If you didn’t comprehend that look in the image below

 

Click on Properties will open up this screen

Correct now click on Environment Tab to see the screen below

Well Path already has something set to it, so just go to the end in Value textbox, and write C:\jdk1.3\bin; as the last value(anywhere infact, you can write it right in the beginning too, as long as the whole items in the list are separated by a semi-colon ;) Press Set once you are through with PATH.

Similarly find classpath variable in list of System Variables, if it is present append your values as you do for path, if it is not present  then write CLASSPATH in textfield  named  Variable and write the value for classpath in Value textfield, it will something like what I have captured in screen shown below

 

 

 

And finally press Apply & You have a permanent setting for PATH and CLASSPATH.

Well thats all you really need to do…….
Wishing you a sunny and bright java,
Mail your suggestions/ comments to me at gaurav007_2000@yahoo.com

* And if you want to learn about Linux & Unix env, go to joonsingh by clicking here.
** Please report errors on this page, I never know when or where I goof-up......