Q:

adding classpath in linux

export CLASSPATH=.;../somejar.jar;../mysql-connector-java-5.1.6-bin.jar
java -Xmx500m folder.subfolder../dit1/some.xml
cd ..

is the above statement for setting the classpath to already existing classpath in linux is correct or not

A:

I don't like setting CLASSPATH.  CLASSPATH is a global variable and as such it is evil: 

If you modify it in one script, suddenly some java programs will stop working.  
If you put there the libraries for all the things which you run, and it gets cluttered. 
You get conflicts if two different applications use different versions of the same library. 
There is no performance gain as libraries in the CLASSPATH are not shared - just their name is shared. 
If you put the dot (.)  or any other relative path in the CLASSPATH that means a different thing in each place - that will cause confusion, for sure. 

Therefore the preferred way is to set the classpath per each run of the jvm, for example:
java -Xmx500m -cp ".:../somejar.jar:../mysql-connector-java-5.1.6-bin.jar"    "folder.subfolder../dit1/some.xml

If it gets long the standard procedure is to wrap it in a bash or batch script to save typing.  

A:

It's always advised to never destructively destroy an existing classpath unless you have a good reason. 
The following line preserves the existing classpath and adds onto it. 
export CLASSPATH="$CLASSPATH:foo.jar:../bar.jar"

A:

Important difference between setting Classpath in Windows and Linux is path separator which is ";" (semi-colon) in Windows and ":" (colon) in Linux.  Also %PATH% is used to represent value of existing path variable in Windows while ${PATH} is used for same purpose in Linux (in the bash shell).  Here is the way to setup classpath in Linux:
export CLASSPATH=${CLASSPATH}:/new/path

but as such Classpath is very tricky and you may wonder why your program is not working even after setting correct Classpath.  Things to note:

-cp options overrides CLASSPATH environment variable. 
Classpath defined in Manifest file overrides both -cp and CLASSPATH envorinment variable. 

Reference: How Classpath works in Java.