Hi Narender,
I don't know a lot about Java and StringBuffer, so I may be misunderstanding your question but I think normal Strings should do it.
aString := 'first part', someStringVariable, 'last part'.
The "," comma will concatenate the strings. Also take a look at the WriteStream class. It is useful for building large strings with less overhead than string concatenation.
stream := WriteStream on: (String new: 1000).
stream nextPutAll: 'first part; nextPutAll: someStringVariable; nextPutAll: 'last part'; cr; cr; tab; nextPutAll: 'some more stuff'.
aString := stream contents.
Lou