How to write the java interpreter/lexical analyzer

Question

How to write For 1 data type, integer, and the only identifiers are single letter (i.e. there are only 26 possible identifiers).

not case sensitive have white space (blank characters, tab characters, and end of line characters) between every lexeme.see this

Answer 1

There's a great NLP engine called OpenNLP written in Java.

Take a look over there code, you'll learn a lot.