The task of translates high level code, i.e., programming languages, into a format that can be understand by a computer - binary code - is the main job of a compiler. Speaking in a simple way, the compiler can be split in 3 parts:

• Lexical Analyzer (LA)
• Syntax Analyzer (SA)
• Semantic Analyzer (SMA)

The Lexical Analyzer is responsible to separate the source code into lexemes, which are the words that compose the code. After separate all lexemes, the LA classify them using Token classification. Keywords, Special Symbols, Identifiers and Operators, are examples of tokens. Remove white spaces and comments of the compiled code is also a role played by the Lexical Analyzer. The output of this process is a table containing the lexemes and their token classification. Lexical errors as invalid constructions of lexemes, e.g. '12variableName', 'na;;me', are also captured by the LA.

This project is an implementation of a simple Lexical Analyzer made in Java. It provides a GUI where the user can type the code and get the tokens of it. It is also possible load the code from a file and make the analysis.

The Lexical Analyzer of this project recognizes the following classes of tokens:

• IDENTIFIER - Variable names;
• STRING - Words between double quotes "";
• INTEGER - Number with no dot ( . );
• FLOAT - Float point numbers;
• PLUS - ( + );
• MINUS - ( - );
• TIMES - ( * ),
• DIVIDE - ( / );
• KEYWORD - for, while, do, if, else, print, switch, case, default and null;
• INVALID;
• ASSIGN_OP - Assignment operator ( = );
• SEMICOLON - ( ; )
• LEFT_PARENTHESIS - '(';
• RIGHT_PARENTHESIS - ')';
• LEFT_BRACE - ( { );
• RIGHT_BRACE - ( } );
• COMMA - ( , );
• DOT - ( . );
• DOTDOT - ( .. );
• COLON - ( : );
• EQUAL - ( == );
• LOWER_OR_EQUALS - ( <= );
• GREATER_OR_EQUALS - ( >= );
• NOT_EQUALS - ( <> );
• GREATER_THAN - ( > );
• LOWER_THAN - ( < );
• AT_SIGN - ( @ ).

P.S. 1: Sentences initiated by // or chunks of sentences between / / are considered comments and are not mentioned in the output.

P.S. 2: The lexemes must be separated by at least one white space(' ') to be recognized as separated things.

This is a very simple example that demonstrates how a Lexical Analyzer can be implemented. This project is also an usage example of Finite-State Automata, a very powerful and useful tool.