Your main must ensure that there is one and only one argument (args). If there are none or more than 1, it must print an appropriate error message and exit. That one argument will be considered as a filename. Your main must then use Files.ReadAllLines to read all of the lines from the file denoted by filename. Your main must instantiate one instance of your Lexer class (to be defined below). You must parse all lines using the lex method of the Lexer class (calling it repeatedly). If lex throws an exception, you must catch the exception, print that there was an exception. You must then print each token out (this is a temporary step to show that it works) once the lexing is complete.

One file must be called Token.java. This file must contain a Token class. The token class is made up of an instance of an enum (tokenType) and a value string. There must be a public accessor for both the enum and the value string; the underlying variables must be private. You may create whatever constructors you choose. The enum must be defined as containing values appropriate to what we will be processing. The definition of the enum should be public, but the instance inside Token must be private. We will add to this enum in the next several assignments. You will find it helpful to create an appropriate ToString overload. The enum should be inside the Token class so you will reference it as: token.tokenType.WORD

The Lexer class must contain a lex method that accepts a single string and returns nothing. The lex method must use one or more state machine(s) to iterate over the input string and create appropriate Tokens. Any character not allowed by your state machine(s) should throw an exception. The lexer needs to accumulate characters for some types (consider 123 we need to accumulate 1, then 2, then 3, then the state machine can tell that the number is complete because the next character is not a number). You may not use regular expressions to do your lexical analysis you must build your own state machine(s).