The main job of the scanner is to identify and return the next token. The value to be returned includes:
the token "name" (e.g., INTLITERAL). Token names are defined in the file sym.java
the line number in the input file on which the token starts
the number of the character on that line at which the token starts
for identifiers, integer literals, and string literals: the actual value (a String, an int, or a String, respectively)
for a string literal, the value should include the double quotes that surround the string, as well as any backslashes used inside the string as part of an "escaped" character(You can start with simple actions, like printing out some message. Before defining rules, remember that you can define macros (like the provided macros LETTER, DIGIT and WHITESPACE). The action of each rule must return a java_cup.runtime.Symbol object.　There are two constructors for the java_cup.runtime.Symbol class:

Symbol(int tokenNumber): this constructor is used when there is no value associated with the token (like for EOF)
Symbol(int tokenNumber, Object tokenVal): this constructor is used when the token has a value (for example, for an INT token the value is the value of the integer))