Question

I have the Java source code for Parser and Lexer of ANTLR 3 in .java file and want to see the actual grammar behind with all rules and etc.

Is it even possible?

Answer 1

Not by some automated tool (AFAIK). But the generated source file(s) contain the parser and lexer rules of the original grammar in its comments, so you can reverse engineer them yourself reasonable easy.

For example, take this dummy grammar:

grammar T;

parse
 : foo
 | bar
 | OTHER
 ;

foo : INT ;
bar : ALPHA ;

INT   : '0'..'9'+ ;
ALPHA : ('a'..'z' | 'A'..'Z')+ ;
OTHER : . ;

If you generate a lexer and parser from it, the parser would look like this:

public class TParser extends Parser {

    // $ANTLR start "parse"
    // T.g:3:1: parse : ( foo | bar | OTHER );
    public final void parse() throws RecognitionException {
        ...
    }
    // $ANTLR end "parse"

    // $ANTLR start "foo"
    // T.g:9:1: foo : INT ;
    public final void foo() throws RecognitionException {
        ...
    }
    // $ANTLR end "foo"


    // $ANTLR start "bar"
    // T.g:10:1: bar : ALPHA ;
    public final void bar() throws RecognitionException {
        ...
    }
    // $ANTLR end "bar"
}

and the lexer like this:

public class TLexer extends Lexer {

    // $ANTLR start "INT"
    public final void mINT() throws RecognitionException {
        // T.g:12:7: ( ( '0' .. '9' )+ )
        ...
    }
    // $ANTLR end "INT"

    // $ANTLR start "ALPHA"
    public final void mALPHA() throws RecognitionException {
        // T.g:13:7: ( ( 'a' .. 'z' | 'A' .. 'Z' )+ )
        ...
    }
    // $ANTLR end "ALPHA"

    // $ANTLR start "OTHER"
    public final void mOTHER() throws RecognitionException {
        // T.g:14:7: ( . )
        ...
    }
    // $ANTLR end "OTHER"
}

As you can see, all the grammar rules are there inside comments in the .java source files.