antlr lexeme value

assembly: instruction* EOF ; 

@parser::members {
  int[] code = new int[ExecuteVM.CODESIZE];    
  private int i = 0;
}

instruction:
        PUSH n = INTEGER {code[i++] = PUSH;
        			  	  code[i++] = Integer.parseInt($n.text);
        }
        
/* Lexer rule */

PUSH		: 'push' ;
INTEGER	 	: '0' | ('-')?(('1'..'9')('0'..'9')*);