Question

I read in a tutorial that when you do something like that :

SimpleNode Program() #Program : {} 
{
    (Class_decl())* <EOF>

    { return jjtThis; }
}

it should create a Programm class which inherits from SimpleNode (once you compile with jjtree), but in my case it doesn’t create such as class. Do I have to create it myself or am I missing something ?

Thanks

Answer 1

Are you first using jjtree on your grammar (before javacc)? It works fine with me:

file: Test.jjt

options {
  MULTI=true;
  NODE_PREFIX="";
}

PARSER_BEGIN(Test)
public class Test {
  public static void main(String[] args) throws Exception {
    Test parser = new Test(new java.io.StringReader("class A; class B;"));
    SimpleNode root = parser.Program();
    root.dump("");
  }
}
PARSER_END(Test)

TOKEN :
{
     < CLASS : "class" >
  |  < SCOL  : ";" >
  |  < ID    : (["a"-"z","A"-"Z"])+ >
}

SKIP :
{
  " " | "\t" | "\r" | "\n"
}

SimpleNode Program() #Program : 
{} 
{
  (Class_decl())* <EOF> {return jjtThis;}
}

void Class_decl() #ClassDecl :
{}
{    
  <CLASS> <ID> <SCOL>
}

And then the commands:

jjtree Test.jjt
javacc Test.jj

which generates the following Java source files:

ClassDecl.java
JJTTestState.java
Node.java
Program.java
SimpleNode.java
TestTreeConstants.java

And both ClassDecl and Program extend SimpleNode:

/* Generated By:JJTree: Do not edit this line. Program.java Version 4.3 */
/* JavaCCOptions:MULTI=true,NODE_USES_PARSER=false,VISITOR=false,TRACK_TOKENS=false,NODE_PREFIX=,NODE_EXTENDS=,NODE_FACTORY=,SUPPORT_CLASS_VISIBILITY_PUBLIC=true */
public
class Program extends SimpleNode {
  ...
}

/* Generated By:JJTree: Do not edit this line. ClassDecl.java Version 4.3 */
/* JavaCCOptions:MULTI=true,NODE_USES_PARSER=false,VISITOR=false,TRACK_TOKENS=false,NODE_PREFIX=,NODE_EXTENDS=,NODE_FACTORY=,SUPPORT_CLASS_VISIBILITY_PUBLIC=true */
public
class ClassDecl extends SimpleNode {
  ...
}

Compiling all source files and running the Test class:

javac -cp . *.java
java -cp . Test

which will print:

Program
 ClassDecl
 ClassDecl

(i.e. Program is the root with two ClassDecl children)

Tested with Java Compiler Compiler Version 5.0.