[antlr-interest] Java Tree Parser: NPE: rulememo == null??

[Randall R Schulz]

On Friday 13 July 2007 16:23, Randall R Schulz wrote:
> Hi,
>
> After a recent round of changes to my tree grammar, most of them in
> parser class methods and other related classes, not the grammar
> itself, the resulting parser is now crashing with an NPE in
> (org.antlr.runtime) BaseRecognizer.memoize(IntStream, int, int). This
> line of code is:
>
>     if ( ruleMemo[ruleIndex]!=null ) { ... }
>
> Exception in thread "main" java.lang.NullPointerException
>         at
> org.antlr.runtime.BaseRecognizer.memoize(BaseRecognizer.java:740)
>
> ... [ other examples of NPE upon access to ruleMemo ] ...

So here's what happend. I added a new constructor to my tree parser that 
takes other parameters (obviously). Here's the problem. The constructor 
supplied by ANTLR looks like this:

  public CLIFBuilder(TreeNodeStream input) {
    super(input);
    ruleMemo = new HashMap[57+1];
  }


Naturally, my constructors don't contain the line that allocates the 
array of HashMaps for ruleMemo.

Is it expressly forbidden to override the constructor of an 
ANTLR-generated parser class? If not, then there needs to be a way to 
handle the need to allocate the ruleMemo array.

At a minimum, there should be some documentation that expresses this 
requirement. If that documentation exists, I couldn't find it.


The solution is simple enough: Where overloaded parser constructors 
might (as mine did) call "super(input)" they should instead 
call "this(input)".


Randall Schulz