Re: [jgrapht-users] NullPointerException in DOTExporter

[John S. <js...@gm...>]

This is due to a regression which slipped into the last release.  The
fix is already in svn, and will be included in the next release.

JVS

On Mon, Feb 21, 2011 at 6:40 PM, Aleksandar Dimitrov
<ale...@go...> wrote:
> Dear jgrapht users and devs,
>
> I believe I've hit a bug, but maybe it's just me overlooking something in the
> docs or my own code.
>
> I would like to render my graphs to the DOT format, with labelled arcs and
> vertices. However, every time I attempt to do that, I receive a Null pointer
> exception from jgrapht:
>
>> Caused by: java.lang.NullPointerException
>>       at org.jgrapht.ext.DOTExporter.renderAttributes(Unknown Source)
>>       at org.jgrapht.ext.DOTExporter.export(Unknown Source)
>
> The code for my dotexporter looks something like this:
>
>
>> final DOTExporter<String,String> dotex = new DOTExporter<String,String>
>>       ( new IntegerNameProvider<String>()
>>       , new VertexNameProvider<String>() { private int i = 0;
>>               public String getVertexName(String t) { i++;return i+t; } }
>>       , null);
>
> The integer variable is there to guarantee uniqueness. The documentation for
> StringVertexNameProvider<V> seemed to require .toString of V to generate
> something unique. I'm familiar with the DOT language, and I believe this would
> only be relevant for the unique ID (which, in my case, IntegerNameProvider
> covers well.) I did leave it in, though, since I only intend the graphs to be
> used for debugging. But they're complex graphs, I'd like to see them properly
> displayed.
>
> The above code is running *inside* an Apache UIMA analysis engine. I doubt that
> this would have anything to do with the error. Removing the VertexNameProvider
> and substituting null for it works. The same happens with the EdgeNameProvider.
>
> I'm using the version jgrapht-jdk1.6-0.8.2 (at least, that's what my JAR file is
> called :-)
>
> I know that this is painfully little debugging information, and I haven't yet
> isolated a runnable minimal case. Unfortunately, I'm rather busy today, and
> probably tomorrow. I'll try to provide further information if needed to
> reproduce the problem later this week.
>
> Thank you in advance (and for writing a really neat library!)
> Aleks
>
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