public class jena{
        public static String queryname=" ";
        public static void main (String [] argv) {
                String classname="zone";
                queryOnotology(classname);

        }
        public  static void queryOnotology(String name)
        {
                String camNS = "http://www.owl-ontologies.com/Ontology1164867953.owl";

                OntModel m = ModelFactory.createOntologyModel();
                OntDocumentManager dm = m.getDocumentManager();
                dm.addAltEntry( "http://www.owl-ontologies.com/Ontology1164867953.owl",
                                "file:d:/TBT.owl"    );
                //java.lang.String docURI, java.lang.String locationURL)
        //Add an entry for an alternative copy of the document with the given document URI.
                m.read( "http://www.owl-ontologies.com/Ontology1164867953.owl" );
                OntClass camera = m.getOntClass( camNS + name);
                System.out.println(" The qeried class is: "+name+".");
                System.out.println(" And its subclasses is:");
                for (Iterator i = camera.listSubClasses(); i.hasNext(); ) {
                  OntClass c = (OntClass) i.next();
                  String subcalssnames=c.getLocalName()+"  ";
              queryname=queryname+subcalssnames;
                //  System.out.print( c.getLocalName() + " " );
                }
                 System.out.print(queryname);

                 queryname=name+queryname;
        }

}

这是jena简单的一个小程序，用来查询子类的，但是总是演示不成功，错误看不太明白
那位大哥帮我看看，谢谢

错误
java.lang.NullPointerException
 at jenatest.jena.queryOnotology(jena.java:169)
 at jenatest.jena.main(jena.java:152)
The qeried class is: zone.
And its subclasses is:
Exception in thread "main"

以下是引用boltbolt在2007-5-24 10:26:00的发言： import java.util.Iterator; import com.hp.hpl.jena.ontology.OntClass; import com.hp.hpl.jena.ontology.OntDocumentManager; import com.hp.hpl.jena.ontology.OntModel; import com.hp.hpl.jena.rdf.model.ModelFactory; public class jena{          public static String queryname=" ";          public static void main (String [] argv) {                  String classname="zone";                  queryOnotology(classname);          }          public  static void queryOnotology(String name)          {                  String camNS = "http://www.owl-ontologies.com/Ontology1164867953.owl";                  OntModel m = ModelFactory.createOntologyModel();                  OntDocumentManager dm = m.getDocumentManager();                  dm.addAltEntry( "http://www.owl-ontologies.com/Ontology1164867953.owl",                                  "file:d:/TBT.owl"    );                  //java.lang.String docURI, java.lang.String locationURL)          //Add an entry for an alternative copy of the document with the given document URI.                  m.read( "http://www.owl-ontologies.com/Ontology1164867953.owl" );                  OntClass camera = m.getOntClass( camNS + name);                  System.out.println(" The qeried class is: "+name+".");                  System.out.println(" And its subclasses is:");                  for (Iterator i = camera.listSubClasses(); i.hasNext(); ) {                    OntClass c = (OntClass) i.next();                    String subcalssnames=c.getLocalName()+"  ";                queryname=queryname+subcalssnames;                  //  System.out.print( c.getLocalName() + " " );                  }                   System.out.print(queryname);                   queryname=name+queryname;          } } 这是jena简单的一个小程序，用来查询子类的，但是总是演示不成功，错误看不太明白 那位大哥帮我看看，谢谢 错误 java.lang.NullPointerException   at jenatest.jena.queryOnotology(jena.java:169)   at jenatest.jena.main(jena.java:152)   The qeried class is: zone.   And its subclasses is: Exception in thread "main"

--------
The qeried class is: #zone.
And its subclasses is:
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