Question

我开始使用Jena（使用com.hp.hpl.jena），我遇到了一个奇怪的问题。

我正在使用示例本体，其中Expert有一个Name作为字符串文字和Research es。我想使用Expert列出OntClass.listDeclaredProperties()的属性，但会产生NullPointerException。以下是代码示例：

        OntClass expert = model.getOntClass(ONTOLOGY_URL + "Expert");
        Iterator it = expert.listInstances();

        // print out the instances of the Expert class
        while (it.hasNext()) {
            Individual oi = (Individual) it.next();
            System.out.println(oi.getLocalName());

            //get the properties of the instances of the Expert class
            Iterator ipp = expert.listDeclaredProperties(false); // NPE here
            while (ipp.hasNext()) {
                OntProperty p = (OntProperty) ipp.next();
                //print out property name and its values
                System.out.println(p.getLocalName());

                for (Iterator ivv = oi.listPropertyValues(p); ivv.hasNext();) {
                    String valuename = ivv.next().toString();
                    System.out.println(valuename);
                }
            }
        }

这是完整的堆栈跟踪：

Exception in thread "main" java.lang.NullPointerException
    at com.hp.hpl.jena.ontology.impl.OntClassImpl.testDomain(OntClassImpl.java:940)
    at com.hp.hpl.jena.ontology.impl.OntClassImpl.hasDeclaredProperty(OntClassImpl.java:628)
    at com.richou.jenasandbox.client.Main.getProperty(Main.java:68)
    at com.richou.jenasandbox.client.Main.main(Main.java:50)

任何可能出错的想法？

NPE on hasDeclaredProperty与Jena 2

0 个答案: