Java引用不正确

Question

我使用的是OWL-S (源代码和javadoc在这里：http://on.cs.unibas.ch/owls-api/apidocs/ )

如果我这样做，我就得到了正确的结果：

public class Example {
    private static ISWRLFactory factory; //is a interface
    private string url = "http://...";
    private Service aService;
    private OWLOntology ont;

    void method_A(){
            URI aURI = URI.create(url);
            OWLKnowledgeBase aKB = OWLFactory.createKB();    
            aService = aKB.readService(aURI);
            ont = aKB.createOntology(aURI);
            ont.createService(aService.getURI());

    }

    void method_B(){
    factory = SWRLFactory.createFactory(ont);
    Atom builtAtom = factory.createNotEqual(x, variab); //x and variab are two variable
    }
   }

但如果我这样做，我就得不到正确的结果：

public class Example {
    private static ISWRLFactory factory; //is a interface
    private string url = "http://...";
    private Service aService;
    private OWLOntology ont;


    void method_A(){
            URI aURI = URI.create(url);
            OWLKnowledgeBase aKB = OWLFactory.createKB();    
            aService = aKB.readService(aURI);
            ont = aKB.createOntology(aURI);
            ont.createService(aService.getURI());
            factory = SWRLFactory.createFactory(ont);
    }

    void method_B(){
    Atom builtAtom = factory.createNotEqual(x, variab); //x and variab are two variable
    }
}

为什么？

Answer 1

在method_A()和method_B()中执行“factory = SWRLFactory.createFactory(ont);”行存在差异。您确定在method_A()和method_B()调用之间没有修改“factory”对象吗？'x‘和'variable’对'factory‘有依赖吗？