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Why can't Java polymorphism catch the correct method when choosing between an object and a vector?

I have two similar methods. One is for processing objects, other vectors:

@SuppressWarnings("unused")
private void printRows(PrintWriter out, Vector<?> dataOb, 
        String[] columns, String[] columnType, 
        Hashtable<?, ?> columnAccessors, 
        String trOptions, String tdOptions)
    throws ServletException 
{
    System.out.println("At Printing Rows, Vector...");
    // If the object is a vector, loop through the elements.
        Vector<?> v = (Vector<?>) dataOb;
        Enumeration<?> e = (Enumeration<?>) v.elements();
        while (e.hasMoreElements())
        {
            tryRow(out, e.nextElement(), 
                        columns, columnType, columnAccessors, trOptions, tdOptions);
        }
}

private void printRows(PrintWriter out, Object dataOb, 
        String[] columns, String[] columnType, 
        Hashtable<?, ?> columnAccessors, 
        String trOptions, String tdOptions) 
    throws ServletException 
{
    System.out.println("At Printing Rows, Object...");
    // If the object is an array, loop through the objects.
        Object[] objects = null;
        try {objects = (Object[]) dataOb;}
        catch (Exception e1) { ExceptionToolkit.exceptionHandler (e1, "Can't assign data to objects"); }

        System.out.println("At Printing Rows, have objects...");
        for (Object object: objects)
            {
                System.out.println("At Printing Rows, have objects, looping...");
                tryRow(out, object, columns, columnType, columnAccessors, trOptions, tdOptions); 
            }
}

If I understand Java and polymorphism correctly, if you call a method with a vector, you need to call the first function, but if I call it with something else that is an object, the second method is called.

However, when my program goes to the function call, somehow it becomes wrong, because instead of processing it correctly, I get the following:

CLASS: class hu.flux.models.PersonColumn: name
CLASS: class hu.flux.models.PersonColumn: phone
At Printing Rows, Object...
Can't assign data to objects: java.lang.ClassCastException: java.util.Vector cannot be cast to [Ljava.lang.Object;
java.lang.ClassCastException: java.util.Vector cannot be cast to [Ljava.lang.Object;
    at hu.flux.tables.TableServlet.printRows(TableServlet.java:97)
    at hu.flux.tables.TableServlet.service(TableServlet.java:52)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
    at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:674)
    at org.apache.catalina.core.ApplicationDispatcher.doInclude(ApplicationDispatcher.java:579)
    at org.apache.catalina.core.ApplicationDispatcher.include(ApplicationDispatcher.java:516)
    at org.apache.jasper.runtime.JspRuntimeLibrary.include(JspRuntimeLibrary.java:930)
    at org.apache.jsp.ShowPeople_jsp._jspService(ShowPeople_jsp.java:68)
    at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:68)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
    at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:376)
    at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:320)
    at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:265)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
    at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:674)
    at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:462)
    at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:401)
    at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:329)
    at hu.flux.ControllerServlet.gotoPage(ControllerServlet.java:84)
    at hu.flux.ControllerServlet.service(ControllerServlet.java:47)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:243)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:201)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:163)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:108)
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:556)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:401)
    at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:242)
    at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:267)
    at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:245)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:260)
    at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
    at java.lang.Thread.run(Thread.java:619)
At Printing Rows, have objects...

If I understand stacktrace correctly, it tells me that it fails because dataOb is a vector, but if it is true, should this method not catch the call?

- Java? - ? , , , ? printRows()?

+3
3

, ... , , , , . , printRows...

:

Object x = new Vector();

printRows(..., x);

printRows (..., Object), , , . , . , , , - , .

printRows (..., Object):

if(x instanceof Vector)
{
    printRows(out, (Vector)dataOb);
}
else
{
   ....
}

.

+4

- Java?

. , . , .

+4

, Vector? ?

0

Source: https://habr.com/ru/post/1771427/

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