How to make structure in JNA?

Question

I get this error when i run the code below;

Exception in thread "AWT-EventQueue-0" java.lang.Error: Structure.getFieldOrder() on class javaapplication2.NewJFrame$APPBARDATA returns names ([cbSize, hWnd, jCallbackMessage, jEdge, rc, sParam]) which do not match declared field names ([])
    at com.sun.jna.Structure.getFields(Structure.java:872)
    at com.sun.jna.Structure.deriveLayout(Structure.java:983)
    at com.sun.jna.Structure.calculateSize(Structure.java:908)
    at com.sun.jna.Structure.calculateSize(Structure.java:896)
    at com.sun.jna.Structure.allocateMemory(Structure.java:357)
    at com.sun.jna.Structure.<init>(Structure.java:191)
    at com.sun.jna.Structure.<init>(Structure.java:180)
    at com.sun.jna.Structure.<init>(Structure.java:167)
    at com.sun.jna.Structure.<init>(Structure.java:159)
    at javaapplication2.NewJFrame$APPBARDATA.<init>(NewJFrame.java:31)
    at javaapplication2.NewJFrame.<init>(NewJFrame.java:56)
    at javaapplication2.NewJFrame$7.run(NewJFrame.java:255)
    at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:251)
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:721)
    at java.awt.EventQueue.access$200(EventQueue.java:103)
    at java.awt.EventQueue$3.run(EventQueue.java:682)
    at java.awt.EventQueue$3.run(EventQueue.java:680)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:691)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:242)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:161)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:150)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:146)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:138)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:91)

my class:

class APPBARDATA extends Structure {

    WinUser.DWORD cbSize;
    WinUser.HWND hWnd;
    WinUser.UINT_PTR uCallbackMessage;
    WinUser.UINT_PTR uEdge;
    WinUser.RECT rc;
    WinUser.LPARAM lParam;

    @Override
    protected List getFieldOrder() {
        return Arrays.asList(new String[]{"cbSize", "hWnd", "uCallbackMessage", "uEdge", "rc", "lParam"});
    }
}

    APPBARDATA pdata = new APPBARDATA();
    pdata.lParam = new WinUser.LPARAM(0);
    pdata.cbSize = new WinUser.DWORD(32);
    pdata.hWnd = WinUser.HWND_BROADCAST;

What is wrong?

Answer 1

Flag your attributes as public because as specified in the doc, JNA use class.getFields() to obtain the list of attributes.

Javadoc of Class.getFields():

Returns an array containing Field objects reflecting all the accessible public fields of the class or interface represented by this Class object. ...