undefined reference to vtable

[Shaun Jackman <sjackman at telus dot net>]

I'm writing a C++ program that calls a Java shared library. I'm seeing
undefined references to the vtable for a class defined using C++.

$ make
g++-3.4  -g -O2   -o HelloWorld  HelloWorld.o -lswt -lswt-pi
HelloWorld.o(.text+0x136): In function `main':
/home/sjackman/work/hello/swt-cni/HelloWorld.cc:62: undefined reference to `java::lang::Object::Object()'
HelloWorld.o(.text+0x13e):/home/sjackman/work/hello/swt-cni/HelloWorld.cc:62: undefined reference to `vtable for ShellSelectionListener'
collect2: ld returned 1 exit status
make: *** [HelloWorld] Error 1

I suspect this will be a rather obvious error on my part. In the mean
time, however, I'm stumped.

As an aside, I think it's positively amazing that it's so simple to
write an application in C++ that uses a library written in Java that
had no intention by the authors of ever being used in this manner.
Gcj is absolutely amazing work!

Thanks,
Shaun


[HelloWorld.cc]
#include <org/eclipse/swt/SWT.h>
#include <org/eclipse/swt/events/SelectionEvent.h>
#include <org/eclipse/swt/events/SelectionListener.h>
#include <org/eclipse/swt/layout/RowLayout.h>
#include <org/eclipse/swt/widgets/Button.h>
#include <org/eclipse/swt/widgets/Display.h>
#include <org/eclipse/swt/widgets/Label.h>
#include <org/eclipse/swt/widgets/Menu.h>
#include <org/eclipse/swt/widgets/Shell.h>
#include <gcj/cni.h>
using namespace org::eclipse::swt;
using namespace org::eclipse::swt::events;
using namespace org::eclipse::swt::layout;
using namespace org::eclipse::swt::widgets;
using namespace java::lang;


/** Main shell. */
Shell* shell;


/** Closes the shell. */
class ShellSelectionListener : public SelectionListener
{
	public:
		virtual void widgetSelected( SelectionEvent* event)
		{
			shell->close();
		}
		virtual void widgetDefaultSelected( SelectionEvent*) {}
		static Class class$;
};
Class ShellSelectionListener::class$;


/** Displays "Hello, world!" using SWT. */
int
main()
{
	JvCreateJavaVM( NULL);
	JvAttachCurrentThread( NULL, NULL);

	Display* display = new Display;

	shell = new Shell( display);
	shell->setText( JvNewStringUTF( "Hello"));

	Menu* menu = new Menu( shell, SWT::BAR);
	shell->setMenuBar( menu);

	Label* label = new Label( shell, SWT::NONE);
	label->setText( JvNewStringUTF( "Hello, world!"));

	Button* button = new Button( shell, SWT::PUSH);
	button->setText( JvNewStringUTF( "Ok"));
	button->addSelectionListener( new ShellSelectionListener);

	RowLayout* rowLayout = new RowLayout();
	rowLayout->type = SWT::VERTICAL;

	shell->setLayout( rowLayout);
	shell->open();

	while( !shell->isDisposed()) {
		if( !display->readAndDispatch())
			display->sleep();
	}
	display->dispose();

	JvDetachCurrentThread();
	return 0;
}