Instrumentation of JComponent

Hello everyone,

I am working on a little project to learn how to use the
Instrumentation framework work. I want to append the current class
name in the tooltip of every JComponent. Seems simple enough, right.
So I started by writing a basic ClassFileTransformer that prints every
class name. I also created a very simple GUI to test my transformer.

It all seems to work fine except that it never see the class
JComponent. At some point it prints "javax/swing/JComponent$1" but
never "javax/swing/JComponent". However if I debug my test code, I can
see that if I leave the mouse over the test label, I stop in my
breakpoint in JComponent.getToolTipText(). How is that possible
without loading the JComponent class? Or am I not understanding what's
going on here?

I've copied my source code below. Thanks in advance for your help.

Cheers,

Tom

=== Source code ===

import java.lang.instrument.ClassFileTransformer;
import java.lang.instrument.IllegalClassFormatException;
import java.lang.instrument.Instrumentation;
import java.security.ProtectionDomain;

import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.SwingUtilities;

public class Premain {

    public static void premain(String agentArguments, Instrumentation
instrumentation) {
        instrumentation.addTransformer(new ClassFileTransformer() {
            public byte[] transform(ClassLoader loader,
                                    String className,
                                    Class<?> classBeingRedefined,
                                    ProtectionDomain protectionDomain,
                                    byte[] classfileBuffer)
                    throws IllegalClassFormatException {
                System.out.println(className);
                return classfileBuffer;
            }
            });
    }

    public static void main(String[] args) {
     SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                createAndShowGUI();
            }
        });
    }

    private static void createAndShowGUI() {
        JFrame frame = new JFrame("Test");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        JLabel label = new JLabel("test");
        label.setToolTipText("test");
        frame.getContentPane().add(label);
        frame.pack();
        frame.setVisible(true);
    }

}