I just created a demo with a JSlider and using the basic Synth LAF, and I can confirm that setting those properties appears to have no effect at all, which is odd, and very annoying too.
I have looked at SynthSliderUI and I can see the protected boolean paintValue being set in private void updateStyle(JSlider c), so if you were to make a custom extension this class, set the value of paintValue to false, and then set your slider's UI to the new UI with setUI(), you might get closer. Either that, or completely override the paint methods, copying code out of the original but removing the part that paints the thumb value.
Now, SynthSliderUI itself is package-private, but that isn't really the issue anyway since you're using a client-provided LAF. If their custom slider UI class is public and non-final, you can make a hacked version as I described above, and apply it to your slider.
If it's final, then you might be able to use reflection to change that paintValue field as a last resort (maybe just before painting your slider). The following hack works for me (take out the reflection call that sets the field to false to see the thumb value being painted):
import java.awt.BorderLayout;
import java.lang.reflect.Field;
import javax.swing.JFrame;
import javax.swing.JSlider;
import javax.swing.SwingUtilities;
import javax.swing.UIManager;
public class SliderDemo {
public static void main(String[] args) throws Exception {
UIManager.setLookAndFeel("javax.swing.plaf.synth.SynthLookAndFeel");
Class<?> sliderUIClass = Class.forName("javax.swing.plaf.synth.SynthSliderUI");
final Field paintValue = sliderUIClass.getDeclaredField("paintValue");
paintValue.setAccessible(true);
SwingUtilities.invokeAndWait(new Runnable() {
@Override
public void run() {
JFrame f = new JFrame();
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
f.setLayout(new BorderLayout());
JSlider slider = new JSlider(3, 6, 4);
try {
paintValue.set(slider.getUI(), false);
} catch (Exception e) {
throw new RuntimeException(e);
}
f.add(slider, BorderLayout.CENTER);
f.pack();
f.setVisible(true);
}
});
}
}
