The SynthSliderUI class invokes the paintTrack method even though the "paintTrack" property of a slider component being painted was set to false. The spec on the JSlider.html#setPaintTrack(boolean) says that the method controls whether or not to paint the slider track.

Here is a sample program that demonstrates this:

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import javax.swing.*;
import javax.swing.plaf.synth.*;
import java.awt.*;

public class Test {

    public static void main(String[] args) throws Exception {
        SwingUtilities.invokeAndWait(new Runnable() {
            @Override
            public void run() {
                runTest();
            }
        });
    }

    private static void runTest() {
        try {
            UIManager.setLookAndFeel(new SynthLookAndFeel());
        } catch (UnsupportedLookAndFeelException e) {
            throw new RuntimeException(e);
        }
        JSlider slider = new JSlider();
        slider.setPaintTrack(false);
        slider.setUI(new SynthSliderUI(slider) {

            @Override
            protected void paintTrack(SynthContext context, Graphics g,
                    Rectangle trackBounds) {
                super.paintTrack(context, g, trackBounds);
                System.out.println("paintTrack called");
            }

        });
        JFrame jFrame = new JFrame();
        jFrame.getContentPane().add(slider);
        jFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        jFrame.pack();
        jFrame.setVisible(true);
    }
}
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