With and extent set if you select JSlider knob and use the keyboard (Left, Right, Home, End, PgUp, PgDn keys) to move the knob,
you can not reach slider's label that corresponds with a value greater then 80, but you can reach further knob positions using the mouse.

I would expect the slider to act the same, regardless of the input device.

JCK Test Failure:
api/javax_swing/interactive/JSliderTests.html#JSlider


Sample Code:

import javax.swing.*;
import javax.swing.event.*;
import java.awt.*;

public class test extends JFrame {
    JSlider aSlider;

    public test() {
        super("JSlider test (Extent=20)");
        aSlider = new JSlider(0);
        aSlider.setMajorTickSpacing(10);
        aSlider.setExtent(20);
        aSlider.setPaintLabels(true);
        aSlider.setPaintTicks(true);
        getContentPane().add(aSlider,BorderLayout.CENTER);
        aSlider.addChangeListener(new ChangeListener() {
          public void stateChanged(ChangeEvent e) {
              setTitle("Extent="+aSlider.getExtent()+", Value="+aSlider.getValue()); }
         });
    }

    public static void main(String[] args) {
        JFrame frame = new test();
        frame.setSize(new Dimension(300,100));
        frame.setVisible(true);
    }
}