This problem only appears on machines that don't support Windows L&F, namely any system except Windows.

Run the program to display the NullPointerException:

java.lang.NullPointerException
        at com.sun.java.swing.plaf.windows.WindowsLookAndFeel.uninitialize(Windo
wsLookAndFeel.java:1192)
        at javax.swing.UIManager.setLookAndFeel(UIManager.java:367)
        at javax.swing.UIManager.setLookAndFeel(UIManager.java:403)
        at SimpleTest$SwitchingThread.run(SimpleTest.java:69)
        at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:147)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:421)
        at java.awt.EventDispatchThread.pumpOneEvent(EventDispatchThread.java:13
6)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:122)

        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:118)

        at java.awt.EventDispatchThread.run(EventDispatchThread.java:98)

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

public class SimpleTest extends JFrame {

    private JButton button;

    private final String[] LNFString = {
        "javax.swing.plaf.metal.MetalLookAndFeel",
        "com.sun.java.swing.plaf.motif.MotifLookAndFeel",
        "com.sun.java.swing.plaf.windows.WindowsLookAndFeel"};

    private static int LNFIndex = 0;


    public static void main(String[] args) {
        new SimpleTest();
    }

    public SimpleTest() {
        button = new JButton("Hello");

        getContentPane().add(button);

        setSize(200, 200);
        show();

        while(true) {
            try {
                Thread.sleep(2000);
            } catch(Exception e) {
                e.printStackTrace();
            }

            switchLNF();
        }
    }


    private void switchLNF() {
        waitTillSwitched(this);
    }

    private void waitTillSwitched(Component comp) {
        SwitchingThread rt = new SwitchingThread(comp);

        try {
            SwingUtilities.invokeAndWait(rt);
        } catch(Exception e) {
            e.printStackTrace();
        }
    }

    class SwitchingThread implements Runnable {
        Component display;
 
        public SwitchingThread(Component display) {
            this.display = display;
        }
 
        public void run() {
            boolean changed = false;
 
            while(!changed) {
                LNFIndex++;
                LNFIndex %= LNFString.length;
 
                try {
                    UIManager.setLookAndFeel(LNFString[LNFIndex]);
                } catch(UnsupportedLookAndFeelException e) {
                    changed = false;
                    e.printStackTrace();
                    continue;
                } catch(Exception e) {
                    e.printStackTrace();
                    continue;
                }
                
                changed = true;
            }
               
            SwingUtilities.updateComponentTreeUI(display);
        }
    }
}

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edmund.lou@eng 2000-10-13
Swing Test Developer
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