How to use Slider in SWT

[Java Tip]

import org.eclipse.swt.SWT;
import org.eclipse.swt.layout.GridData;
import org.eclipse.swt.layout.GridLayout;
import org.eclipse.swt.widgets.Display;
import org.eclipse.swt.widgets.Event;
import org.eclipse.swt.widgets.Label;
import org.eclipse.swt.widgets.Listener;
import org.eclipse.swt.widgets.Shell;
import org.eclipse.swt.widgets.Slider;
import org.eclipse.swt.widgets.Text;

public class SampleSlider {
  Display display = new Display();
  Shell shell = new Shell(display);

  Slider slider;
  Text value;
  public SampleSlider() {
    shell.setLayout(new GridLayout(1, true));
    Label label = new Label(shell, SWT.NULL);
    label.setText("Volume:");
    slider = new Slider(shell, SWT.VERTICAL);
    slider.setBounds(0, 0, 40, 200);
    slider.setMaximum(24);
    slider.setMinimum(0);
    slider.setIncrement(1);
    slider.setPageIncrement(5);
    slider.setThumb(4);
    slider.addListener(SWT.Selection, new Listener() {
      public void handleEvent(Event event) {
        int perspectiveValue = slider.getMaximum() - slider.getSelection() + slider.getMinimum() - slider.getThumb();
        value.setText("Vol: " + perspectiveValue);
      }
    });
    value = new Text(shell, SWT.BORDER | SWT.SINGLE);

    value.setEditable(false);
    slider.setLayoutData(new GridData(GridData.HORIZONTAL_ALIGN_CENTER));
    value.setLayoutData(new GridData(GridData.HORIZONTAL_ALIGN_CENTER));

    shell.pack();
    shell.open();
    //textUser.forceFocus();

    // Set up the event loop.
    while (!shell.isDisposed()) {
      if (!display.readAndDispatch()) {
        // If no more entries in event queue
        display.sleep();
      }
    }

    display.dispose();
  }

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