Bug 128298 ViewerSorter.compare() does not need to be overridden from superclass
The ViewerComparator class was added as a superclass of ViewerSorter (for ICU4J). ViewerSorter overrides compare() from ViewerComparator, but this is not necessary if in the superclass implementation getComparator().compare() is called, instead of comparator.compare().
bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/ViewerSorter.java
* A viewer sorter is used by a {@link StructuredViewer} to reorder the elements 
 * provided by its content provider.
 * <p>
 * The default <code>compare</code> method compares elements using two steps. 
 * The first step uses the values returned from <code>category</code>. 
 * By default, all elements are in the same category. 
 * The second level is based on a case insensitive compare of the strings obtained 
 * from the content viewer's label provider via <code>ILabelProvider.getText</code>.
 * </p>
 * <p>
 * Subclasses may implement the <code>isSorterProperty</code> method;
 * they may reimplement the <code>category</code> method to provide 
 * categorization; and they may override the <code>compare</code> methods
 * to provide a totally different way of sorting elements.
 * </p>
 * @see IStructuredContentProvider
 * @see StructuredViewer
 */
public class ViewerSorter extends ViewerComparator{
    /**
     * The collator used to sort strings.
     */
    protected Collator collator;
    /**
     * Creates a new viewer sorter, which uses the default collator
     * to sort strings.
     */
    public ViewerSorter() {
        this(Collator.getInstance());
    }