bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/ViewerSorter.java

/*******************************************************************************
 * Copyright (c) 2000, 2004 IBM Corporation and others.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *******************************************************************************/
package org.eclipse.jface.viewers;

import java.text.Collator;
import java.util.Arrays;
import java.util.Comparator;

/**
 * A viewer sorter is used by a structured viewer 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 {
    /**
     * 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());
    }

    /**
     * Creates a new viewer sorter, which uses the given collator
     * to sort strings.
     *
     * @param collator the collator to use to sort strings
     */
    public ViewerSorter(Collator collator) {
        this.collator = collator;
    }

    /**
     * Returns the category of the given element. The category is a
     * number used to allocate elements to bins; the bins are arranged
     * in ascending numeric order. The elements within a bin are arranged
     * via a second level sort criterion.
     * <p>
     * The default implementation of this framework method returns
     * <code>0</code>. Subclasses may reimplement this method to provide
     * non-trivial categorization.
     * </p>
     *
     * @param element the element
     * @return the category
     */
    public int category(Object element) {
        return 0;
    }

    /**
     * Returns a negative, zero, or positive number depending on whether
     * the first element is less than, equal to, or greater than
     * the second element.
     * <p>
     * The default implementation of this method is based on
     * comparing the elements' categories as computed by the <code>category</code>
     * framework method. Elements within the same category are further 
     * subjected to a case insensitive compare of their label strings, either
     * as computed by the content viewer's label provider, or their 
     * <code>toString</code> values in other cases. Subclasses may override.
     * </p>
     * 
     * @param viewer the viewer
     * @param e1 the first element
     * @param e2 the second element
     * @return a negative number if the first element is less  than the 
     *  second element; the value <code>0</code> if the first element is
     *  equal to the second element; and a positive number if the first
     *  element is greater than the second element
     */
    public int compare(Viewer viewer, Object e1, Object e2) {

        int cat1 = category(e1);
        int cat2 = category(e2);

        if (cat1 != cat2)
            return cat1 - cat2;

        // cat1 == cat2

        String name1;
        String name2;

        if (viewer == null || !(viewer instanceof ContentViewer)) {
            name1 = e1.toString();
            name2 = e2.toString();
        } else {
            IBaseLabelProvider prov = ((ContentViewer) viewer)
                    .getLabelProvider();
            if (prov instanceof ILabelProvider) {
                ILabelProvider lprov = (ILabelProvider) prov;
                name1 = lprov.getText(e1);
                name2 = lprov.getText(e2);
            } else {
                name1 = e1.toString();
                name2 = e2.toString();
            }
        }
        if (name1 == null)
            name1 = "";//$NON-NLS-1$
        if (name2 == null)
            name2 = "";//$NON-NLS-1$
        return collator.compare(name1, name2);
    }

    /**
     * Returns the collator used to sort strings.
     *
     * @return the collator used to sort strings
     */
    public Collator getCollator() {
        return collator;
    }

    /**
     * Returns whether this viewer sorter would be affected 
     * by a change to the given property of the given element.
     * <p>
     * The default implementation of this method returns <code>false</code>.
     * Subclasses may reimplement.
     * </p>
     *
     * @param element the element
     * @param property the property
     * @return <code>true</code> if the sorting would be affected,
     *    and <code>false</code> if it would be unaffected
     */
    public boolean isSorterProperty(Object element, String property) {
        return false;
    }

    /**
     * Sorts the given elements in-place, modifying the given array.
     * <p>
     * The default implementation of this method uses the 
     * java.util.Arrays#sort algorithm on the given array, 
     * calling <code>compare</code> to compare elements.
     * </p>
     * <p>
     * Subclasses may reimplement this method to provide a more optimized implementation.
     * </p>
     *
     * @param viewer the viewer
     * @param elements the elements to sort
     */
    public void sort(final Viewer viewer, Object[] elements) {
        Arrays.sort(elements, new Comparator() {
            public int compare(Object a, Object b) {
                return ViewerSorter.this.compare(viewer, a, b);
            }
        });
    }
}