- /*
- * Copyright 2001-2004 The Apache Software Foundation
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- * http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
- package org.apache.commons.collections.comparators;
-
- import java.io.Serializable;
- import java.util.Comparator;
-
- /**
- * A {@link Comparator Comparator} that compares
- * {@link Comparable Comparable} objects.
- * <p />
- * This Comparator is useful, for example,
- * for enforcing the natural order in custom implementations
- * of SortedSet and SortedMap.
- * <p />
- * Note: In the 2.0 and 2.1 releases of Commons Collections,
- * this class would throw a {@link ClassCastException} if
- * either of the arguments to {@link #compare(Object, Object) compare}
- * were <code>null</code>, not {@link Comparable Comparable},
- * or for which {@link Comparable#compareTo(Object) compareTo} gave
- * inconsistent results. This is no longer the case. See
- * {@link #compare(Object, Object) compare} for details.
- *
- * @since Commons Collections 2.0
- * @version $Revision: 1.15 $ $Date: 2004/05/15 13:24:11 $
- *
- * @author Henri Yandell
- *
- * @see java.util.Collections#reverseOrder()
- */
- public class ComparableComparator implements Comparator, Serializable {
-
- /** Serialization version. */
- private static final long serialVersionUID=-291439688585137865L;
-
- /** The singleton instance. */
- private static final ComparableComparator instance = new ComparableComparator();
-
- //-----------------------------------------------------------------------
- /**
- * Gets the singleton instance of a ComparableComparator.
- * <p>
- * Developers are encouraged to use the comparator returned from this method
- * instead of constructing a new instance to reduce allocation and GC overhead
- * when multiple comparable comparators may be used in the same VM.
- *
- * @return the singleton ComparableComparator
- */
- public static ComparableComparator getInstance() {
- return instance;
- }
-
- //-----------------------------------------------------------------------
- /**
- * Constructor whose use should be avoided.
- * <p>
- * Please use the {@link #getInstance()} method whenever possible.
- */
- public ComparableComparator() {
- super();
- }
-
- //-----------------------------------------------------------------------
- /**
- * Compare the two {@link Comparable Comparable} arguments.
- * This method is equivalent to:
- * <pre>((Comparable)obj1).compareTo(obj2)</pre>
- *
- * @param obj1 the first object to compare
- * @param obj2 the second object to compare
- * @return negative if obj1 is less, positive if greater, zero if equal
- * @throws NullPointerException when <i>obj1</i> is <code>null</code>,
- * or when <code>((Comparable)obj1).compareTo(obj2)</code> does
- * @throws ClassCastException when <i>obj1</i> is not a <code>Comparable</code>,
- * or when <code>((Comparable)obj1).compareTo(obj2)</code> does
- */
- public int compare(Object obj1, Object obj2) {
- return ((Comparable)obj1).compareTo(obj2);
- }
-
- //-----------------------------------------------------------------------
- /**
- * Implement a hash code for this comparator that is consistent with
- * {@link #equals(Object) equals}.
- *
- * @return a hash code for this comparator.
- * @since Commons Collections 3.0
- */
- public int hashCode() {
- return "ComparableComparator".hashCode();
- }
-
- /**
- * Returns <code>true</code> iff <i>that</i> Object is
- * is a {@link Comparator Comparator} whose ordering is
- * known to be equivalent to mine.
- * <p>
- * This implementation returns <code>true</code>
- * iff <code><i>object</i>.{@link Object#getClass() getClass()}</code>
- * equals <code>this.getClass()</code>.
- * Subclasses may want to override this behavior to remain consistent
- * with the {@link Comparator#equals(Object)} contract.
- *
- * @param object the object to compare with
- * @return true if equal
- * @since Commons Collections 3.0
- */
- public boolean equals(Object object) {
- return (this == object) ||
- ((null != object) && (object.getClass().equals(this.getClass())));
- }
-
- }