Copying from Collections to Lang

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/lang/trunk@1154831 13f79535-47bb-0310-9956-ffa450edef68

src/main/java/org/apache/commons/lang3/compare/ReverseComparator.java

@@ -0,0 +1,126 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You 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;
+
+import org.apache.commons.collections.ComparatorUtils;
+
+/**
+ * Reverses the order of another comparator by reversing the arguments
+ * to its {@link #compare(Object, Object) compare} method.
+ *
+ * @since Commons Collections 2.0
+ * @version $Revision$ $Date$
+ *
+ * @author Michael A. Smith
+ *
+ * @see java.util.Collections#reverseOrder()
+ */
+public class ReverseComparator<E> implements Comparator<E>, Serializable {
+
+    /** Serialization version from Collections 2.0. */
+    private static final long serialVersionUID = 2858887242028539265L;
+
+    /** The comparator being decorated. */
+    private final Comparator<E> comparator;
+
+    //-----------------------------------------------------------------------
+    /**
+     * Creates a comparator that compares objects based on the inverse of their
+     * natural ordering.  Using this Constructor will create a ReverseComparator
+     * that is functionally identical to the Comparator returned by
+     * java.util.Collections.<b>reverseOrder()</b>.
+     * 
+     * @see java.util.Collections#reverseOrder()
+     */
+    public ReverseComparator() {
+        this(null);
+    }
+
+    /**
+     * Creates a comparator that inverts the comparison
+     * of the given comparator.  If you pass in <code>null</code>,
+     * the ReverseComparator defaults to reversing the
+     * natural order, as per 
+     * {@link java.util.Collections#reverseOrder()}</b>.
+     * 
+     * @param comparator Comparator to reverse
+     */
+    @SuppressWarnings("unchecked")
+    public ReverseComparator(Comparator<E> comparator) {
+        this.comparator = comparator == null ? ComparatorUtils.NATURAL_COMPARATOR : comparator;
+    }
+
+    //-----------------------------------------------------------------------
+    /**
+     * Compares two objects in reverse order.
+     * 
+     * @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
+     */
+    public int compare(E obj1, E obj2) {
+        return comparator.compare(obj2, obj1);
+    }
+
+    //-----------------------------------------------------------------------
+    /**
+     * Implement a hash code for this comparator that is consistent with
+     * {@link #equals(Object) equals}.
+     * 
+     * @return a suitable hash code
+     * @since Commons Collections 3.0
+     */
+    @Override
+    public int hashCode() {
+        return "ReverseComparator".hashCode() ^ comparator.hashCode();
+    }
+
+    /**
+     * Returns <code>true</code> iff <i>that</i> Object is 
+     * is a {@link 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>, and the underlying 
+     * comparators are equal.
+     * Subclasses may want to override this behavior to remain consistent
+     * with the {@link Comparator#equals(Object) equals} contract.
+     * 
+     * @param object  the object to compare to
+     * @return true if equal
+     * @since Commons Collections 3.0
+     */
+    @Override
+    public boolean equals(Object object) {
+        if (this == object) {
+            return true;
+        }
+        if (null == object) {
+            return false;
+        }
+        if (object.getClass().equals(this.getClass())) {
+            ReverseComparator<?> thatrc = (ReverseComparator<?>) object;
+            return comparator.equals(thatrc.comparator);
+        }
+        return false;
+    }
+
+}