/*
 * 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.collections4.comparators;

import java.io.Serializable;
import java.util.Comparator;

A Comparator that compares Comparable objects. 
 This Comparator is useful, for example, for enforcing the natural order in custom implementations of SortedSet and SortedMap. 
 Note: In the 2.0 and 2.1 releases of Commons Collections, this class would throw a ClassCastException if either of the arguments to compare were null, not Comparable, or for which compareTo gave inconsistent results. This is no longer the case. See compare for details. 
Type parameters:
<E> – the type of objects compared by this comparator
See Also:
Collections.reverseOrder()
Since:
2.0/**
 * 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 {@link java.util.SortedSet SortedSet} and
 * {@link java.util.SortedMap SortedMap}.
 * </p>
 * <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.
 * </p>
 *
 * @param <E> the type of objects compared by this comparator
 *
 * @since 2.0
 * @see java.util.Collections#reverseOrder()
 */
public class ComparableComparator<E extends Comparable<? super E>> implements Comparator<E>, Serializable {

    
Serialization version. /** Serialization version. */
    private static final long serialVersionUID=-291439688585137865L;

    
The singleton instance. /** The singleton instance. */
    @SuppressWarnings("rawtypes")
    public static final ComparableComparator INSTANCE = new ComparableComparator();

    //-----------------------------------------------------------------------
    
Gets the singleton instance of a ComparableComparator.

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.
Type parameters:
<E> –  the element type
Returns:
the singleton ComparableComparator
Since:
4.0/**
     * 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.
     *
     * @param <E>  the element type
     * @return the singleton ComparableComparator
     * @since 4.0
     */
    public static <E extends Comparable<? super E>> ComparableComparator<E> comparableComparator() {
        return INSTANCE;
    }

    //-----------------------------------------------------------------------
    
Constructor whose use should be avoided.
 Please use the comparableComparator() method whenever possible. /**
     * Constructor whose use should be avoided.
     * <p>
     * Please use the {@link #comparableComparator()} method whenever possible.
     */
    public ComparableComparator() {
        super();
    }

    //-----------------------------------------------------------------------
    
Compare the two Comparable arguments. This method is equivalent to: 
((Comparable)obj1).compareTo(obj2)
Params:
obj1 –  the first object to compare
obj2 –  the second object to compare
Throws:
NullPointerException – if obj1 is null,
        or when ((Comparable)obj1).compareTo(obj2) does
ClassCastException – if obj1 is not a Comparable,
        or when ((Comparable)obj1).compareTo(obj2) does
Returns:
negative if obj1 is less, positive if greater, zero if equal/**
     * 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 if <i>obj1</i> is <code>null</code>,
     *         or when <code>((Comparable)obj1).compareTo(obj2)</code> does
     * @throws ClassCastException if <i>obj1</i> is not a <code>Comparable</code>,
     *         or when <code>((Comparable)obj1).compareTo(obj2)</code> does
     */
    @Override
    public int compare(final E obj1, final E obj2) {
        return obj1.compareTo(obj2);
    }

    //-----------------------------------------------------------------------
    
Implement a hash code for this comparator that is consistent with equals. 
Returns:
a hash code for this comparator.
Since:
3.0/**
     * Implement a hash code for this comparator that is consistent with
     * {@link #equals(Object) equals}.
     *
     * @return a hash code for this comparator.
     * @since 3.0
     */
    @Override
    public int hashCode() {
        return "ComparableComparator".hashCode();
    }

    
Returns true iff that Object is is a Comparator whose ordering is known to be equivalent to mine. 
 This implementation returns true iff object.getClass() equals
this.getClass(). Subclasses may want to override this behavior to remain consistent with the Comparator.equals(Object) contract. 
Params:
object –  the object to compare with
Returns:
true if equal
Since:
3.0/**
     * Returns {@code true} 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} 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 {@code true} if equal
     * @since 3.0
     */
    @Override
    public boolean equals(final Object object) {
        return this == object ||
               null != object && object.getClass().equals(this.getClass());
    }

}