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	/*
	* 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;

	import org.apache.commons.collections4.ComparatorUtils;

	/**
	* A Comparator that will compare nulls to be either lower or higher than
	* other objects.
	*
	* @param <E> the type of objects compared by this comparator
	* @since 2.0
	*/
	public class NullComparator<E> implements Comparator<E>, Serializable {

	/** Serialization version. */
	private static final long serialVersionUID = -5820772575483504339L;

	/**
	* The comparator to use when comparing two non-<code>null</code> objects.
	**/
	private final Comparator<? super E> nonNullComparator;

	/**
	* Specifies whether a <code>null</code> are compared as higher than
	* non-<code>null</code> objects.
	**/
	private final boolean nullsAreHigh;

	//-----------------------------------------------------------------------
	/**
	* Construct an instance that sorts <code>null</code> higher than any
	* non-<code>null</code> object it is compared with. When comparing two
	* non-<code>null</code> objects, the {@link ComparableComparator} is
	* used.
	**/
	public NullComparator() {
	this(ComparatorUtils.NATURAL_COMPARATOR, true);
	}

	/**
	* Construct an instance that sorts <code>null</code> higher than any
	* non-<code>null</code> object it is compared with. When comparing two
	* non-<code>null</code> objects, the specified {@link Comparator} is
	* used.
	*
	* @param nonNullComparator the comparator to use when comparing two
	* non-<code>null</code> objects. This argument cannot be
	* <code>null</code>
	*
	* @throws NullPointerException if <code>nonNullComparator</code> is
	* <code>null</code>
	**/
	public NullComparator(final Comparator<? super E> nonNullComparator) {
	this(nonNullComparator, true);
	}

	/**
	* Construct an instance that sorts <code>null</code> higher or lower than
	* any non-<code>null</code> object it is compared with. When comparing
	* two non-<code>null</code> objects, the {@link ComparableComparator} is
	* used.
	*
	* @param nullsAreHigh a <code>true</code> value indicates that
	* <code>null</code> should be compared as higher than a
	* non-<code>null</code> object. A <code>false</code> value indicates
	* that <code>null</code> should be compared as lower than a
	* non-<code>null</code> object.
	**/
	public NullComparator(final boolean nullsAreHigh) {
	this(ComparatorUtils.NATURAL_COMPARATOR, nullsAreHigh);
	}

	/**
	* Construct an instance that sorts <code>null</code> higher or lower than
	* any non-<code>null</code> object it is compared with. When comparing
	* two non-<code>null</code> objects, the specified {@link Comparator} is
	* used.
	*
	* @param nonNullComparator the comparator to use when comparing two
	* non-<code>null</code> objects. This argument cannot be
	* <code>null</code>
	*
	* @param nullsAreHigh a <code>true</code> value indicates that
	* <code>null</code> should be compared as higher than a
	* non-<code>null</code> object. A <code>false</code> value indicates
	* that <code>null</code> should be compared as lower than a
	* non-<code>null</code> object.
	*
	* @throws NullPointerException if <code>nonNullComparator</code> is
	* <code>null</code>
	**/
	public NullComparator(final Comparator<? super E> nonNullComparator, final boolean nullsAreHigh) {
	this.nonNullComparator = nonNullComparator;
	this.nullsAreHigh = nullsAreHigh;

	if (nonNullComparator == null) {
	throw new NullPointerException("null nonNullComparator");
	}
	}

	//-----------------------------------------------------------------------
	/**
	* Perform a comparison between two objects. If both objects are
	* <code>null</code>, a <code>0</code> value is returned. If one object
	* is <code>null</code> and the other is not, the result is determined on
	* whether the Comparator was constructed to have nulls as higher or lower
	* than other objects. If neither object is <code>null</code>, an
	* underlying comparator specified in the constructor (or the default) is
	* used to compare the non-<code>null</code> objects.
	*
	* @param o1 the first object to compare
	* @param o2 the object to compare it to.
	* @return <code>-1</code> if <code>o1</code> is "lower" than (less than,
	* before, etc.) <code>o2</code>; <code>1</code> if <code>o1</code> is
	* "higher" than (greater than, after, etc.) <code>o2</code>; or
	* <code>0</code> if <code>o1</code> and <code>o2</code> are equal.
	**/
	@Override
	public int compare(final E o1, final E o2) {
	if(o1 == o2) { return 0; }
	if(o1 == null) { return this.nullsAreHigh ? 1 : -1; }
	if(o2 == null) { return this.nullsAreHigh ? -1 : 1; }
	return this.nonNullComparator.compare(o1, o2);
	}

	//-----------------------------------------------------------------------
	/**
	* Implement a hash code for this comparator that is consistent with
	* {@link #equals(Object)}.
	*
	* @return a hash code for this comparator.
	**/
	@Override
	public int hashCode() {
	return (nullsAreHigh ? -1 : 1) * nonNullComparator.hashCode();
	}

	/**
	* Determines whether the specified object represents a comparator that is
	* equal to this comparator.
	*
	* @param obj the object to compare this comparator with.
	*
	* @return <code>true</code> if the specified object is a NullComparator
	* with equivalent <code>null</code> comparison behavior
	* (i.e. <code>null</code> high or low) and with equivalent underlying
	* non-<code>null</code> object comparators.
	**/
	@Override
	public boolean equals(final Object obj) {
	if(obj == null) { return false; }
	if(obj == this) { return true; }
	if(!obj.getClass().equals(this.getClass())) { return false; }

	final NullComparator<?> other = (NullComparator<?>) obj;

	return this.nullsAreHigh == other.nullsAreHigh &&
	this.nonNullComparator.equals(other.nonNullComparator);
	}

	}

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