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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;

	/**
	* A {@link Comparator} for {@link Boolean} objects that can sort either
	* true or false first.
	*
	* @see #getTrueFirstComparator()
	* @see #getFalseFirstComparator()
	* @see #booleanComparator(boolean)
	*
	* @since 3.0
	*/
	public final class BooleanComparator implements Comparator<Boolean>, Serializable {

	/** Serialization version. */
	private static final long serialVersionUID = 1830042991606340609L;

	/** Constant "true first" reference. */
	private static final BooleanComparator TRUE_FIRST = new BooleanComparator(true);

	/** Constant "false first" reference. */
	private static final BooleanComparator FALSE_FIRST = new BooleanComparator(false);

	/** <code>true</code> iff <code>true</code> values sort before <code>false</code> values. */
	private boolean trueFirst = false;

	//-----------------------------------------------------------------------
	/**
	* Returns a BooleanComparator instance that sorts
	* <code>true</code> values before <code>false</code> values.
	* <p>
	* Clients are encouraged to use the value returned from
	* this method instead of constructing a new instance
	* to reduce allocation and garbage collection overhead when
	* multiple BooleanComparators may be used in the same
	* virtual machine.
	* </p>
	*
	* @return the true first singleton BooleanComparator
	*/
	public static BooleanComparator getTrueFirstComparator() {
	return TRUE_FIRST;
	}

	/**
	* Returns a BooleanComparator instance that sorts
	* <code>false</code> values before <code>true</code> values.
	* <p>
	* Clients are encouraged to use the value returned from
	* this method instead of constructing a new instance
	* to reduce allocation and garbage collection overhead when
	* multiple BooleanComparators may be used in the same
	* virtual machine.
	* </p>
	*
	* @return the false first singleton BooleanComparator
	*/
	public static BooleanComparator getFalseFirstComparator() {
	return FALSE_FIRST;
	}

	/**
	* Returns a BooleanComparator instance that sorts
	* <code><i>trueFirst</i></code> values before
	* <code>!<i>trueFirst</i></code> values.
	* <p>
	* Clients are encouraged to use the value returned from
	* this method instead of constructing a new instance
	* to reduce allocation and garbage collection overhead when
	* multiple BooleanComparators may be used in the same
	* virtual machine.
	* </p>
	*
	* @param trueFirst when <code>true</code>, sort
	* <code>true</code> <code>Boolean</code>s before <code>false</code>
	* @return a singleton BooleanComparator instance
	* @since 4.0
	*/
	public static BooleanComparator booleanComparator(final boolean trueFirst) {
	return trueFirst ? TRUE_FIRST : FALSE_FIRST;
	}

	//-----------------------------------------------------------------------
	/**
	* Creates a <code>BooleanComparator</code> that sorts
	* <code>false</code> values before <code>true</code> values.
	* <p>
	* Equivalent to {@link #BooleanComparator(boolean) BooleanComparator(false)}.
	* <p>
	* Please use the static factory instead whenever possible.
	*/
	public BooleanComparator() {
	this(false);
	}

	/**
	* Creates a <code>BooleanComparator</code> that sorts
	* <code><i>trueFirst</i></code> values before
	* <code>!<i>trueFirst</i></code> values.
	* <p>
	* Please use the static factories instead whenever possible.
	*
	* @param trueFirst when <code>true</code>, sort
	* <code>true</code> boolean values before <code>false</code>
	*/
	public BooleanComparator(final boolean trueFirst) {
	this.trueFirst = trueFirst;
	}

	//-----------------------------------------------------------------------
	/**
	* Compares two non-<code>null</code> <code>Boolean</code> objects
	* according to the value of {@link #sortsTrueFirst()}.
	*
	* @param b1 the first boolean to compare
	* @param b2 the second boolean to compare
	* @return negative if obj1 is less, positive if greater, zero if equal
	* @throws NullPointerException when either argument <code>null</code>
	*/
	@Override
	public int compare(final Boolean b1, final Boolean b2) {
	final boolean v1 = b1.booleanValue();
	final boolean v2 = b2.booleanValue();

	return (v1 ^ v2) ? ( (v1 ^ trueFirst) ? 1 : -1 ) : 0;
	}

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

	/**
	* 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>that</i></code> is a {@link BooleanComparator}
	* whose value of {@link #sortsTrueFirst()} is equal to mine.
	*
	* @param object the object to compare to
	* @return true if equal
	*/
	@Override
	public boolean equals(final Object object) {
	return (this == object) \|\|
	((object instanceof BooleanComparator) &&
	(this.trueFirst == ((BooleanComparator)object).trueFirst));
	}

	//-----------------------------------------------------------------------
	/**
	* Returns <code>true</code> iff
	* I sort <code>true</code> values before
	* <code>false</code> values. In other words,
	* returns <code>true</code> iff
	* {@link #compare(Boolean,Boolean) compare(Boolean.FALSE,Boolean.TRUE)}
	* returns a positive value.
	*
	* @return the trueFirst flag
	*/
	public boolean sortsTrueFirst() {
	return trueFirst;
	}

	}

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