001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.commons.collections4.comparators;
018
019import java.io.Serializable;
020import java.util.Comparator;
021
022/**
023 * A {@link Comparator} for {@link Boolean} objects that can sort either
024 * true or false first.
025 *
026 * @see #getTrueFirstComparator()
027 * @see #getFalseFirstComparator()
028 * @see #booleanComparator(boolean)
029 *
030 * @since 3.0
031 */
032public final class BooleanComparator implements Comparator<Boolean>, Serializable {
033
034    /** Serialization version. */
035    private static final long serialVersionUID = 1830042991606340609L;
036
037    /** Constant "true first" reference. */
038    private static final BooleanComparator TRUE_FIRST = new BooleanComparator(true);
039
040    /** Constant "false first" reference. */
041    private static final BooleanComparator FALSE_FIRST = new BooleanComparator(false);
042
043    /** <code>true</code> iff <code>true</code> values sort before <code>false</code> values. */
044    private boolean trueFirst = false;
045
046    //-----------------------------------------------------------------------
047    /**
048     * Returns a BooleanComparator instance that sorts
049     * <code>true</code> values before <code>false</code> values.
050     * <p>
051     * Clients are encouraged to use the value returned from
052     * this method instead of constructing a new instance
053     * to reduce allocation and garbage collection overhead when
054     * multiple BooleanComparators may be used in the same
055     * virtual machine.
056     * </p>
057     *
058     * @return the true first singleton BooleanComparator
059     */
060    public static BooleanComparator getTrueFirstComparator() {
061        return TRUE_FIRST;
062    }
063
064    /**
065     * Returns a BooleanComparator instance that sorts
066     * <code>false</code> values before <code>true</code> values.
067     * <p>
068     * Clients are encouraged to use the value returned from
069     * this method instead of constructing a new instance
070     * to reduce allocation and garbage collection overhead when
071     * multiple BooleanComparators may be used in the same
072     * virtual machine.
073     * </p>
074     *
075     * @return the false first singleton BooleanComparator
076     */
077    public static BooleanComparator getFalseFirstComparator() {
078        return FALSE_FIRST;
079    }
080
081    /**
082     * Returns a BooleanComparator instance that sorts
083     * <code><i>trueFirst</i></code> values before
084     * <code>&#x21;<i>trueFirst</i></code> values.
085     * <p>
086     * Clients are encouraged to use the value returned from
087     * this method instead of constructing a new instance
088     * to reduce allocation and garbage collection overhead when
089     * multiple BooleanComparators may be used in the same
090     * virtual machine.
091     * </p>
092     *
093     * @param trueFirst when <code>true</code>, sort
094     * <code>true</code> <code>Boolean</code>s before <code>false</code>
095     * @return a singleton BooleanComparator instance
096     * @since 4.0
097     */
098    public static BooleanComparator booleanComparator(final boolean trueFirst) {
099        return trueFirst ? TRUE_FIRST : FALSE_FIRST;
100    }
101
102    //-----------------------------------------------------------------------
103    /**
104     * Creates a <code>BooleanComparator</code> that sorts
105     * <code>false</code> values before <code>true</code> values.
106     * <p>
107     * Equivalent to {@link #BooleanComparator(boolean) BooleanComparator(false)}.
108     * <p>
109     * Please use the static factory instead whenever possible.
110     */
111    public BooleanComparator() {
112        this(false);
113    }
114
115    /**
116     * Creates a <code>BooleanComparator</code> that sorts
117     * <code><i>trueFirst</i></code> values before
118     * <code>&#x21;<i>trueFirst</i></code> values.
119     * <p>
120     * Please use the static factories instead whenever possible.
121     *
122     * @param trueFirst when <code>true</code>, sort
123     *  <code>true</code> boolean values before <code>false</code>
124     */
125    public BooleanComparator(final boolean trueFirst) {
126        this.trueFirst = trueFirst;
127    }
128
129    //-----------------------------------------------------------------------
130    /**
131     * Compares two non-<code>null</code> <code>Boolean</code> objects
132     * according to the value of {@link #sortsTrueFirst()}.
133     *
134     * @param b1  the first boolean to compare
135     * @param b2  the second boolean to compare
136     * @return negative if obj1 is less, positive if greater, zero if equal
137     * @throws NullPointerException when either argument <code>null</code>
138     */
139    @Override
140    public int compare(final Boolean b1, final Boolean b2) {
141        final boolean v1 = b1.booleanValue();
142        final boolean v2 = b2.booleanValue();
143
144        return (v1 ^ v2) ? ( (v1 ^ trueFirst) ? 1 : -1 ) : 0;
145    }
146
147    //-----------------------------------------------------------------------
148    /**
149     * Implement a hash code for this comparator that is consistent with
150     * {@link #equals(Object) equals}.
151     *
152     * @return a hash code for this comparator.
153     */
154    @Override
155    public int hashCode() {
156        final int hash = "BooleanComparator".hashCode();
157        return trueFirst ? -1 * hash : hash;
158    }
159
160    /**
161     * Returns <code>true</code> iff <i>that</i> Object is
162     * is a {@link Comparator} whose ordering is known to be
163     * equivalent to mine.
164     * <p>
165     * This implementation returns <code>true</code>
166     * iff <code><i>that</i></code> is a {@link BooleanComparator}
167     * whose value of {@link #sortsTrueFirst()} is equal to mine.
168     *
169     * @param object  the object to compare to
170     * @return true if equal
171     */
172    @Override
173    public boolean equals(final Object object) {
174        return (this == object) ||
175               ((object instanceof BooleanComparator) &&
176                (this.trueFirst == ((BooleanComparator)object).trueFirst));
177    }
178
179    //-----------------------------------------------------------------------
180    /**
181     * Returns <code>true</code> iff
182     * I sort <code>true</code> values before
183     * <code>false</code> values.  In other words,
184     * returns <code>true</code> iff
185     * {@link #compare(Boolean,Boolean) compare(Boolean.FALSE,Boolean.TRUE)}
186     * returns a positive value.
187     *
188     * @return the trueFirst flag
189     */
190    public boolean sortsTrueFirst() {
191        return trueFirst;
192    }
193
194}