    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 * @since 3.0
    030 */
    031public final class BooleanComparator implements Comparator<Boolean>, Serializable {
    032
    033    /** Serialization version. */
    034    private static final long serialVersionUID = 1830042991606340609L;
    035
    036    /** Constant "true first" reference. */
    037    private static final BooleanComparator TRUE_FIRST = new BooleanComparator(true);
    038
    039    /** Constant "false first" reference. */
    040    private static final BooleanComparator FALSE_FIRST = new BooleanComparator(false);
    041
    042    /**
    043     * Returns a BooleanComparator instance that sorts
    044     * {@code <em>trueFirst</em>} values before
    045     * {@code &#x21;<em>trueFirst</em>} values.
    046     * <p>
    047     * Clients are encouraged to use the value returned from
    048     * this method instead of constructing a new instance
    049     * to reduce allocation and garbage collection overhead when
    050     * multiple BooleanComparators may be used in the same
    051     * virtual machine.
    052     * </p>
    053     *
    054     * @param trueFirst when {@code true}, sort
    055     * {@code true} {@code Boolean}s before {@code false}
    056     * @return a singleton BooleanComparator instance
    057     * @since 4.0
    058     */
    059    public static BooleanComparator booleanComparator(final boolean trueFirst) {
    060        return trueFirst ? TRUE_FIRST : FALSE_FIRST;
    061    }
    062
    063    /**
    064     * Returns a BooleanComparator instance that sorts
    065     * {@code false} values before {@code true} values.
    066     * <p>
    067     * Clients are encouraged to use the value returned from
    068     * this method instead of constructing a new instance
    069     * to reduce allocation and garbage collection overhead when
    070     * multiple BooleanComparators may be used in the same
    071     * virtual machine.
    072     * </p>
    073     *
    074     * @return the false first singleton BooleanComparator
    075     */
    076    public static BooleanComparator getFalseFirstComparator() {
    077        return FALSE_FIRST;
    078    }
    079
    080    /**
    081     * Returns a BooleanComparator instance that sorts
    082     * {@code true} values before {@code false} values.
    083     * <p>
    084     * Clients are encouraged to use the value returned from
    085     * this method instead of constructing a new instance
    086     * to reduce allocation and garbage collection overhead when
    087     * multiple BooleanComparators may be used in the same
    088     * virtual machine.
    089     * </p>
    090     *
    091     * @return the true first singleton BooleanComparator
    092     */
    093    public static BooleanComparator getTrueFirstComparator() {
    094        return TRUE_FIRST;
    095    }
    096
    097    /** {@code true} iff {@code true} values sort before {@code false} values. */
    098    private final boolean trueFirst;
    099
    100    /**
    101     * Creates a {@code BooleanComparator} that sorts
    102     * {@code false} values before {@code true} values.
    103     * <p>
    104     * Equivalent to {@link #BooleanComparator(boolean) BooleanComparator(false)}.
    105     * <p>
    106     * Please use the static factory instead whenever possible.
    107     */
    108    public BooleanComparator() {
    109        this(false);
    110    }
    111
    112    /**
    113     * Creates a {@code BooleanComparator} that sorts
    114     * {@code <em>trueFirst</em>} values before
    115     * {@code &#x21;<em>trueFirst</em>} values.
    116     * <p>
    117     * Please use the static factories instead whenever possible.
    118     *
    119     * @param trueFirst when {@code true}, sort
    120     *  {@code true} boolean values before {@code false}
    121     */
    122    public BooleanComparator(final boolean trueFirst) {
    123        this.trueFirst = trueFirst;
    124    }
    125
    126    /**
    127     * Compares two non-{@code null} {@code Boolean} objects
    128     * according to the value of {@link #sortsTrueFirst()}.
    129     *
    130     * @param b1  the first boolean to compare
    131     * @param b2  the second boolean to compare
    132     * @return negative if obj1 is less, positive if greater, zero if equal
    133     * @throws NullPointerException when either argument {@code null}
    134     */
    135    @Override
    136    public int compare(final Boolean b1, final Boolean b2) {
    137        final boolean v1 = b1.booleanValue();
    138        final boolean v2 = b2.booleanValue();
    139
    140        return v1 ^ v2 ? v1 ^ trueFirst ? 1 : -1 : 0;
    141    }
    142
    143    /**
    144     * Returns {@code true} iff <em>that</em> Object is
    145     * a {@link Comparator} whose ordering is known to be
    146     * equivalent to mine.
    147     * <p>
    148     * This implementation returns {@code true}
    149     * iff {@code <em>that</em>} is a {@link BooleanComparator}
    150     * whose value of {@link #sortsTrueFirst()} is equal to mine.
    151     *
    152     * @param object  the object to compare to
    153     * @return true if equal
    154     */
    155    @Override
    156    public boolean equals(final Object object) {
    157        return this == object ||
    158               object instanceof BooleanComparator &&
    159                trueFirst == ((BooleanComparator) object).trueFirst;
    160    }
    161
    162    /**
    163     * Implement a hash code for this comparator that is consistent with
    164     * {@link #equals(Object) equals}.
    165     *
    166     * @return a hash code for this comparator.
    167     */
    168    @Override
    169    public int hashCode() {
    170        final int hash = "BooleanComparator".hashCode();
    171        return trueFirst ? -1 * hash : hash;
    172    }
    173
    174    /**
    175     * Returns {@code true} iff
    176     * I sort {@code true} values before
    177     * {@code false} values.  In other words,
    178     * returns {@code true} iff
    179     * {@link #compare(Boolean,Boolean) compare(Boolean.FALSE,Boolean.TRUE)}
    180     * returns a positive value.
    181     *
    182     * @return the trueFirst flag
    183     */
    184    public boolean sortsTrueFirst() {
    185        return trueFirst;
    186    }
    187
    188}