    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.functors;
    018
    019import java.io.Serializable;
    020import java.util.Comparator;
    021import java.util.Objects;
    022
    023import org.apache.commons.collections4.Predicate;
    024
    025/**
    026 * Predicate that compares the input object with the one stored in the predicate using a comparator.
    027 * In addition, the comparator result can be evaluated in accordance to a supplied criterion value.
    028 *
    029 * <p>In order to demonstrate the use of the predicate, the following variables are declared:</p>
    030 *
    031 * <pre>
    032 * Integer ONE = Integer.valueOf(1);
    033 * Integer TWO = Integer.valueOf(2);
    034 *
    035 * Comparator comparator = new Comparator() {
    036 *
    037 *     public int compare(Object first, Object second) {
    038 *         return ((Integer) second) - ((Integer) first);
    039 *     }
    040 *
    041 * };
    042 * </pre>
    043 *
    044 * <p>Using the declared variables, the {@code ComparatorPredicate} can be used in the
    045 * following way:</p>
    046 *
    047 * <pre>
    048 * ComparatorPredicate.comparatorPredicate(ONE, comparator).evaluate(TWO);
    049 * </pre>
    050 *
    051 * <p>The input variable {@code TWO} in compared to the stored variable {@code ONE} using
    052 * the supplied {@code comparator}. This is the default usage of the predicate and will return
    053 * {@code true} if the underlying comparator returns {@code 0}. In addition to the default
    054 * usage of the predicate, it is possible to evaluate the comparator's result in several ways. The
    055 * following {@link Criterion} enumeration values are provided by the predicate:
    056 * </p>
    057 *
    058 * <ul>
    059 *     <li>EQUAL</li>
    060 *     <li>GREATER</li>
    061 *     <li>GREATER_OR_EQUAL</li>
    062 *     <li>LESS</li>
    063 *     <li>LESS_OR_EQUAL</li>
    064 * </ul>
    065 *
    066 * <p>The following examples demonstrates how these constants can be used in order to manipulate the
    067 * evaluation of a comparator result.</p>
    068 *
    069 * <pre>
    070 * ComparatorPredicate.comparatorPredicate(ONE, comparator,<b>ComparatorPredicate.Criterion.GREATER</b>).evaluate(TWO);
    071 * </pre>
    072 *
    073 * <p>The input variable TWO is compared to the stored variable ONE using the supplied {@code comparator}
    074 * using the {@code GREATER} evaluation criterion constant. This instructs the predicate to
    075 * return {@code true} if the comparator returns a value greater than {@code 0}.</p>
    076 *
    077 * @since 4.0
    078 */
    079public class ComparatorPredicate<T> implements Predicate<T>, Serializable {
    080
    081    public enum Criterion {
    082        EQUAL, GREATER, LESS, GREATER_OR_EQUAL, LESS_OR_EQUAL,
    083    }
    084
    085    private static final long serialVersionUID = -1863209236504077399L;
    086
    087    // Instance variables:
    088
    089    /**
    090     * Factory to create the comparator predicate
    091     *
    092     * @param <T> the type that the predicate queries
    093     * @param object  the object to compare to
    094     * @param comparator  the comparator to use for comparison
    095     * @return the predicate
    096     * @throws NullPointerException if comparator is null
    097     */
    098    public static <T> Predicate<T> comparatorPredicate(final T object, final Comparator<T> comparator) {
    099        return comparatorPredicate(object, comparator, Criterion.EQUAL);
    100    }
    101
    102    /**
    103     * Factory to create the comparator predicate
    104     *
    105     * @param <T> the type that the predicate queries
    106     * @param object  the object to compare to
    107     * @param comparator  the comparator to use for comparison
    108     * @param criterion  the criterion to use to evaluate comparison
    109     * @return the predicate
    110     * @throws NullPointerException if comparator or criterion is null
    111     */
    112    public static <T> Predicate<T> comparatorPredicate(final T object, final Comparator<T> comparator,
    113                                                       final Criterion criterion) {
    114        return new ComparatorPredicate<>(object, Objects.requireNonNull(comparator, "comparator"),
    115                Objects.requireNonNull(criterion, "criterion"));
    116    }
    117
    118    /** The internal object to compare with */
    119    private final T object;
    120
    121    /** The comparator to use for comparison */
    122    private final Comparator<T> comparator;
    123
    124    /** The comparison evaluation criterion to use */
    125    private final Criterion criterion;
    126
    127    /**
    128     * Constructor that performs no validation.
    129     * Use {@code comparatorPredicate} if you want that.
    130     *
    131     * @param object  the object to compare to
    132     * @param comparator  the comparator to use for comparison
    133     * @param criterion  the criterion to use to evaluate comparison
    134     */
    135    public ComparatorPredicate(final T object, final Comparator<T> comparator, final Criterion criterion) {
    136        this.object = object;
    137        this.comparator = comparator;
    138        this.criterion = criterion;
    139    }
    140
    141    /**
    142     * Evaluates the predicate. The predicate evaluates to {@code true} in the following cases:
    143     *
    144     * <ul>
    145     * <li>{@code comparator.compare(object, input) == 0 &amp;&amp; criterion == EQUAL}</li>
    146     * <li>{@code comparator.compare(object, input) &lt; 0 &amp;&amp; criterion == LESS}</li>
    147     * <li>{@code comparator.compare(object, input) &gt; 0 &amp;&amp; criterion == GREATER}</li>
    148     * <li>{@code comparator.compare(object, input) &gt;= 0 &amp;&amp; criterion == GREATER_OR_EQUAL}</li>
    149     * <li>{@code comparator.compare(object, input) &lt;= 0 &amp;&amp; criterion == LESS_OR_EQUAL}</li>
    150     * </ul>
    151     *
    152     * @see org.apache.commons.collections4.Predicate#evaluate(Object)
    153     * @see java.util.Comparator#compare(Object first, Object second)
    154     *
    155     * @param target  the target object to compare to
    156     * @return {@code true} if the comparison succeeds according to the selected criterion
    157     * @throws IllegalStateException if the criterion is invalid (really not possible)
    158     */
    159    @Override
    160    public boolean evaluate(final T target) {
    161
    162        boolean result = false;
    163        final int comparison = comparator.compare(object, target);
    164        switch (criterion) {
    165        case EQUAL:
    166            result = comparison == 0;
    167            break;
    168        case GREATER:
    169            result = comparison > 0;
    170            break;
    171        case LESS:
    172            result = comparison < 0;
    173            break;
    174        case GREATER_OR_EQUAL:
    175            result = comparison >= 0;
    176            break;
    177        case LESS_OR_EQUAL:
    178            result = comparison <= 0;
    179            break;
    180        default:
    181            throw new IllegalStateException("The current criterion '" + criterion + "' is invalid.");
    182        }
    183
    184        return result;
    185    }
    186}