1 /*
2 * Licensed to the Apache Software Foundation (ASF) under one or more
3 * contributor license agreements. See the NOTICE file distributed with
4 * this work for additional information regarding copyright ownership.
5 * The ASF licenses this file to You under the Apache License, Version 2.0
6 * (the "License"); you may not use this file except in compliance with
7 * the License. You may obtain a copy of the License at
8 *
9 * http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 */
17 package org.apache.commons.collections4.functors;
18
19 import java.io.Serializable;
20 import java.util.Comparator;
21 import java.util.Objects;
22
23 import org.apache.commons.collections4.Predicate;
24
25 /**
26 * Predicate that compares the input object with the one stored in the predicate using a comparator.
27 * In addition, the comparator result can be evaluated in accordance to a supplied criterion value.
28 *
29 * <p>In order to demonstrate the use of the predicate, the following variables are declared:</p>
30 *
31 * <pre>
32 * Integer ONE = Integer.valueOf(1);
33 * Integer TWO = Integer.valueOf(2);
34 *
35 * Comparator comparator = new Comparator() {
36 *
37 * public int compare(Object first, Object second) {
38 * return ((Integer) second) - ((Integer) first);
39 * }
40 *
41 * };
42 * </pre>
43 *
44 * <p>Using the declared variables, the {@code ComparatorPredicate} can be used in the
45 * following way:</p>
46 *
47 * <pre>
48 * ComparatorPredicate.comparatorPredicate(ONE, comparator).test(TWO);
49 * </pre>
50 *
51 * <p>The input variable {@code TWO} in compared to the stored variable {@code ONE} using
52 * the supplied {@code comparator}. This is the default usage of the predicate and will return
53 * {@code true} if the underlying comparator returns {@code 0}. In addition to the default
54 * usage of the predicate, it is possible to evaluate the comparator's result in several ways. The
55 * following {@link Criterion} enumeration values are provided by the predicate:
56 * </p>
57 *
58 * <ul>
59 * <li>EQUAL</li>
60 * <li>GREATER</li>
61 * <li>GREATER_OR_EQUAL</li>
62 * <li>LESS</li>
63 * <li>LESS_OR_EQUAL</li>
64 * </ul>
65 *
66 * <p>The following examples demonstrates how these constants can be used in order to manipulate the
67 * evaluation of a comparator result.</p>
68 *
69 * <pre>
70 * ComparatorPredicate.comparatorPredicate(ONE, comparator,<strong>ComparatorPredicate.Criterion.GREATER</strong>).test(TWO);
71 * </pre>
72 *
73 * <p>The input variable TWO is compared to the stored variable ONE using the supplied {@code comparator}
74 * using the {@code GREATER} evaluation criterion constant. This instructs the predicate to
75 * return {@code true} if the comparator returns a value greater than {@code 0}.</p>
76 *
77 * @param <T> the type of the input to the predicate.
78 * @since 4.0
79 */
80 public class ComparatorPredicate<T> extends AbstractPredicate<T> implements Serializable {
81
82 /**
83 * Enumerates the comparator criteria.
84 */
85 public enum Criterion {
86
87 /**
88 * Equal criterion.
89 */
90 EQUAL,
91
92 /**
93 * Greater criterion.
94 */
95 GREATER,
96
97 /**
98 * Less criterion.
99 */
100 LESS,
101
102 /**
103 * Greater or equal criterion.
104 */
105 GREATER_OR_EQUAL,
106
107 /**
108 * Less or equal Criterion.
109 */
110 LESS_OR_EQUAL,
111 }
112
113 private static final long serialVersionUID = -1863209236504077399L;
114
115 /**
116 * Creates the comparator predicate
117 *
118 * @param <T> the type that the predicate queries
119 * @param object the object to compare to
120 * @param comparator the comparator to use for comparison
121 * @return the predicate
122 * @throws NullPointerException if comparator is null
123 */
124 public static <T> Predicate<T> comparatorPredicate(final T object, final Comparator<T> comparator) {
125 return comparatorPredicate(object, comparator, Criterion.EQUAL);
126 }
127
128 /**
129 * Creates the comparator predicate
130 *
131 * @param <T> the type that the predicate queries
132 * @param object the object to compare to
133 * @param comparator the comparator to use for comparison
134 * @param criterion the criterion to use to evaluate comparison
135 * @return the predicate
136 * @throws NullPointerException if comparator or criterion is null
137 */
138 public static <T> Predicate<T> comparatorPredicate(final T object, final Comparator<T> comparator,
139 final Criterion criterion) {
140 return new ComparatorPredicate<>(object, Objects.requireNonNull(comparator, "comparator"),
141 Objects.requireNonNull(criterion, "criterion"));
142 }
143
144 /** The internal object to compare with */
145 private final T object;
146
147 /** The comparator to use for comparison */
148 private final Comparator<T> comparator;
149
150 /** The comparison evaluation criterion to use */
151 private final Criterion criterion;
152
153 /**
154 * Constructor that performs no validation.
155 * Use {@code comparatorPredicate} if you want that.
156 *
157 * @param object the object to compare to
158 * @param comparator the comparator to use for comparison
159 * @param criterion the criterion to use to evaluate comparison
160 */
161 public ComparatorPredicate(final T object, final Comparator<T> comparator, final Criterion criterion) {
162 this.object = object;
163 this.comparator = comparator;
164 this.criterion = criterion;
165 }
166
167 /**
168 * Evaluates the predicate. The predicate evaluates to {@code true} in the following cases:
169 *
170 * <ul>
171 * <li>{@code comparator.compare(object, input) == 0 && criterion == EQUAL}</li>
172 * <li>{@code comparator.compare(object, input) < 0 && criterion == LESS}</li>
173 * <li>{@code comparator.compare(object, input) > 0 && criterion == GREATER}</li>
174 * <li>{@code comparator.compare(object, input) >= 0 && criterion == GREATER_OR_EQUAL}</li>
175 * <li>{@code comparator.compare(object, input) <= 0 && criterion == LESS_OR_EQUAL}</li>
176 * </ul>
177 *
178 * @see org.apache.commons.collections4.Predicate#test(Object)
179 * @see java.util.Comparator#compare(Object first, Object second)
180 * @param target the target object to compare to
181 * @return {@code true} if the comparison succeeds according to the selected criterion
182 * @throws IllegalStateException if the criterion is invalid (really not possible)
183 */
184 @Override
185 public boolean test(final T target) {
186
187 boolean result = false;
188 final int comparison = comparator.compare(object, target);
189 switch (criterion) {
190 case EQUAL:
191 result = comparison == 0;
192 break;
193 case GREATER:
194 result = comparison > 0;
195 break;
196 case LESS:
197 result = comparison < 0;
198 break;
199 case GREATER_OR_EQUAL:
200 result = comparison >= 0;
201 break;
202 case LESS_OR_EQUAL:
203 result = comparison <= 0;
204 break;
205 default:
206 throw new IllegalStateException("The current criterion '" + criterion + "' is invalid.");
207 }
208
209 return result;
210 }
211 }