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.HashSet;
21 import java.util.Set;
22
23 import org.apache.commons.collections4.Predicate;
24
25 /**
26 * Predicate implementation that returns true the first time an object is
27 * passed into the predicate.
28 *
29 * @param <T> the type of the input to the predicate.
30 * @since 3.0
31 */
32 public final class UniquePredicate<T> extends AbstractPredicate<T> implements Serializable {
33
34 /** Serial version UID */
35 private static final long serialVersionUID = -3319417438027438040L;
36
37 /**
38 * Creates the predicate.
39 *
40 * @param <T> the type that the predicate queries
41 * @return the predicate
42 * @throws IllegalArgumentException if the predicate is null
43 */
44 public static <T> Predicate<T> uniquePredicate() {
45 return new UniquePredicate<>();
46 }
47
48 /** The set of previously seen objects */
49 private final Set<T> iSet = new HashSet<>();
50
51 /**
52 * Constructor that performs no validation.
53 * Use {@code uniquePredicate} if you want that.
54 */
55 public UniquePredicate() {
56 }
57
58 /**
59 * Evaluates the predicate returning true if the input object hasn't been
60 * received yet.
61 *
62 * @param object the input object
63 * @return true if this is the first time the object is seen
64 */
65 @Override
66 public boolean test(final T object) {
67 return iSet.add(object);
68 }
69
70 }