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