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.HashSet; 021import java.util.Set; 022 023import org.apache.commons.collections4.Predicate; 024 025/** 026 * Predicate implementation that returns true the first time an object is 027 * passed into the predicate. 028 * 029 * @since 3.0 030 */ 031public final class UniquePredicate<T> implements Predicate<T>, Serializable { 032 033 /** Serial version UID */ 034 private static final long serialVersionUID = -3319417438027438040L; 035 036 /** 037 * Factory to create the predicate. 038 * 039 * @param <T> the type that the predicate queries 040 * @return the predicate 041 * @throws IllegalArgumentException if the predicate is null 042 */ 043 public static <T> Predicate<T> uniquePredicate() { 044 return new UniquePredicate<>(); 045 } 046 047 /** The set of previously seen objects */ 048 private final Set<T> iSet = new HashSet<>(); 049 050 /** 051 * Constructor that performs no validation. 052 * Use {@code uniquePredicate} if you want that. 053 */ 054 public UniquePredicate() { 055 } 056 057 /** 058 * Evaluates the predicate returning true if the input object hasn't been 059 * received yet. 060 * 061 * @param object the input object 062 * @return true if this is the first time the object is seen 063 */ 064 @Override 065 public boolean evaluate(final T object) { 066 return iSet.add(object); 067 } 068 069}