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 */ 017 package org.apache.commons.collections.functors; 018 019 import java.io.Serializable; 020 import java.util.HashSet; 021 import java.util.Set; 022 023 import org.apache.commons.collections.Predicate; 024 025 /** 026 * Predicate implementation that returns true the first time an object is 027 * passed into the predicate. 028 * 029 * @since Commons Collections 3.0 030 * @version $Revision: 646777 $ $Date: 2008-04-10 13:33:15 +0100 (Thu, 10 Apr 2008) $ 031 * 032 * @author Stephen Colebourne 033 */ 034 public final class UniquePredicate implements Predicate, Serializable { 035 036 /** Serial version UID */ 037 private static final long serialVersionUID = -3319417438027438040L; 038 039 /** The set of previously seen objects */ 040 private final Set iSet = new HashSet(); 041 042 /** 043 * Factory to create the predicate. 044 * 045 * @return the predicate 046 * @throws IllegalArgumentException if the predicate is null 047 */ 048 public static Predicate getInstance() { 049 return new UniquePredicate(); 050 } 051 052 /** 053 * Constructor that performs no validation. 054 * Use <code>getInstance</code> if you want that. 055 */ 056 public UniquePredicate() { 057 super(); 058 } 059 060 /** 061 * Evaluates the predicate returning true if the input object hasn't been 062 * received yet. 063 * 064 * @param object the input object 065 * @return true if this is the first time the object is seen 066 */ 067 public boolean evaluate(Object object) { 068 return iSet.add(object); 069 } 070 071 }