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 *  Licensed to the Apache Software Foundation (ASF) under one or more
 *  contributor license agreements.  See the NOTICE file distributed with
 *  this work for additional information regarding copyright ownership.
 *  The ASF licenses this file to You under the Apache License, Version 2.0
 *  (the "License"); you may not use this file except in compliance with
 *  the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
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 */
package org.apache.commons.collections.functors;

import java.io.Serializable;
import java.util.HashSet;
import java.util.Set;

import org.apache.commons.collections.Predicate;

Predicate implementation that returns true the first time an object is
passed into the predicate.
Author:
Stephen Colebourne
Since:
Commons Collections 3.0
Version:
$Revision: 646777 $ $Date: 2008-04-10 14:33:15 +0200 (Thu, 10 Apr 2008) $/**
 * Predicate implementation that returns true the first time an object is
 * passed into the predicate.
 * 
 * @since Commons Collections 3.0
 * @version $Revision: 646777 $ $Date: 2008-04-10 14:33:15 +0200 (Thu, 10 Apr 2008) $
 *
 * @author Stephen Colebourne
 */
public final class UniquePredicate implements Predicate, Serializable {

    
Serial version UID /** Serial version UID */
    private static final long serialVersionUID = -3319417438027438040L;
    
    
The set of previously seen objects /** The set of previously seen objects */
    private final Set iSet = new HashSet();
    
    
Factory to create the predicate.
Throws:
IllegalArgumentException – if the predicate is null
Returns:
the predicate/**
     * Factory to create the predicate.
     * 
     * @return the predicate
     * @throws IllegalArgumentException if the predicate is null
     */
    public static Predicate getInstance() {
        return new UniquePredicate();
    }

    
Constructor that performs no validation.
Use getInstance if you want that.
/**
     * Constructor that performs no validation.
     * Use <code>getInstance</code> if you want that.
     */
    public UniquePredicate() {
        super();
    }

    
Evaluates the predicate returning true if the input object hasn't been
received yet.
Params:
object –  the input object
Returns:
true if this is the first time the object is seen/**
     * Evaluates the predicate returning true if the input object hasn't been
     * received yet.
     * 
     * @param object  the input object
     * @return true if this is the first time the object is seen
     */
    public boolean evaluate(Object object) {
        return iSet.add(object);
    }

}