Commons Collections example source code file (UniquePredicate.java)

This example Commons Collections source code file (UniquePredicate.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Commons Collections tags/keywords

hashset, hashset, io, predicate, predicate, serializable, serializable, set, uniquepredicate, uniquepredicate, util

The Commons Collections UniquePredicate.java source code

/*
 *  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
 *  limitations under the License.
 */
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.
 * 
 * @since Commons Collections 3.0
 * @version $Revision: 646777 $ $Date: 2008-04-10 13:33:15 +0100 (Thu, 10 Apr 2008) $
 *
 * @author Stephen Colebourne
 */
public final class UniquePredicate implements Predicate, Serializable {

    /** Serial version UID */
    private static final long serialVersionUID = -3319417438027438040L;
    
    /** The set of previously seen objects */
    private final Set iSet = new HashSet();
    
    /**
     * 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 <code>getInstance if you want that.
     */
    public UniquePredicate() {
        super();
    }

    /**
     * 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);
    }

}