org.apache.commons.collections.functors.UniquePredicate Maven / Gradle / Ivy
/*
* 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 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);
}
}