/*
 *  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 org.apache.commons.collections.Predicate;

/**
 * Predicate implementation that returns true if the input is null.
 * 
 * @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 NullPredicate implements Predicate, Serializable {

    /** Serial version UID */
    private static final long serialVersionUID = 7533784454832764388L;
    
    /** Singleton predicate instance */
    public static final Predicate INSTANCE = new NullPredicate();

    /**
     * Factory returning the singleton instance.
     * 
     * @return the singleton instance
     * @since Commons Collections 3.1
     */
    public static Predicate getInstance() {
        return INSTANCE;
    }

    /**
     * Restricted constructor.
     */
    private NullPredicate() {
        super();
    }

    /**
     * Evaluates the predicate returning true if the input is null.
     * 
     * @param object  the input object
     * @return true if input is null
     */
    public boolean evaluate(Object object) {
        return (object == null);
    }

}
