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 */
017package org.apache.commons.collections4.functors;
018
019import java.io.Serializable;
020
021import org.apache.commons.collections4.Predicate;
022
023/**
024 * Predicate implementation that returns true if the input is null.
025 *
026 * @param <T> the type of the input to the predicate.
027 * @since 3.0
028 */
029public final class NullPredicate<T> extends AbstractPredicate<T> implements Serializable {
030
031    /** Serial version UID */
032    private static final long serialVersionUID = 7533784454832764388L;
033
034    /** Singleton predicate instance */
035    @SuppressWarnings("rawtypes")
036    public static final Predicate INSTANCE = new NullPredicate<>();
037
038    /**
039     * Factory returning the singleton instance.
040     *
041     * @param <T> the type that the predicate queries
042     * @return the singleton instance
043     * @since 3.1
044     */
045    public static <T> Predicate<T> nullPredicate() {
046        return INSTANCE;
047    }
048
049    /**
050     * Restricted constructor.
051     */
052    private NullPredicate() {
053    }
054
055    /**
056     * Returns the singleton instance.
057     *
058     * @return the singleton instance.
059     */
060    private Object readResolve() {
061        return INSTANCE;
062    }
063
064    /**
065     * Evaluates the predicate returning true if the input is null.
066     *
067     * @param object  the input object
068     * @return true if input is null
069     */
070    @Override
071    public boolean test(final T object) {
072        return object == null;
073    }
074
075}