    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.Closure;
    022
    023/**
    024 * Closure implementation that does nothing.
    025 *
    026 * @since 3.0
    027 */
    028public final class NOPClosure<E> implements Closure<E>, Serializable {
    029
    030    /** Serial version UID */
    031    private static final long serialVersionUID = 3518477308466486130L;
    032
    033    /** Singleton predicate instance */
    034    @SuppressWarnings("rawtypes")
    035    public static final Closure INSTANCE = new NOPClosure<>();
    036
    037    /**
    038     * Factory returning the singleton instance.
    039     *
    040     * @param <E> the type that the closure acts on
    041     * @return the singleton instance
    042     * @since 3.1
    043     */
    044    @SuppressWarnings("unchecked")
    045    public static <E> Closure<E> nopClosure() {
    046        return INSTANCE;
    047    }
    048
    049    /**
    050     * Constructor.
    051     */
    052    private NOPClosure() {
    053        super();
    054    }
    055
    056    /**
    057     * Do nothing.
    058     *
    059     * @param input  the input object
    060     */
    061    @Override
    062    public void execute(final E input) {
    063        // do nothing
    064    }
    065
    066    private Object readResolve() {
    067        return INSTANCE;
    068    }
    069
    070}