    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 *      https://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 * @param <T> The type of the input to the operation.
    027 * @since 3.0
    028 */
    029public final class NOPClosure<T> implements Closure<T>, Serializable {
    030
    031    /** Serial version UID */
    032    private static final long serialVersionUID = 3518477308466486130L;
    033
    034    /** Singleton predicate instance */
    035    @SuppressWarnings("rawtypes")
    036    public static final Closure INSTANCE = new NOPClosure<>();
    037
    038    /**
    039     * Factory returning the singleton instance.
    040     *
    041     * @param <E> The type that the closure acts on
    042     * @return The singleton instance
    043     * @since 3.1
    044     */
    045    public static <E> Closure<E> nopClosure() {
    046        return INSTANCE;
    047    }
    048
    049    /**
    050     * Constructs a new instance.
    051     */
    052    private NOPClosure() {
    053    }
    054
    055    /**
    056     * Do nothing.
    057     *
    058     * @param input  The input object
    059     */
    060    @Override
    061    public void execute(final T input) {
    062        // do nothing
    063    }
    064
    065    /**
    066     * Returns the singleton instance.
    067     *
    068     * @return The singleton instance.
    069     */
    070    private Object readResolve() {
    071        return INSTANCE;
    072    }
    073
    074}