    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.configuration2.interpol;
    018
    019/**
    020 * <p>
    021 * A simple dummy {@code Lookup} implementation.
    022 * </p>
    023 * <p>
    024 * This implementation always returns <b>null</b> for a passed in variable
    025 * indicating that it cannot resolve that variable. This is useful for instance
    026 * as an application of the <em>null object</em> pattern.
    027 * </p>
    028 * <p>
    029 * This class does not define any state, therefore a single instance can be
    030 * shared. To enforce usage of only a single instance this class is actually an
    031 * enumeration.
    032 * </p>
    033 *
    034 * @since 2.0
    035 */
    036public enum DummyLookup implements Lookup
    037{
    038    /** The single instance of this class. */
    039    INSTANCE;
    040
    041    /**
    042     * {@inheritDoc} This implementation always returns <b>null</b>.
    043     */
    044    @Override
    045    public Object lookup(final String variable)
    046    {
    047        return null;
    048    }
    049}