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}