001 /* 002 * Copyright (c) 2007-2015 Concurrent, Inc. All Rights Reserved. 003 * 004 * Project and contact information: http://www.cascading.org/ 005 * 006 * This file is part of the Cascading project. 007 * 008 * Licensed under the Apache License, Version 2.0 (the "License"); 009 * you may not use this file except in compliance with the License. 010 * You may obtain a copy of the License at 011 * 012 * http://www.apache.org/licenses/LICENSE-2.0 013 * 014 * Unless required by applicable law or agreed to in writing, software 015 * distributed under the License is distributed on an "AS IS" BASIS, 016 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 017 * See the License for the specific language governing permissions and 018 * limitations under the License. 019 */ 020 021 package cascading.scheme; 022 023 import java.io.IOException; 024 025 import cascading.flow.FlowProcess; 026 import cascading.tap.Tap; 027 import cascading.tuple.Fields; 028 029 /** 030 * Class NullScheme is a {@link Scheme} that neither reads or writes any values. 031 * <p/> 032 * It is typically used as a placeholder where a Scheme instance is needed but generally ignored. 033 */ 034 public class NullScheme<Config, Input, Output, SourceContext, SinkContext> extends Scheme<Config, Input, Output, SourceContext, SinkContext> 035 { 036 public NullScheme() 037 { 038 } 039 040 public NullScheme( Fields sourceFields, Fields sinkFields ) 041 { 042 super( sourceFields, sinkFields ); 043 } 044 045 @Override 046 public void sourceConfInit( FlowProcess<Config> flowProcess, Tap<Config, Input, Output> tap, Config conf ) 047 { 048 } 049 050 @Override 051 public void sinkConfInit( FlowProcess<Config> flowProcess, Tap<Config, Input, Output> tap, Config conf ) 052 { 053 } 054 055 @Override 056 public boolean source( FlowProcess<Config> flowProcess, SourceCall<SourceContext, Input> sourceCall ) throws IOException 057 { 058 return false; 059 } 060 061 @Override 062 public void sink( FlowProcess<Config> flowProcess, SinkCall<SinkContext, Output> sinkCall ) throws IOException 063 { 064 065 } 066 067 @Override 068 public String toString() 069 { 070 return getClass().getSimpleName(); 071 } 072 }