    001    /*
    002     * Copyright (c) 2007-2014 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.pipe.assembly;
    022
    023    import java.beans.ConstructorProperties;
    024
    025    import cascading.operation.NoOp;
    026    import cascading.pipe.Each;
    027    import cascading.pipe.Pipe;
    028    import cascading.pipe.SubAssembly;
    029    import cascading.tuple.Fields;
    030
    031    /**
    032     * Class Discard is a {@link cascading.pipe.SubAssembly} that will retain all incoming fields except those given on the constructor.
    033     * <p/>
    034     * Use this pipe to narrow a stream of tuples, removing unused data.
    035     *
    036     * @see Retain
    037     */
    038    public class Discard extends SubAssembly
    039      {
    040      @ConstructorProperties({"previous", "discardFields"})
    041      public Discard( Pipe previous, Fields discardFields )
    042        {
    043        super( previous );
    044
    045        if( discardFields == null )
    046          throw new IllegalArgumentException( "discardFields may not be null" );
    047
    048        setTails( new Each( previous, discardFields, new NoOp(), Fields.SWAP ) );
    049        }
    050      }