# MultiReader.java

    /*
    ** Module   : MultiReader.java
    ** Abstract : a reader which allows its input to be switched
    **
    ** Copyright (c) 2008-2017, Golden Code Development Corporation.
    **
    ** -#- -I- --Date-- -T- --JPRM-- ----------------Description-----------------
    ** 001 GES 20080308 NEW   @37541 First version which multiplexes readers
    **                               into a single reader.
    */
    /*
    ** This program is free software: you can redistribute it and/or modify
    ** it under the terms of the GNU Affero General Public License as
    ** published by the Free Software Foundation, either version 3 of the
    ** License, or (at your option) any later version.
    **
    ** This program is distributed in the hope that it will be useful,
    ** but WITHOUT ANY WARRANTY; without even the implied warranty of
    ** MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    ** GNU Affero General Public License for more details.
    **
    ** You may find a copy of the GNU Affero GPL version 3 at the following
    ** location: https://www.gnu.org/licenses/agpl-3.0.en.html
    **
    ** Additional terms under GNU Affero GPL version 3 section 7:
    **
    **   Under Section 7 of the GNU Affero GPL version 3, the following additional
    **   terms apply to the works covered under the License.  These additional terms
    **   are non-permissive additional terms allowed under Section 7 of the GNU
    **   Affero GPL version 3 and may not be removed by you.
    **
    **   0. Attribution Requirement.
    **
    **     You must preserve all legal notices or author attributions in the covered
    **     work or Appropriate Legal Notices displayed by works containing the covered
    **     work.  You may not remove from the covered work any author or developer
    **     credit already included within the covered work.
    **
    **   1. No License To Use Trademarks.
    **
    **     This license does not grant any license or rights to use the trademarks
    **     Golden Code, FWD, any Golden Code or FWD logo, or any other trademarks
    **     of Golden Code Development Corporation. You are not authorized to use the
    **     name Golden Code, FWD, or the names of any author or contributor, for
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    **
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    **     the covered work, without written authorization.
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    **
    **     You may not represent the covered work as solely your work.  All modified
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    **     Corporation or FWD.  All modified versions must contain the notices of
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    */

    package com.goldencode.p2j.io;

    import java.io.*;

    /**
     * Implements a simple switchable reader based on any number of underlying
     * readers. Readers can be switched to at any time. There is no history or
     * buffering kept inside this class. This means that there is no reading
     * ahead and no stacking or automatic "switch back" capability.  Likewise
     * only one reader is used at a time and once replaced, the previous reader
     * is not referenced or remembered in any way.
     * <p>
     * When instantiated, there may be no connection to any reader. If the
     * {@link #read} method is called while in this state, a <code>-1</code> is
     * returned signalling the <code>EOF</code> condition.
     * <p>
     * Once the {@link #switchTo} method is called, <code>read()</code>
     * delegates the work to the <code>read()</code> method of the current
     * underlying reader.
     * <p>
     * This class may be useful in many situations. For instance,
     * <code>PushbackReader</code> can provide pushback functionality for multiple
     * underlying readers once in an efficient way.
     */
    public class MultiReader
    extends FilterReader
    {
       /**
        * Default constructor. Creates an instance with no associated reader.
        */
       public MultiReader()
       {
          super(new StringReader(""));
       }

       /**
        * Creates an instance with the specified associated reader as the
        * current reader.
        *
        * @param    reader
        *           The reader that should be used first.
        */
       public MultiReader(Reader reader)
       {
          super(reader);
       }

       /**
        * Switches input to the specified reader.
        *
        * @param   reader
        *          The reader to be switched to.
        */
       public void switchTo(Reader reader)
       {
          super.in = reader;
       }

       /**
        * Reads the next byte from the current stream. If no stream was
        * switched to, returns <code>-1</code> as the indication of the
        * <code>EOF</code> condition.
        *
        * @return   The character read, as an integer in the range 0 to 65535
        *           (0x0000-0xFFFF), or -1 if the end of the stream has been
        *           reached or if no reader was switched to.
        *
        * @throws   IOException
        *           If any error occurs in reading from the underlying reader.
        */
       public int read()
       throws IOException
       {
          if (super.in == null)
          {
             return -1;
          }

          return super.read();
       }
    }