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   * Copyright (c) 1994, 2010, Oracle and/or its affiliates. All rights reserved.
   * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   *
   * This code is free software; you can redistribute it and/or modify it
   * under the terms of the GNU General Public License version 2 only, as
   * published by the Free Software Foundation.  Oracle designates this
   * particular file as subject to the "Classpath" exception as provided
   * by Oracle in the LICENSE file that accompanied this code.
   *
   * This code 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 General Public License
   * version 2 for more details (a copy is included in the LICENSE file that
   * accompanied this code).
   *
   * You should have received a copy of the GNU General Public License version
   * 2 along with this work; if not, write to the Free Software Foundation,
   * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
   *
   * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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   */
  
  package java.io;
  
  /**
   * A <code>FilterInputStream</code> contains
   * some other input stream, which it uses as
   * its  basic source of data, possibly transforming
   * the data along the way or providing  additional
   * functionality. The class <code>FilterInputStream</code>
   * itself simply overrides all  methods of
   * <code>InputStream</code> with versions that
   * pass all requests to the contained  input
   * stream. Subclasses of <code>FilterInputStream</code>
   * may further override some of  these methods
   * and may also provide additional methods
   * and fields.
   *
   * @author  Jonathan Payne
   * @since   JDK1.0
   */
  public
  class FilterInputStream extends InputStream {
      /**
       * The input stream to be filtered.
       */
      protected volatile InputStream in;
  
      /**
       * Creates a <code>FilterInputStream</code>
       * by assigning the  argument <code>in</code>
       * to the field <code>this.in</code> so as
       * to remember it for later use.
       *
       * @param   in   the underlying input stream, or <code>null</code> if
       *          this instance is to be created without an underlying stream.
       */
      protected FilterInputStream(InputStream in) {
          this.in = in;
      }
  
      /**
       * Reads the next byte of data from this input stream. The value
       * byte is returned as an <code>int</code> in the range
       * <code>0</code> to <code>255</code>. If no byte is available
       * because the end of the stream has been reached, the value
       * <code>-1</code> is returned. This method blocks until input data
       * is available, the end of the stream is detected, or an exception
       * is thrown.
       * <p>
       * This method
       * simply performs <code>in.read()</code> and returns the result.
       *
       * @return     the next byte of data, or <code>-1</code> if the end of the
       *             stream is reached.
       * @exception  IOException  if an I/O error occurs.
       * @see        FilterInputStream#in
       */
      public int read() throws IOException {
          return in.read();
      }
  
      /**
       * Reads up to <code>byte.length</code> bytes of data from this
       * input stream into an array of bytes. This method blocks until some
       * input is available.
       * <p>
       * This method simply performs the call
       * <code>read(b, 0, b.length)</code> and returns
       * the  result. It is important that it does
       * <i>not</i> do <code>in.read(b)</code> instead;
       * certain subclasses of  <code>FilterInputStream</code>
       * depend on the implementation strategy actually
       * used.
       *
       * @param      b   the buffer into which the data is read.
       * @return     the total number of bytes read into the buffer, or
       *             <code>-1</code> if there is no more data because the end of
       *             the stream has been reached.
       * @exception  IOException  if an I/O error occurs.
       * @see        FilterInputStream#read(byte[], int, int)
       */
      public int read(byte b[]) throws IOException {
          return read(b, 0, b.length);
      }
  
      /**
       * Reads up to <code>len</code> bytes of data from this input stream
       * into an array of bytes. If <code>len</code> is not zero, the method
       * blocks until some input is available; otherwise, no
       * bytes are read and <code>0</code> is returned.
       * <p>
       * This method simply performs <code>in.read(b, off, len)</code>
       * and returns the result.
       *
       * @param      b     the buffer into which the data is read.
       * @param      off   the start offset in the destination array <code>b</code>
       * @param      len   the maximum number of bytes read.
       * @return     the total number of bytes read into the buffer, or
       *             <code>-1</code> if there is no more data because the end of
       *             the stream has been reached.
       * @exception  NullPointerException If <code>b</code> is <code>null</code>.
       * @exception  IndexOutOfBoundsException If <code>off</code> is negative,
       * <code>len</code> is negative, or <code>len</code> is greater than
       * <code>b.length - off</code>
       * @exception  IOException  if an I/O error occurs.
       * @see        FilterInputStream#in
       */
      public int read(byte b[], int off, int len) throws IOException {
          return in.read(b, off, len);
      }
  
      /**
       * Skips over and discards <code>n</code> bytes of data from the
       * input stream. The <code>skip</code> method may, for a variety of
       * reasons, end up skipping over some smaller number of bytes,
       * possibly <code>0</code>. The actual number of bytes skipped is
       * returned.
       * <p>
       * This method simply performs <code>in.skip(n)</code>.
       *
       * @param      n   the number of bytes to be skipped.
       * @return     the actual number of bytes skipped.
       * @exception  IOException  if the stream does not support seek,
       *                          or if some other I/O error occurs.
       */
      public long skip(long n) throws IOException {
          return in.skip(n);
      }
  
      /**
       * Returns an estimate of the number of bytes that can be read (or
       * skipped over) from this input stream without blocking by the next
       * caller of a method for this input stream. The next caller might be
       * the same thread or another thread.  A single read or skip of this
       * many bytes will not block, but may read or skip fewer bytes.
       * <p>
       * This method returns the result of {@link #in in}.available().
       *
       * @return     an estimate of the number of bytes that can be read (or skipped
       *             over) from this input stream without blocking.
       * @exception  IOException  if an I/O error occurs.
       */
      public int available() throws IOException {
          return in.available();
      }
  
      /**
       * Closes this input stream and releases any system resources
       * associated with the stream.
       * This
       * method simply performs <code>in.close()</code>.
       *
       * @exception  IOException  if an I/O error occurs.
       * @see        FilterInputStream#in
       */
      public void close() throws IOException {
          in.close();
      }
  
      /**
       * Marks the current position in this input stream. A subsequent
       * call to the <code>reset</code> method repositions this stream at
       * the last marked position so that subsequent reads re-read the same bytes.
       * <p>
       * The <code>readlimit</code> argument tells this input stream to
       * allow that many bytes to be read before the mark position gets
       * invalidated.
       * <p>
       * This method simply performs <code>in.mark(readlimit)</code>.
       *
       * @param   readlimit   the maximum limit of bytes that can be read before
       *                      the mark position becomes invalid.
       * @see     FilterInputStream#in
       * @see     FilterInputStream#reset()
       */
      public synchronized void mark(int readlimit) {
          in.mark(readlimit);
      }
  
      /**
       * Repositions this stream to the position at the time the
       * <code>mark</code> method was last called on this input stream.
       * <p>
       * This method
       * simply performs <code>in.reset()</code>.
       * <p>
       * Stream marks are intended to be used in
       * situations where you need to read ahead a little to see what's in
       * the stream. Often this is most easily done by invoking some
       * general parser. If the stream is of the type handled by the
       * parse, it just chugs along happily. If the stream is not of
       * that type, the parser should toss an exception when it fails.
       * If this happens within readlimit bytes, it allows the outer
       * code to reset the stream and try another parser.
       *
       * @exception  IOException  if the stream has not been marked or if the
       *               mark has been invalidated.
       * @see        FilterInputStream#in
       * @see        FilterInputStream#mark(int)
       */
      public synchronized void reset() throws IOException {
          in.reset();
      }
  
      /**
       * Tests if this input stream supports the <code>mark</code>
       * and <code>reset</code> methods.
       * This method
       * simply performs <code>in.markSupported()</code>.
       *
       * @return  <code>true</code> if this stream type supports the
       *          <code>mark</code> and <code>reset</code> method;
       *          <code>false</code> otherwise.
       * @see     FilterInputStream#in
       * @see     InputStream#mark(int)
       * @see     InputStream#reset()
       */
      public boolean markSupported() {
          return in.markSupported();
      }
  }
  