content: /*
   * Copyright (c) 1996, 2012, 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
   * or visit www.oracle.com if you need additional information or have any
   * questions.
   */
  
  package java.io;
  
  
  /**
   * Abstract class for reading character streams.  The only methods that a
   * subclass must implement are read(char[], int, int) and close().  Most
   * subclasses, however, will override some of the methods defined here in order
   * to provide higher efficiency, additional functionality, or both.
   *
   *
   * @see BufferedReader
   * @see   LineNumberReader
   * @see CharArrayReader
   * @see InputStreamReader
   * @see   FileReader
   * @see FilterReader
   * @see   PushbackReader
   * @see PipedReader
   * @see StringReader
   * @see Writer
   *
   * @author      Mark Reinhold
   * @since       JDK1.1
   */
  
  public abstract class Reader implements Readable, Closeable {
  
      /**
       * The object used to synchronize operations on this stream.  For
       * efficiency, a character-stream object may use an object other than
       * itself to protect critical sections.  A subclass should therefore use
       * the object in this field rather than <tt>this</tt> or a synchronized
       * method.
       */
      protected Object lock;
  
      /**
       * Creates a new character-stream reader whose critical sections will
       * synchronize on the reader itself.
       */
      protected Reader() {
          this.lock = this;
      }
  
      /**
       * Creates a new character-stream reader whose critical sections will
       * synchronize on the given object.
       *
       * @param lock  The Object to synchronize on.
       */
      protected Reader(Object lock) {
          if (lock == null) {
              throw new NullPointerException();
          }
          this.lock = lock;
      }
  
      /**
       * Attempts to read characters into the specified character buffer.
       * The buffer is used as a repository of characters as-is: the only
       * changes made are the results of a put operation. No flipping or
       * rewinding of the buffer is performed.
       *
       * @param target the buffer to read characters into
       * @return The number of characters added to the buffer, or
       *         -1 if this source of characters is at its end
       * @throws IOException if an I/O error occurs
       * @throws NullPointerException if target is null
       * @throws java.nio.ReadOnlyBufferException if target is a read only buffer
       * @since 1.5
       */
      public int read(java.nio.CharBuffer target) throws IOException {
          int len = target.remaining();
          char[] cbuf = new char[len];
          int n = read(cbuf, 0, len);
          if (n > 0)
              target.put(cbuf, 0, n);
          return n;
      }
  
      /**
       * Reads a single character.  This method will block until a character is
       * available, an I/O error occurs, or the end of the stream is reached.
       *
       * <p> Subclasses that intend to support efficient single-character input
       * should override this method.
       *
       * @return     The character read, as an integer in the range 0 to 65535
       *             (<tt>0x00-0xffff</tt>), or -1 if the end of the stream has
       *             been reached
       *
       * @exception  IOException  If an I/O error occurs
       */
      public int read() throws IOException {
          char cb[] = new char[1];
          if (read(cb, 0, 1) == -1)
              return -1;
          else
              return cb[0];
      }
  
      /**
       * Reads characters into an array.  This method will block until some input
       * is available, an I/O error occurs, or the end of the stream is reached.
       *
       * @param       cbuf  Destination buffer
       *
       * @return      The number of characters read, or -1
       *              if the end of the stream
       *              has been reached
       *
       * @exception   IOException  If an I/O error occurs
       */
      public int read(char cbuf[]) throws IOException {
          return read(cbuf, 0, cbuf.length);
      }
  
      /**
       * Reads characters into a portion of an array.  This method will block
       * until some input is available, an I/O error occurs, or the end of the
       * stream is reached.
       *
       * @param      cbuf  Destination buffer
       * @param      off   Offset at which to start storing characters
       * @param      len   Maximum number of characters to read
       *
       * @return     The number of characters read, or -1 if the end of the
       *             stream has been reached
       *
       * @exception  IOException  If an I/O error occurs
       */
      abstract public int read(char cbuf[], int off, int len) throws IOException;
  
      /** Maximum skip-buffer size */
      private static final int maxSkipBufferSize = 8192;
  
      /** Skip buffer, null until allocated */
      private char skipBuffer[] = null;
  
      /**
       * Skips characters.  This method will block until some characters are
       * available, an I/O error occurs, or the end of the stream is reached.
       *
       * @param  n  The number of characters to skip
       *
       * @return    The number of characters actually skipped
       *
       * @exception  IllegalArgumentException  If <code>n</code> is negative.
       * @exception  IOException  If an I/O error occurs
       */
      public long skip(long n) throws IOException {
          if (n < 0L)
              throw new IllegalArgumentException("skip value is negative");
          int nn = (int) Math.min(n, maxSkipBufferSize);
          synchronized (lock) {
              if ((skipBuffer == null) || (skipBuffer.length < nn))
                  skipBuffer = new char[nn];
              long r = n;
              while (r > 0) {
                  int nc = read(skipBuffer, 0, (int)Math.min(r, nn));
                  if (nc == -1)
                      break;
                  r -= nc;
              }
              return n - r;
          }
      }
  
      /**
       * Tells whether this stream is ready to be read.
       *
       * @return True if the next read() is guaranteed not to block for input,
       * false otherwise.  Note that returning false does not guarantee that the
       * next read will block.
       *
       * @exception  IOException  If an I/O error occurs
       */
      public boolean ready() throws IOException {
          return false;
      }
  
      /**
       * Tells whether this stream supports the mark() operation. The default
       * implementation always returns false. Subclasses should override this
       * method.
       *
       * @return true if and only if this stream supports the mark operation.
       */
      public boolean markSupported() {
          return false;
      }
  
      /**
       * Marks the present position in the stream.  Subsequent calls to reset()
       * will attempt to reposition the stream to this point.  Not all
       * character-input streams support the mark() operation.
       *
       * @param  readAheadLimit  Limit on the number of characters that may be
       *                         read while still preserving the mark.  After
       *                         reading this many characters, attempting to
       *                         reset the stream may fail.
       *
       * @exception  IOException  If the stream does not support mark(),
       *                          or if some other I/O error occurs
       */
      public void mark(int readAheadLimit) throws IOException {
          throw new IOException("mark() not supported");
      }
  
      /**
       * Resets the stream.  If the stream has been marked, then attempt to
       * reposition it at the mark.  If the stream has not been marked, then
       * attempt to reset it in some way appropriate to the particular stream,
       * for example by repositioning it to its starting point.  Not all
       * character-input streams support the reset() operation, and some support
       * reset() without supporting mark().
       *
       * @exception  IOException  If the stream has not been marked,
       *                          or if the mark has been invalidated,
       *                          or if the stream does not support reset(),
       *                          or if some other I/O error occurs
       */
      public void reset() throws IOException {
          throw new IOException("reset() not supported");
      }
  
      /**
       * Closes the stream and releases any system resources associated with
       * it.  Once the stream has been closed, further read(), ready(),
       * mark(), reset(), or skip() invocations will throw an IOException.
       * Closing a previously closed stream has no effect.
       *
       * @exception  IOException  If an I/O error occurs
       */
       abstract public void close() throws IOException;
  
  }
  