/*

  * Copyright (c) 1996, 2006, 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;

 /**

  * 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 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;

 }