/*

 * Copyright 1996-2006 Sun Microsystems, Inc.  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.  Sun designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Sun 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,

 * CA 95054 USA or visit www.sun.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 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;

}