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 * Copyright (c) 1996, 2019, 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;

import java.nio.CharBuffer;

import java.util.Objects;

/**

 * 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       1.1

 */

public abstract class Reader implements Readable, Closeable {

    private static final int TRANSFER_BUFFER_SIZE = 8192;

    /**

     * Returns a new {@code Reader} that reads no characters. The returned

     * stream is initially open.  The stream is closed by calling the

     * {@code close()} method.  Subsequent calls to {@code close()} have no

     * effect.

     *

     * <p> While the stream is open, the {@code read()}, {@code read(char[])},

     * {@code read(char[], int, int)}, {@code read(Charbuffer)}, {@code

     * ready()}, {@code skip(long)}, and {@code transferTo()} methods all

     * behave as if end of stream has been reached. After the stream has been

     * closed, these methods all throw {@code IOException}.

     *

     * <p> The {@code markSupported()} method returns {@code false}.  The

     * {@code mark()} and {@code reset()} methods throw an {@code IOException}.

     *

     * <p> The {@link #lock object} used to synchronize operations on the

     * returned {@code Reader} is not specified.

     *

     * @return a {@code Reader} which reads no characters

     *

     * @since 11

     */

    public static Reader nullReader() {

        return new Reader() {

            private volatile boolean closed;

            private void ensureOpen() throws IOException {

                if (closed) {

                    throw new IOException("Stream closed");

                }

            }

            @Override

            public int read() throws IOException {

                ensureOpen();

                return -1;

            }

            @Override

            public int read(char[] cbuf, int off, int len) throws IOException {

                Objects.checkFromIndexSize(off, len, cbuf.length);

                ensureOpen();

                if (len == 0) {

                    return 0;

                }

                return -1;

            }

            @Override

            public int read(CharBuffer target) throws IOException {

                Objects.requireNonNull(target);

                ensureOpen();

                if (target.hasRemaining()) {

                    return -1;

                }

                return 0;

            }

            @Override

            public boolean ready() throws IOException {

                ensureOpen();

                return false;

            }

            @Override

            public long skip(long n) throws IOException {

                ensureOpen();

                return 0L;

            }

            @Override

            public long transferTo(Writer out) throws IOException {

                Objects.requireNonNull(out);

                ensureOpen();

                return 0L;

            }

            @Override

            public void close() {

                closed = true;

            }

        };

    }

    /**

     * 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 {@code this} 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

     *             ({@code 0x00-0xffff}), or -1 if the end of the stream has

     *             been reached

     *

     * @throws     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

     *

     * @throws      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

     *

     * @throws     IOException  If an I/O error occurs

     * @throws     IndexOutOfBoundsException

     *             If {@code off} is negative, or {@code len} is negative,

     *             or {@code len} is greater than {@code cbuf.length - off}

     */

    public abstract 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

     *

     * @throws     IllegalArgumentException  If {@code n} is negative.

     * @throws     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.

     *

     * @throws     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.

     *

     * @throws     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().

     *

     * @throws     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.

     *

     * @throws     IOException  If an I/O error occurs

     */

     public abstract void close() throws IOException;

    /**

     * Reads all characters from this reader and writes the characters to the

     * given writer in the order that they are read. On return, this reader

     * will be at end of the stream. This method does not close either reader

     * or writer.

     * <p>

     * This method may block indefinitely reading from the reader, or

     * writing to the writer. The behavior for the case where the reader

     * and/or writer is <i>asynchronously closed</i>, or the thread

     * interrupted during the transfer, is highly reader and writer

     * specific, and therefore not specified.

     * <p>

     * If an I/O error occurs reading from the reader or writing to the

     * writer, then it may do so after some characters have been read or

     * written. Consequently the reader may not be at end of the stream and

     * one, or both, streams may be in an inconsistent state. It is strongly

     * recommended that both streams be promptly closed if an I/O error occurs.

     *

     * @param  out the writer, non-null

     * @return the number of characters transferred

     * @throws IOException if an I/O error occurs when reading or writing

     * @throws NullPointerException if {@code out} is {@code null}

     *

     * @since 10

     */

    public long transferTo(Writer out) throws IOException {

        Objects.requireNonNull(out, "out");

        long transferred = 0;

        char[] buffer = new char[TRANSFER_BUFFER_SIZE];

        int nRead;

        while ((nRead = read(buffer, 0, TRANSFER_BUFFER_SIZE)) >= 0) {

            out.write(buffer, 0, nRead);

            transferred += nRead;

        }

        return transferred;

    }

}