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	/*
	* Copyright (c) 1996, 2021, 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;


	import java.nio.CharBuffer;
	import java.nio.ReadOnlyBufferException;
	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(CharBuffer target) throws IOException {
	if (target.isReadOnly())
	throw new ReadOnlyBufferException();

	int nread;
	if (target.hasArray()) {
	char[] cbuf = target.array();
	int pos = target.position();
	int rem = Math.max(target.limit() - pos, 0);
	int off = target.arrayOffset() + pos;
	nread = this.read(cbuf, off, rem);
	if (nread > 0)
	target.position(pos + nread);
	} else {
	int len = target.remaining();
	char[] cbuf = new char[len];
	nread = read(cbuf, 0, len);
	if (nread > 0)
	target.put(cbuf, 0, nread);
	}
	return nread;
	}

	/**
	* 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.
	*
	* <p> If the length of {@code cbuf} is zero, then no characters are read
	* and {@code 0} is returned; otherwise, there is an attempt to read at
	* least one character. If no character is available because the stream is
	* at its end, the value {@code -1} is returned; otherwise, at least one
	* character is read and stored into {@code cbuf}.
	*
	* @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.
	*
	* <p> If {@code len} is zero, then no characters are read and {@code 0} is
	* returned; otherwise, there is an attempt to read at least one character.
	* If no character is available because the stream is at its end, the value
	* {@code -1} is returned; otherwise, at least one character is read and
	* stored into {@code cbuf}.
	*
	* @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 IndexOutOfBoundsException
	* If {@code off} is negative, or {@code len} is negative,
	* or {@code len} is greater than {@code cbuf.length - off}
	* @throws IOException If an I/O error occurs
	*/
	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.
	* If the stream is already at its end before this method is invoked,
	* then no characters are skipped and zero is returned.
	*
	* @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;
	}

	}

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