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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.util.Objects;

	/**
	* A character-stream reader that allows characters to be pushed back into the
	* stream.
	*
	* @author Mark Reinhold
	* @since 1.1
	*/

	public class PushbackReader extends FilterReader {

	/** Pushback buffer */
	private char[] buf;

	/** Current position in buffer */
	private int pos;

	/**
	* Creates a new pushback reader with a pushback buffer of the given size.
	*
	* @param in The reader from which characters will be read
	* @param size The size of the pushback buffer
	* @throws IllegalArgumentException if {@code size <= 0}
	*/
	public PushbackReader(Reader in, int size) {
	super(in);
	if (size <= 0) {
	throw new IllegalArgumentException("size <= 0");
	}
	this.buf = new char[size];
	this.pos = size;
	}

	/**
	* Creates a new pushback reader with a one-character pushback buffer.
	*
	* @param in The reader from which characters will be read
	*/
	public PushbackReader(Reader in) {
	this(in, 1);
	}

	/** Checks to make sure that the stream has not been closed. */
	private void ensureOpen() throws IOException {
	if (buf == null)
	throw new IOException("Stream closed");
	}

	/**
	* Reads a single character.
	*
	* @return The character read, or -1 if the end of the stream has been
	* reached
	*
	* @throws IOException If an I/O error occurs
	*/
	public int read() throws IOException {
	synchronized (lock) {
	ensureOpen();
	if (pos < buf.length)
	return buf[pos++];
	else
	return super.read();
	}
	}

	/**
	* {@inheritDoc}
	*/
	public int read(char[] cbuf, int off, int len) throws IOException {
	synchronized (lock) {
	ensureOpen();
	try {
	Objects.checkFromIndexSize(off, len, cbuf.length);
	if (len == 0) {
	return 0;
	}
	int avail = buf.length - pos;
	if (avail > 0) {
	if (len < avail)
	avail = len;
	System.arraycopy(buf, pos, cbuf, off, avail);
	pos += avail;
	off += avail;
	len -= avail;
	}
	if (len > 0) {
	len = super.read(cbuf, off, len);
	if (len == -1) {
	return (avail == 0) ? -1 : avail;
	}
	return avail + len;
	}
	return avail;
	} catch (ArrayIndexOutOfBoundsException e) {
	throw new IndexOutOfBoundsException();
	}
	}
	}

	/**
	* Pushes back a single character by copying it to the front of the
	* pushback buffer. After this method returns, the next character to be read
	* will have the value {@code (char)c}.
	*
	* @param c The int value representing a character to be pushed back
	*
	* @throws IOException If the pushback buffer is full,
	* or if some other I/O error occurs
	*/
	public void unread(int c) throws IOException {
	synchronized (lock) {
	ensureOpen();
	if (pos == 0)
	throw new IOException("Pushback buffer overflow");
	buf[--pos] = (char) c;
	}
	}

	/**
	* Pushes back a portion of an array of characters by copying it to the
	* front of the pushback buffer. After this method returns, the next
	* character to be read will have the value {@code cbuf[off]}, the
	* character after that will have the value {@code cbuf[off+1]}, and
	* so forth.
	*
	* @param cbuf Character array
	* @param off Offset of first character to push back
	* @param len Number of characters to push back
	*
	* @throws IOException If there is insufficient room in the pushback
	* buffer, or if some other I/O error occurs
	*/
	public void unread(char[] cbuf, int off, int len) throws IOException {
	synchronized (lock) {
	ensureOpen();
	if (len > pos)
	throw new IOException("Pushback buffer overflow");
	pos -= len;
	System.arraycopy(cbuf, off, buf, pos, len);
	}
	}

	/**
	* Pushes back an array of characters by copying it to the front of the
	* pushback buffer. After this method returns, the next character to be
	* read will have the value {@code cbuf[0]}, the character after that
	* will have the value {@code cbuf[1]}, and so forth.
	*
	* @param cbuf Character array to push back
	*
	* @throws IOException If there is insufficient room in the pushback
	* buffer, or if some other I/O error occurs
	*/
	public void unread(char[] cbuf) throws IOException {
	unread(cbuf, 0, cbuf.length);
	}

	/**
	* Tells whether this stream is ready to be read.
	*
	* @throws IOException If an I/O error occurs
	*/
	public boolean ready() throws IOException {
	synchronized (lock) {
	ensureOpen();
	return (pos < buf.length) \|\| super.ready();
	}
	}

	/**
	* Marks the present position in the stream. The {@code mark}
	* for class {@code PushbackReader} always throws an exception.
	*
	* @throws IOException Always, since mark is not supported
	*/
	public void mark(int readAheadLimit) throws IOException {
	throw new IOException("mark/reset not supported");
	}

	/**
	* Resets the stream. The {@code reset} method of
	* {@code PushbackReader} always throws an exception.
	*
	* @throws IOException Always, since reset is not supported
	*/
	public void reset() throws IOException {
	throw new IOException("mark/reset not supported");
	}

	/**
	* Tells whether this stream supports the mark() operation, which it does
	* not.
	*/
	public boolean markSupported() {
	return false;
	}

	/**
	* Closes the stream and releases any system resources associated with
	* it. Once the stream has been closed, further read(),
	* unread(), ready(), or skip() invocations will throw an IOException.
	* Closing a previously closed stream has no effect. This method will block
	* while there is another thread blocking on the reader.
	*
	* @throws IOException If an I/O error occurs
	*/
	public void close() throws IOException {
	synchronized (lock) {
	super.close();
	buf = null;
	}
	}

	/**
	* {@inheritDoc}
	*/
	public long skip(long n) throws IOException {
	if (n < 0L)
	throw new IllegalArgumentException("skip value is negative");
	synchronized (lock) {
	ensureOpen();
	int avail = buf.length - pos;
	if (avail > 0) {
	if (n <= avail) {
	pos += n;
	return n;
	} else {
	pos = buf.length;
	n -= avail;
	}
	}
	return avail + super.skip(n);
	}
	}
	}

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