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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 whose source is a string.
	*
	* @author Mark Reinhold
	* @since 1.1
	*/

	public class StringReader extends Reader {

	private String str;
	private int length;
	private int next = 0;
	private int mark = 0;

	/**
	* Creates a new string reader.
	*
	* @param s String providing the character stream.
	*/
	public StringReader(String s) {
	this.str = s;
	this.length = s.length();
	}

	/** Check to make sure that the stream has not been closed */
	private void ensureOpen() throws IOException {
	if (str == 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 (next >= length)
	return -1;
	return str.charAt(next++);
	}
	}

	/**
	* Reads characters into a portion of an array.
	*
	* <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 {@inheritDoc}
	* @param off {@inheritDoc}
	* @param len {@inheritDoc}
	*
	* @return {@inheritDoc}
	*
	* @throws IndexOutOfBoundsException {@inheritDoc}
	* @throws IOException {@inheritDoc}
	*/
	public int read(char[] cbuf, int off, int len) throws IOException {
	synchronized (lock) {
	ensureOpen();
	Objects.checkFromIndexSize(off, len, cbuf.length);
	if (len == 0) {
	return 0;
	}
	if (next >= length)
	return -1;
	int n = Math.min(length - next, len);
	str.getChars(next, next + n, cbuf, off);
	next += n;
	return n;
	}
	}

	/**
	* Skips characters. If the stream is already at its end before this method
	* is invoked, then no characters are skipped and zero is returned.
	*
	* <p>The {@code n} parameter may be negative, even though the
	* {@code skip} method of the {@link Reader} superclass throws
	* an exception in this case. Negative values of {@code n} cause the
	* stream to skip backwards. Negative return values indicate a skip
	* backwards. It is not possible to skip backwards past the beginning of
	* the string.
	*
	* <p>If the entire string has been read or skipped, then this method has
	* no effect and always returns {@code 0}.
	*
	* @param n {@inheritDoc}
	*
	* @return {@inheritDoc}
	*
	* @throws IOException {@inheritDoc}
	*/
	public long skip(long n) throws IOException {
	synchronized (lock) {
	ensureOpen();
	if (next >= length)
	return 0;
	// Bound skip by beginning and end of the source
	long r = Math.min(length - next, n);
	r = Math.max(-next, r);
	next += r;
	return r;
	}
	}

	/**
	* Tells whether this stream is ready to be read.
	*
	* @return True if the next read() is guaranteed not to block for input
	*
	* @throws IOException If the stream is closed
	*/
	public boolean ready() throws IOException {
	synchronized (lock) {
	ensureOpen();
	return true;
	}
	}

	/**
	* Tells whether this stream supports the mark() operation, which it does.
	*/
	public boolean markSupported() {
	return true;
	}

	/**
	* Marks the present position in the stream. Subsequent calls to reset()
	* will reposition the stream to this point.
	*
	* @param readAheadLimit Limit on the number of characters that may be
	* read while still preserving the mark. Because
	* the stream's input comes from a string, there
	* is no actual limit, so this argument must not
	* be negative, but is otherwise ignored.
	*
	* @throws IllegalArgumentException If {@code readAheadLimit < 0}
	* @throws IOException If an I/O error occurs
	*/
	public void mark(int readAheadLimit) throws IOException {
	if (readAheadLimit < 0){
	throw new IllegalArgumentException("Read-ahead limit < 0");
	}
	synchronized (lock) {
	ensureOpen();
	mark = next;
	}
	}

	/**
	* Resets the stream to the most recent mark, or to the beginning of the
	* string if it has never been marked.
	*
	* @throws IOException If an I/O error occurs
	*/
	public void reset() throws IOException {
	synchronized (lock) {
	ensureOpen();
	next = mark;
	}
	}

	/**
	* Closes the stream and releases any system resources associated with
	* it. Once the stream has been closed, further read(),
	* ready(), mark(), or reset() 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.
	*/
	public void close() {
	synchronized (lock) {
	str = null;
	}
	}
	}

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