content: /*
   * Copyright (c) 1996, 2013, 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;
  
  
  /**
   * A character stream whose source is a string.
   *
   * @author      Mark Reinhold
   * @since       JDK1.1
   */
  
  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
       *
       * @exception  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.
       *
       * @param      cbuf  Destination buffer
       * @param      off   Offset at which to start writing 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
       */
      public int read(char cbuf[], int off, int len) throws IOException {
          synchronized (lock) {
              ensureOpen();
              if ((off < 0) || (off > cbuf.length) || (len < 0) ||
                  ((off + len) > cbuf.length) || ((off + len) < 0)) {
                  throw new IndexOutOfBoundsException();
              } else 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 the specified number of characters in the stream. Returns
       * the number of characters that were skipped.
       *
       * <p>The <code>ns</code> parameter may be negative, even though the
       * <code>skip</code> method of the {@link Reader} superclass throws
       * an exception in this case. Negative values of <code>ns</code> 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 0.
       *
       * @exception  IOException  If an I/O error occurs
       */
      public long skip(long ns) throws IOException {
          synchronized (lock) {
              ensureOpen();
              if (next >= length)
                  return 0;
              // Bound skip by beginning and end of the source
              long n = Math.min(length - next, ns);
              n = Math.max(-next, n);
              next += n;
              return n;
          }
      }
  
      /**
       * Tells whether this stream is ready to be read.
       *
       * @return True if the next read() is guaranteed not to block for input
       *
       * @exception  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.
       *
       * @exception  IllegalArgumentException  If {@code readAheadLimit < 0}
       * @exception  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.
       *
       * @exception  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.
       */
      public void close() {
          str = null;
      }
  }
  