/*

  * Copyright (c) 1996, 2005, 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 readAheadLimit is < 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;

     }

 }