001/* CharSequence.java -- Anything that has an indexed sequence of chars
002   Copyright (C) 2001, 2002 Free Software Foundation, Inc.
003
004This file is part of GNU Classpath.
005
006GNU Classpath is free software; you can redistribute it and/or modify
007it under the terms of the GNU General Public License as published by
008the Free Software Foundation; either version 2, or (at your option)
009any later version.
010
011GNU Classpath is distributed in the hope that it will be useful, but
012WITHOUT ANY WARRANTY; without even the implied warranty of
013MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
014General Public License for more details.
015
016You should have received a copy of the GNU General Public License
017along with GNU Classpath; see the file COPYING.  If not, write to the
018Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
01902110-1301 USA.
020
021Linking this library statically or dynamically with other modules is
022making a combined work based on this library.  Thus, the terms and
023conditions of the GNU General Public License cover the whole
024combination.
025
026As a special exception, the copyright holders of this library give you
027permission to link this library with independent modules to produce an
028executable, regardless of the license terms of these independent
029modules, and to copy and distribute the resulting executable under
030terms of your choice, provided that you also meet, for each linked
031independent module, the terms and conditions of the license of that
032module.  An independent module is a module which is not derived from
033or based on this library.  If you modify this library, you may extend
034this exception to your version of the library, but you are not
035obligated to do so.  If you do not wish to do so, delete this
036exception statement from your version. */
037
038
039package java.lang;
040
041/**
042 * General functions on a sequence of chars. This interface is implemented
043 * by <code>String</code>, <code>StringBuffer</code> and
044 * <code>CharBuffer</code> to give a uniform way to get chars at a certain
045 * index, the number of characters in the sequence and a subrange of the
046 * chars. Indexes start at 0 and the last index is <code>length()-1</code>.
047 *
048 * <p>Even when classes implement this interface they are not always
049 * exchangeble because they might implement their compare, equals or hash
050 * function differently. This means that in general one should not use a
051 * <code>CharSequence</code> as keys in collections since two sequences
052 * with the same chars at the same indexes with the same length might not
053 * have the same hash code, be equal or be comparable since the are
054 * represented by different classes.
055 *
056 * @author Mark Wielaard (mark@klomp.org)
057 * @since 1.4
058 * @status updated to 1.4
059 */
060public interface CharSequence
061{
062  /**
063   * Returns the character at the given index.
064   *
065   * @param i the index to retrieve from
066   * @return the character at that location
067   * @throws IndexOutOfBoundsException if i &lt; 0 || i &gt;= length() - 1
068   */
069  char charAt(int i);
070
071  /**
072   * Returns the length of the sequence. This is the number of 16-bit
073   * characters in the sequence, which may differ from the length of the
074   * underlying encoding.
075   *
076   * @return the sequence length
077   */
078  int length();
079
080  /**
081   * Returns a new <code>CharSequence</code> of the indicated range.
082   *
083   * @param begin the start index (inclusive)
084   * @param end the end index (exclusive)
085   * @return a subsequence of this
086   * @throws IndexOutOfBoundsException if begin &gt; end || begin &lt; 0 ||
087   *         end &gt; length()
088   */
089  CharSequence subSequence(int begin, int end);
090
091  /**
092   * Returns the complete <code>CharSequence</code> as a <code>String</code>.
093   * Classes that implement this interface should return a <code>String</code>
094   * which contains only the characters in the sequence in the correct order.
095   *
096   * @return the character sequence as a String
097   */
098  String toString();
099}