001    /* CharSequence.java -- Anything that has an indexed sequence of chars
002       Copyright (C) 2001, 2002 Free Software Foundation, Inc.
003    
004    This file is part of GNU Classpath.
005    
006    GNU Classpath is free software; you can redistribute it and/or modify
007    it under the terms of the GNU General Public License as published by
008    the Free Software Foundation; either version 2, or (at your option)
009    any later version.
010    
011    GNU Classpath is distributed in the hope that it will be useful, but
012    WITHOUT ANY WARRANTY; without even the implied warranty of
013    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
014    General Public License for more details.
015    
016    You should have received a copy of the GNU General Public License
017    along with GNU Classpath; see the file COPYING.  If not, write to the
018    Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
019    02110-1301 USA.
020    
021    Linking this library statically or dynamically with other modules is
022    making a combined work based on this library.  Thus, the terms and
023    conditions of the GNU General Public License cover the whole
024    combination.
025    
026    As a special exception, the copyright holders of this library give you
027    permission to link this library with independent modules to produce an
028    executable, regardless of the license terms of these independent
029    modules, and to copy and distribute the resulting executable under
030    terms of your choice, provided that you also meet, for each linked
031    independent module, the terms and conditions of the license of that
032    module.  An independent module is a module which is not derived from
033    or based on this library.  If you modify this library, you may extend
034    this exception to your version of the library, but you are not
035    obligated to do so.  If you do not wish to do so, delete this
036    exception statement from your version. */
037    
038    
039    package 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     */
060    public 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    }