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    1   /*
    2    * Copyright (c) 2000, 2003, Oracle and/or its affiliates. All rights reserved.
    3    * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
    4    *
    5    * This code is free software; you can redistribute it and/or modify it
    6    * under the terms of the GNU General Public License version 2 only, as
    7    * published by the Free Software Foundation.  Oracle designates this
    8    * particular file as subject to the "Classpath" exception as provided
    9    * by Oracle in the LICENSE file that accompanied this code.
   10    *
   11    * This code is distributed in the hope that it will be useful, but WITHOUT
   12    * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
   13    * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
   14    * version 2 for more details (a copy is included in the LICENSE file that
   15    * accompanied this code).
   16    *
   17    * You should have received a copy of the GNU General Public License version
   18    * 2 along with this work; if not, write to the Free Software Foundation,
   19    * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
   20    *
   21    * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
   22    * or visit www.oracle.com if you need additional information or have any
   23    * questions.
   24    */
   25   
   26   package java.lang;
   27   
   28   
   29   /**
   30    * A <tt>CharSequence</tt> is a readable sequence of <code>char</code> values. This
   31    * interface provides uniform, read-only access to many different kinds of
   32    * <code>char</code> sequences.
   33    * A <code>char</code> value represents a character in the <i>Basic
   34    * Multilingual Plane (BMP)</i> or a surrogate. Refer to <a
   35    * href="Character.html#unicode">Unicode Character Representation</a> for details.
   36    *
   37    * <p> This interface does not refine the general contracts of the {@link
   38    * java.lang.Object#equals(java.lang.Object) equals} and {@link
   39    * java.lang.Object#hashCode() hashCode} methods.  The result of comparing two
   40    * objects that implement <tt>CharSequence</tt> is therefore, in general,
   41    * undefined.  Each object may be implemented by a different class, and there
   42    * is no guarantee that each class will be capable of testing its instances
   43    * for equality with those of the other.  It is therefore inappropriate to use
   44    * arbitrary <tt>CharSequence</tt> instances as elements in a set or as keys in
   45    * a map. </p>
   46    *
   47    * @author Mike McCloskey
   48    * @since 1.4
   49    * @spec JSR-51
   50    */
   51   
   52   public interface CharSequence {
   53   
   54       /**
   55        * Returns the length of this character sequence.  The length is the number
   56        * of 16-bit <code>char</code>s in the sequence.</p>
   57        *
   58        * @return  the number of <code>char</code>s in this sequence
   59        */
   60       int length();
   61   
   62       /**
   63        * Returns the <code>char</code> value at the specified index.  An index ranges from zero
   64        * to <tt>length() - 1</tt>.  The first <code>char</code> value of the sequence is at
   65        * index zero, the next at index one, and so on, as for array
   66        * indexing. </p>
   67        *
   68        * <p>If the <code>char</code> value specified by the index is a
   69        * <a href="{@docRoot}/java/lang/Character.html#unicode">surrogate</a>, the surrogate
   70        * value is returned.
   71        *
   72        * @param   index   the index of the <code>char</code> value to be returned
   73        *
   74        * @return  the specified <code>char</code> value
   75        *
   76        * @throws  IndexOutOfBoundsException
   77        *          if the <tt>index</tt> argument is negative or not less than
   78        *          <tt>length()</tt>
   79        */
   80       char charAt(int index);
   81   
   82       /**
   83        * Returns a new <code>CharSequence</code> that is a subsequence of this sequence.
   84        * The subsequence starts with the <code>char</code> value at the specified index and
   85        * ends with the <code>char</code> value at index <tt>end - 1</tt>.  The length
   86        * (in <code>char</code>s) of the
   87        * returned sequence is <tt>end - start</tt>, so if <tt>start == end</tt>
   88        * then an empty sequence is returned. </p>
   89        *
   90        * @param   start   the start index, inclusive
   91        * @param   end     the end index, exclusive
   92        *
   93        * @return  the specified subsequence
   94        *
   95        * @throws  IndexOutOfBoundsException
   96        *          if <tt>start</tt> or <tt>end</tt> are negative,
   97        *          if <tt>end</tt> is greater than <tt>length()</tt>,
   98        *          or if <tt>start</tt> is greater than <tt>end</tt>
   99        */
  100       CharSequence subSequence(int start, int end);
  101   
  102       /**
  103        * Returns a string containing the characters in this sequence in the same
  104        * order as this sequence.  The length of the string will be the length of
  105        * this sequence. </p>
  106        *
  107        * @return  a string consisting of exactly this sequence of characters
  108        */
  109       public String toString();
  110   
  111   }

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