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/* gnu/regexp/CharIndexed.java

   Copyright (C) 1998-2001, 2004, 2006 Free Software Foundation, Inc.

This file is part of GNU Classpath.

GNU Classpath is free software; you can redistribute it and/or modify

it under the terms of the GNU General Public License as published by

the Free Software Foundation; either version 2, or (at your option)

any later version.

GNU Classpath 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 for more details.

You should have received a copy of the GNU General Public License

along with GNU Classpath; see the file COPYING.  If not, write to the

Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA

02110-1301 USA.

Linking this library statically or dynamically with other modules is

making a combined work based on this library.  Thus, the terms and

conditions of the GNU General Public License cover the whole

combination.

As a special exception, the copyright holders of this library give you

permission to link this library with independent modules to produce an

executable, regardless of the license terms of these independent

modules, and to copy and distribute the resulting executable under

terms of your choice, provided that you also meet, for each linked

independent module, the terms and conditions of the license of that

module.  An independent module is a module which is not derived from

or based on this library.  If you modify this library, you may extend

this exception to your version of the library, but you are not

obligated to do so.  If you do not wish to do so, delete this

exception statement from your version. */

package gnu.regexp;

/**

 * Defines the interface used internally so that different types of source

 * text can be accessed in the same way.  Built-in concrete classes provide

 * support for String, StringBuffer, InputStream and char[] types.

 * A class that is CharIndexed supports the notion of a cursor within a

 * block of text.  The cursor must be able to be advanced via the move()

 * method.  The charAt() method returns the character at the cursor position

 * plus a given offset.

 *

 * @author <A HREF="mailto:wes@cacas.org">Wes Biggs</A>

 */

public interface CharIndexed {

    /**

     * Defines a constant (0xFFFF was somewhat arbitrarily chosen)

     * that can be returned by the charAt() function indicating that

     * the specified index is out of range.

     */

    char OUT_OF_BOUNDS = '\uFFFF';

    /**

     * Returns the character at the given offset past the current cursor

     * position in the input.  The index of the current position is zero.

     * It is possible for this method to be called with a negative index.

     * This happens when using the '^' operator in multiline matching mode

     * or the '\b' or '\<' word boundary operators.  In any case, the lower

     * bound is currently fixed at -2 (for '^' with a two-character newline).

     *

     * @param index the offset position in the character field to examine

     * @return the character at the specified index, or the OUT_OF_BOUNDS

     *   character defined by this interface.

     */

    char charAt(int index);

    /**

     * Shifts the input buffer by a given number of positions.  Returns

     * true if the new cursor position is valid.

     */

    boolean move(int index);

    /**

     * Returns true if the most recent move() operation placed the cursor

     * position at a valid position in the input.

     */

    boolean isValid();

    /**

     * Returns another CharIndexed containing length characters to the left

     * of the given index. The given length is an expected maximum and

     * the returned CharIndexed may not necessarily contain so many characters.

     */

    CharIndexed lookBehind(int index, int length);

    /**

     * Returns the effective length of this CharIndexed

     */

    int length();

}