/*
 * @(#)CharSequence.java	1.9 05/11/17
 *
 * Copyright 2006 Sun Microsystems, Inc. All rights reserved.
 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */

package java.lang;


/**
 * A <tt>CharSequence</tt> is a readable sequence of <code>char</code> values. This
 * interface provides uniform, read-only access to many different kinds of
 * <code>char</code> sequences.
 * A <code>char</code> value represents a character in the <i>Basic
 * Multilingual Plane (BMP)</i> or a surrogate. Refer to <a
 * href="Character.html#unicode">Unicode Character Representation</a> for details.
 *
 * <p> This interface does not refine the general contracts of the {@link
 * java.lang.Object#equals(java.lang.Object) equals} and {@link
 * java.lang.Object#hashCode() hashCode} methods.  The result of comparing two
 * objects that implement <tt>CharSequence</tt> is therefore, in general,
 * undefined.  Each object may be implemented by a different class, and there
 * is no guarantee that each class will be capable of testing its instances
 * for equality with those of the other.  It is therefore inappropriate to use
 * arbitrary <tt>CharSequence</tt> instances as elements in a set or as keys in
 * a map. </p>
 *
 * @author Mike McCloskey
 * @version 1.9 05/11/17
 * @since 1.4
 * @spec JSR-51
 */

public interface CharSequence {

    /**
     * Returns the length of this character sequence.  The length is the number
     * of 16-bit <code>char</code>s in the sequence.</p>
     *
     * @return  the number of <code>char</code>s in this sequence
     */
    int length();

    /**
     * Returns the <code>char</code> value at the specified index.  An index ranges from zero
     * to <tt>length() - 1</tt>.  The first <code>char</code> value of the sequence is at
     * index zero, the next at index one, and so on, as for array
     * indexing. </p>
     *
     * <p>If the <code>char</code> value specified by the index is a
     * <a href="Character.html#unicode">surrogate</a>, the surrogate
     * value is returned.
     *
     * @param   index   the index of the <code>char</code> value to be returned
     *
     * @return  the specified <code>char</code> value
     *
     * @throws  IndexOutOfBoundsException
     *          if the <tt>index</tt> argument is negative or not less than
     *          <tt>length()</tt>
     */
    char charAt(int index);

    /**
     * Returns a new <code>CharSequence</code> that is a subsequence of this sequence.
     * The subsequence starts with the <code>char</code> value at the specified index and
     * ends with the <code>char</code> value at index <tt>end - 1</tt>.  The length
     * (in <code>char</code>s) of the
     * returned sequence is <tt>end - start</tt>, so if <tt>start == end</tt>
     * then an empty sequence is returned. </p>
     * 
     * @param   start   the start index, inclusive
     * @param   end     the end index, exclusive
     *
     * @return  the specified subsequence
     *
     * @throws  IndexOutOfBoundsException
     *          if <tt>start</tt> or <tt>end</tt> are negative,
     *          if <tt>end</tt> is greater than <tt>length()</tt>,
     *          or if <tt>start</tt> is greater than <tt>end</tt>
     */
    CharSequence subSequence(int start, int end);

    /**
     * Returns a string containing the characters in this sequence in the same
     * order as this sequence.  The length of the string will be the length of
     * this sequence. </p>
     *
     * @return  a string consisting of exactly this sequence of characters
     */
    public String toString();

}