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 * Copyright (c) 2000, 2013, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code 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

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

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

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

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 */

package java.lang;

import java.util.NoSuchElementException;

import java.util.PrimitiveIterator;

import java.util.Spliterator;

import java.util.Spliterators;

import java.util.function.IntConsumer;

import java.util.stream.IntStream;

import java.util.stream.StreamSupport;

/**

 * A {@code CharSequence} is a readable sequence of {@code char} values. This

 * interface provides uniform, read-only access to many different kinds of

 * {@code char} sequences.

 * A {@code char} 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 {@code CharSequence} 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 {@code CharSequence} instances as elements in a set or as keys in

 * a map. </p>

 *

 * @author Mike McCloskey

 * @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}s in the sequence.

     *

     * @return  the number of {@code char}s in this sequence

     */

    int length();

    /**

     * Returns the {@code char} value at the specified index.  An index ranges from zero

     * to {@code length() - 1}.  The first {@code char} value of the sequence is at

     * index zero, the next at index one, and so on, as for array

     * indexing.

     *

     * <p>If the {@code char} value specified by the index is a

     * <a href="{@docRoot}/java/lang/Character.html#unicode">surrogate</a>, the surrogate

     * value is returned.

     *

     * @param   index   the index of the {@code char} value to be returned

     *

     * @return  the specified {@code char} value

     *

     * @throws  IndexOutOfBoundsException

     *          if the {@code index} argument is negative or not less than

     *          {@code length()}

     */

    char charAt(int index);

    /**

     * Returns a {@code CharSequence} that is a subsequence of this sequence.

     * The subsequence starts with the {@code char} value at the specified index and

     * ends with the {@code char} value at index {@code end - 1}.  The length

     * (in {@code char}s) of the

     * returned sequence is {@code end - start}, so if {@code start == end}

     * then an empty sequence is returned.

     *

     * @param   start   the start index, inclusive

     * @param   end     the end index, exclusive

     *

     * @return  the specified subsequence

     *

     * @throws  IndexOutOfBoundsException

     *          if {@code start} or {@code end} are negative,

     *          if {@code end} is greater than {@code length()},

     *          or if {@code start} is greater than {@code end}

     */

    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.

     *

     * @return  a string consisting of exactly this sequence of characters

     */

    public String toString();

    /**

     * Returns a stream of {@code int} zero-extending the {@code char} values

     * from this sequence.  Any char which maps to a <a

     * href="{@docRoot}/java/lang/Character.html#unicode">surrogate code

     * point</a> is passed through uninterpreted.

     *

     * <p>If the sequence is mutated while the stream is being read, the

     * result is undefined.

     *

     * @return an IntStream of char values from this sequence

     * @since 1.8

     */

    public default IntStream chars() {

        class CharIterator implements PrimitiveIterator.OfInt {

            int cur = 0;

            public boolean hasNext() {

                return cur < length();

            }

            public int nextInt() {

                if (hasNext()) {

                    return charAt(cur++);

                } else {

                    throw new NoSuchElementException();

                }

            }

            @Override

            public void forEachRemaining(IntConsumer block) {

                for (; cur < length(); cur++) {

                    block.accept(charAt(cur));

                }

            }

        }

        return StreamSupport.intStream(() ->

                Spliterators.spliterator(

                        new CharIterator(),

                        length(),

                        Spliterator.ORDERED),

                Spliterator.SUBSIZED | Spliterator.SIZED | Spliterator.ORDERED,

                false);

    }

    /**

     * Returns a stream of code point values from this sequence.  Any surrogate

     * pairs encountered in the sequence are combined as if by {@linkplain

     * Character#toCodePoint Character.toCodePoint} and the result is passed

     * to the stream. Any other code units, including ordinary BMP characters,

     * unpaired surrogates, and undefined code units, are zero-extended to

     * {@code int} values which are then passed to the stream.

     *

     * <p>If the sequence is mutated while the stream is being read, the result

     * is undefined.

     *

     * @return an IntStream of Unicode code points from this sequence

     * @since 1.8

     */

    public default IntStream codePoints() {

        class CodePointIterator implements PrimitiveIterator.OfInt {

            int cur = 0;

            @Override

            public void forEachRemaining(IntConsumer block) {

                final int length = length();

                int i = cur;

                try {

                    while (i < length) {

                        char c1 = charAt(i++);

                        if (!Character.isHighSurrogate(c1) || i >= length) {

                            block.accept(c1);

                        } else {

                            char c2 = charAt(i);

                            if (Character.isLowSurrogate(c2)) {

                                i++;

                                block.accept(Character.toCodePoint(c1, c2));

                            } else {

                                block.accept(c1);

                            }

                        }

                    }

                } finally {

                    cur = i;

                }

            }

            public boolean hasNext() {

                return cur < length();

            }

            public int nextInt() {

                final int length = length();

                if (cur >= length) {

                    throw new NoSuchElementException();

                }

                char c1 = charAt(cur++);

                if (Character.isHighSurrogate(c1) && cur < length) {

                    char c2 = charAt(cur);

                    if (Character.isLowSurrogate(c2)) {

                        cur++;

                        return Character.toCodePoint(c1, c2);

                    }

                }

                return c1;

            }

        }

        return StreamSupport.intStream(() ->

                Spliterators.spliteratorUnknownSize(

                        new CodePointIterator(),

                        Spliterator.ORDERED),

                Spliterator.ORDERED,

                false);

    }

}