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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
   * or visit www.oracle.com if you need additional information or have any
   * questions.
   */
  
  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 <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
   * Object#equals(Object) equals} and {@link
   * 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
   * @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.
       *
       * @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>If the <code>char</code> 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</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 <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.
       *
       * @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.
       *
       * @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);
      }
  }
  