https://github.com/google/guava/guava: Guava is a suite of core and expanded libraries that include utility classes, google's collections, io classes, and much much more. 
/*
 * Copyright (C) 2008 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 */

package com.google.common.primitives;

import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkElementIndex;
import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.base.Preconditions.checkPositionIndexes;

import com.google.common.annotations.Beta;
import com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.GwtIncompatible;
import java.io.Serializable;
import java.util.AbstractList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
import java.util.RandomAccess;
import org.checkerframework.checker.nullness.qual.Nullable;


Static utility methods pertaining to char primitives, that are not already found in either Character or Arrays. 
All the operations in this class treat char values strictly numerically; they are neither Unicode-aware nor locale-dependent. 
See the Guava User Guide article on primitive utilities.

Author:Kevin Bourrillion
Since:1.0
/**
 * Static utility methods pertaining to {@code char} primitives, that are not already found in
 * either {@link Character} or {@link Arrays}.
 *
 * <p>All the operations in this class treat {@code char} values strictly numerically; they are
 * neither Unicode-aware nor locale-dependent.
 *
 * <p>See the Guava User Guide article on <a
 * href="https://github.com/google/guava/wiki/PrimitivesExplained">primitive utilities</a>.
 *
 * @author Kevin Bourrillion
 * @since 1.0
 */
@GwtCompatible(emulated = true)
public final class Chars {
  private Chars() {}

  
The number of bytes required to represent a primitive char value. 
Java 8 users: use Character.BYTES instead. 
/**
   * The number of bytes required to represent a primitive {@code char} value.
   *
   * <p><b>Java 8 users:</b> use {@link Character#BYTES} instead.
   */
  public static final int BYTES = Character.SIZE / Byte.SIZE;

  
Returns a hash code for value; equal to the result of invoking ((Character)
value).hashCode(). 
Java 8 users: use Character.hashCode(char) instead. 
Params:
  • value – a primitive char value
Returns:a hash code for the value
/**
   * Returns a hash code for {@code value}; equal to the result of invoking {@code ((Character)
   * value).hashCode()}.
   *
   * <p><b>Java 8 users:</b> use {@link Character#hashCode(char)} instead.
   *
   * @param value a primitive {@code char} value
   * @return a hash code for the value
   */
  public static int hashCode(char value) {
    return value;
  }

  
Returns the char value that is equal to value, if possible. 
Params:
  • value – any value in the range of the char type
Throws:
Returns:the char value that equals value
/**
   * Returns the {@code char} value that is equal to {@code value}, if possible.
   *
   * @param value any value in the range of the {@code char} type
   * @return the {@code char} value that equals {@code value}
   * @throws IllegalArgumentException if {@code value} is greater than {@link Character#MAX_VALUE}
   *     or less than {@link Character#MIN_VALUE}
   */
  public static char checkedCast(long value) {
    char result = (char) value;
    checkArgument(result == value, "Out of range: %s", value);
    return result;
  }

  
Returns the char nearest in value to value. 
Params:
  • value – any long value
Returns:the same value cast to char if it is in the range of the char type, Character.MAX_VALUE if it is too large, or Character.MIN_VALUE if it is too small
/**
   * Returns the {@code char} nearest in value to {@code value}.
   *
   * @param value any {@code long} value
   * @return the same value cast to {@code char} if it is in the range of the {@code char} type,
   *     {@link Character#MAX_VALUE} if it is too large, or {@link Character#MIN_VALUE} if it is too
   *     small
   */
  public static char saturatedCast(long value) {
    if (value > Character.MAX_VALUE) {
      return Character.MAX_VALUE;
    }
    if (value < Character.MIN_VALUE) {
      return Character.MIN_VALUE;
    }
    return (char) value;
  }

  
Compares the two specified char values. The sign of the value returned is the same as that of ((Character) a).compareTo(b). 
Note for Java 7 and later: this method should be treated as deprecated; use the equivalent Character.compare method instead. 
Params:
  • a – the first char to compare
  • b – the second char to compare
Returns:a negative value if a is less than b; a positive value if a is greater than b; or zero if they are equal
/**
   * Compares the two specified {@code char} values. The sign of the value returned is the same as
   * that of {@code ((Character) a).compareTo(b)}.
   *
   * <p><b>Note for Java 7 and later:</b> this method should be treated as deprecated; use the
   * equivalent {@link Character#compare} method instead.
   *
   * @param a the first {@code char} to compare
   * @param b the second {@code char} to compare
   * @return a negative value if {@code a} is less than {@code b}; a positive value if {@code a} is
   *     greater than {@code b}; or zero if they are equal
   */
  public static int compare(char a, char b) {
    return a - b; // safe due to restricted range
  }

  
Returns true if target is present as an element anywhere in array. 
Params:
  • array – an array of char values, possibly empty
  • target – a primitive char value
Returns:true if array[i] == target for some value of i
/**
   * Returns {@code true} if {@code target} is present as an element anywhere in {@code array}.
   *
   * @param array an array of {@code char} values, possibly empty
   * @param target a primitive {@code char} value
   * @return {@code true} if {@code array[i] == target} for some value of {@code i}
   */
  public static boolean contains(char[] array, char target) {
    for (char value : array) {
      if (value == target) {
        return true;
      }
    }
    return false;
  }

  
Returns the index of the first appearance of the value target in array. 
Params:
  • array – an array of char values, possibly empty
  • target – a primitive char value
Returns:the least index i for which array[i] == target, or -1 if no such index exists.
/**
   * Returns the index of the first appearance of the value {@code target} in {@code array}.
   *
   * @param array an array of {@code char} values, possibly empty
   * @param target a primitive {@code char} value
   * @return the least index {@code i} for which {@code array[i] == target}, or {@code -1} if no
   *     such index exists.
   */
  public static int indexOf(char[] array, char target) {
    return indexOf(array, target, 0, array.length);
  }

  // TODO(kevinb): consider making this public
  private static int indexOf(char[] array, char target, int start, int end) {
    for (int i = start; i < end; i++) {
      if (array[i] == target) {
        return i;
      }
    }
    return -1;
  }

  
Returns the start position of the first occurrence of the specified target within array, or -1 if there is no such occurrence. 
More formally, returns the lowest index i such that Arrays.copyOfRange(array,
i, i + target.length) contains exactly the same elements as target. 
Params:
  • array – the array to search for the sequence target
  • target – the array to search for as a sub-sequence of array
/**
   * Returns the start position of the first occurrence of the specified {@code target} within
   * {@code array}, or {@code -1} if there is no such occurrence.
   *
   * <p>More formally, returns the lowest index {@code i} such that {@code Arrays.copyOfRange(array,
   * i, i + target.length)} contains exactly the same elements as {@code target}.
   *
   * @param array the array to search for the sequence {@code target}
   * @param target the array to search for as a sub-sequence of {@code array}
   */
  public static int indexOf(char[] array, char[] target) {
    checkNotNull(array, "array");
    checkNotNull(target, "target");
    if (target.length == 0) {
      return 0;
    }

    outer:
    for (int i = 0; i < array.length - target.length + 1; i++) {
      for (int j = 0; j < target.length; j++) {
        if (array[i + j] != target[j]) {
          continue outer;
        }
      }
      return i;
    }
    return -1;
  }

  
Returns the index of the last appearance of the value target in array. 
Params:
  • array – an array of char values, possibly empty
  • target – a primitive char value
Returns:the greatest index i for which array[i] == target, or -1 if no such index exists.
/**
   * Returns the index of the last appearance of the value {@code target} in {@code array}.
   *
   * @param array an array of {@code char} values, possibly empty
   * @param target a primitive {@code char} value
   * @return the greatest index {@code i} for which {@code array[i] == target}, or {@code -1} if no
   *     such index exists.
   */
  public static int lastIndexOf(char[] array, char target) {
    return lastIndexOf(array, target, 0, array.length);
  }

  // TODO(kevinb): consider making this public
  private static int lastIndexOf(char[] array, char target, int start, int end) {
    for (int i = end - 1; i >= start; i--) {
      if (array[i] == target) {
        return i;
      }
    }
    return -1;
  }

  
Returns the least value present in array. 
Params:
  • array – a nonempty array of char values
Throws:
Returns:the value present in array that is less than or equal to every other value in the array
/**
   * Returns the least value present in {@code array}.
   *
   * @param array a <i>nonempty</i> array of {@code char} values
   * @return the value present in {@code array} that is less than or equal to every other value in
   *     the array
   * @throws IllegalArgumentException if {@code array} is empty
   */
  public static char min(char... array) {
    checkArgument(array.length > 0);
    char min = array[0];
    for (int i = 1; i < array.length; i++) {
      if (array[i] < min) {
        min = array[i];
      }
    }
    return min;
  }

  
Returns the greatest value present in array. 
Params:
  • array – a nonempty array of char values
Throws:
Returns:the value present in array that is greater than or equal to every other value in the array
/**
   * Returns the greatest value present in {@code array}.
   *
   * @param array a <i>nonempty</i> array of {@code char} values
   * @return the value present in {@code array} that is greater than or equal to every other value
   *     in the array
   * @throws IllegalArgumentException if {@code array} is empty
   */
  public static char max(char... array) {
    checkArgument(array.length > 0);
    char max = array[0];
    for (int i = 1; i < array.length; i++) {
      if (array[i] > max) {
        max = array[i];
      }
    }
    return max;
  }

  
Returns the value nearest to value which is within the closed range [min..max]. 
If value is within the range [min..max], value is returned unchanged. If value is less than min, min is returned, and if 
value is greater than max, max is returned. 
Params:
  • value – the char value to constrain
  • min – the lower bound (inclusive) of the range to constrain value to
  • max – the upper bound (inclusive) of the range to constrain value to
Throws:
Since:21.0
/**
   * Returns the value nearest to {@code value} which is within the closed range {@code [min..max]}.
   *
   * <p>If {@code value} is within the range {@code [min..max]}, {@code value} is returned
   * unchanged. If {@code value} is less than {@code min}, {@code min} is returned, and if {@code
   * value} is greater than {@code max}, {@code max} is returned.
   *
   * @param value the {@code char} value to constrain
   * @param min the lower bound (inclusive) of the range to constrain {@code value} to
   * @param max the upper bound (inclusive) of the range to constrain {@code value} to
   * @throws IllegalArgumentException if {@code min > max}
   * @since 21.0
   */
  @Beta
  public static char constrainToRange(char value, char min, char max) {
    checkArgument(min <= max, "min (%s) must be less than or equal to max (%s)", min, max);
    return value < min ? min : value < max ? value : max;
  }

  
Returns the values from each provided array combined into a single array. For example, 
concat(new char[] {a, b}, new char[] {}, new char[] {c} returns the array {a, b, c}. 
Params:
  • arrays – zero or more char arrays
Returns:a single array containing all the values from the source arrays, in order
/**
   * Returns the values from each provided array combined into a single array. For example, {@code
   * concat(new char[] {a, b}, new char[] {}, new char[] {c}} returns the array {@code {a, b, c}}.
   *
   * @param arrays zero or more {@code char} arrays
   * @return a single array containing all the values from the source arrays, in order
   */
  public static char[] concat(char[]... arrays) {
    int length = 0;
    for (char[] array : arrays) {
      length += array.length;
    }
    char[] result = new char[length];
    int pos = 0;
    for (char[] array : arrays) {
      System.arraycopy(array, 0, result, pos, array.length);
      pos += array.length;
    }
    return result;
  }

  
Returns a big-endian representation of value in a 2-element byte array; equivalent to ByteBuffer.allocate(2).putChar(value).array(). For example, the input value 
'\\u5432' would yield the byte array {0x54, 0x32}. 
If you need to convert and concatenate several values (possibly even of different types), use a shared ByteBuffer instance, or use ByteStreams.newDataOutput() to get a growable buffer. 
/**
   * Returns a big-endian representation of {@code value} in a 2-element byte array; equivalent to
   * {@code ByteBuffer.allocate(2).putChar(value).array()}. For example, the input value {@code
   * '\\u5432'} would yield the byte array {@code {0x54, 0x32}}.
   *
   * <p>If you need to convert and concatenate several values (possibly even of different types),
   * use a shared {@link java.nio.ByteBuffer} instance, or use {@link
   * com.google.common.io.ByteStreams#newDataOutput()} to get a growable buffer.
   */
  @GwtIncompatible // doesn't work
  public static byte[] toByteArray(char value) {
    return new byte[] {(byte) (value >> 8), (byte) value};
  }

  
Returns the char value whose big-endian representation is stored in the first 2 bytes of bytes; equivalent to ByteBuffer.wrap(bytes).getChar(). For example, the input byte array {0x54, 0x32} would yield the char value '\\u5432'. 
Arguably, it's preferable to use ByteBuffer; that library exposes much more flexibility at little cost in readability. 
Throws:
/**
   * Returns the {@code char} value whose big-endian representation is stored in the first 2 bytes
   * of {@code bytes}; equivalent to {@code ByteBuffer.wrap(bytes).getChar()}. For example, the
   * input byte array {@code {0x54, 0x32}} would yield the {@code char} value {@code '\\u5432'}.
   *
   * <p>Arguably, it's preferable to use {@link java.nio.ByteBuffer}; that library exposes much more
   * flexibility at little cost in readability.
   *
   * @throws IllegalArgumentException if {@code bytes} has fewer than 2 elements
   */
  @GwtIncompatible // doesn't work
  public static char fromByteArray(byte[] bytes) {
    checkArgument(bytes.length >= BYTES, "array too small: %s < %s", bytes.length, BYTES);
    return fromBytes(bytes[0], bytes[1]);
  }

  
Returns the char value whose byte representation is the given 2 bytes, in big-endian order; equivalent to Chars.fromByteArray(new byte[] {b1, b2}). 
Since:7.0
/**
   * Returns the {@code char} value whose byte representation is the given 2 bytes, in big-endian
   * order; equivalent to {@code Chars.fromByteArray(new byte[] {b1, b2})}.
   *
   * @since 7.0
   */
  @GwtIncompatible // doesn't work
  public static char fromBytes(byte b1, byte b2) {
    return (char) ((b1 << 8) | (b2 & 0xFF));
  }

  
Returns an array containing the same values as array, but guaranteed to be of a specified minimum length. If array already has a length of at least minLength, it is returned directly. Otherwise, a new array of size minLength + padding is returned, containing the values of array, and zeroes in the remaining places. 
Params:
  • array – the source array
  • minLength – the minimum length the returned array must guarantee
  • padding – an extra amount to "grow" the array by if growth is necessary
Throws:
Returns:an array containing the values of array, with guaranteed minimum length 
    minLength
/**
   * Returns an array containing the same values as {@code array}, but guaranteed to be of a
   * specified minimum length. If {@code array} already has a length of at least {@code minLength},
   * it is returned directly. Otherwise, a new array of size {@code minLength + padding} is
   * returned, containing the values of {@code array}, and zeroes in the remaining places.
   *
   * @param array the source array
   * @param minLength the minimum length the returned array must guarantee
   * @param padding an extra amount to "grow" the array by if growth is necessary
   * @throws IllegalArgumentException if {@code minLength} or {@code padding} is negative
   * @return an array containing the values of {@code array}, with guaranteed minimum length {@code
   *     minLength}
   */
  public static char[] ensureCapacity(char[] array, int minLength, int padding) {
    checkArgument(minLength >= 0, "Invalid minLength: %s", minLength);
    checkArgument(padding >= 0, "Invalid padding: %s", padding);
    return (array.length < minLength) ? Arrays.copyOf(array, minLength + padding) : array;
  }

  
Returns a string containing the supplied char values separated by separator. For example, join("-", '1', '2', '3') returns the string "1-2-3". 
Params:
  • separator – the text that should appear between consecutive values in the resulting string
    (but not at the start or end)
  • array – an array of char values, possibly empty
/**
   * Returns a string containing the supplied {@code char} values separated by {@code separator}.
   * For example, {@code join("-", '1', '2', '3')} returns the string {@code "1-2-3"}.
   *
   * @param separator the text that should appear between consecutive values in the resulting string
   *     (but not at the start or end)
   * @param array an array of {@code char} values, possibly empty
   */
  public static String join(String separator, char... array) {
    checkNotNull(separator);
    int len = array.length;
    if (len == 0) {
      return "";
    }

    StringBuilder builder = new StringBuilder(len + separator.length() * (len - 1));
    builder.append(array[0]);
    for (int i = 1; i < len; i++) {
      builder.append(separator).append(array[i]);
    }
    return builder.toString();
  }

  
Returns a comparator that compares two char arrays lexicographically. That is, it compares, using compare(char, char)), the first pair of values that follow any common prefix, or when one array is a prefix of the other, treats the shorter array as the lesser. For example, [] < ['a'] < ['a', 'b'] < ['b']. 
The returned comparator is inconsistent with Object.equals(Object) (since arrays support only identity equality), but it is consistent with Arrays.equals(char[], char[]). 
Since:2.0
/**
   * Returns a comparator that compares two {@code char} arrays <a
   * href="http://en.wikipedia.org/wiki/Lexicographical_order">lexicographically</a>. That is, it
   * compares, using {@link #compare(char, char)}), the first pair of values that follow any common
   * prefix, or when one array is a prefix of the other, treats the shorter array as the lesser. For
   * example, {@code [] < ['a'] < ['a', 'b'] < ['b']}.
   *
   * <p>The returned comparator is inconsistent with {@link Object#equals(Object)} (since arrays
   * support only identity equality), but it is consistent with {@link Arrays#equals(char[],
   * char[])}.
   *
   * @since 2.0
   */
  public static Comparator<char[]> lexicographicalComparator() {
    return LexicographicalComparator.INSTANCE;
  }

  private enum LexicographicalComparator implements Comparator<char[]> {
    INSTANCE;

    @Override
    public int compare(char[] left, char[] right) {
      int minLength = Math.min(left.length, right.length);
      for (int i = 0; i < minLength; i++) {
        int result = Chars.compare(left[i], right[i]);
        if (result != 0) {
          return result;
        }
      }
      return left.length - right.length;
    }

    @Override
    public String toString() {
      return "Chars.lexicographicalComparator()";
    }
  }

  
Copies a collection of Character instances into a new array of primitive char values. 
Elements are copied from the argument collection as if by collection.toArray(). Calling this method is as thread-safe as calling that method. 
Params:
  • collection – a collection of Character objects
Throws:
Returns:an array containing the same values as collection, in the same order, converted to primitives
/**
   * Copies a collection of {@code Character} instances into a new array of primitive {@code char}
   * values.
   *
   * <p>Elements are copied from the argument collection as if by {@code collection.toArray()}.
   * Calling this method is as thread-safe as calling that method.
   *
   * @param collection a collection of {@code Character} objects
   * @return an array containing the same values as {@code collection}, in the same order, converted
   *     to primitives
   * @throws NullPointerException if {@code collection} or any of its elements is null
   */
  public static char[] toArray(Collection<Character> collection) {
    if (collection instanceof CharArrayAsList) {
      return ((CharArrayAsList) collection).toCharArray();
    }

    Object[] boxedArray = collection.toArray();
    int len = boxedArray.length;
    char[] array = new char[len];
    for (int i = 0; i < len; i++) {
      // checkNotNull for GWT (do not optimize)
      array[i] = (Character) checkNotNull(boxedArray[i]);
    }
    return array;
  }

  
Sorts the elements of array in descending order. 
Since:23.1
/**
   * Sorts the elements of {@code array} in descending order.
   *
   * @since 23.1
   */
  public static void sortDescending(char[] array) {
    checkNotNull(array);
    sortDescending(array, 0, array.length);
  }

  
Sorts the elements of array between fromIndex inclusive and toIndex exclusive in descending order. 
Since:23.1
/**
   * Sorts the elements of {@code array} between {@code fromIndex} inclusive and {@code toIndex}
   * exclusive in descending order.
   *
   * @since 23.1
   */
  public static void sortDescending(char[] array, int fromIndex, int toIndex) {
    checkNotNull(array);
    checkPositionIndexes(fromIndex, toIndex, array.length);
    Arrays.sort(array, fromIndex, toIndex);
    reverse(array, fromIndex, toIndex);
  }

  
Reverses the elements of array. This is equivalent to 
Collections.reverse(Chars.asList(array)), but is likely to be more efficient. 
Since:23.1
/**
   * Reverses the elements of {@code array}. This is equivalent to {@code
   * Collections.reverse(Chars.asList(array))}, but is likely to be more efficient.
   *
   * @since 23.1
   */
  public static void reverse(char[] array) {
    checkNotNull(array);
    reverse(array, 0, array.length);
  }

  
Reverses the elements of array between fromIndex inclusive and toIndex exclusive. This is equivalent to 
Collections.reverse(Chars.asList(array).subList(fromIndex, toIndex)), but is likely to be more efficient. 
Throws:
Since:23.1
/**
   * Reverses the elements of {@code array} between {@code fromIndex} inclusive and {@code toIndex}
   * exclusive. This is equivalent to {@code
   * Collections.reverse(Chars.asList(array).subList(fromIndex, toIndex))}, but is likely to be more
   * efficient.
   *
   * @throws IndexOutOfBoundsException if {@code fromIndex < 0}, {@code toIndex > array.length}, or
   *     {@code toIndex > fromIndex}
   * @since 23.1
   */
  public static void reverse(char[] array, int fromIndex, int toIndex) {
    checkNotNull(array);
    checkPositionIndexes(fromIndex, toIndex, array.length);
    for (int i = fromIndex, j = toIndex - 1; i < j; i++, j--) {
      char tmp = array[i];
      array[i] = array[j];
      array[j] = tmp;
    }
  }

  
Returns a fixed-size list backed by the specified array, similar to Arrays.asList(Object[]). The list supports List.set(int, Object), but any attempt to set a value to null will result in a NullPointerException. 
The returned list maintains the values, but not the identities, of Character objects written to or read from it. For example, whether list.get(0) == list.get(0) is true for the returned list is unspecified. 
Params:
  • backingArray – the array to back the list
Returns:a list view of the array
/**
   * Returns a fixed-size list backed by the specified array, similar to {@link
   * Arrays#asList(Object[])}. The list supports {@link List#set(int, Object)}, but any attempt to
   * set a value to {@code null} will result in a {@link NullPointerException}.
   *
   * <p>The returned list maintains the values, but not the identities, of {@code Character} objects
   * written to or read from it. For example, whether {@code list.get(0) == list.get(0)} is true for
   * the returned list is unspecified.
   *
   * @param backingArray the array to back the list
   * @return a list view of the array
   */
  public static List<Character> asList(char... backingArray) {
    if (backingArray.length == 0) {
      return Collections.emptyList();
    }
    return new CharArrayAsList(backingArray);
  }

  @GwtCompatible
  private static class CharArrayAsList extends AbstractList<Character>
      implements RandomAccess, Serializable {
    final char[] array;
    final int start;
    final int end;

    CharArrayAsList(char[] array) {
      this(array, 0, array.length);
    }

    CharArrayAsList(char[] array, int start, int end) {
      this.array = array;
      this.start = start;
      this.end = end;
    }

    @Override
    public int size() {
      return end - start;
    }

    @Override
    public boolean isEmpty() {
      return false;
    }

    @Override
    public Character get(int index) {
      checkElementIndex(index, size());
      return array[start + index];
    }

    @Override
    public boolean contains(Object target) {
      // Overridden to prevent a ton of boxing
      return (target instanceof Character)
          && Chars.indexOf(array, (Character) target, start, end) != -1;
    }

    @Override
    public int indexOf(Object target) {
      // Overridden to prevent a ton of boxing
      if (target instanceof Character) {
        int i = Chars.indexOf(array, (Character) target, start, end);
        if (i >= 0) {
          return i - start;
        }
      }
      return -1;
    }

    @Override
    public int lastIndexOf(Object target) {
      // Overridden to prevent a ton of boxing
      if (target instanceof Character) {
        int i = Chars.lastIndexOf(array, (Character) target, start, end);
        if (i >= 0) {
          return i - start;
        }
      }
      return -1;
    }

    @Override
    public Character set(int index, Character element) {
      checkElementIndex(index, size());
      char oldValue = array[start + index];
      // checkNotNull for GWT (do not optimize)
      array[start + index] = checkNotNull(element);
      return oldValue;
    }

    @Override
    public List<Character> subList(int fromIndex, int toIndex) {
      int size = size();
      checkPositionIndexes(fromIndex, toIndex, size);
      if (fromIndex == toIndex) {
        return Collections.emptyList();
      }
      return new CharArrayAsList(array, start + fromIndex, start + toIndex);
    }

    @Override
    public boolean equals(@Nullable Object object) {
      if (object == this) {
        return true;
      }
      if (object instanceof CharArrayAsList) {
        CharArrayAsList that = (CharArrayAsList) object;
        int size = size();
        if (that.size() != size) {
          return false;
        }
        for (int i = 0; i < size; i++) {
          if (array[start + i] != that.array[that.start + i]) {
            return false;
          }
        }
        return true;
      }
      return super.equals(object);
    }

    @Override
    public int hashCode() {
      int result = 1;
      for (int i = start; i < end; i++) {
        result = 31 * result + Chars.hashCode(array[i]);
      }
      return result;
    }

    @Override
    public String toString() {
      StringBuilder builder = new StringBuilder(size() * 3);
      builder.append('[').append(array[start]);
      for (int i = start + 1; i < end; i++) {
        builder.append(", ").append(array[i]);
      }
      return builder.append(']').toString();
    }

    char[] toCharArray() {
      return Arrays.copyOfRange(array, start, end);
    }

    private static final long serialVersionUID = 0;
  }
}