Source code

001/*
002 * Copyright (C) 2008 The Guava Authors
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
005 * in compliance with the License. You may obtain a copy of the License at
006 *
007 * http://www.apache.org/licenses/LICENSE-2.0
008 *
009 * Unless required by applicable law or agreed to in writing, software distributed under the License
010 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
011 * or implied. See the License for the specific language governing permissions and limitations under
012 * the License.
013 */
014
015package com.google.common.primitives;
016
017import static com.google.common.base.Preconditions.checkArgument;
018import static com.google.common.base.Preconditions.checkElementIndex;
019import static com.google.common.base.Preconditions.checkNotNull;
020import static com.google.common.base.Preconditions.checkPositionIndexes;
021
022import com.google.common.annotations.GwtCompatible;
023import com.google.common.base.Converter;
024import java.io.Serializable;
025import java.util.AbstractList;
026import java.util.Arrays;
027import java.util.Collection;
028import java.util.Collections;
029import java.util.Comparator;
030import java.util.List;
031import java.util.RandomAccess;
032import javax.annotation.CheckForNull;
033
034/**
035 * Static utility methods pertaining to {@code long} primitives, that are not already found in
036 * either {@link Long} or {@link Arrays}.
037 *
038 * <p>See the Guava User Guide article on <a
039 * href="https://github.com/google/guava/wiki/PrimitivesExplained">primitive utilities</a>.
040 *
041 * @author Kevin Bourrillion
042 * @since 1.0
043 */
044@GwtCompatible
045@ElementTypesAreNonnullByDefault
046public final class Longs {
047  private Longs() {}
048
049  /**
050   * The number of bytes required to represent a primitive {@code long} value.
051   *
052   * <p><b>Java 8 users:</b> use {@link Long#BYTES} instead.
053   */
054  public static final int BYTES = Long.SIZE / Byte.SIZE;
055
056  /**
057   * The largest power of two that can be represented as a {@code long}.
058   *
059   * @since 10.0
060   */
061  public static final long MAX_POWER_OF_TWO = 1L << (Long.SIZE - 2);
062
063  /**
064   * Returns a hash code for {@code value}; equal to the result of invoking {@code ((Long)
065   * value).hashCode()}.
066   *
067   * <p>This method always return the value specified by {@link Long#hashCode()} in java, which
068   * might be different from {@code ((Long) value).hashCode()} in GWT because {@link
069   * Long#hashCode()} in GWT does not obey the JRE contract.
070   *
071   * <p><b>Java 8 users:</b> use {@link Long#hashCode(long)} instead.
072   *
073   * @param value a primitive {@code long} value
074   * @return a hash code for the value
075   */
076  public static int hashCode(long value) {
077    return (int) (value ^ (value >>> 32));
078  }
079
080  /**
081   * Compares the two specified {@code long} values. The sign of the value returned is the same as
082   * that of {@code ((Long) a).compareTo(b)}.
083   *
084   * <p><b>Note for Java 7 and later:</b> this method should be treated as deprecated; use the
085   * equivalent {@link Long#compare} method instead.
086   *
087   * @param a the first {@code long} to compare
088   * @param b the second {@code long} to compare
089   * @return a negative value if {@code a} is less than {@code b}; a positive value if {@code a} is
090   *     greater than {@code b}; or zero if they are equal
091   */
092  public static int compare(long a, long b) {
093    return (a < b) ? -1 : ((a > b) ? 1 : 0);
094  }
095
096  /**
097   * Returns {@code true} if {@code target} is present as an element anywhere in {@code array}.
098   *
099   * @param array an array of {@code long} values, possibly empty
100   * @param target a primitive {@code long} value
101   * @return {@code true} if {@code array[i] == target} for some value of {@code i}
102   */
103  public static boolean contains(long[] array, long target) {
104    for (long value : array) {
105      if (value == target) {
106        return true;
107      }
108    }
109    return false;
110  }
111
112  /**
113   * Returns the index of the first appearance of the value {@code target} in {@code array}.
114   *
115   * @param array an array of {@code long} values, possibly empty
116   * @param target a primitive {@code long} value
117   * @return the least index {@code i} for which {@code array[i] == target}, or {@code -1} if no
118   *     such index exists.
119   */
120  public static int indexOf(long[] array, long target) {
121    return indexOf(array, target, 0, array.length);
122  }
123
124  // TODO(kevinb): consider making this public
125  private static int indexOf(long[] array, long target, int start, int end) {
126    for (int i = start; i < end; i++) {
127      if (array[i] == target) {
128        return i;
129      }
130    }
131    return -1;
132  }
133
134  /**
135   * Returns the start position of the first occurrence of the specified {@code target} within
136   * {@code array}, or {@code -1} if there is no such occurrence.
137   *
138   * <p>More formally, returns the lowest index {@code i} such that {@code Arrays.copyOfRange(array,
139   * i, i + target.length)} contains exactly the same elements as {@code target}.
140   *
141   * @param array the array to search for the sequence {@code target}
142   * @param target the array to search for as a sub-sequence of {@code array}
143   */
144  public static int indexOf(long[] array, long[] target) {
145    checkNotNull(array, "array");
146    checkNotNull(target, "target");
147    if (target.length == 0) {
148      return 0;
149    }
150
151    outer:
152    for (int i = 0; i < array.length - target.length + 1; i++) {
153      for (int j = 0; j < target.length; j++) {
154        if (array[i + j] != target[j]) {
155          continue outer;
156        }
157      }
158      return i;
159    }
160    return -1;
161  }
162
163  /**
164   * Returns the index of the last appearance of the value {@code target} in {@code array}.
165   *
166   * @param array an array of {@code long} values, possibly empty
167   * @param target a primitive {@code long} value
168   * @return the greatest index {@code i} for which {@code array[i] == target}, or {@code -1} if no
169   *     such index exists.
170   */
171  public static int lastIndexOf(long[] array, long target) {
172    return lastIndexOf(array, target, 0, array.length);
173  }
174
175  // TODO(kevinb): consider making this public
176  private static int lastIndexOf(long[] array, long target, int start, int end) {
177    for (int i = end - 1; i >= start; i--) {
178      if (array[i] == target) {
179        return i;
180      }
181    }
182    return -1;
183  }
184
185  /**
186   * Returns the least value present in {@code array}.
187   *
188   * @param array a <i>nonempty</i> array of {@code long} values
189   * @return the value present in {@code array} that is less than or equal to every other value in
190   *     the array
191   * @throws IllegalArgumentException if {@code array} is empty
192   */
193  public static long min(long... array) {
194    checkArgument(array.length > 0);
195    long min = array[0];
196    for (int i = 1; i < array.length; i++) {
197      if (array[i] < min) {
198        min = array[i];
199      }
200    }
201    return min;
202  }
203
204  /**
205   * Returns the greatest value present in {@code array}.
206   *
207   * @param array a <i>nonempty</i> array of {@code long} values
208   * @return the value present in {@code array} that is greater than or equal to every other value
209   *     in the array
210   * @throws IllegalArgumentException if {@code array} is empty
211   */
212  public static long max(long... array) {
213    checkArgument(array.length > 0);
214    long max = array[0];
215    for (int i = 1; i < array.length; i++) {
216      if (array[i] > max) {
217        max = array[i];
218      }
219    }
220    return max;
221  }
222
223  /**
224   * Returns the value nearest to {@code value} which is within the closed range {@code [min..max]}.
225   *
226   * <p>If {@code value} is within the range {@code [min..max]}, {@code value} is returned
227   * unchanged. If {@code value} is less than {@code min}, {@code min} is returned, and if {@code
228   * value} is greater than {@code max}, {@code max} is returned.
229   *
230   * @param value the {@code long} value to constrain
231   * @param min the lower bound (inclusive) of the range to constrain {@code value} to
232   * @param max the upper bound (inclusive) of the range to constrain {@code value} to
233   * @throws IllegalArgumentException if {@code min > max}
234   * @since 21.0
235   */
236  public static long constrainToRange(long value, long min, long max) {
237    checkArgument(min <= max, "min (%s) must be less than or equal to max (%s)", min, max);
238    return Math.min(Math.max(value, min), max);
239  }
240
241  /**
242   * Returns the values from each provided array combined into a single array. For example, {@code
243   * concat(new long[] {a, b}, new long[] {}, new long[] {c}} returns the array {@code {a, b, c}}.
244   *
245   * @param arrays zero or more {@code long} arrays
246   * @return a single array containing all the values from the source arrays, in order
247   */
248  public static long[] concat(long[]... arrays) {
249    int length = 0;
250    for (long[] array : arrays) {
251      length += array.length;
252    }
253    long[] result = new long[length];
254    int pos = 0;
255    for (long[] array : arrays) {
256      System.arraycopy(array, 0, result, pos, array.length);
257      pos += array.length;
258    }
259    return result;
260  }
261
262  /**
263   * Returns a big-endian representation of {@code value} in an 8-element byte array; equivalent to
264   * {@code ByteBuffer.allocate(8).putLong(value).array()}. For example, the input value {@code
265   * 0x1213141516171819L} would yield the byte array {@code {0x12, 0x13, 0x14, 0x15, 0x16, 0x17,
266   * 0x18, 0x19}}.
267   *
268   * <p>If you need to convert and concatenate several values (possibly even of different types),
269   * use a shared {@link java.nio.ByteBuffer} instance, or use {@link
270   * com.google.common.io.ByteStreams#newDataOutput()} to get a growable buffer.
271   */
272  public static byte[] toByteArray(long value) {
273    // Note that this code needs to stay compatible with GWT, which has known
274    // bugs when narrowing byte casts of long values occur.
275    byte[] result = new byte[8];
276    for (int i = 7; i >= 0; i--) {
277      result[i] = (byte) (value & 0xffL);
278      value >>= 8;
279    }
280    return result;
281  }
282
283  /**
284   * Returns the {@code long} value whose big-endian representation is stored in the first 8 bytes
285   * of {@code bytes}; equivalent to {@code ByteBuffer.wrap(bytes).getLong()}. For example, the
286   * input byte array {@code {0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18, 0x19}} would yield the
287   * {@code long} value {@code 0x1213141516171819L}.
288   *
289   * <p>Arguably, it's preferable to use {@link java.nio.ByteBuffer}; that library exposes much more
290   * flexibility at little cost in readability.
291   *
292   * @throws IllegalArgumentException if {@code bytes} has fewer than 8 elements
293   */
294  public static long fromByteArray(byte[] bytes) {
295    checkArgument(bytes.length >= BYTES, "array too small: %s < %s", bytes.length, BYTES);
296    return fromBytes(
297        bytes[0], bytes[1], bytes[2], bytes[3], bytes[4], bytes[5], bytes[6], bytes[7]);
298  }
299
300  /**
301   * Returns the {@code long} value whose byte representation is the given 8 bytes, in big-endian
302   * order; equivalent to {@code Longs.fromByteArray(new byte[] {b1, b2, b3, b4, b5, b6, b7, b8})}.
303   *
304   * @since 7.0
305   */
306  public static long fromBytes(
307      byte b1, byte b2, byte b3, byte b4, byte b5, byte b6, byte b7, byte b8) {
308    return (b1 & 0xFFL) << 56
309        | (b2 & 0xFFL) << 48
310        | (b3 & 0xFFL) << 40
311        | (b4 & 0xFFL) << 32
312        | (b5 & 0xFFL) << 24
313        | (b6 & 0xFFL) << 16
314        | (b7 & 0xFFL) << 8
315        | (b8 & 0xFFL);
316  }
317
318  /*
319   * Moving asciiDigits into this static holder class lets ProGuard eliminate and inline the Longs
320   * class.
321   */
322  static final class AsciiDigits {
323    private AsciiDigits() {}
324
325    private static final byte[] asciiDigits;
326
327    static {
328      byte[] result = new byte[128];
329      Arrays.fill(result, (byte) -1);
330      for (int i = 0; i < 10; i++) {
331        result['0' + i] = (byte) i;
332      }
333      for (int i = 0; i < 26; i++) {
334        result['A' + i] = (byte) (10 + i);
335        result['a' + i] = (byte) (10 + i);
336      }
337      asciiDigits = result;
338    }
339
340    static int digit(char c) {
341      return (c < 128) ? asciiDigits[c] : -1;
342    }
343  }
344
345  /**
346   * Parses the specified string as a signed decimal long value. The ASCII character {@code '-'} (
347   * <code>'&#92;u002D'</code>) is recognized as the minus sign.
348   *
349   * <p>Unlike {@link Long#parseLong(String)}, this method returns {@code null} instead of throwing
350   * an exception if parsing fails. Additionally, this method only accepts ASCII digits, and returns
351   * {@code null} if non-ASCII digits are present in the string.
352   *
353   * <p>Note that strings prefixed with ASCII {@code '+'} are rejected, even under JDK 7, despite
354   * the change to {@link Long#parseLong(String)} for that version.
355   *
356   * @param string the string representation of a long value
357   * @return the long value represented by {@code string}, or {@code null} if {@code string} has a
358   *     length of zero or cannot be parsed as a long value
359   * @throws NullPointerException if {@code string} is {@code null}
360   * @since 14.0
361   */
362  @CheckForNull
363  public static Long tryParse(String string) {
364    return tryParse(string, 10);
365  }
366
367  /**
368   * Parses the specified string as a signed long value using the specified radix. The ASCII
369   * character {@code '-'} (<code>'&#92;u002D'</code>) is recognized as the minus sign.
370   *
371   * <p>Unlike {@link Long#parseLong(String, int)}, this method returns {@code null} instead of
372   * throwing an exception if parsing fails. Additionally, this method only accepts ASCII digits,
373   * and returns {@code null} if non-ASCII digits are present in the string.
374   *
375   * <p>Note that strings prefixed with ASCII {@code '+'} are rejected, even under JDK 7, despite
376   * the change to {@link Long#parseLong(String, int)} for that version.
377   *
378   * @param string the string representation of a long value
379   * @param radix the radix to use when parsing
380   * @return the long value represented by {@code string} using {@code radix}, or {@code null} if
381   *     {@code string} has a length of zero or cannot be parsed as a long value
382   * @throws IllegalArgumentException if {@code radix < Character.MIN_RADIX} or {@code radix >
383   *     Character.MAX_RADIX}
384   * @throws NullPointerException if {@code string} is {@code null}
385   * @since 19.0
386   */
387  @CheckForNull
388  public static Long tryParse(String string, int radix) {
389    if (checkNotNull(string).isEmpty()) {
390      return null;
391    }
392    if (radix < Character.MIN_RADIX || radix > Character.MAX_RADIX) {
393      throw new IllegalArgumentException(
394          "radix must be between MIN_RADIX and MAX_RADIX but was " + radix);
395    }
396    boolean negative = string.charAt(0) == '-';
397    int index = negative ? 1 : 0;
398    if (index == string.length()) {
399      return null;
400    }
401    int digit = AsciiDigits.digit(string.charAt(index++));
402    if (digit < 0 || digit >= radix) {
403      return null;
404    }
405    long accum = -digit;
406
407    long cap = Long.MIN_VALUE / radix;
408
409    while (index < string.length()) {
410      digit = AsciiDigits.digit(string.charAt(index++));
411      if (digit < 0 || digit >= radix || accum < cap) {
412        return null;
413      }
414      accum *= radix;
415      if (accum < Long.MIN_VALUE + digit) {
416        return null;
417      }
418      accum -= digit;
419    }
420
421    if (negative) {
422      return accum;
423    } else if (accum == Long.MIN_VALUE) {
424      return null;
425    } else {
426      return -accum;
427    }
428  }
429
430  private static final class LongConverter extends Converter<String, Long> implements Serializable {
431    static final LongConverter INSTANCE = new LongConverter();
432
433    @Override
434    protected Long doForward(String value) {
435      return Long.decode(value);
436    }
437
438    @Override
439    protected String doBackward(Long value) {
440      return value.toString();
441    }
442
443    @Override
444    public String toString() {
445      return "Longs.stringConverter()";
446    }
447
448    private Object readResolve() {
449      return INSTANCE;
450    }
451
452    private static final long serialVersionUID = 1;
453  }
454
455  /**
456   * Returns a serializable converter object that converts between strings and longs using {@link
457   * Long#decode} and {@link Long#toString()}. The returned converter throws {@link
458   * NumberFormatException} if the input string is invalid.
459   *
460   * <p><b>Warning:</b> please see {@link Long#decode} to understand exactly how strings are parsed.
461   * For example, the string {@code "0123"} is treated as <i>octal</i> and converted to the value
462   * {@code 83L}.
463   *
464   * @since 16.0
465   */
466  public static Converter<String, Long> stringConverter() {
467    return LongConverter.INSTANCE;
468  }
469
470  /**
471   * Returns an array containing the same values as {@code array}, but guaranteed to be of a
472   * specified minimum length. If {@code array} already has a length of at least {@code minLength},
473   * it is returned directly. Otherwise, a new array of size {@code minLength + padding} is
474   * returned, containing the values of {@code array}, and zeroes in the remaining places.
475   *
476   * @param array the source array
477   * @param minLength the minimum length the returned array must guarantee
478   * @param padding an extra amount to "grow" the array by if growth is necessary
479   * @throws IllegalArgumentException if {@code minLength} or {@code padding} is negative
480   * @return an array containing the values of {@code array}, with guaranteed minimum length {@code
481   *     minLength}
482   */
483  public static long[] ensureCapacity(long[] array, int minLength, int padding) {
484    checkArgument(minLength >= 0, "Invalid minLength: %s", minLength);
485    checkArgument(padding >= 0, "Invalid padding: %s", padding);
486    return (array.length < minLength) ? Arrays.copyOf(array, minLength + padding) : array;
487  }
488
489  /**
490   * Returns a string containing the supplied {@code long} values separated by {@code separator}.
491   * For example, {@code join("-", 1L, 2L, 3L)} returns the string {@code "1-2-3"}.
492   *
493   * @param separator the text that should appear between consecutive values in the resulting string
494   *     (but not at the start or end)
495   * @param array an array of {@code long} values, possibly empty
496   */
497  public static String join(String separator, long... array) {
498    checkNotNull(separator);
499    if (array.length == 0) {
500      return "";
501    }
502
503    // For pre-sizing a builder, just get the right order of magnitude
504    StringBuilder builder = new StringBuilder(array.length * 10);
505    builder.append(array[0]);
506    for (int i = 1; i < array.length; i++) {
507      builder.append(separator).append(array[i]);
508    }
509    return builder.toString();
510  }
511
512  /**
513   * Returns a comparator that compares two {@code long} arrays <a
514   * href="http://en.wikipedia.org/wiki/Lexicographical_order">lexicographically</a>. That is, it
515   * compares, using {@link #compare(long, long)}), the first pair of values that follow any common
516   * prefix, or when one array is a prefix of the other, treats the shorter array as the lesser. For
517   * example, {@code [] < [1L] < [1L, 2L] < [2L]}.
518   *
519   * <p>The returned comparator is inconsistent with {@link Object#equals(Object)} (since arrays
520   * support only identity equality), but it is consistent with {@link Arrays#equals(long[],
521   * long[])}.
522   *
523   * @since 2.0
524   */
525  public static Comparator<long[]> lexicographicalComparator() {
526    return LexicographicalComparator.INSTANCE;
527  }
528
529  private enum LexicographicalComparator implements Comparator<long[]> {
530    INSTANCE;
531
532    @Override
533    public int compare(long[] left, long[] right) {
534      int minLength = Math.min(left.length, right.length);
535      for (int i = 0; i < minLength; i++) {
536        int result = Longs.compare(left[i], right[i]);
537        if (result != 0) {
538          return result;
539        }
540      }
541      return left.length - right.length;
542    }
543
544    @Override
545    public String toString() {
546      return "Longs.lexicographicalComparator()";
547    }
548  }
549
550  /**
551   * Sorts the elements of {@code array} in descending order.
552   *
553   * @since 23.1
554   */
555  public static void sortDescending(long[] array) {
556    checkNotNull(array);
557    sortDescending(array, 0, array.length);
558  }
559
560  /**
561   * Sorts the elements of {@code array} between {@code fromIndex} inclusive and {@code toIndex}
562   * exclusive in descending order.
563   *
564   * @since 23.1
565   */
566  public static void sortDescending(long[] array, int fromIndex, int toIndex) {
567    checkNotNull(array);
568    checkPositionIndexes(fromIndex, toIndex, array.length);
569    Arrays.sort(array, fromIndex, toIndex);
570    reverse(array, fromIndex, toIndex);
571  }
572
573  /**
574   * Reverses the elements of {@code array}. This is equivalent to {@code
575   * Collections.reverse(Longs.asList(array))}, but is likely to be more efficient.
576   *
577   * @since 23.1
578   */
579  public static void reverse(long[] array) {
580    checkNotNull(array);
581    reverse(array, 0, array.length);
582  }
583
584  /**
585   * Reverses the elements of {@code array} between {@code fromIndex} inclusive and {@code toIndex}
586   * exclusive. This is equivalent to {@code
587   * Collections.reverse(Longs.asList(array).subList(fromIndex, toIndex))}, but is likely to be more
588   * efficient.
589   *
590   * @throws IndexOutOfBoundsException if {@code fromIndex < 0}, {@code toIndex > array.length}, or
591   *     {@code toIndex > fromIndex}
592   * @since 23.1
593   */
594  public static void reverse(long[] array, int fromIndex, int toIndex) {
595    checkNotNull(array);
596    checkPositionIndexes(fromIndex, toIndex, array.length);
597    for (int i = fromIndex, j = toIndex - 1; i < j; i++, j--) {
598      long tmp = array[i];
599      array[i] = array[j];
600      array[j] = tmp;
601    }
602  }
603
604  /**
605   * Performs a right rotation of {@code array} of "distance" places, so that the first element is
606   * moved to index "distance", and the element at index {@code i} ends up at index {@code (distance
607   * + i) mod array.length}. This is equivalent to {@code Collections.rotate(Longs.asList(array),
608   * distance)}, but is considerably faster and avoids allocation and garbage collection.
609   *
610   * <p>The provided "distance" may be negative, which will rotate left.
611   *
612   * @since 32.0.0
613   */
614  public static void rotate(long[] array, int distance) {
615    rotate(array, distance, 0, array.length);
616  }
617
618  /**
619   * Performs a right rotation of {@code array} between {@code fromIndex} inclusive and {@code
620   * toIndex} exclusive. This is equivalent to {@code
621   * Collections.rotate(Longs.asList(array).subList(fromIndex, toIndex), distance)}, but is
622   * considerably faster and avoids allocations and garbage collection.
623   *
624   * <p>The provided "distance" may be negative, which will rotate left.
625   *
626   * @throws IndexOutOfBoundsException if {@code fromIndex < 0}, {@code toIndex > array.length}, or
627   *     {@code toIndex > fromIndex}
628   * @since 32.0.0
629   */
630  public static void rotate(long[] array, int distance, int fromIndex, int toIndex) {
631    // See Ints.rotate for more details about possible algorithms here.
632    checkNotNull(array);
633    checkPositionIndexes(fromIndex, toIndex, array.length);
634    if (array.length <= 1) {
635      return;
636    }
637
638    int length = toIndex - fromIndex;
639    // Obtain m = (-distance mod length), a non-negative value less than "length". This is how many
640    // places left to rotate.
641    int m = -distance % length;
642    m = (m < 0) ? m + length : m;
643    // The current index of what will become the first element of the rotated section.
644    int newFirstIndex = m + fromIndex;
645    if (newFirstIndex == fromIndex) {
646      return;
647    }
648
649    reverse(array, fromIndex, newFirstIndex);
650    reverse(array, newFirstIndex, toIndex);
651    reverse(array, fromIndex, toIndex);
652  }
653
654  /**
655   * Returns an array containing each value of {@code collection}, converted to a {@code long} value
656   * in the manner of {@link Number#longValue}.
657   *
658   * <p>Elements are copied from the argument collection as if by {@code collection.toArray()}.
659   * Calling this method is as thread-safe as calling that method.
660   *
661   * @param collection a collection of {@code Number} instances
662   * @return an array containing the same values as {@code collection}, in the same order, converted
663   *     to primitives
664   * @throws NullPointerException if {@code collection} or any of its elements is null
665   * @since 1.0 (parameter was {@code Collection<Long>} before 12.0)
666   */
667  public static long[] toArray(Collection<? extends Number> collection) {
668    if (collection instanceof LongArrayAsList) {
669      return ((LongArrayAsList) collection).toLongArray();
670    }
671
672    Object[] boxedArray = collection.toArray();
673    int len = boxedArray.length;
674    long[] array = new long[len];
675    for (int i = 0; i < len; i++) {
676      // checkNotNull for GWT (do not optimize)
677      array[i] = ((Number) checkNotNull(boxedArray[i])).longValue();
678    }
679    return array;
680  }
681
682  /**
683   * Returns a fixed-size list backed by the specified array, similar to {@link
684   * Arrays#asList(Object[])}. The list supports {@link List#set(int, Object)}, but any attempt to
685   * set a value to {@code null} will result in a {@link NullPointerException}.
686   *
687   * <p>The returned list maintains the values, but not the identities, of {@code Long} objects
688   * written to or read from it. For example, whether {@code list.get(0) == list.get(0)} is true for
689   * the returned list is unspecified.
690   *
691   * <p>The returned list is serializable.
692   *
693   * <p><b>Note:</b> when possible, you should represent your data as an {@link ImmutableLongArray}
694   * instead, which has an {@link ImmutableLongArray#asList asList} view.
695   *
696   * @param backingArray the array to back the list
697   * @return a list view of the array
698   */
699  public static List<Long> asList(long... backingArray) {
700    if (backingArray.length == 0) {
701      return Collections.emptyList();
702    }
703    return new LongArrayAsList(backingArray);
704  }
705
706  @GwtCompatible
707  private static class LongArrayAsList extends AbstractList<Long>
708      implements RandomAccess, Serializable {
709    final long[] array;
710    final int start;
711    final int end;
712
713    LongArrayAsList(long[] array) {
714      this(array, 0, array.length);
715    }
716
717    LongArrayAsList(long[] array, int start, int end) {
718      this.array = array;
719      this.start = start;
720      this.end = end;
721    }
722
723    @Override
724    public int size() {
725      return end - start;
726    }
727
728    @Override
729    public boolean isEmpty() {
730      return false;
731    }
732
733    @Override
734    public Long get(int index) {
735      checkElementIndex(index, size());
736      return array[start + index];
737    }
738
739    @Override
740    public boolean contains(@CheckForNull Object target) {
741      // Overridden to prevent a ton of boxing
742      return (target instanceof Long) && Longs.indexOf(array, (Long) target, start, end) != -1;
743    }
744
745    @Override
746    public int indexOf(@CheckForNull Object target) {
747      // Overridden to prevent a ton of boxing
748      if (target instanceof Long) {
749        int i = Longs.indexOf(array, (Long) target, start, end);
750        if (i >= 0) {
751          return i - start;
752        }
753      }
754      return -1;
755    }
756
757    @Override
758    public int lastIndexOf(@CheckForNull Object target) {
759      // Overridden to prevent a ton of boxing
760      if (target instanceof Long) {
761        int i = Longs.lastIndexOf(array, (Long) target, start, end);
762        if (i >= 0) {
763          return i - start;
764        }
765      }
766      return -1;
767    }
768
769    @Override
770    public Long set(int index, Long element) {
771      checkElementIndex(index, size());
772      long oldValue = array[start + index];
773      // checkNotNull for GWT (do not optimize)
774      array[start + index] = checkNotNull(element);
775      return oldValue;
776    }
777
778    @Override
779    public List<Long> subList(int fromIndex, int toIndex) {
780      int size = size();
781      checkPositionIndexes(fromIndex, toIndex, size);
782      if (fromIndex == toIndex) {
783        return Collections.emptyList();
784      }
785      return new LongArrayAsList(array, start + fromIndex, start + toIndex);
786    }
787
788    @Override
789    public boolean equals(@CheckForNull Object object) {
790      if (object == this) {
791        return true;
792      }
793      if (object instanceof LongArrayAsList) {
794        LongArrayAsList that = (LongArrayAsList) object;
795        int size = size();
796        if (that.size() != size) {
797          return false;
798        }
799        for (int i = 0; i < size; i++) {
800          if (array[start + i] != that.array[that.start + i]) {
801            return false;
802          }
803        }
804        return true;
805      }
806      return super.equals(object);
807    }
808
809    @Override
810    public int hashCode() {
811      int result = 1;
812      for (int i = start; i < end; i++) {
813        result = 31 * result + Longs.hashCode(array[i]);
814      }
815      return result;
816    }
817
818    @Override
819    public String toString() {
820      StringBuilder builder = new StringBuilder(size() * 10);
821      builder.append('[').append(array[start]);
822      for (int i = start + 1; i < end; i++) {
823        builder.append(", ").append(array[i]);
824      }
825      return builder.append(']').toString();
826    }
827
828    long[] toLongArray() {
829      return Arrays.copyOfRange(array, start, end);
830    }
831
832    private static final long serialVersionUID = 0;
833  }
834}