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.annotations.GwtIncompatible;
024import com.google.common.base.Converter;
025import com.google.errorprone.annotations.InlineMe;
026import java.io.Serializable;
027import java.util.AbstractList;
028import java.util.Arrays;
029import java.util.Collection;
030import java.util.Collections;
031import java.util.Comparator;
032import java.util.List;
033import java.util.RandomAccess;
034import java.util.Spliterator;
035import java.util.Spliterators;
036import org.jspecify.annotations.Nullable;
037
038/**
039 * Static utility methods pertaining to {@code int} primitives, that are not already found in either
040 * {@link Integer} or {@link Arrays}.
041 *
042 * <p>See the Guava User Guide article on <a
043 * href="https://github.com/google/guava/wiki/PrimitivesExplained">primitive utilities</a>.
044 *
045 * @author Kevin Bourrillion
046 * @since 1.0
047 */
048@GwtCompatible(emulated = true)
049public final class Ints extends IntsMethodsForWeb {
050  private Ints() {}
051
052  /**
053   * The number of bytes required to represent a primitive {@code int} value.
054   *
055   * <p><b>Java 8+ users:</b> use {@link Integer#BYTES} instead.
056   */
057  public static final int BYTES = Integer.SIZE / Byte.SIZE;
058
059  /**
060   * The largest power of two that can be represented as an {@code int}.
061   *
062   * @since 10.0
063   */
064  public static final int MAX_POWER_OF_TWO = 1 << (Integer.SIZE - 2);
065
066  /**
067   * Returns a hash code for {@code value}; equal to the result of invoking {@code ((Integer)
068   * value).hashCode()}.
069   *
070   * <p><b>Java 8+ users:</b> use {@link Integer#hashCode(int)} instead.
071   *
072   * @param value a primitive {@code int} value
073   * @return a hash code for the value
074   */
075  public static int hashCode(int value) {
076    return value;
077  }
078
079  /**
080   * Returns the {@code int} value that is equal to {@code value}, if possible.
081   *
082   * @param value any value in the range of the {@code int} type
083   * @return the {@code int} value that equals {@code value}
084   * @throws IllegalArgumentException if {@code value} is greater than {@link Integer#MAX_VALUE} or
085   *     less than {@link Integer#MIN_VALUE}
086   */
087  public static int checkedCast(long value) {
088    int result = (int) value;
089    checkArgument(result == value, "Out of range: %s", value);
090    return result;
091  }
092
093  /**
094   * Returns the {@code int} nearest in value to {@code value}.
095   *
096   * @param value any {@code long} value
097   * @return the same value cast to {@code int} if it is in the range of the {@code int} type,
098   *     {@link Integer#MAX_VALUE} if it is too large, or {@link Integer#MIN_VALUE} if it is too
099   *     small
100   */
101  public static int saturatedCast(long value) {
102    if (value > Integer.MAX_VALUE) {
103      return Integer.MAX_VALUE;
104    }
105    if (value < Integer.MIN_VALUE) {
106      return Integer.MIN_VALUE;
107    }
108    return (int) value;
109  }
110
111  /**
112   * Compares the two specified {@code int} values. The sign of the value returned is the same as
113   * that of {@code ((Integer) a).compareTo(b)}.
114   *
115   * <p><b>Note:</b> this method is now unnecessary and should be treated as deprecated; use the
116   * equivalent {@link Integer#compare} method instead.
117   *
118   * @param a the first {@code int} to compare
119   * @param b the second {@code int} to compare
120   * @return a negative value if {@code a} is less than {@code b}; a positive value if {@code a} is
121   *     greater than {@code b}; or zero if they are equal
122   */
123  @InlineMe(replacement = "Integer.compare(a, b)")
124  public static int compare(int a, int b) {
125    return Integer.compare(a, b);
126  }
127
128  /**
129   * Returns {@code true} if {@code target} is present as an element anywhere in {@code array}.
130   *
131   * @param array an array of {@code int} values, possibly empty
132   * @param target a primitive {@code int} value
133   * @return {@code true} if {@code array[i] == target} for some value of {@code i}
134   */
135  public static boolean contains(int[] array, int target) {
136    for (int value : array) {
137      if (value == target) {
138        return true;
139      }
140    }
141    return false;
142  }
143
144  /**
145   * Returns the index of the first appearance of the value {@code target} in {@code array}.
146   *
147   * @param array an array of {@code int} values, possibly empty
148   * @param target a primitive {@code int} value
149   * @return the least index {@code i} for which {@code array[i] == target}, or {@code -1} if no
150   *     such index exists.
151   */
152  public static int indexOf(int[] array, int target) {
153    return indexOf(array, target, 0, array.length);
154  }
155
156  // TODO(kevinb): consider making this public
157  private static int indexOf(int[] array, int target, int start, int end) {
158    for (int i = start; i < end; i++) {
159      if (array[i] == target) {
160        return i;
161      }
162    }
163    return -1;
164  }
165
166  /**
167   * Returns the start position of the first occurrence of the specified {@code target} within
168   * {@code array}, or {@code -1} if there is no such occurrence.
169   *
170   * <p>More formally, returns the lowest index {@code i} such that {@code Arrays.copyOfRange(array,
171   * i, i + target.length)} contains exactly the same elements as {@code target}.
172   *
173   * @param array the array to search for the sequence {@code target}
174   * @param target the array to search for as a sub-sequence of {@code array}
175   */
176  public static int indexOf(int[] array, int[] target) {
177    checkNotNull(array, "array");
178    checkNotNull(target, "target");
179    if (target.length == 0) {
180      return 0;
181    }
182
183    outer:
184    for (int i = 0; i < array.length - target.length + 1; i++) {
185      for (int j = 0; j < target.length; j++) {
186        if (array[i + j] != target[j]) {
187          continue outer;
188        }
189      }
190      return i;
191    }
192    return -1;
193  }
194
195  /**
196   * Returns the index of the last appearance of the value {@code target} in {@code array}.
197   *
198   * @param array an array of {@code int} values, possibly empty
199   * @param target a primitive {@code int} value
200   * @return the greatest index {@code i} for which {@code array[i] == target}, or {@code -1} if no
201   *     such index exists.
202   */
203  public static int lastIndexOf(int[] array, int target) {
204    return lastIndexOf(array, target, 0, array.length);
205  }
206
207  // TODO(kevinb): consider making this public
208  private static int lastIndexOf(int[] array, int target, int start, int end) {
209    for (int i = end - 1; i >= start; i--) {
210      if (array[i] == target) {
211        return i;
212      }
213    }
214    return -1;
215  }
216
217  /**
218   * Returns the least value present in {@code array}.
219   *
220   * @param array a <i>nonempty</i> array of {@code int} values
221   * @return the value present in {@code array} that is less than or equal to every other value in
222   *     the array
223   * @throws IllegalArgumentException if {@code array} is empty
224   */
225  @GwtIncompatible(
226      "Available in GWT! Annotation is to avoid conflict with GWT specialization of base class.")
227  public static int min(int... array) {
228    checkArgument(array.length > 0);
229    int min = array[0];
230    for (int i = 1; i < array.length; i++) {
231      if (array[i] < min) {
232        min = array[i];
233      }
234    }
235    return min;
236  }
237
238  /**
239   * Returns the greatest value present in {@code array}.
240   *
241   * @param array a <i>nonempty</i> array of {@code int} values
242   * @return the value present in {@code array} that is greater than or equal to every other value
243   *     in the array
244   * @throws IllegalArgumentException if {@code array} is empty
245   */
246  @GwtIncompatible(
247      "Available in GWT! Annotation is to avoid conflict with GWT specialization of base class.")
248  public static int max(int... array) {
249    checkArgument(array.length > 0);
250    int max = array[0];
251    for (int i = 1; i < array.length; i++) {
252      if (array[i] > max) {
253        max = array[i];
254      }
255    }
256    return max;
257  }
258
259  /**
260   * Returns the value nearest to {@code value} which is within the closed range {@code [min..max]}.
261   *
262   * <p>If {@code value} is within the range {@code [min..max]}, {@code value} is returned
263   * unchanged. If {@code value} is less than {@code min}, {@code min} is returned, and if {@code
264   * value} is greater than {@code max}, {@code max} is returned.
265   *
266   * <p><b>Java 21+ users:</b> Use {@code Math.clamp} instead. Note that that method is capable of
267   * constraining a {@code long} input to an {@code int} range.
268   *
269   * @param value the {@code int} value to constrain
270   * @param min the lower bound (inclusive) of the range to constrain {@code value} to
271   * @param max the upper bound (inclusive) of the range to constrain {@code value} to
272   * @throws IllegalArgumentException if {@code min > max}
273   * @since 21.0
274   */
275  // A call to bare "min" or "max" would resolve to our varargs method, not to any static import.
276  @SuppressWarnings("StaticImportPreferred")
277  public static int constrainToRange(int value, int min, int max) {
278    checkArgument(min <= max, "min (%s) must be less than or equal to max (%s)", min, max);
279    return Math.min(Math.max(value, min), max);
280  }
281
282  /**
283   * Returns the values from each provided array combined into a single array. For example, {@code
284   * concat(new int[] {a, b}, new int[] {}, new int[] {c}} returns the array {@code {a, b, c}}.
285   *
286   * @param arrays zero or more {@code int} arrays
287   * @return a single array containing all the values from the source arrays, in order
288   * @throws IllegalArgumentException if the total number of elements in {@code arrays} does not fit
289   *     in an {@code int}
290   */
291  public static int[] concat(int[]... arrays) {
292    long length = 0;
293    for (int[] array : arrays) {
294      length += array.length;
295    }
296    int[] result = new int[checkNoOverflow(length)];
297    int pos = 0;
298    for (int[] array : arrays) {
299      System.arraycopy(array, 0, result, pos, array.length);
300      pos += array.length;
301    }
302    return result;
303  }
304
305  private static int checkNoOverflow(long result) {
306    checkArgument(
307        result == (int) result,
308        "the total number of elements (%s) in the arrays must fit in an int",
309        result);
310    return (int) result;
311  }
312
313  /**
314   * Returns a big-endian representation of {@code value} in a 4-element byte array; equivalent to
315   * {@code ByteBuffer.allocate(4).putInt(value).array()}. For example, the input value {@code
316   * 0x12131415} would yield the byte array {@code {0x12, 0x13, 0x14, 0x15}}.
317   *
318   * <p>If you need to convert and concatenate several values (possibly even of different types),
319   * use a shared {@link java.nio.ByteBuffer} instance, or use {@link
320   * com.google.common.io.ByteStreams#newDataOutput()} to get a growable buffer.
321   */
322  public static byte[] toByteArray(int value) {
323    return new byte[] {
324      (byte) (value >> 24), (byte) (value >> 16), (byte) (value >> 8), (byte) value
325    };
326  }
327
328  /**
329   * Returns the {@code int} value whose big-endian representation is stored in the first 4 bytes of
330   * {@code bytes}; equivalent to {@code ByteBuffer.wrap(bytes).getInt()}. For example, the input
331   * byte array {@code {0x12, 0x13, 0x14, 0x15, 0x33}} would yield the {@code int} value {@code
332   * 0x12131415}.
333   *
334   * <p>Arguably, it's preferable to use {@link java.nio.ByteBuffer}; that library exposes much more
335   * flexibility at little cost in readability.
336   *
337   * @throws IllegalArgumentException if {@code bytes} has fewer than 4 elements
338   */
339  public static int fromByteArray(byte[] bytes) {
340    checkArgument(bytes.length >= BYTES, "array too small: %s < %s", bytes.length, BYTES);
341    return fromBytes(bytes[0], bytes[1], bytes[2], bytes[3]);
342  }
343
344  /**
345   * Returns the {@code int} value whose byte representation is the given 4 bytes, in big-endian
346   * order; equivalent to {@code Ints.fromByteArray(new byte[] {b1, b2, b3, b4})}.
347   *
348   * @since 7.0
349   */
350  public static int fromBytes(byte b1, byte b2, byte b3, byte b4) {
351    return b1 << 24 | (b2 & 0xFF) << 16 | (b3 & 0xFF) << 8 | (b4 & 0xFF);
352  }
353
354  private static final class IntConverter extends Converter<String, Integer>
355      implements Serializable {
356    static final Converter<String, Integer> INSTANCE = new IntConverter();
357
358    @Override
359    protected Integer doForward(String value) {
360      return Integer.decode(value);
361    }
362
363    @Override
364    protected String doBackward(Integer value) {
365      return value.toString();
366    }
367
368    @Override
369    public String toString() {
370      return "Ints.stringConverter()";
371    }
372
373    private Object readResolve() {
374      return INSTANCE;
375    }
376
377    private static final long serialVersionUID = 1;
378  }
379
380  /**
381   * Returns a serializable converter object that converts between strings and integers using {@link
382   * Integer#decode} and {@link Integer#toString()}. The returned converter throws {@link
383   * NumberFormatException} if the input string is invalid.
384   *
385   * <p><b>Warning:</b> please see {@link Integer#decode} to understand exactly how strings are
386   * parsed. For example, the string {@code "0123"} is treated as <i>octal</i> and converted to the
387   * value {@code 83}.
388   *
389   * @since 16.0
390   */
391  public static Converter<String, Integer> stringConverter() {
392    return IntConverter.INSTANCE;
393  }
394
395  /**
396   * Returns an array containing the same values as {@code array}, but guaranteed to be of a
397   * specified minimum length. If {@code array} already has a length of at least {@code minLength},
398   * it is returned directly. Otherwise, a new array of size {@code minLength + padding} is
399   * returned, containing the values of {@code array}, and zeroes in the remaining places.
400   *
401   * @param array the source array
402   * @param minLength the minimum length the returned array must guarantee
403   * @param padding an extra amount to "grow" the array by if growth is necessary
404   * @throws IllegalArgumentException if {@code minLength} or {@code padding} is negative
405   * @return an array containing the values of {@code array}, with guaranteed minimum length {@code
406   *     minLength}
407   */
408  public static int[] ensureCapacity(int[] array, int minLength, int padding) {
409    checkArgument(minLength >= 0, "Invalid minLength: %s", minLength);
410    checkArgument(padding >= 0, "Invalid padding: %s", padding);
411    return (array.length < minLength) ? Arrays.copyOf(array, minLength + padding) : array;
412  }
413
414  /**
415   * Returns a string containing the supplied {@code int} values separated by {@code separator}. For
416   * example, {@code join("-", 1, 2, 3)} returns the string {@code "1-2-3"}.
417   *
418   * @param separator the text that should appear between consecutive values in the resulting string
419   *     (but not at the start or end)
420   * @param array an array of {@code int} values, possibly empty
421   */
422  public static String join(String separator, int... array) {
423    checkNotNull(separator);
424    if (array.length == 0) {
425      return "";
426    }
427
428    // For pre-sizing a builder, just get the right order of magnitude
429    StringBuilder builder = new StringBuilder(array.length * 5);
430    builder.append(array[0]);
431    for (int i = 1; i < array.length; i++) {
432      builder.append(separator).append(array[i]);
433    }
434    return builder.toString();
435  }
436
437  /**
438   * Returns a comparator that compares two {@code int} arrays <a
439   * href="http://en.wikipedia.org/wiki/Lexicographical_order">lexicographically</a>. That is, it
440   * compares, using {@link #compare(int, int)}), the first pair of values that follow any common
441   * prefix, or when one array is a prefix of the other, treats the shorter array as the lesser. For
442   * example, {@code [] < [1] < [1, 2] < [2]}.
443   *
444   * <p>The returned comparator is inconsistent with {@link Object#equals(Object)} (since arrays
445   * support only identity equality), but it is consistent with {@link Arrays#equals(int[], int[])}.
446   *
447   * @since 2.0
448   */
449  public static Comparator<int[]> lexicographicalComparator() {
450    return LexicographicalComparator.INSTANCE;
451  }
452
453  private enum LexicographicalComparator implements Comparator<int[]> {
454    INSTANCE;
455
456    @Override
457    // A call to bare "min" or "max" would resolve to our varargs method, not to any static import.
458    @SuppressWarnings("StaticImportPreferred")
459    public int compare(int[] left, int[] right) {
460      int minLength = Math.min(left.length, right.length);
461      for (int i = 0; i < minLength; i++) {
462        int result = Integer.compare(left[i], right[i]);
463        if (result != 0) {
464          return result;
465        }
466      }
467      return left.length - right.length;
468    }
469
470    @Override
471    public String toString() {
472      return "Ints.lexicographicalComparator()";
473    }
474  }
475
476  /**
477   * Sorts the elements of {@code array} in descending order.
478   *
479   * @since 23.1
480   */
481  public static void sortDescending(int[] array) {
482    checkNotNull(array);
483    sortDescending(array, 0, array.length);
484  }
485
486  /**
487   * Sorts the elements of {@code array} between {@code fromIndex} inclusive and {@code toIndex}
488   * exclusive in descending order.
489   *
490   * @since 23.1
491   */
492  public static void sortDescending(int[] array, int fromIndex, int toIndex) {
493    checkNotNull(array);
494    checkPositionIndexes(fromIndex, toIndex, array.length);
495    Arrays.sort(array, fromIndex, toIndex);
496    reverse(array, fromIndex, toIndex);
497  }
498
499  /**
500   * Reverses the elements of {@code array}. This is equivalent to {@code
501   * Collections.reverse(Ints.asList(array))}, but is likely to be more efficient.
502   *
503   * @since 23.1
504   */
505  public static void reverse(int[] array) {
506    checkNotNull(array);
507    reverse(array, 0, array.length);
508  }
509
510  /**
511   * Reverses the elements of {@code array} between {@code fromIndex} inclusive and {@code toIndex}
512   * exclusive. This is equivalent to {@code
513   * Collections.reverse(Ints.asList(array).subList(fromIndex, toIndex))}, but is likely to be more
514   * efficient.
515   *
516   * @throws IndexOutOfBoundsException if {@code fromIndex < 0}, {@code toIndex > array.length}, or
517   *     {@code toIndex > fromIndex}
518   * @since 23.1
519   */
520  public static void reverse(int[] array, int fromIndex, int toIndex) {
521    checkNotNull(array);
522    checkPositionIndexes(fromIndex, toIndex, array.length);
523    for (int i = fromIndex, j = toIndex - 1; i < j; i++, j--) {
524      int tmp = array[i];
525      array[i] = array[j];
526      array[j] = tmp;
527    }
528  }
529
530  /**
531   * Performs a right rotation of {@code array} of "distance" places, so that the first element is
532   * moved to index "distance", and the element at index {@code i} ends up at index {@code (distance
533   * + i) mod array.length}. This is equivalent to {@code Collections.rotate(Ints.asList(array),
534   * distance)}, but is considerably faster and avoids allocation and garbage collection.
535   *
536   * <p>The provided "distance" may be negative, which will rotate left.
537   *
538   * @since 32.0.0
539   */
540  public static void rotate(int[] array, int distance) {
541    rotate(array, distance, 0, array.length);
542  }
543
544  /**
545   * Performs a right rotation of {@code array} between {@code fromIndex} inclusive and {@code
546   * toIndex} exclusive. This is equivalent to {@code
547   * Collections.rotate(Ints.asList(array).subList(fromIndex, toIndex), distance)}, but is
548   * considerably faster and avoids allocations and garbage collection.
549   *
550   * <p>The provided "distance" may be negative, which will rotate left.
551   *
552   * @throws IndexOutOfBoundsException if {@code fromIndex < 0}, {@code toIndex > array.length}, or
553   *     {@code toIndex > fromIndex}
554   * @since 32.0.0
555   */
556  public static void rotate(int[] array, int distance, int fromIndex, int toIndex) {
557    // There are several well-known algorithms for rotating part of an array (or, equivalently,
558    // exchanging two blocks of memory). This classic text by Gries and Mills mentions several:
559    // https://ecommons.cornell.edu/bitstream/handle/1813/6292/81-452.pdf.
560    // (1) "Reversal", the one we have here.
561    // (2) "Dolphin". If we're rotating an array a of size n by a distance of d, then element a[0]
562    //     ends up at a[d], which in turn ends up at a[2d], and so on until we get back to a[0].
563    //     (All indices taken mod n.) If d and n are mutually prime, all elements will have been
564    //     moved at that point. Otherwise, we can rotate the cycle a[1], a[1 + d], a[1 + 2d], etc,
565    //     then a[2] etc, and so on until we have rotated all elements. There are gcd(d, n) cycles
566    //     in all.
567    // (3) "Successive". We can consider that we are exchanging a block of size d (a[0..d-1]) with a
568    //     block of size n-d (a[d..n-1]), where in general these blocks have different sizes. If we
569    //     imagine a line separating the first block from the second, we can proceed by exchanging
570    //     the smaller of these blocks with the far end of the other one. That leaves us with a
571    //     smaller version of the same problem.
572    //     Say we are rotating abcdefgh by 5. We start with abcde|fgh. The smaller block is [fgh]:
573    //     [abc]de|[fgh] -> [fgh]de|[abc]. Now [fgh] is in the right place, but we need to swap [de]
574    //     with [abc]: fgh[de]|a[bc] -> fgh[bc]|a[de]. Now we need to swap [a] with [bc]:
575    //     fgh[b]c|[a]de -> fgh[a]c|[b]de. Finally we need to swap [c] with [b]:
576    //     fgha[c]|[b]de -> fgha[b]|[c]de. Because these two blocks are the same size, we are done.
577    // The Dolphin algorithm is attractive because it does the fewest array reads and writes: each
578    // array slot is read and written exactly once. However, it can have very poor memory locality:
579    // benchmarking shows it can take 7 times longer than the other two in some cases. The other two
580    // do n swaps, minus a delta (0 or 2 for Reversal, gcd(d, n) for Successive), so that's about
581    // twice as many reads and writes. But benchmarking shows that they usually perform better than
582    // Dolphin. Reversal is about as good as Successive on average, and it is much simpler,
583    // especially since we already have a `reverse` method.
584    checkNotNull(array);
585    checkPositionIndexes(fromIndex, toIndex, array.length);
586    if (array.length <= 1) {
587      return;
588    }
589
590    int length = toIndex - fromIndex;
591    // Obtain m = (-distance mod length), a non-negative value less than "length". This is how many
592    // places left to rotate.
593    int m = -distance % length;
594    m = (m < 0) ? m + length : m;
595    // The current index of what will become the first element of the rotated section.
596    int newFirstIndex = m + fromIndex;
597    if (newFirstIndex == fromIndex) {
598      return;
599    }
600
601    reverse(array, fromIndex, newFirstIndex);
602    reverse(array, newFirstIndex, toIndex);
603    reverse(array, fromIndex, toIndex);
604  }
605
606  /**
607   * Returns an array containing each value of {@code collection}, converted to a {@code int} value
608   * in the manner of {@link Number#intValue}.
609   *
610   * <p>Elements are copied from the argument collection as if by {@code collection.toArray()}.
611   * Calling this method is as thread-safe as calling that method.
612   *
613   * @param collection a collection of {@code Number} instances
614   * @return an array containing the same values as {@code collection}, in the same order, converted
615   *     to primitives
616   * @throws NullPointerException if {@code collection} or any of its elements is null
617   * @since 1.0 (parameter was {@code Collection<Integer>} before 12.0)
618   */
619  public static int[] toArray(Collection<? extends Number> collection) {
620    if (collection instanceof IntArrayAsList) {
621      return ((IntArrayAsList) collection).toIntArray();
622    }
623
624    Object[] boxedArray = collection.toArray();
625    int len = boxedArray.length;
626    int[] array = new int[len];
627    for (int i = 0; i < len; i++) {
628      // checkNotNull for GWT (do not optimize)
629      array[i] = ((Number) checkNotNull(boxedArray[i])).intValue();
630    }
631    return array;
632  }
633
634  /**
635   * Returns a fixed-size list backed by the specified array, similar to {@link
636   * Arrays#asList(Object[])}. The list supports {@link List#set(int, Object)}, but any attempt to
637   * set a value to {@code null} will result in a {@link NullPointerException}.
638   *
639   * <p>The returned list maintains the values, but not the identities, of {@code Integer} objects
640   * written to or read from it. For example, whether {@code list.get(0) == list.get(0)} is true for
641   * the returned list is unspecified.
642   *
643   * <p>The returned list is serializable.
644   *
645   * <p><b>Note:</b> when possible, you should represent your data as an {@link ImmutableIntArray}
646   * instead, which has an {@link ImmutableIntArray#asList asList} view.
647   *
648   * @param backingArray the array to back the list
649   * @return a list view of the array
650   */
651  public static List<Integer> asList(int... backingArray) {
652    if (backingArray.length == 0) {
653      return Collections.emptyList();
654    }
655    return new IntArrayAsList(backingArray);
656  }
657
658  @GwtCompatible
659  private static class IntArrayAsList extends AbstractList<Integer>
660      implements RandomAccess, Serializable {
661    final int[] array;
662    final int start;
663    final int end;
664
665    IntArrayAsList(int[] array) {
666      this(array, 0, array.length);
667    }
668
669    IntArrayAsList(int[] array, int start, int end) {
670      this.array = array;
671      this.start = start;
672      this.end = end;
673    }
674
675    @Override
676    public int size() {
677      return end - start;
678    }
679
680    @Override
681    public boolean isEmpty() {
682      return false;
683    }
684
685    @Override
686    public Integer get(int index) {
687      checkElementIndex(index, size());
688      return array[start + index];
689    }
690
691    @Override
692    public Spliterator.OfInt spliterator() {
693      return Spliterators.spliterator(array, start, end, 0);
694    }
695
696    @Override
697    public boolean contains(@Nullable Object target) {
698      // Overridden to prevent a ton of boxing
699      return (target instanceof Integer) && Ints.indexOf(array, (Integer) target, start, end) != -1;
700    }
701
702    @Override
703    public int indexOf(@Nullable Object target) {
704      // Overridden to prevent a ton of boxing
705      if (target instanceof Integer) {
706        int i = Ints.indexOf(array, (Integer) target, start, end);
707        if (i >= 0) {
708          return i - start;
709        }
710      }
711      return -1;
712    }
713
714    @Override
715    public int lastIndexOf(@Nullable Object target) {
716      // Overridden to prevent a ton of boxing
717      if (target instanceof Integer) {
718        int i = Ints.lastIndexOf(array, (Integer) target, start, end);
719        if (i >= 0) {
720          return i - start;
721        }
722      }
723      return -1;
724    }
725
726    @Override
727    public Integer set(int index, Integer element) {
728      checkElementIndex(index, size());
729      int oldValue = array[start + index];
730      // checkNotNull for GWT (do not optimize)
731      array[start + index] = checkNotNull(element);
732      return oldValue;
733    }
734
735    @Override
736    public List<Integer> subList(int fromIndex, int toIndex) {
737      int size = size();
738      checkPositionIndexes(fromIndex, toIndex, size);
739      if (fromIndex == toIndex) {
740        return Collections.emptyList();
741      }
742      return new IntArrayAsList(array, start + fromIndex, start + toIndex);
743    }
744
745    @Override
746    public boolean equals(@Nullable Object object) {
747      if (object == this) {
748        return true;
749      }
750      if (object instanceof IntArrayAsList) {
751        IntArrayAsList that = (IntArrayAsList) object;
752        int size = size();
753        if (that.size() != size) {
754          return false;
755        }
756        for (int i = 0; i < size; i++) {
757          if (array[start + i] != that.array[that.start + i]) {
758            return false;
759          }
760        }
761        return true;
762      }
763      return super.equals(object);
764    }
765
766    @Override
767    public int hashCode() {
768      int result = 1;
769      for (int i = start; i < end; i++) {
770        result = 31 * result + Ints.hashCode(array[i]);
771      }
772      return result;
773    }
774
775    @Override
776    public String toString() {
777      StringBuilder builder = new StringBuilder(size() * 5);
778      builder.append('[').append(array[start]);
779      for (int i = start + 1; i < end; i++) {
780        builder.append(", ").append(array[i]);
781      }
782      return builder.append(']').toString();
783    }
784
785    int[] toIntArray() {
786      return Arrays.copyOfRange(array, start, end);
787    }
788
789    private static final long serialVersionUID = 0;
790  }
791
792  /**
793   * Parses the specified string as a signed decimal integer value. The ASCII character {@code '-'}
794   * (<code>'&#92;u002D'</code>) is recognized as the minus sign.
795   *
796   * <p>Unlike {@link Integer#parseInt(String)}, this method returns {@code null} instead of
797   * throwing an exception if parsing fails. Additionally, this method only accepts ASCII digits,
798   * and returns {@code null} if non-ASCII digits are present in the string.
799   *
800   * <p>Note that strings prefixed with ASCII {@code '+'} are rejected, even though {@link
801   * Integer#parseInt(String)} accepts them.
802   *
803   * @param string the string representation of an integer value
804   * @return the integer value represented by {@code string}, or {@code null} if {@code string} has
805   *     a length of zero or cannot be parsed as an integer value
806   * @throws NullPointerException if {@code string} is {@code null}
807   * @since 11.0
808   */
809  public static @Nullable Integer tryParse(String string) {
810    return tryParse(string, 10);
811  }
812
813  /**
814   * Parses the specified string as a signed integer value using the specified radix. The ASCII
815   * character {@code '-'} (<code>'&#92;u002D'</code>) is recognized as the minus sign.
816   *
817   * <p>Unlike {@link Integer#parseInt(String, int)}, this method returns {@code null} instead of
818   * throwing an exception if parsing fails. Additionally, this method only accepts ASCII digits,
819   * and returns {@code null} if non-ASCII digits are present in the string.
820   *
821   * <p>Note that strings prefixed with ASCII {@code '+'} are rejected, even though {@link
822   * Integer#parseInt(String)} accepts them.
823   *
824   * @param string the string representation of an integer value
825   * @param radix the radix to use when parsing
826   * @return the integer value represented by {@code string} using {@code radix}, or {@code null} if
827   *     {@code string} has a length of zero or cannot be parsed as an integer value
828   * @throws IllegalArgumentException if {@code radix < Character.MIN_RADIX} or {@code radix >
829   *     Character.MAX_RADIX}
830   * @throws NullPointerException if {@code string} is {@code null}
831   * @since 19.0
832   */
833  public static @Nullable Integer tryParse(String string, int radix) {
834    Long result = Longs.tryParse(string, radix);
835    if (result == null || result.longValue() != result.intValue()) {
836      return null;
837    } else {
838      return result.intValue();
839    }
840  }
841}