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.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 javax.annotation.CheckForNull;
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)
049@ElementTypesAreNonnullByDefault
050public final class Ints extends IntsMethodsForWeb {
051  private Ints() {}
052
053  /**
054   * The number of bytes required to represent a primitive {@code int} value.
055   *
056   * <p><b>Java 8+ users:</b> use {@link Integer#BYTES} instead.
057   */
058  public static final int BYTES = Integer.SIZE / Byte.SIZE;
059
060  /**
061   * The largest power of two that can be represented as an {@code int}.
062   *
063   * @since 10.0
064   */
065  public static final int MAX_POWER_OF_TWO = 1 << (Integer.SIZE - 2);
066
067  /**
068   * Returns a hash code for {@code value}; equal to the result of invoking {@code ((Integer)
069   * value).hashCode()}.
070   *
071   * <p><b>Java 8+ users:</b> use {@link Integer#hashCode(int)} instead.
072   *
073   * @param value a primitive {@code int} value
074   * @return a hash code for the value
075   */
076  public static int hashCode(int value) {
077    return value;
078  }
079
080  /**
081   * Returns the {@code int} value that is equal to {@code value}, if possible.
082   *
083   * @param value any value in the range of the {@code int} type
084   * @return the {@code int} value that equals {@code value}
085   * @throws IllegalArgumentException if {@code value} is greater than {@link Integer#MAX_VALUE} or
086   *     less than {@link Integer#MIN_VALUE}
087   */
088  public static int checkedCast(long value) {
089    int result = (int) value;
090    checkArgument(result == value, "Out of range: %s", value);
091    return result;
092  }
093
094  /**
095   * Returns the {@code int} nearest in value to {@code value}.
096   *
097   * @param value any {@code long} value
098   * @return the same value cast to {@code int} if it is in the range of the {@code int} type,
099   *     {@link Integer#MAX_VALUE} if it is too large, or {@link Integer#MIN_VALUE} if it is too
100   *     small
101   */
102  public static int saturatedCast(long value) {
103    if (value > Integer.MAX_VALUE) {
104      return Integer.MAX_VALUE;
105    }
106    if (value < Integer.MIN_VALUE) {
107      return Integer.MIN_VALUE;
108    }
109    return (int) value;
110  }
111
112  /**
113   * Compares the two specified {@code int} values. The sign of the value returned is the same as
114   * that of {@code ((Integer) a).compareTo(b)}.
115   *
116   * <p><b>Note:</b> this method is now unnecessary and should be treated as deprecated; use the
117   * equivalent {@link Integer#compare} method instead.
118   *
119   * @param a the first {@code int} to compare
120   * @param b the second {@code int} to compare
121   * @return a negative value if {@code a} is less than {@code b}; a positive value if {@code a} is
122   *     greater than {@code b}; or zero if they are equal
123   */
124  @InlineMe(replacement = "Integer.compare(a, b)")
125  public static int compare(int a, int b) {
126    return Integer.compare(a, b);
127  }
128
129  /**
130   * Returns {@code true} if {@code target} is present as an element anywhere in {@code array}.
131   *
132   * @param array an array of {@code int} values, possibly empty
133   * @param target a primitive {@code int} value
134   * @return {@code true} if {@code array[i] == target} for some value of {@code i}
135   */
136  public static boolean contains(int[] array, int target) {
137    for (int value : array) {
138      if (value == target) {
139        return true;
140      }
141    }
142    return false;
143  }
144
145  /**
146   * Returns the index of the first appearance of the value {@code target} in {@code array}.
147   *
148   * @param array an array of {@code int} values, possibly empty
149   * @param target a primitive {@code int} value
150   * @return the least index {@code i} for which {@code array[i] == target}, or {@code -1} if no
151   *     such index exists.
152   */
153  public static int indexOf(int[] array, int target) {
154    return indexOf(array, target, 0, array.length);
155  }
156
157  // TODO(kevinb): consider making this public
158  private static int indexOf(int[] array, int target, int start, int end) {
159    for (int i = start; i < end; i++) {
160      if (array[i] == target) {
161        return i;
162      }
163    }
164    return -1;
165  }
166
167  /**
168   * Returns the start position of the first occurrence of the specified {@code target} within
169   * {@code array}, or {@code -1} if there is no such occurrence.
170   *
171   * <p>More formally, returns the lowest index {@code i} such that {@code Arrays.copyOfRange(array,
172   * i, i + target.length)} contains exactly the same elements as {@code target}.
173   *
174   * @param array the array to search for the sequence {@code target}
175   * @param target the array to search for as a sub-sequence of {@code array}
176   */
177  public static int indexOf(int[] array, int[] target) {
178    checkNotNull(array, "array");
179    checkNotNull(target, "target");
180    if (target.length == 0) {
181      return 0;
182    }
183
184    outer:
185    for (int i = 0; i < array.length - target.length + 1; i++) {
186      for (int j = 0; j < target.length; j++) {
187        if (array[i + j] != target[j]) {
188          continue outer;
189        }
190      }
191      return i;
192    }
193    return -1;
194  }
195
196  /**
197   * Returns the index of the last appearance of the value {@code target} in {@code array}.
198   *
199   * @param array an array of {@code int} values, possibly empty
200   * @param target a primitive {@code int} value
201   * @return the greatest index {@code i} for which {@code array[i] == target}, or {@code -1} if no
202   *     such index exists.
203   */
204  public static int lastIndexOf(int[] array, int target) {
205    return lastIndexOf(array, target, 0, array.length);
206  }
207
208  // TODO(kevinb): consider making this public
209  private static int lastIndexOf(int[] array, int target, int start, int end) {
210    for (int i = end - 1; i >= start; i--) {
211      if (array[i] == target) {
212        return i;
213      }
214    }
215    return -1;
216  }
217
218  /**
219   * Returns the least value present in {@code array}.
220   *
221   * @param array a <i>nonempty</i> array of {@code int} values
222   * @return the value present in {@code array} that is less than or equal to every other value in
223   *     the array
224   * @throws IllegalArgumentException if {@code array} is empty
225   */
226  @GwtIncompatible(
227      "Available in GWT! Annotation is to avoid conflict with GWT specialization of base class.")
228  public static int min(int... array) {
229    checkArgument(array.length > 0);
230    int min = array[0];
231    for (int i = 1; i < array.length; i++) {
232      if (array[i] < min) {
233        min = array[i];
234      }
235    }
236    return min;
237  }
238
239  /**
240   * Returns the greatest value present in {@code array}.
241   *
242   * @param array a <i>nonempty</i> array of {@code int} values
243   * @return the value present in {@code array} that is greater than or equal to every other value
244   *     in the array
245   * @throws IllegalArgumentException if {@code array} is empty
246   */
247  @GwtIncompatible(
248      "Available in GWT! Annotation is to avoid conflict with GWT specialization of base class.")
249  public static int max(int... array) {
250    checkArgument(array.length > 0);
251    int max = array[0];
252    for (int i = 1; i < array.length; i++) {
253      if (array[i] > max) {
254        max = array[i];
255      }
256    }
257    return max;
258  }
259
260  /**
261   * Returns the value nearest to {@code value} which is within the closed range {@code [min..max]}.
262   *
263   * <p>If {@code value} is within the range {@code [min..max]}, {@code value} is returned
264   * unchanged. If {@code value} is less than {@code min}, {@code min} is returned, and if {@code
265   * value} is greater than {@code max}, {@code max} is returned.
266   *
267   * <p><b>Java 21+ users:</b> Use {@code Math.clamp} instead. Note that that method is capable of
268   * constraining a {@code long} input to an {@code int} range.
269   *
270   * @param value the {@code int} value to constrain
271   * @param min the lower bound (inclusive) of the range to constrain {@code value} to
272   * @param max the upper bound (inclusive) of the range to constrain {@code value} to
273   * @throws IllegalArgumentException if {@code min > max}
274   * @since 21.0
275   */
276  // A call to bare "min" or "max" would resolve to our varargs method, not to any static import.
277  @SuppressWarnings("StaticImportPreferred")
278  public static int constrainToRange(int value, int min, int max) {
279    checkArgument(min <= max, "min (%s) must be less than or equal to max (%s)", min, max);
280    return Math.min(Math.max(value, min), max);
281  }
282
283  /**
284   * Returns the values from each provided array combined into a single array. For example, {@code
285   * concat(new int[] {a, b}, new int[] {}, new int[] {c}} returns the array {@code {a, b, c}}.
286   *
287   * @param arrays zero or more {@code int} arrays
288   * @return a single array containing all the values from the source arrays, in order
289   * @throws IllegalArgumentException if the total number of elements in {@code arrays} does not fit
290   *     in an {@code int}
291   */
292  public static int[] concat(int[]... arrays) {
293    long length = 0;
294    for (int[] array : arrays) {
295      length += array.length;
296    }
297    int[] result = new int[checkNoOverflow(length)];
298    int pos = 0;
299    for (int[] array : arrays) {
300      System.arraycopy(array, 0, result, pos, array.length);
301      pos += array.length;
302    }
303    return result;
304  }
305
306  private static int checkNoOverflow(long result) {
307    checkArgument(
308        result == (int) result,
309        "the total number of elements (%s) in the arrays must fit in an int",
310        result);
311    return (int) result;
312  }
313
314  /**
315   * Returns a big-endian representation of {@code value} in a 4-element byte array; equivalent to
316   * {@code ByteBuffer.allocate(4).putInt(value).array()}. For example, the input value {@code
317   * 0x12131415} would yield the byte array {@code {0x12, 0x13, 0x14, 0x15}}.
318   *
319   * <p>If you need to convert and concatenate several values (possibly even of different types),
320   * use a shared {@link java.nio.ByteBuffer} instance, or use {@link
321   * com.google.common.io.ByteStreams#newDataOutput()} to get a growable buffer.
322   */
323  public static byte[] toByteArray(int value) {
324    return new byte[] {
325      (byte) (value >> 24), (byte) (value >> 16), (byte) (value >> 8), (byte) value
326    };
327  }
328
329  /**
330   * Returns the {@code int} value whose big-endian representation is stored in the first 4 bytes of
331   * {@code bytes}; equivalent to {@code ByteBuffer.wrap(bytes).getInt()}. For example, the input
332   * byte array {@code {0x12, 0x13, 0x14, 0x15, 0x33}} would yield the {@code int} value {@code
333   * 0x12131415}.
334   *
335   * <p>Arguably, it's preferable to use {@link java.nio.ByteBuffer}; that library exposes much more
336   * flexibility at little cost in readability.
337   *
338   * @throws IllegalArgumentException if {@code bytes} has fewer than 4 elements
339   */
340  public static int fromByteArray(byte[] bytes) {
341    checkArgument(bytes.length >= BYTES, "array too small: %s < %s", bytes.length, BYTES);
342    return fromBytes(bytes[0], bytes[1], bytes[2], bytes[3]);
343  }
344
345  /**
346   * Returns the {@code int} value whose byte representation is the given 4 bytes, in big-endian
347   * order; equivalent to {@code Ints.fromByteArray(new byte[] {b1, b2, b3, b4})}.
348   *
349   * @since 7.0
350   */
351  public static int fromBytes(byte b1, byte b2, byte b3, byte b4) {
352    return b1 << 24 | (b2 & 0xFF) << 16 | (b3 & 0xFF) << 8 | (b4 & 0xFF);
353  }
354
355  private static final class IntConverter extends Converter<String, Integer>
356      implements Serializable {
357    static final Converter<String, Integer> INSTANCE = new IntConverter();
358
359    @Override
360    protected Integer doForward(String value) {
361      return Integer.decode(value);
362    }
363
364    @Override
365    protected String doBackward(Integer value) {
366      return value.toString();
367    }
368
369    @Override
370    public String toString() {
371      return "Ints.stringConverter()";
372    }
373
374    private Object readResolve() {
375      return INSTANCE;
376    }
377
378    private static final long serialVersionUID = 1;
379  }
380
381  /**
382   * Returns a serializable converter object that converts between strings and integers using {@link
383   * Integer#decode} and {@link Integer#toString()}. The returned converter throws {@link
384   * NumberFormatException} if the input string is invalid.
385   *
386   * <p><b>Warning:</b> please see {@link Integer#decode} to understand exactly how strings are
387   * parsed. For example, the string {@code "0123"} is treated as <i>octal</i> and converted to the
388   * value {@code 83}.
389   *
390   * @since 16.0
391   */
392  public static Converter<String, Integer> stringConverter() {
393    return IntConverter.INSTANCE;
394  }
395
396  /**
397   * Returns an array containing the same values as {@code array}, but guaranteed to be of a
398   * specified minimum length. If {@code array} already has a length of at least {@code minLength},
399   * it is returned directly. Otherwise, a new array of size {@code minLength + padding} is
400   * returned, containing the values of {@code array}, and zeroes in the remaining places.
401   *
402   * @param array the source array
403   * @param minLength the minimum length the returned array must guarantee
404   * @param padding an extra amount to "grow" the array by if growth is necessary
405   * @throws IllegalArgumentException if {@code minLength} or {@code padding} is negative
406   * @return an array containing the values of {@code array}, with guaranteed minimum length {@code
407   *     minLength}
408   */
409  public static int[] ensureCapacity(int[] array, int minLength, int padding) {
410    checkArgument(minLength >= 0, "Invalid minLength: %s", minLength);
411    checkArgument(padding >= 0, "Invalid padding: %s", padding);
412    return (array.length < minLength) ? Arrays.copyOf(array, minLength + padding) : array;
413  }
414
415  /**
416   * Returns a string containing the supplied {@code int} values separated by {@code separator}. For
417   * example, {@code join("-", 1, 2, 3)} returns the string {@code "1-2-3"}.
418   *
419   * @param separator the text that should appear between consecutive values in the resulting string
420   *     (but not at the start or end)
421   * @param array an array of {@code int} values, possibly empty
422   */
423  public static String join(String separator, int... array) {
424    checkNotNull(separator);
425    if (array.length == 0) {
426      return "";
427    }
428
429    // For pre-sizing a builder, just get the right order of magnitude
430    StringBuilder builder = new StringBuilder(array.length * 5);
431    builder.append(array[0]);
432    for (int i = 1; i < array.length; i++) {
433      builder.append(separator).append(array[i]);
434    }
435    return builder.toString();
436  }
437
438  /**
439   * Returns a comparator that compares two {@code int} arrays <a
440   * href="http://en.wikipedia.org/wiki/Lexicographical_order">lexicographically</a>. That is, it
441   * compares, using {@link #compare(int, int)}), the first pair of values that follow any common
442   * prefix, or when one array is a prefix of the other, treats the shorter array as the lesser. For
443   * example, {@code [] < [1] < [1, 2] < [2]}.
444   *
445   * <p>The returned comparator is inconsistent with {@link Object#equals(Object)} (since arrays
446   * support only identity equality), but it is consistent with {@link Arrays#equals(int[], int[])}.
447   *
448   * @since 2.0
449   */
450  public static Comparator<int[]> lexicographicalComparator() {
451    return LexicographicalComparator.INSTANCE;
452  }
453
454  private enum LexicographicalComparator implements Comparator<int[]> {
455    INSTANCE;
456
457    @Override
458    // A call to bare "min" or "max" would resolve to our varargs method, not to any static import.
459    @SuppressWarnings("StaticImportPreferred")
460    public int compare(int[] left, int[] right) {
461      int minLength = Math.min(left.length, right.length);
462      for (int i = 0; i < minLength; i++) {
463        int result = Integer.compare(left[i], right[i]);
464        if (result != 0) {
465          return result;
466        }
467      }
468      return left.length - right.length;
469    }
470
471    @Override
472    public String toString() {
473      return "Ints.lexicographicalComparator()";
474    }
475  }
476
477  /**
478   * Sorts the elements of {@code array} in descending order.
479   *
480   * @since 23.1
481   */
482  public static void sortDescending(int[] array) {
483    checkNotNull(array);
484    sortDescending(array, 0, array.length);
485  }
486
487  /**
488   * Sorts the elements of {@code array} between {@code fromIndex} inclusive and {@code toIndex}
489   * exclusive in descending order.
490   *
491   * @since 23.1
492   */
493  public static void sortDescending(int[] array, int fromIndex, int toIndex) {
494    checkNotNull(array);
495    checkPositionIndexes(fromIndex, toIndex, array.length);
496    Arrays.sort(array, fromIndex, toIndex);
497    reverse(array, fromIndex, toIndex);
498  }
499
500  /**
501   * Reverses the elements of {@code array}. This is equivalent to {@code
502   * Collections.reverse(Ints.asList(array))}, but is likely to be more efficient.
503   *
504   * @since 23.1
505   */
506  public static void reverse(int[] array) {
507    checkNotNull(array);
508    reverse(array, 0, array.length);
509  }
510
511  /**
512   * Reverses the elements of {@code array} between {@code fromIndex} inclusive and {@code toIndex}
513   * exclusive. This is equivalent to {@code
514   * Collections.reverse(Ints.asList(array).subList(fromIndex, toIndex))}, but is likely to be more
515   * efficient.
516   *
517   * @throws IndexOutOfBoundsException if {@code fromIndex < 0}, {@code toIndex > array.length}, or
518   *     {@code toIndex > fromIndex}
519   * @since 23.1
520   */
521  public static void reverse(int[] array, int fromIndex, int toIndex) {
522    checkNotNull(array);
523    checkPositionIndexes(fromIndex, toIndex, array.length);
524    for (int i = fromIndex, j = toIndex - 1; i < j; i++, j--) {
525      int tmp = array[i];
526      array[i] = array[j];
527      array[j] = tmp;
528    }
529  }
530
531  /**
532   * Performs a right rotation of {@code array} of "distance" places, so that the first element is
533   * moved to index "distance", and the element at index {@code i} ends up at index {@code (distance
534   * + i) mod array.length}. This is equivalent to {@code Collections.rotate(Ints.asList(array),
535   * distance)}, but is considerably faster and avoids allocation and garbage collection.
536   *
537   * <p>The provided "distance" may be negative, which will rotate left.
538   *
539   * @since 32.0.0
540   */
541  public static void rotate(int[] array, int distance) {
542    rotate(array, distance, 0, array.length);
543  }
544
545  /**
546   * Performs a right rotation of {@code array} between {@code fromIndex} inclusive and {@code
547   * toIndex} exclusive. This is equivalent to {@code
548   * Collections.rotate(Ints.asList(array).subList(fromIndex, toIndex), distance)}, but is
549   * considerably faster and avoids allocations and garbage collection.
550   *
551   * <p>The provided "distance" may be negative, which will rotate left.
552   *
553   * @throws IndexOutOfBoundsException if {@code fromIndex < 0}, {@code toIndex > array.length}, or
554   *     {@code toIndex > fromIndex}
555   * @since 32.0.0
556   */
557  public static void rotate(int[] array, int distance, int fromIndex, int toIndex) {
558    // There are several well-known algorithms for rotating part of an array (or, equivalently,
559    // exchanging two blocks of memory). This classic text by Gries and Mills mentions several:
560    // https://ecommons.cornell.edu/bitstream/handle/1813/6292/81-452.pdf.
561    // (1) "Reversal", the one we have here.
562    // (2) "Dolphin". If we're rotating an array a of size n by a distance of d, then element a[0]
563    //     ends up at a[d], which in turn ends up at a[2d], and so on until we get back to a[0].
564    //     (All indices taken mod n.) If d and n are mutually prime, all elements will have been
565    //     moved at that point. Otherwise, we can rotate the cycle a[1], a[1 + d], a[1 + 2d], etc,
566    //     then a[2] etc, and so on until we have rotated all elements. There are gcd(d, n) cycles
567    //     in all.
568    // (3) "Successive". We can consider that we are exchanging a block of size d (a[0..d-1]) with a
569    //     block of size n-d (a[d..n-1]), where in general these blocks have different sizes. If we
570    //     imagine a line separating the first block from the second, we can proceed by exchanging
571    //     the smaller of these blocks with the far end of the other one. That leaves us with a
572    //     smaller version of the same problem.
573    //     Say we are rotating abcdefgh by 5. We start with abcde|fgh. The smaller block is [fgh]:
574    //     [abc]de|[fgh] -> [fgh]de|[abc]. Now [fgh] is in the right place, but we need to swap [de]
575    //     with [abc]: fgh[de]|a[bc] -> fgh[bc]|a[de]. Now we need to swap [a] with [bc]:
576    //     fgh[b]c|[a]de -> fgh[a]c|[b]de. Finally we need to swap [c] with [b]:
577    //     fgha[c]|[b]de -> fgha[b]|[c]de. Because these two blocks are the same size, we are done.
578    // The Dolphin algorithm is attractive because it does the fewest array reads and writes: each
579    // array slot is read and written exactly once. However, it can have very poor memory locality:
580    // benchmarking shows it can take 7 times longer than the other two in some cases. The other two
581    // do n swaps, minus a delta (0 or 2 for Reversal, gcd(d, n) for Successive), so that's about
582    // twice as many reads and writes. But benchmarking shows that they usually perform better than
583    // Dolphin. Reversal is about as good as Successive on average, and it is much simpler,
584    // especially since we already have a `reverse` method.
585    checkNotNull(array);
586    checkPositionIndexes(fromIndex, toIndex, array.length);
587    if (array.length <= 1) {
588      return;
589    }
590
591    int length = toIndex - fromIndex;
592    // Obtain m = (-distance mod length), a non-negative value less than "length". This is how many
593    // places left to rotate.
594    int m = -distance % length;
595    m = (m < 0) ? m + length : m;
596    // The current index of what will become the first element of the rotated section.
597    int newFirstIndex = m + fromIndex;
598    if (newFirstIndex == fromIndex) {
599      return;
600    }
601
602    reverse(array, fromIndex, newFirstIndex);
603    reverse(array, newFirstIndex, toIndex);
604    reverse(array, fromIndex, toIndex);
605  }
606
607  /**
608   * Returns an array containing each value of {@code collection}, converted to a {@code int} value
609   * in the manner of {@link Number#intValue}.
610   *
611   * <p>Elements are copied from the argument collection as if by {@code collection.toArray()}.
612   * Calling this method is as thread-safe as calling that method.
613   *
614   * @param collection a collection of {@code Number} instances
615   * @return an array containing the same values as {@code collection}, in the same order, converted
616   *     to primitives
617   * @throws NullPointerException if {@code collection} or any of its elements is null
618   * @since 1.0 (parameter was {@code Collection<Integer>} before 12.0)
619   */
620  public static int[] toArray(Collection<? extends Number> collection) {
621    if (collection instanceof IntArrayAsList) {
622      return ((IntArrayAsList) collection).toIntArray();
623    }
624
625    Object[] boxedArray = collection.toArray();
626    int len = boxedArray.length;
627    int[] array = new int[len];
628    for (int i = 0; i < len; i++) {
629      // checkNotNull for GWT (do not optimize)
630      array[i] = ((Number) checkNotNull(boxedArray[i])).intValue();
631    }
632    return array;
633  }
634
635  /**
636   * Returns a fixed-size list backed by the specified array, similar to {@link
637   * Arrays#asList(Object[])}. The list supports {@link List#set(int, Object)}, but any attempt to
638   * set a value to {@code null} will result in a {@link NullPointerException}.
639   *
640   * <p>The returned list maintains the values, but not the identities, of {@code Integer} objects
641   * written to or read from it. For example, whether {@code list.get(0) == list.get(0)} is true for
642   * the returned list is unspecified.
643   *
644   * <p>The returned list is serializable.
645   *
646   * <p><b>Note:</b> when possible, you should represent your data as an {@link ImmutableIntArray}
647   * instead, which has an {@link ImmutableIntArray#asList asList} view.
648   *
649   * @param backingArray the array to back the list
650   * @return a list view of the array
651   */
652  public static List<Integer> asList(int... backingArray) {
653    if (backingArray.length == 0) {
654      return Collections.emptyList();
655    }
656    return new IntArrayAsList(backingArray);
657  }
658
659  @GwtCompatible
660  private static class IntArrayAsList extends AbstractList<Integer>
661      implements RandomAccess, Serializable {
662    final int[] array;
663    final int start;
664    final int end;
665
666    IntArrayAsList(int[] array) {
667      this(array, 0, array.length);
668    }
669
670    IntArrayAsList(int[] array, int start, int end) {
671      this.array = array;
672      this.start = start;
673      this.end = end;
674    }
675
676    @Override
677    public int size() {
678      return end - start;
679    }
680
681    @Override
682    public boolean isEmpty() {
683      return false;
684    }
685
686    @Override
687    public Integer get(int index) {
688      checkElementIndex(index, size());
689      return array[start + index];
690    }
691
692    @Override
693    public Spliterator.OfInt spliterator() {
694      return Spliterators.spliterator(array, start, end, 0);
695    }
696
697    @Override
698    public boolean contains(@CheckForNull Object target) {
699      // Overridden to prevent a ton of boxing
700      return (target instanceof Integer) && Ints.indexOf(array, (Integer) target, start, end) != -1;
701    }
702
703    @Override
704    public int indexOf(@CheckForNull Object target) {
705      // Overridden to prevent a ton of boxing
706      if (target instanceof Integer) {
707        int i = Ints.indexOf(array, (Integer) target, start, end);
708        if (i >= 0) {
709          return i - start;
710        }
711      }
712      return -1;
713    }
714
715    @Override
716    public int lastIndexOf(@CheckForNull Object target) {
717      // Overridden to prevent a ton of boxing
718      if (target instanceof Integer) {
719        int i = Ints.lastIndexOf(array, (Integer) target, start, end);
720        if (i >= 0) {
721          return i - start;
722        }
723      }
724      return -1;
725    }
726
727    @Override
728    public Integer set(int index, Integer element) {
729      checkElementIndex(index, size());
730      int oldValue = array[start + index];
731      // checkNotNull for GWT (do not optimize)
732      array[start + index] = checkNotNull(element);
733      return oldValue;
734    }
735
736    @Override
737    public List<Integer> subList(int fromIndex, int toIndex) {
738      int size = size();
739      checkPositionIndexes(fromIndex, toIndex, size);
740      if (fromIndex == toIndex) {
741        return Collections.emptyList();
742      }
743      return new IntArrayAsList(array, start + fromIndex, start + toIndex);
744    }
745
746    @Override
747    public boolean equals(@CheckForNull Object object) {
748      if (object == this) {
749        return true;
750      }
751      if (object instanceof IntArrayAsList) {
752        IntArrayAsList that = (IntArrayAsList) object;
753        int size = size();
754        if (that.size() != size) {
755          return false;
756        }
757        for (int i = 0; i < size; i++) {
758          if (array[start + i] != that.array[that.start + i]) {
759            return false;
760          }
761        }
762        return true;
763      }
764      return super.equals(object);
765    }
766
767    @Override
768    public int hashCode() {
769      int result = 1;
770      for (int i = start; i < end; i++) {
771        result = 31 * result + Ints.hashCode(array[i]);
772      }
773      return result;
774    }
775
776    @Override
777    public String toString() {
778      StringBuilder builder = new StringBuilder(size() * 5);
779      builder.append('[').append(array[start]);
780      for (int i = start + 1; i < end; i++) {
781        builder.append(", ").append(array[i]);
782      }
783      return builder.append(']').toString();
784    }
785
786    int[] toIntArray() {
787      return Arrays.copyOfRange(array, start, end);
788    }
789
790    private static final long serialVersionUID = 0;
791  }
792
793  /**
794   * Parses the specified string as a signed decimal integer value. The ASCII character {@code '-'}
795   * (<code>'&#92;u002D'</code>) is recognized as the minus sign.
796   *
797   * <p>Unlike {@link Integer#parseInt(String)}, this method returns {@code null} instead of
798   * throwing an exception if parsing fails. Additionally, this method only accepts ASCII digits,
799   * and returns {@code null} if non-ASCII digits are present in the string.
800   *
801   * <p>Note that strings prefixed with ASCII {@code '+'} are rejected, even though {@link
802   * Integer#parseInt(String)} accepts them.
803   *
804   * @param string the string representation of an integer value
805   * @return the integer value represented by {@code string}, or {@code null} if {@code string} has
806   *     a length of zero or cannot be parsed as an integer value
807   * @throws NullPointerException if {@code string} is {@code null}
808   * @since 11.0
809   */
810  @CheckForNull
811  public static Integer tryParse(String string) {
812    return tryParse(string, 10);
813  }
814
815  /**
816   * Parses the specified string as a signed integer value using the specified radix. The ASCII
817   * character {@code '-'} (<code>'&#92;u002D'</code>) is recognized as the minus sign.
818   *
819   * <p>Unlike {@link Integer#parseInt(String, int)}, this method returns {@code null} instead of
820   * throwing an exception if parsing fails. Additionally, this method only accepts ASCII digits,
821   * and returns {@code null} if non-ASCII digits are present in the string.
822   *
823   * <p>Note that strings prefixed with ASCII {@code '+'} are rejected, even though {@link
824   * Integer#parseInt(String)} accepts them.
825   *
826   * @param string the string representation of an integer value
827   * @param radix the radix to use when parsing
828   * @return the integer value represented by {@code string} using {@code radix}, or {@code null} if
829   *     {@code string} has a length of zero or cannot be parsed as an integer value
830   * @throws IllegalArgumentException if {@code radix < Character.MIN_RADIX} or {@code radix >
831   *     Character.MAX_RADIX}
832   * @throws NullPointerException if {@code string} is {@code null}
833   * @since 19.0
834   */
835  @CheckForNull
836  public static Integer tryParse(String string, int radix) {
837    Long result = Longs.tryParse(string, radix);
838    if (result == null || result.longValue() != result.intValue()) {
839      return null;
840    } else {
841      return result.intValue();
842    }
843  }
844}