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