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   * @param value the {@code int} value to constrain
268   * @param min the lower bound (inclusive) of the range to constrain {@code value} to
269   * @param max the upper bound (inclusive) of the range to constrain {@code value} to
270   * @throws IllegalArgumentException if {@code min > max}
271   * @since 21.0
272   */
273  public static int constrainToRange(int value, int min, int max) {
274    checkArgument(min <= max, "min (%s) must be less than or equal to max (%s)", min, max);
275    return Math.min(Math.max(value, min), max);
276  }
277
278  /**
279   * Returns the values from each provided array combined into a single array. For example, {@code
280   * concat(new int[] {a, b}, new int[] {}, new int[] {c}} returns the array {@code {a, b, c}}.
281   *
282   * @param arrays zero or more {@code int} arrays
283   * @return a single array containing all the values from the source arrays, in order
284   */
285  public static int[] concat(int[]... arrays) {
286    int length = 0;
287    for (int[] array : arrays) {
288      length += array.length;
289    }
290    int[] result = new int[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  /**
300   * Returns a big-endian representation of {@code value} in a 4-element byte array; equivalent to
301   * {@code ByteBuffer.allocate(4).putInt(value).array()}. For example, the input value {@code
302   * 0x12131415} would yield the byte array {@code {0x12, 0x13, 0x14, 0x15}}.
303   *
304   * <p>If you need to convert and concatenate several values (possibly even of different types),
305   * use a shared {@link java.nio.ByteBuffer} instance, or use {@link
306   * com.google.common.io.ByteStreams#newDataOutput()} to get a growable buffer.
307   */
308  public static byte[] toByteArray(int value) {
309    return new byte[] {
310      (byte) (value >> 24), (byte) (value >> 16), (byte) (value >> 8), (byte) value
311    };
312  }
313
314  /**
315   * Returns the {@code int} value whose big-endian representation is stored in the first 4 bytes of
316   * {@code bytes}; equivalent to {@code ByteBuffer.wrap(bytes).getInt()}. For example, the input
317   * byte array {@code {0x12, 0x13, 0x14, 0x15, 0x33}} would yield the {@code int} value {@code
318   * 0x12131415}.
319   *
320   * <p>Arguably, it's preferable to use {@link java.nio.ByteBuffer}; that library exposes much more
321   * flexibility at little cost in readability.
322   *
323   * @throws IllegalArgumentException if {@code bytes} has fewer than 4 elements
324   */
325  public static int fromByteArray(byte[] bytes) {
326    checkArgument(bytes.length >= BYTES, "array too small: %s < %s", bytes.length, BYTES);
327    return fromBytes(bytes[0], bytes[1], bytes[2], bytes[3]);
328  }
329
330  /**
331   * Returns the {@code int} value whose byte representation is the given 4 bytes, in big-endian
332   * order; equivalent to {@code Ints.fromByteArray(new byte[] {b1, b2, b3, b4})}.
333   *
334   * @since 7.0
335   */
336  public static int fromBytes(byte b1, byte b2, byte b3, byte b4) {
337    return b1 << 24 | (b2 & 0xFF) << 16 | (b3 & 0xFF) << 8 | (b4 & 0xFF);
338  }
339
340  private static final class IntConverter extends Converter<String, Integer>
341      implements Serializable {
342    static final Converter<String, Integer> INSTANCE = new IntConverter();
343
344    @Override
345    protected Integer doForward(String value) {
346      return Integer.decode(value);
347    }
348
349    @Override
350    protected String doBackward(Integer value) {
351      return value.toString();
352    }
353
354    @Override
355    public String toString() {
356      return "Ints.stringConverter()";
357    }
358
359    private Object readResolve() {
360      return INSTANCE;
361    }
362
363    private static final long serialVersionUID = 1;
364  }
365
366  /**
367   * Returns a serializable converter object that converts between strings and integers using {@link
368   * Integer#decode} and {@link Integer#toString()}. The returned converter throws {@link
369   * NumberFormatException} if the input string is invalid.
370   *
371   * <p><b>Warning:</b> please see {@link Integer#decode} to understand exactly how strings are
372   * parsed. For example, the string {@code "0123"} is treated as <i>octal</i> and converted to the
373   * value {@code 83}.
374   *
375   * @since 16.0
376   */
377  public static Converter<String, Integer> stringConverter() {
378    return IntConverter.INSTANCE;
379  }
380
381  /**
382   * Returns an array containing the same values as {@code array}, but guaranteed to be of a
383   * specified minimum length. If {@code array} already has a length of at least {@code minLength},
384   * it is returned directly. Otherwise, a new array of size {@code minLength + padding} is
385   * returned, containing the values of {@code array}, and zeroes in the remaining places.
386   *
387   * @param array the source array
388   * @param minLength the minimum length the returned array must guarantee
389   * @param padding an extra amount to "grow" the array by if growth is necessary
390   * @throws IllegalArgumentException if {@code minLength} or {@code padding} is negative
391   * @return an array containing the values of {@code array}, with guaranteed minimum length {@code
392   *     minLength}
393   */
394  public static int[] ensureCapacity(int[] array, int minLength, int padding) {
395    checkArgument(minLength >= 0, "Invalid minLength: %s", minLength);
396    checkArgument(padding >= 0, "Invalid padding: %s", padding);
397    return (array.length < minLength) ? Arrays.copyOf(array, minLength + padding) : array;
398  }
399
400  /**
401   * Returns a string containing the supplied {@code int} values separated by {@code separator}. For
402   * example, {@code join("-", 1, 2, 3)} returns the string {@code "1-2-3"}.
403   *
404   * @param separator the text that should appear between consecutive values in the resulting string
405   *     (but not at the start or end)
406   * @param array an array of {@code int} values, possibly empty
407   */
408  public static String join(String separator, int... array) {
409    checkNotNull(separator);
410    if (array.length == 0) {
411      return "";
412    }
413
414    // For pre-sizing a builder, just get the right order of magnitude
415    StringBuilder builder = new StringBuilder(array.length * 5);
416    builder.append(array[0]);
417    for (int i = 1; i < array.length; i++) {
418      builder.append(separator).append(array[i]);
419    }
420    return builder.toString();
421  }
422
423  /**
424   * Returns a comparator that compares two {@code int} arrays <a
425   * href="http://en.wikipedia.org/wiki/Lexicographical_order">lexicographically</a>. That is, it
426   * compares, using {@link #compare(int, int)}), the first pair of values that follow any common
427   * prefix, or when one array is a prefix of the other, treats the shorter array as the lesser. For
428   * example, {@code [] < [1] < [1, 2] < [2]}.
429   *
430   * <p>The returned comparator is inconsistent with {@link Object#equals(Object)} (since arrays
431   * support only identity equality), but it is consistent with {@link Arrays#equals(int[], int[])}.
432   *
433   * @since 2.0
434   */
435  public static Comparator<int[]> lexicographicalComparator() {
436    return LexicographicalComparator.INSTANCE;
437  }
438
439  private enum LexicographicalComparator implements Comparator<int[]> {
440    INSTANCE;
441
442    @Override
443    public int compare(int[] left, int[] right) {
444      int minLength = Math.min(left.length, right.length);
445      for (int i = 0; i < minLength; i++) {
446        int result = Integer.compare(left[i], right[i]);
447        if (result != 0) {
448          return result;
449        }
450      }
451      return left.length - right.length;
452    }
453
454    @Override
455    public String toString() {
456      return "Ints.lexicographicalComparator()";
457    }
458  }
459
460  /**
461   * Sorts the elements of {@code array} in descending order.
462   *
463   * @since 23.1
464   */
465  public static void sortDescending(int[] array) {
466    checkNotNull(array);
467    sortDescending(array, 0, array.length);
468  }
469
470  /**
471   * Sorts the elements of {@code array} between {@code fromIndex} inclusive and {@code toIndex}
472   * exclusive in descending order.
473   *
474   * @since 23.1
475   */
476  public static void sortDescending(int[] array, int fromIndex, int toIndex) {
477    checkNotNull(array);
478    checkPositionIndexes(fromIndex, toIndex, array.length);
479    Arrays.sort(array, fromIndex, toIndex);
480    reverse(array, fromIndex, toIndex);
481  }
482
483  /**
484   * Reverses the elements of {@code array}. This is equivalent to {@code
485   * Collections.reverse(Ints.asList(array))}, but is likely to be more efficient.
486   *
487   * @since 23.1
488   */
489  public static void reverse(int[] array) {
490    checkNotNull(array);
491    reverse(array, 0, array.length);
492  }
493
494  /**
495   * Reverses the elements of {@code array} between {@code fromIndex} inclusive and {@code toIndex}
496   * exclusive. This is equivalent to {@code
497   * Collections.reverse(Ints.asList(array).subList(fromIndex, toIndex))}, but is likely to be more
498   * efficient.
499   *
500   * @throws IndexOutOfBoundsException if {@code fromIndex < 0}, {@code toIndex > array.length}, or
501   *     {@code toIndex > fromIndex}
502   * @since 23.1
503   */
504  public static void reverse(int[] array, int fromIndex, int toIndex) {
505    checkNotNull(array);
506    checkPositionIndexes(fromIndex, toIndex, array.length);
507    for (int i = fromIndex, j = toIndex - 1; i < j; i++, j--) {
508      int tmp = array[i];
509      array[i] = array[j];
510      array[j] = tmp;
511    }
512  }
513
514  /**
515   * Performs a right rotation of {@code array} of "distance" places, so that the first element is
516   * moved to index "distance", and the element at index {@code i} ends up at index {@code (distance
517   * + i) mod array.length}. This is equivalent to {@code Collections.rotate(Ints.asList(array),
518   * distance)}, but is considerably faster and avoids allocation and garbage collection.
519   *
520   * <p>The provided "distance" may be negative, which will rotate left.
521   *
522   * @since 32.0.0
523   */
524  public static void rotate(int[] array, int distance) {
525    rotate(array, distance, 0, array.length);
526  }
527
528  /**
529   * Performs a right rotation of {@code array} between {@code fromIndex} inclusive and {@code
530   * toIndex} exclusive. This is equivalent to {@code
531   * Collections.rotate(Ints.asList(array).subList(fromIndex, toIndex), distance)}, but is
532   * considerably faster and avoids allocations and garbage collection.
533   *
534   * <p>The provided "distance" may be negative, which will rotate left.
535   *
536   * @throws IndexOutOfBoundsException if {@code fromIndex < 0}, {@code toIndex > array.length}, or
537   *     {@code toIndex > fromIndex}
538   * @since 32.0.0
539   */
540  public static void rotate(int[] array, int distance, int fromIndex, int toIndex) {
541    // There are several well-known algorithms for rotating part of an array (or, equivalently,
542    // exchanging two blocks of memory). This classic text by Gries and Mills mentions several:
543    // https://ecommons.cornell.edu/bitstream/handle/1813/6292/81-452.pdf.
544    // (1) "Reversal", the one we have here.
545    // (2) "Dolphin". If we're rotating an array a of size n by a distance of d, then element a[0]
546    //     ends up at a[d], which in turn ends up at a[2d], and so on until we get back to a[0].
547    //     (All indices taken mod n.) If d and n are mutually prime, all elements will have been
548    //     moved at that point. Otherwise, we can rotate the cycle a[1], a[1 + d], a[1 + 2d], etc,
549    //     then a[2] etc, and so on until we have rotated all elements. There are gcd(d, n) cycles
550    //     in all.
551    // (3) "Successive". We can consider that we are exchanging a block of size d (a[0..d-1]) with a
552    //     block of size n-d (a[d..n-1]), where in general these blocks have different sizes. If we
553    //     imagine a line separating the first block from the second, we can proceed by exchanging
554    //     the smaller of these blocks with the far end of the other one. That leaves us with a
555    //     smaller version of the same problem.
556    //     Say we are rotating abcdefgh by 5. We start with abcde|fgh. The smaller block is [fgh]:
557    //     [abc]de|[fgh] -> [fgh]de|[abc]. Now [fgh] is in the right place, but we need to swap [de]
558    //     with [abc]: fgh[de]|a[bc] -> fgh[bc]|a[de]. Now we need to swap [a] with [bc]:
559    //     fgh[b]c|[a]de -> fgh[a]c|[b]de. Finally we need to swap [c] with [b]:
560    //     fgha[c]|[b]de -> fgha[b]|[c]de. Because these two blocks are the same size, we are done.
561    // The Dolphin algorithm is attractive because it does the fewest array reads and writes: each
562    // array slot is read and written exactly once. However, it can have very poor memory locality:
563    // benchmarking shows it can take 7 times longer than the other two in some cases. The other two
564    // do n swaps, minus a delta (0 or 2 for Reversal, gcd(d, n) for Successive), so that's about
565    // twice as many reads and writes. But benchmarking shows that they usually perform better than
566    // Dolphin. Reversal is about as good as Successive on average, and it is much simpler,
567    // especially since we already have a `reverse` method.
568    checkNotNull(array);
569    checkPositionIndexes(fromIndex, toIndex, array.length);
570    if (array.length <= 1) {
571      return;
572    }
573
574    int length = toIndex - fromIndex;
575    // Obtain m = (-distance mod length), a non-negative value less than "length". This is how many
576    // places left to rotate.
577    int m = -distance % length;
578    m = (m < 0) ? m + length : m;
579    // The current index of what will become the first element of the rotated section.
580    int newFirstIndex = m + fromIndex;
581    if (newFirstIndex == fromIndex) {
582      return;
583    }
584
585    reverse(array, fromIndex, newFirstIndex);
586    reverse(array, newFirstIndex, toIndex);
587    reverse(array, fromIndex, toIndex);
588  }
589
590  /**
591   * Returns an array containing each value of {@code collection}, converted to a {@code int} value
592   * in the manner of {@link Number#intValue}.
593   *
594   * <p>Elements are copied from the argument collection as if by {@code collection.toArray()}.
595   * Calling this method is as thread-safe as calling that method.
596   *
597   * @param collection a collection of {@code Number} instances
598   * @return an array containing the same values as {@code collection}, in the same order, converted
599   *     to primitives
600   * @throws NullPointerException if {@code collection} or any of its elements is null
601   * @since 1.0 (parameter was {@code Collection<Integer>} before 12.0)
602   */
603  public static int[] toArray(Collection<? extends Number> collection) {
604    if (collection instanceof IntArrayAsList) {
605      return ((IntArrayAsList) collection).toIntArray();
606    }
607
608    Object[] boxedArray = collection.toArray();
609    int len = boxedArray.length;
610    int[] array = new int[len];
611    for (int i = 0; i < len; i++) {
612      // checkNotNull for GWT (do not optimize)
613      array[i] = ((Number) checkNotNull(boxedArray[i])).intValue();
614    }
615    return array;
616  }
617
618  /**
619   * Returns a fixed-size list backed by the specified array, similar to {@link
620   * Arrays#asList(Object[])}. The list supports {@link List#set(int, Object)}, but any attempt to
621   * set a value to {@code null} will result in a {@link NullPointerException}.
622   *
623   * <p>The returned list maintains the values, but not the identities, of {@code Integer} objects
624   * written to or read from it. For example, whether {@code list.get(0) == list.get(0)} is true for
625   * the returned list is unspecified.
626   *
627   * <p>The returned list is serializable.
628   *
629   * <p><b>Note:</b> when possible, you should represent your data as an {@link ImmutableIntArray}
630   * instead, which has an {@link ImmutableIntArray#asList asList} view.
631   *
632   * @param backingArray the array to back the list
633   * @return a list view of the array
634   */
635  public static List<Integer> asList(int... backingArray) {
636    if (backingArray.length == 0) {
637      return Collections.emptyList();
638    }
639    return new IntArrayAsList(backingArray);
640  }
641
642  @GwtCompatible
643  private static class IntArrayAsList extends AbstractList<Integer>
644      implements RandomAccess, Serializable {
645    final int[] array;
646    final int start;
647    final int end;
648
649    IntArrayAsList(int[] array) {
650      this(array, 0, array.length);
651    }
652
653    IntArrayAsList(int[] array, int start, int end) {
654      this.array = array;
655      this.start = start;
656      this.end = end;
657    }
658
659    @Override
660    public int size() {
661      return end - start;
662    }
663
664    @Override
665    public boolean isEmpty() {
666      return false;
667    }
668
669    @Override
670    public Integer get(int index) {
671      checkElementIndex(index, size());
672      return array[start + index];
673    }
674
675    @Override
676    public Spliterator.OfInt spliterator() {
677      return Spliterators.spliterator(array, start, end, 0);
678    }
679
680    @Override
681    public boolean contains(@CheckForNull Object target) {
682      // Overridden to prevent a ton of boxing
683      return (target instanceof Integer) && Ints.indexOf(array, (Integer) target, start, end) != -1;
684    }
685
686    @Override
687    public int indexOf(@CheckForNull Object target) {
688      // Overridden to prevent a ton of boxing
689      if (target instanceof Integer) {
690        int i = Ints.indexOf(array, (Integer) target, start, end);
691        if (i >= 0) {
692          return i - start;
693        }
694      }
695      return -1;
696    }
697
698    @Override
699    public int lastIndexOf(@CheckForNull Object target) {
700      // Overridden to prevent a ton of boxing
701      if (target instanceof Integer) {
702        int i = Ints.lastIndexOf(array, (Integer) target, start, end);
703        if (i >= 0) {
704          return i - start;
705        }
706      }
707      return -1;
708    }
709
710    @Override
711    public Integer set(int index, Integer element) {
712      checkElementIndex(index, size());
713      int oldValue = array[start + index];
714      // checkNotNull for GWT (do not optimize)
715      array[start + index] = checkNotNull(element);
716      return oldValue;
717    }
718
719    @Override
720    public List<Integer> subList(int fromIndex, int toIndex) {
721      int size = size();
722      checkPositionIndexes(fromIndex, toIndex, size);
723      if (fromIndex == toIndex) {
724        return Collections.emptyList();
725      }
726      return new IntArrayAsList(array, start + fromIndex, start + toIndex);
727    }
728
729    @Override
730    public boolean equals(@CheckForNull Object object) {
731      if (object == this) {
732        return true;
733      }
734      if (object instanceof IntArrayAsList) {
735        IntArrayAsList that = (IntArrayAsList) object;
736        int size = size();
737        if (that.size() != size) {
738          return false;
739        }
740        for (int i = 0; i < size; i++) {
741          if (array[start + i] != that.array[that.start + i]) {
742            return false;
743          }
744        }
745        return true;
746      }
747      return super.equals(object);
748    }
749
750    @Override
751    public int hashCode() {
752      int result = 1;
753      for (int i = start; i < end; i++) {
754        result = 31 * result + Ints.hashCode(array[i]);
755      }
756      return result;
757    }
758
759    @Override
760    public String toString() {
761      StringBuilder builder = new StringBuilder(size() * 5);
762      builder.append('[').append(array[start]);
763      for (int i = start + 1; i < end; i++) {
764        builder.append(", ").append(array[i]);
765      }
766      return builder.append(']').toString();
767    }
768
769    int[] toIntArray() {
770      return Arrays.copyOfRange(array, start, end);
771    }
772
773    private static final long serialVersionUID = 0;
774  }
775
776  /**
777   * Parses the specified string as a signed decimal integer value. The ASCII character {@code '-'}
778   * (<code>'&#92;u002D'</code>) is recognized as the minus sign.
779   *
780   * <p>Unlike {@link Integer#parseInt(String)}, this method returns {@code null} instead of
781   * throwing an exception if parsing fails. Additionally, this method only accepts ASCII digits,
782   * and returns {@code null} if non-ASCII digits are present in the string.
783   *
784   * <p>Note that strings prefixed with ASCII {@code '+'} are rejected, even though {@link
785   * Integer#parseInt(String)} accepts them.
786   *
787   * @param string the string representation of an integer value
788   * @return the integer value represented by {@code string}, or {@code null} if {@code string} has
789   *     a length of zero or cannot be parsed as an integer value
790   * @throws NullPointerException if {@code string} is {@code null}
791   * @since 11.0
792   */
793  @CheckForNull
794  public static Integer tryParse(String string) {
795    return tryParse(string, 10);
796  }
797
798  /**
799   * Parses the specified string as a signed integer value using the specified radix. The ASCII
800   * character {@code '-'} (<code>'&#92;u002D'</code>) is recognized as the minus sign.
801   *
802   * <p>Unlike {@link Integer#parseInt(String, int)}, this method returns {@code null} instead of
803   * throwing an exception if parsing fails. Additionally, this method only accepts ASCII digits,
804   * and returns {@code null} if non-ASCII digits are present in the string.
805   *
806   * <p>Note that strings prefixed with ASCII {@code '+'} are rejected, even though {@link
807   * Integer#parseInt(String)} accepts them.
808   *
809   * @param string the string representation of an integer value
810   * @param radix the radix to use when parsing
811   * @return the integer value represented by {@code string} using {@code radix}, or {@code null} if
812   *     {@code string} has a length of zero or cannot be parsed as an integer value
813   * @throws IllegalArgumentException if {@code radix < Character.MIN_RADIX} or {@code radix >
814   *     Character.MAX_RADIX}
815   * @throws NullPointerException if {@code string} is {@code null}
816   * @since 19.0
817   */
818  @CheckForNull
819  public static Integer tryParse(String string, int radix) {
820    Long result = Longs.tryParse(string, radix);
821    if (result == null || result.longValue() != result.intValue()) {
822      return null;
823    } else {
824      return result.intValue();
825    }
826  }
827}