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;
021import static java.lang.Math.max;
022import static java.lang.Math.min;
023
024import com.google.common.annotations.GwtCompatible;
025import com.google.common.annotations.GwtIncompatible;
026import com.google.common.base.Converter;
027import com.google.errorprone.annotations.InlineMe;
028import java.io.Serializable;
029import java.util.AbstractList;
030import java.util.Arrays;
031import java.util.Collection;
032import java.util.Collections;
033import java.util.Comparator;
034import java.util.List;
035import java.util.RandomAccess;
036import java.util.Spliterator;
037import java.util.Spliterators;
038import javax.annotation.CheckForNull;
039
040/**
041 * Static utility methods pertaining to {@code int} primitives, that are not already found in either
042 * {@link Integer} or {@link Arrays}.
043 *
044 * <p>See the Guava User Guide article on <a
045 * href="https://github.com/google/guava/wiki/PrimitivesExplained">primitive utilities</a>.
046 *
047 * @author Kevin Bourrillion
048 * @since 1.0
049 */
050@GwtCompatible(emulated = true)
051@ElementTypesAreNonnullByDefault
052public final class Ints extends IntsMethodsForWeb {
053  private Ints() {}
054
055  /**
056   * The number of bytes required to represent a primitive {@code int} value.
057   *
058   * <p><b>Java 8+ users:</b> use {@link Integer#BYTES} instead.
059   */
060  public static final int BYTES = Integer.SIZE / Byte.SIZE;
061
062  /**
063   * The largest power of two that can be represented as an {@code int}.
064   *
065   * @since 10.0
066   */
067  public static final int MAX_POWER_OF_TWO = 1 << (Integer.SIZE - 2);
068
069  /**
070   * Returns a hash code for {@code value}; equal to the result of invoking {@code ((Integer)
071   * value).hashCode()}.
072   *
073   * <p><b>Java 8+ users:</b> use {@link Integer#hashCode(int)} instead.
074   *
075   * @param value a primitive {@code int} value
076   * @return a hash code for the value
077   */
078  public static int hashCode(int value) {
079    return value;
080  }
081
082  /**
083   * Returns the {@code int} value that is equal to {@code value}, if possible.
084   *
085   * @param value any value in the range of the {@code int} type
086   * @return the {@code int} value that equals {@code value}
087   * @throws IllegalArgumentException if {@code value} is greater than {@link Integer#MAX_VALUE} or
088   *     less than {@link Integer#MIN_VALUE}
089   */
090  public static int checkedCast(long value) {
091    int result = (int) value;
092    checkArgument(result == value, "Out of range: %s", value);
093    return result;
094  }
095
096  /**
097   * Returns the {@code int} nearest in value to {@code value}.
098   *
099   * @param value any {@code long} value
100   * @return the same value cast to {@code int} if it is in the range of the {@code int} type,
101   *     {@link Integer#MAX_VALUE} if it is too large, or {@link Integer#MIN_VALUE} if it is too
102   *     small
103   */
104  public static int saturatedCast(long value) {
105    if (value > Integer.MAX_VALUE) {
106      return Integer.MAX_VALUE;
107    }
108    if (value < Integer.MIN_VALUE) {
109      return Integer.MIN_VALUE;
110    }
111    return (int) value;
112  }
113
114  /**
115   * Compares the two specified {@code int} values. The sign of the value returned is the same as
116   * that of {@code ((Integer) a).compareTo(b)}.
117   *
118   * <p><b>Note:</b> this method is now unnecessary and should be treated as deprecated; use the
119   * equivalent {@link Integer#compare} method instead.
120   *
121   * @param a the first {@code int} to compare
122   * @param b the second {@code int} to compare
123   * @return a negative value if {@code a} is less than {@code b}; a positive value if {@code a} is
124   *     greater than {@code b}; or zero if they are equal
125   */
126  @InlineMe(replacement = "Integer.compare(a, b)")
127  public static int compare(int a, int b) {
128    return Integer.compare(a, b);
129  }
130
131  /**
132   * Returns {@code true} if {@code target} is present as an element anywhere in {@code array}.
133   *
134   * @param array an array of {@code int} values, possibly empty
135   * @param target a primitive {@code int} value
136   * @return {@code true} if {@code array[i] == target} for some value of {@code i}
137   */
138  public static boolean contains(int[] array, int target) {
139    for (int value : array) {
140      if (value == target) {
141        return true;
142      }
143    }
144    return false;
145  }
146
147  /**
148   * Returns the index of the first appearance of the value {@code target} in {@code array}.
149   *
150   * @param array an array of {@code int} values, possibly empty
151   * @param target a primitive {@code int} value
152   * @return the least index {@code i} for which {@code array[i] == target}, or {@code -1} if no
153   *     such index exists.
154   */
155  public static int indexOf(int[] array, int target) {
156    return indexOf(array, target, 0, array.length);
157  }
158
159  // TODO(kevinb): consider making this public
160  private static int indexOf(int[] array, int target, int start, int end) {
161    for (int i = start; i < end; i++) {
162      if (array[i] == target) {
163        return i;
164      }
165    }
166    return -1;
167  }
168
169  /**
170   * Returns the start position of the first occurrence of the specified {@code target} within
171   * {@code array}, or {@code -1} if there is no such occurrence.
172   *
173   * <p>More formally, returns the lowest index {@code i} such that {@code Arrays.copyOfRange(array,
174   * i, i + target.length)} contains exactly the same elements as {@code target}.
175   *
176   * @param array the array to search for the sequence {@code target}
177   * @param target the array to search for as a sub-sequence of {@code array}
178   */
179  public static int indexOf(int[] array, int[] target) {
180    checkNotNull(array, "array");
181    checkNotNull(target, "target");
182    if (target.length == 0) {
183      return 0;
184    }
185
186    outer:
187    for (int i = 0; i < array.length - target.length + 1; i++) {
188      for (int j = 0; j < target.length; j++) {
189        if (array[i + j] != target[j]) {
190          continue outer;
191        }
192      }
193      return i;
194    }
195    return -1;
196  }
197
198  /**
199   * Returns the index of the last appearance of the value {@code target} in {@code array}.
200   *
201   * @param array an array of {@code int} values, possibly empty
202   * @param target a primitive {@code int} value
203   * @return the greatest index {@code i} for which {@code array[i] == target}, or {@code -1} if no
204   *     such index exists.
205   */
206  public static int lastIndexOf(int[] array, int target) {
207    return lastIndexOf(array, target, 0, array.length);
208  }
209
210  // TODO(kevinb): consider making this public
211  private static int lastIndexOf(int[] array, int target, int start, int end) {
212    for (int i = end - 1; i >= start; i--) {
213      if (array[i] == target) {
214        return i;
215      }
216    }
217    return -1;
218  }
219
220  /**
221   * Returns the least value present in {@code array}.
222   *
223   * @param array a <i>nonempty</i> array of {@code int} values
224   * @return the value present in {@code array} that is less than or equal to every other value in
225   *     the array
226   * @throws IllegalArgumentException if {@code array} is empty
227   */
228  @GwtIncompatible(
229      "Available in GWT! Annotation is to avoid conflict with GWT specialization of base class.")
230  public static int min(int... array) {
231    checkArgument(array.length > 0);
232    int min = array[0];
233    for (int i = 1; i < array.length; i++) {
234      if (array[i] < min) {
235        min = array[i];
236      }
237    }
238    return min;
239  }
240
241  /**
242   * Returns the greatest value present in {@code array}.
243   *
244   * @param array a <i>nonempty</i> array of {@code int} values
245   * @return the value present in {@code array} that is greater than or equal to every other value
246   *     in the array
247   * @throws IllegalArgumentException if {@code array} is empty
248   */
249  @GwtIncompatible(
250      "Available in GWT! Annotation is to avoid conflict with GWT specialization of base class.")
251  public static int max(int... array) {
252    checkArgument(array.length > 0);
253    int max = array[0];
254    for (int i = 1; i < array.length; i++) {
255      if (array[i] > max) {
256        max = array[i];
257      }
258    }
259    return max;
260  }
261
262  /**
263   * Returns the value nearest to {@code value} which is within the closed range {@code [min..max]}.
264   *
265   * <p>If {@code value} is within the range {@code [min..max]}, {@code value} is returned
266   * unchanged. If {@code value} is less than {@code min}, {@code min} is returned, and if {@code
267   * value} is greater than {@code max}, {@code max} is returned.
268   *
269   * <p><b>Java 21+ users:</b> Use {@code Math.clamp} instead. Note that that method is capable of
270   * constraining a {@code long} input to an {@code int} range.
271   *
272   * @param value the {@code int} value to constrain
273   * @param min the lower bound (inclusive) of the range to constrain {@code value} to
274   * @param max the upper bound (inclusive) of the range to constrain {@code value} to
275   * @throws IllegalArgumentException if {@code min > max}
276   * @since 21.0
277   */
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 min(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    public int compare(int[] left, int[] right) {
459      int minLength = min(left.length, right.length);
460      for (int i = 0; i < minLength; i++) {
461        int result = Integer.compare(left[i], right[i]);
462        if (result != 0) {
463          return result;
464        }
465      }
466      return left.length - right.length;
467    }
468
469    @Override
470    public String toString() {
471      return "Ints.lexicographicalComparator()";
472    }
473  }
474
475  /**
476   * Sorts the elements of {@code array} in descending order.
477   *
478   * @since 23.1
479   */
480  public static void sortDescending(int[] array) {
481    checkNotNull(array);
482    sortDescending(array, 0, array.length);
483  }
484
485  /**
486   * Sorts the elements of {@code array} between {@code fromIndex} inclusive and {@code toIndex}
487   * exclusive in descending order.
488   *
489   * @since 23.1
490   */
491  public static void sortDescending(int[] array, int fromIndex, int toIndex) {
492    checkNotNull(array);
493    checkPositionIndexes(fromIndex, toIndex, array.length);
494    Arrays.sort(array, fromIndex, toIndex);
495    reverse(array, fromIndex, toIndex);
496  }
497
498  /**
499   * Reverses the elements of {@code array}. This is equivalent to {@code
500   * Collections.reverse(Ints.asList(array))}, but is likely to be more efficient.
501   *
502   * @since 23.1
503   */
504  public static void reverse(int[] array) {
505    checkNotNull(array);
506    reverse(array, 0, array.length);
507  }
508
509  /**
510   * Reverses the elements of {@code array} between {@code fromIndex} inclusive and {@code toIndex}
511   * exclusive. This is equivalent to {@code
512   * Collections.reverse(Ints.asList(array).subList(fromIndex, toIndex))}, but is likely to be more
513   * efficient.
514   *
515   * @throws IndexOutOfBoundsException if {@code fromIndex < 0}, {@code toIndex > array.length}, or
516   *     {@code toIndex > fromIndex}
517   * @since 23.1
518   */
519  public static void reverse(int[] array, int fromIndex, int toIndex) {
520    checkNotNull(array);
521    checkPositionIndexes(fromIndex, toIndex, array.length);
522    for (int i = fromIndex, j = toIndex - 1; i < j; i++, j--) {
523      int tmp = array[i];
524      array[i] = array[j];
525      array[j] = tmp;
526    }
527  }
528
529  /**
530   * Performs a right rotation of {@code array} of "distance" places, so that the first element is
531   * moved to index "distance", and the element at index {@code i} ends up at index {@code (distance
532   * + i) mod array.length}. This is equivalent to {@code Collections.rotate(Ints.asList(array),
533   * distance)}, but is considerably faster and avoids allocation and garbage collection.
534   *
535   * <p>The provided "distance" may be negative, which will rotate left.
536   *
537   * @since 32.0.0
538   */
539  public static void rotate(int[] array, int distance) {
540    rotate(array, distance, 0, array.length);
541  }
542
543  /**
544   * Performs a right rotation of {@code array} between {@code fromIndex} inclusive and {@code
545   * toIndex} exclusive. This is equivalent to {@code
546   * Collections.rotate(Ints.asList(array).subList(fromIndex, toIndex), distance)}, but is
547   * considerably faster and avoids allocations and garbage collection.
548   *
549   * <p>The provided "distance" may be negative, which will rotate left.
550   *
551   * @throws IndexOutOfBoundsException if {@code fromIndex < 0}, {@code toIndex > array.length}, or
552   *     {@code toIndex > fromIndex}
553   * @since 32.0.0
554   */
555  public static void rotate(int[] array, int distance, int fromIndex, int toIndex) {
556    // There are several well-known algorithms for rotating part of an array (or, equivalently,
557    // exchanging two blocks of memory). This classic text by Gries and Mills mentions several:
558    // https://ecommons.cornell.edu/bitstream/handle/1813/6292/81-452.pdf.
559    // (1) "Reversal", the one we have here.
560    // (2) "Dolphin". If we're rotating an array a of size n by a distance of d, then element a[0]
561    //     ends up at a[d], which in turn ends up at a[2d], and so on until we get back to a[0].
562    //     (All indices taken mod n.) If d and n are mutually prime, all elements will have been
563    //     moved at that point. Otherwise, we can rotate the cycle a[1], a[1 + d], a[1 + 2d], etc,
564    //     then a[2] etc, and so on until we have rotated all elements. There are gcd(d, n) cycles
565    //     in all.
566    // (3) "Successive". We can consider that we are exchanging a block of size d (a[0..d-1]) with a
567    //     block of size n-d (a[d..n-1]), where in general these blocks have different sizes. If we
568    //     imagine a line separating the first block from the second, we can proceed by exchanging
569    //     the smaller of these blocks with the far end of the other one. That leaves us with a
570    //     smaller version of the same problem.
571    //     Say we are rotating abcdefgh by 5. We start with abcde|fgh. The smaller block is [fgh]:
572    //     [abc]de|[fgh] -> [fgh]de|[abc]. Now [fgh] is in the right place, but we need to swap [de]
573    //     with [abc]: fgh[de]|a[bc] -> fgh[bc]|a[de]. Now we need to swap [a] with [bc]:
574    //     fgh[b]c|[a]de -> fgh[a]c|[b]de. Finally we need to swap [c] with [b]:
575    //     fgha[c]|[b]de -> fgha[b]|[c]de. Because these two blocks are the same size, we are done.
576    // The Dolphin algorithm is attractive because it does the fewest array reads and writes: each
577    // array slot is read and written exactly once. However, it can have very poor memory locality:
578    // benchmarking shows it can take 7 times longer than the other two in some cases. The other two
579    // do n swaps, minus a delta (0 or 2 for Reversal, gcd(d, n) for Successive), so that's about
580    // twice as many reads and writes. But benchmarking shows that they usually perform better than
581    // Dolphin. Reversal is about as good as Successive on average, and it is much simpler,
582    // especially since we already have a `reverse` method.
583    checkNotNull(array);
584    checkPositionIndexes(fromIndex, toIndex, array.length);
585    if (array.length <= 1) {
586      return;
587    }
588
589    int length = toIndex - fromIndex;
590    // Obtain m = (-distance mod length), a non-negative value less than "length". This is how many
591    // places left to rotate.
592    int m = -distance % length;
593    m = (m < 0) ? m + length : m;
594    // The current index of what will become the first element of the rotated section.
595    int newFirstIndex = m + fromIndex;
596    if (newFirstIndex == fromIndex) {
597      return;
598    }
599
600    reverse(array, fromIndex, newFirstIndex);
601    reverse(array, newFirstIndex, toIndex);
602    reverse(array, fromIndex, toIndex);
603  }
604
605  /**
606   * Returns an array containing each value of {@code collection}, converted to a {@code int} value
607   * in the manner of {@link Number#intValue}.
608   *
609   * <p>Elements are copied from the argument collection as if by {@code collection.toArray()}.
610   * Calling this method is as thread-safe as calling that method.
611   *
612   * @param collection a collection of {@code Number} instances
613   * @return an array containing the same values as {@code collection}, in the same order, converted
614   *     to primitives
615   * @throws NullPointerException if {@code collection} or any of its elements is null
616   * @since 1.0 (parameter was {@code Collection<Integer>} before 12.0)
617   */
618  public static int[] toArray(Collection<? extends Number> collection) {
619    if (collection instanceof IntArrayAsList) {
620      return ((IntArrayAsList) collection).toIntArray();
621    }
622
623    Object[] boxedArray = collection.toArray();
624    int len = boxedArray.length;
625    int[] array = new int[len];
626    for (int i = 0; i < len; i++) {
627      // checkNotNull for GWT (do not optimize)
628      array[i] = ((Number) checkNotNull(boxedArray[i])).intValue();
629    }
630    return array;
631  }
632
633  /**
634   * Returns a fixed-size list backed by the specified array, similar to {@link
635   * Arrays#asList(Object[])}. The list supports {@link List#set(int, Object)}, but any attempt to
636   * set a value to {@code null} will result in a {@link NullPointerException}.
637   *
638   * <p>The returned list maintains the values, but not the identities, of {@code Integer} objects
639   * written to or read from it. For example, whether {@code list.get(0) == list.get(0)} is true for
640   * the returned list is unspecified.
641   *
642   * <p>The returned list is serializable.
643   *
644   * <p><b>Note:</b> when possible, you should represent your data as an {@link ImmutableIntArray}
645   * instead, which has an {@link ImmutableIntArray#asList asList} view.
646   *
647   * @param backingArray the array to back the list
648   * @return a list view of the array
649   */
650  public static List<Integer> asList(int... backingArray) {
651    if (backingArray.length == 0) {
652      return Collections.emptyList();
653    }
654    return new IntArrayAsList(backingArray);
655  }
656
657  @GwtCompatible
658  private static class IntArrayAsList extends AbstractList<Integer>
659      implements RandomAccess, Serializable {
660    final int[] array;
661    final int start;
662    final int end;
663
664    IntArrayAsList(int[] array) {
665      this(array, 0, array.length);
666    }
667
668    IntArrayAsList(int[] array, int start, int end) {
669      this.array = array;
670      this.start = start;
671      this.end = end;
672    }
673
674    @Override
675    public int size() {
676      return end - start;
677    }
678
679    @Override
680    public boolean isEmpty() {
681      return false;
682    }
683
684    @Override
685    public Integer get(int index) {
686      checkElementIndex(index, size());
687      return array[start + index];
688    }
689
690    @Override
691    public Spliterator.OfInt spliterator() {
692      return Spliterators.spliterator(array, start, end, 0);
693    }
694
695    @Override
696    public boolean contains(@CheckForNull Object target) {
697      // Overridden to prevent a ton of boxing
698      return (target instanceof Integer) && Ints.indexOf(array, (Integer) target, start, end) != -1;
699    }
700
701    @Override
702    public int indexOf(@CheckForNull Object target) {
703      // Overridden to prevent a ton of boxing
704      if (target instanceof Integer) {
705        int i = Ints.indexOf(array, (Integer) target, start, end);
706        if (i >= 0) {
707          return i - start;
708        }
709      }
710      return -1;
711    }
712
713    @Override
714    public int lastIndexOf(@CheckForNull Object target) {
715      // Overridden to prevent a ton of boxing
716      if (target instanceof Integer) {
717        int i = Ints.lastIndexOf(array, (Integer) target, start, end);
718        if (i >= 0) {
719          return i - start;
720        }
721      }
722      return -1;
723    }
724
725    @Override
726    public Integer set(int index, Integer element) {
727      checkElementIndex(index, size());
728      int oldValue = array[start + index];
729      // checkNotNull for GWT (do not optimize)
730      array[start + index] = checkNotNull(element);
731      return oldValue;
732    }
733
734    @Override
735    public List<Integer> subList(int fromIndex, int toIndex) {
736      int size = size();
737      checkPositionIndexes(fromIndex, toIndex, size);
738      if (fromIndex == toIndex) {
739        return Collections.emptyList();
740      }
741      return new IntArrayAsList(array, start + fromIndex, start + toIndex);
742    }
743
744    @Override
745    public boolean equals(@CheckForNull Object object) {
746      if (object == this) {
747        return true;
748      }
749      if (object instanceof IntArrayAsList) {
750        IntArrayAsList that = (IntArrayAsList) object;
751        int size = size();
752        if (that.size() != size) {
753          return false;
754        }
755        for (int i = 0; i < size; i++) {
756          if (array[start + i] != that.array[that.start + i]) {
757            return false;
758          }
759        }
760        return true;
761      }
762      return super.equals(object);
763    }
764
765    @Override
766    public int hashCode() {
767      int result = 1;
768      for (int i = start; i < end; i++) {
769        result = 31 * result + Ints.hashCode(array[i]);
770      }
771      return result;
772    }
773
774    @Override
775    public String toString() {
776      StringBuilder builder = new StringBuilder(size() * 5);
777      builder.append('[').append(array[start]);
778      for (int i = start + 1; i < end; i++) {
779        builder.append(", ").append(array[i]);
780      }
781      return builder.append(']').toString();
782    }
783
784    int[] toIntArray() {
785      return Arrays.copyOfRange(array, start, end);
786    }
787
788    private static final long serialVersionUID = 0;
789  }
790
791  /**
792   * Parses the specified string as a signed decimal integer value. The ASCII character {@code '-'}
793   * (<code>'&#92;u002D'</code>) is recognized as the minus sign.
794   *
795   * <p>Unlike {@link Integer#parseInt(String)}, this method returns {@code null} instead of
796   * throwing an exception if parsing fails. Additionally, this method only accepts ASCII digits,
797   * and returns {@code null} if non-ASCII digits are present in the string.
798   *
799   * <p>Note that strings prefixed with ASCII {@code '+'} are rejected, even though {@link
800   * Integer#parseInt(String)} accepts them.
801   *
802   * @param string the string representation of an integer value
803   * @return the integer value represented by {@code string}, or {@code null} if {@code string} has
804   *     a length of zero or cannot be parsed as an integer value
805   * @throws NullPointerException if {@code string} is {@code null}
806   * @since 11.0
807   */
808  @CheckForNull
809  public static Integer tryParse(String string) {
810    return tryParse(string, 10);
811  }
812
813  /**
814   * Parses the specified string as a signed integer value using the specified radix. The ASCII
815   * character {@code '-'} (<code>'&#92;u002D'</code>) is recognized as the minus sign.
816   *
817   * <p>Unlike {@link Integer#parseInt(String, int)}, this method returns {@code null} instead of
818   * throwing an exception if parsing fails. Additionally, this method only accepts ASCII digits,
819   * and returns {@code null} if non-ASCII digits are present in the string.
820   *
821   * <p>Note that strings prefixed with ASCII {@code '+'} are rejected, even though {@link
822   * Integer#parseInt(String)} accepts them.
823   *
824   * @param string the string representation of an integer value
825   * @param radix the radix to use when parsing
826   * @return the integer value represented by {@code string} using {@code radix}, or {@code null} if
827   *     {@code string} has a length of zero or cannot be parsed as an integer value
828   * @throws IllegalArgumentException if {@code radix < Character.MIN_RADIX} or {@code radix >
829   *     Character.MAX_RADIX}
830   * @throws NullPointerException if {@code string} is {@code null}
831   * @since 19.0
832   */
833  @CheckForNull
834  public static Integer tryParse(String string, int radix) {
835    Long result = Longs.tryParse(string, radix);
836    if (result == null || result.longValue() != result.intValue()) {
837      return null;
838    } else {
839      return result.intValue();
840    }
841  }
842}