001/*
002 * Copyright (C) 2017 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.checkNotNull;
019
020import com.google.common.annotations.Beta;
021import com.google.common.annotations.GwtCompatible;
022import com.google.common.base.Preconditions;
023import com.google.errorprone.annotations.CanIgnoreReturnValue;
024import com.google.errorprone.annotations.CheckReturnValue;
025import com.google.errorprone.annotations.Immutable;
026import java.io.Serializable;
027import java.util.AbstractList;
028import java.util.Arrays;
029import java.util.Collection;
030import java.util.List;
031import java.util.RandomAccess;
032import java.util.Spliterator;
033import java.util.Spliterators;
034import java.util.function.IntConsumer;
035import java.util.stream.IntStream;
036import org.checkerframework.checker.nullness.qual.Nullable;
037
038/**
039 * An immutable array of {@code int} values, with an API resembling {@link List}.
040 *
041 * <p>Advantages compared to {@code int[]}:
042 *
043 * <ul>
044 *   <li>All the many well-known advantages of immutability (read <i>Effective Java</i>, second
045 *       edition, Item 15).
046 *   <li>Has the value-based (not identity-based) {@link #equals}, {@link #hashCode}, and {@link
047 *       #toString} behavior you expect.
048 *   <li>Offers useful operations beyond just {@code get} and {@code length}, so you don't have to
049 *       hunt through classes like {@link Arrays} and {@link Ints} for them.
050 *   <li>Supports a copy-free {@link #subArray} view, so methods that accept this type don't need to
051 *       add overloads that accept start and end indexes.
052 *   <li>Can be streamed without "breaking the chain": {@code foo.getBarInts().stream()...}.
053 *   <li>Access to all collection-based utilities via {@link #asList} (though at the cost of
054 *       allocating garbage).
055 * </ul>
056 *
057 * <p>Disadvantages compared to {@code int[]}:
058 *
059 * <ul>
060 *   <li>Memory footprint has a fixed overhead (about 24 bytes per instance).
061 *   <li><i>Some</i> construction use cases force the data to be copied (though several construction
062 *       APIs are offered that don't).
063 *   <li>Can't be passed directly to methods that expect {@code int[]} (though the most common
064 *       utilities do have replacements here).
065 *   <li>Dependency on {@code com.google.common} / Guava.
066 * </ul>
067 *
068 * <p>Advantages compared to {@link com.google.common.collect.ImmutableList ImmutableList}{@code
069 * <Integer>}:
070 *
071 * <ul>
072 *   <li>Improved memory compactness and locality.
073 *   <li>Can be queried without allocating garbage.
074 *   <li>Access to {@code IntStream} features (like {@link IntStream#sum}) using {@code stream()}
075 *       instead of the awkward {@code stream().mapToInt(v -> v)}.
076 * </ul>
077 *
078 * <p>Disadvantages compared to {@code ImmutableList<Integer>}:
079 *
080 * <ul>
081 *   <li>Can't be passed directly to methods that expect {@code Iterable}, {@code Collection}, or
082 *       {@code List} (though the most common utilities do have replacements here, and there is a
083 *       lazy {@link #asList} view).
084 * </ul>
085 *
086 * @since 22.0
087 */
088@Beta
089@GwtCompatible
090@Immutable
091public final class ImmutableIntArray implements Serializable {
092  private static final ImmutableIntArray EMPTY = new ImmutableIntArray(new int[0]);
093
094  /** Returns the empty array. */
095  public static ImmutableIntArray of() {
096    return EMPTY;
097  }
098
099  /** Returns an immutable array containing a single value. */
100  public static ImmutableIntArray of(int e0) {
101    return new ImmutableIntArray(new int[] {e0});
102  }
103
104  /** Returns an immutable array containing the given values, in order. */
105  public static ImmutableIntArray of(int e0, int e1) {
106    return new ImmutableIntArray(new int[] {e0, e1});
107  }
108
109  /** Returns an immutable array containing the given values, in order. */
110  public static ImmutableIntArray of(int e0, int e1, int e2) {
111    return new ImmutableIntArray(new int[] {e0, e1, e2});
112  }
113
114  /** Returns an immutable array containing the given values, in order. */
115  public static ImmutableIntArray of(int e0, int e1, int e2, int e3) {
116    return new ImmutableIntArray(new int[] {e0, e1, e2, e3});
117  }
118
119  /** Returns an immutable array containing the given values, in order. */
120  public static ImmutableIntArray of(int e0, int e1, int e2, int e3, int e4) {
121    return new ImmutableIntArray(new int[] {e0, e1, e2, e3, e4});
122  }
123
124  /** Returns an immutable array containing the given values, in order. */
125  public static ImmutableIntArray of(int e0, int e1, int e2, int e3, int e4, int e5) {
126    return new ImmutableIntArray(new int[] {e0, e1, e2, e3, e4, e5});
127  }
128
129  // TODO(kevinb): go up to 11?
130
131  /**
132   * Returns an immutable array containing the given values, in order.
133   *
134   * <p>The array {@code rest} must not be longer than {@code Integer.MAX_VALUE - 1}.
135   */
136  // Use (first, rest) so that `of(someIntArray)` won't compile (they should use copyOf), which is
137  // okay since we have to copy the just-created array anyway.
138  public static ImmutableIntArray of(int first, int... rest) {
139    checkArgument(
140        rest.length <= Integer.MAX_VALUE - 1,
141        "the total number of elements must fit in an int");
142    int[] array = new int[rest.length + 1];
143    array[0] = first;
144    System.arraycopy(rest, 0, array, 1, rest.length);
145    return new ImmutableIntArray(array);
146  }
147
148  /** Returns an immutable array containing the given values, in order. */
149  public static ImmutableIntArray copyOf(int[] values) {
150    return values.length == 0 ? EMPTY : new ImmutableIntArray(Arrays.copyOf(values, values.length));
151  }
152
153  /** Returns an immutable array containing the given values, in order. */
154  public static ImmutableIntArray copyOf(Collection<Integer> values) {
155    return values.isEmpty() ? EMPTY : new ImmutableIntArray(Ints.toArray(values));
156  }
157
158  /**
159   * Returns an immutable array containing the given values, in order.
160   *
161   * <p><b>Performance note:</b> this method delegates to {@link #copyOf(Collection)} if {@code
162   * values} is a {@link Collection}. Otherwise it creates a {@link #builder} and uses {@link
163   * Builder#addAll(Iterable)}, with all the performance implications associated with that.
164   */
165  public static ImmutableIntArray copyOf(Iterable<Integer> values) {
166    if (values instanceof Collection) {
167      return copyOf((Collection<Integer>) values);
168    }
169    return builder().addAll(values).build();
170  }
171
172  /** Returns an immutable array containing all the values from {@code stream}, in order. */
173  public static ImmutableIntArray copyOf(IntStream stream) {
174    // Note this uses very different growth behavior from copyOf(Iterable) and the builder.
175    int[] array = stream.toArray();
176    return (array.length == 0) ? EMPTY : new ImmutableIntArray(array);
177  }
178
179  /**
180   * Returns a new, empty builder for {@link ImmutableIntArray} instances, sized to hold up to
181   * {@code initialCapacity} values without resizing. The returned builder is not thread-safe.
182   *
183   * <p><b>Performance note:</b> When feasible, {@code initialCapacity} should be the exact number
184   * of values that will be added, if that knowledge is readily available. It is better to guess a
185   * value slightly too high than slightly too low. If the value is not exact, the {@link
186   * ImmutableIntArray} that is built will very likely occupy more memory than strictly necessary;
187   * to trim memory usage, build using {@code builder.build().trimmed()}.
188   */
189  public static Builder builder(int initialCapacity) {
190    checkArgument(initialCapacity >= 0, "Invalid initialCapacity: %s", initialCapacity);
191    return new Builder(initialCapacity);
192  }
193
194  /**
195   * Returns a new, empty builder for {@link ImmutableIntArray} instances, with a default initial
196   * capacity. The returned builder is not thread-safe.
197   *
198   * <p><b>Performance note:</b> The {@link ImmutableIntArray} that is built will very likely occupy
199   * more memory than necessary; to trim memory usage, build using {@code
200   * builder.build().trimmed()}.
201   */
202  public static Builder builder() {
203    return new Builder(10);
204  }
205
206  /**
207   * A builder for {@link ImmutableIntArray} instances; obtained using {@link
208   * ImmutableIntArray#builder}.
209   */
210  @CanIgnoreReturnValue
211  public static final class Builder {
212    private int[] array;
213    private int count = 0; // <= array.length
214
215    Builder(int initialCapacity) {
216      array = new int[initialCapacity];
217    }
218
219    /**
220     * Appends {@code value} to the end of the values the built {@link ImmutableIntArray} will
221     * contain.
222     */
223    public Builder add(int value) {
224      ensureRoomFor(1);
225      array[count] = value;
226      count += 1;
227      return this;
228    }
229
230    /**
231     * Appends {@code values}, in order, to the end of the values the built {@link
232     * ImmutableIntArray} will contain.
233     */
234    public Builder addAll(int[] values) {
235      ensureRoomFor(values.length);
236      System.arraycopy(values, 0, array, count, values.length);
237      count += values.length;
238      return this;
239    }
240
241    /**
242     * Appends {@code values}, in order, to the end of the values the built {@link
243     * ImmutableIntArray} will contain.
244     */
245    public Builder addAll(Iterable<Integer> values) {
246      if (values instanceof Collection) {
247        return addAll((Collection<Integer>) values);
248      }
249      for (Integer value : values) {
250        add(value);
251      }
252      return this;
253    }
254
255    /**
256     * Appends {@code values}, in order, to the end of the values the built {@link
257     * ImmutableIntArray} will contain.
258     */
259    public Builder addAll(Collection<Integer> values) {
260      ensureRoomFor(values.size());
261      for (Integer value : values) {
262        array[count++] = value;
263      }
264      return this;
265    }
266
267    /**
268     * Appends all values from {@code stream}, in order, to the end of the values the built {@link
269     * ImmutableIntArray} will contain.
270     */
271    public Builder addAll(IntStream stream) {
272      Spliterator.OfInt spliterator = stream.spliterator();
273      long size = spliterator.getExactSizeIfKnown();
274      if (size > 0) { // known *and* nonempty
275        ensureRoomFor(Ints.saturatedCast(size));
276      }
277      spliterator.forEachRemaining((IntConsumer) this::add);
278      return this;
279    }
280
281    /**
282     * Appends {@code values}, in order, to the end of the values the built {@link
283     * ImmutableIntArray} will contain.
284     */
285    public Builder addAll(ImmutableIntArray values) {
286      ensureRoomFor(values.length());
287      System.arraycopy(values.array, values.start, array, count, values.length());
288      count += values.length();
289      return this;
290    }
291
292    private void ensureRoomFor(int numberToAdd) {
293      int newCount = count + numberToAdd; // TODO(kevinb): check overflow now?
294      if (newCount > array.length) {
295        int[] newArray = new int[expandedCapacity(array.length, newCount)];
296        System.arraycopy(array, 0, newArray, 0, count);
297        this.array = newArray;
298      }
299    }
300
301    // Unfortunately this is pasted from ImmutableCollection.Builder.
302    private static int expandedCapacity(int oldCapacity, int minCapacity) {
303      if (minCapacity < 0) {
304        throw new AssertionError("cannot store more than MAX_VALUE elements");
305      }
306      // careful of overflow!
307      int newCapacity = oldCapacity + (oldCapacity >> 1) + 1;
308      if (newCapacity < minCapacity) {
309        newCapacity = Integer.highestOneBit(minCapacity - 1) << 1;
310      }
311      if (newCapacity < 0) {
312        newCapacity = Integer.MAX_VALUE; // guaranteed to be >= newCapacity
313      }
314      return newCapacity;
315    }
316
317    /**
318     * Returns a new immutable array. The builder can continue to be used after this call, to append
319     * more values and build again.
320     *
321     * <p><b>Performance note:</b> the returned array is backed by the same array as the builder, so
322     * no data is copied as part of this step, but this may occupy more memory than strictly
323     * necessary. To copy the data to a right-sized backing array, use {@code .build().trimmed()}.
324     */
325    @CheckReturnValue
326    public ImmutableIntArray build() {
327      return count == 0 ? EMPTY : new ImmutableIntArray(array, 0, count);
328    }
329  }
330
331  // Instance stuff here
332
333  // The array is never mutated after storing in this field and the construction strategies ensure
334  // it doesn't escape this class
335  @SuppressWarnings("Immutable")
336  private final int[] array;
337
338  /*
339   * TODO(kevinb): evaluate the trade-offs of going bimorphic to save these two fields from most
340   * instances. Note that the instances that would get smaller are the right set to care about
341   * optimizing, because the rest have the option of calling `trimmed`.
342   */
343
344  private final transient int start; // it happens that we only serialize instances where this is 0
345  private final int end; // exclusive
346
347  private ImmutableIntArray(int[] array) {
348    this(array, 0, array.length);
349  }
350
351  private ImmutableIntArray(int[] array, int start, int end) {
352    this.array = array;
353    this.start = start;
354    this.end = end;
355  }
356
357  /** Returns the number of values in this array. */
358  public int length() {
359    return end - start;
360  }
361
362  /** Returns {@code true} if there are no values in this array ({@link #length} is zero). */
363  public boolean isEmpty() {
364    return end == start;
365  }
366
367  /**
368   * Returns the {@code int} value present at the given index.
369   *
370   * @throws IndexOutOfBoundsException if {@code index} is negative, or greater than or equal to
371   *     {@link #length}
372   */
373  public int get(int index) {
374    Preconditions.checkElementIndex(index, length());
375    return array[start + index];
376  }
377
378  /**
379   * Returns the smallest index for which {@link #get} returns {@code target}, or {@code -1} if no
380   * such index exists. Equivalent to {@code asList().indexOf(target)}.
381   */
382  public int indexOf(int target) {
383    for (int i = start; i < end; i++) {
384      if (array[i] == target) {
385        return i - start;
386      }
387    }
388    return -1;
389  }
390
391  /**
392   * Returns the largest index for which {@link #get} returns {@code target}, or {@code -1} if no
393   * such index exists. Equivalent to {@code asList().lastIndexOf(target)}.
394   */
395  public int lastIndexOf(int target) {
396    for (int i = end - 1; i >= start; i--) {
397      if (array[i] == target) {
398        return i - start;
399      }
400    }
401    return -1;
402  }
403
404  /**
405   * Returns {@code true} if {@code target} is present at any index in this array. Equivalent to
406   * {@code asList().contains(target)}.
407   */
408  public boolean contains(int target) {
409    return indexOf(target) >= 0;
410  }
411
412  /** Invokes {@code consumer} for each value contained in this array, in order. */
413  public void forEach(IntConsumer consumer) {
414    checkNotNull(consumer);
415    for (int i = start; i < end; i++) {
416      consumer.accept(array[i]);
417    }
418  }
419
420  /** Returns a stream over the values in this array, in order. */
421  public IntStream stream() {
422    return Arrays.stream(array, start, end);
423  }
424
425  /** Returns a new, mutable copy of this array's values, as a primitive {@code int[]}. */
426  public int[] toArray() {
427    return Arrays.copyOfRange(array, start, end);
428  }
429
430  /**
431   * Returns a new immutable array containing the values in the specified range.
432   *
433   * <p><b>Performance note:</b> The returned array has the same full memory footprint as this one
434   * does (no actual copying is performed). To reduce memory usage, use {@code subArray(start,
435   * end).trimmed()}.
436   */
437  public ImmutableIntArray subArray(int startIndex, int endIndex) {
438    Preconditions.checkPositionIndexes(startIndex, endIndex, length());
439    return startIndex == endIndex
440        ? EMPTY
441        : new ImmutableIntArray(array, start + startIndex, start + endIndex);
442  }
443
444  private Spliterator.OfInt spliterator() {
445    return Spliterators.spliterator(array, start, end, Spliterator.IMMUTABLE | Spliterator.ORDERED);
446  }
447
448  /**
449   * Returns an immutable <i>view</i> of this array's values as a {@code List}; note that {@code
450   * int} values are boxed into {@link Integer} instances on demand, which can be very expensive.
451   * The returned list should be used once and discarded. For any usages beyond that, pass the
452   * returned list to {@link com.google.common.collect.ImmutableList#copyOf(Collection)
453   * ImmutableList.copyOf} and use that list instead.
454   */
455  public List<Integer> asList() {
456    /*
457     * Typically we cache this kind of thing, but much repeated use of this view is a performance
458     * anti-pattern anyway. If we cache, then everyone pays a price in memory footprint even if
459     * they never use this method.
460     */
461    return new AsList(this);
462  }
463
464  static class AsList extends AbstractList<Integer> implements RandomAccess, Serializable {
465    private final ImmutableIntArray parent;
466
467    private AsList(ImmutableIntArray parent) {
468      this.parent = parent;
469    }
470
471    // inherit: isEmpty, containsAll, toArray x2, iterator, listIterator, stream, forEach, mutations
472
473    @Override
474    public int size() {
475      return parent.length();
476    }
477
478    @Override
479    public Integer get(int index) {
480      return parent.get(index);
481    }
482
483    @Override
484    public boolean contains(Object target) {
485      return indexOf(target) >= 0;
486    }
487
488    @Override
489    public int indexOf(Object target) {
490      return target instanceof Integer ? parent.indexOf((Integer) target) : -1;
491    }
492
493    @Override
494    public int lastIndexOf(Object target) {
495      return target instanceof Integer ? parent.lastIndexOf((Integer) target) : -1;
496    }
497
498    @Override
499    public List<Integer> subList(int fromIndex, int toIndex) {
500      return parent.subArray(fromIndex, toIndex).asList();
501    }
502
503    // The default List spliterator is not efficiently splittable
504    @Override
505    public Spliterator<Integer> spliterator() {
506      return parent.spliterator();
507    }
508
509    @Override
510    public boolean equals(@Nullable Object object) {
511      if (object instanceof AsList) {
512        AsList that = (AsList) object;
513        return this.parent.equals(that.parent);
514      }
515      // We could delegate to super now but it would still box too much
516      if (!(object instanceof List)) {
517        return false;
518      }
519      List<?> that = (List<?>) object;
520      if (this.size() != that.size()) {
521        return false;
522      }
523      int i = parent.start;
524      // Since `that` is very likely RandomAccess we could avoid allocating this iterator...
525      for (Object element : that) {
526        if (!(element instanceof Integer) || parent.array[i++] != (Integer) element) {
527          return false;
528        }
529      }
530      return true;
531    }
532
533    // Because we happen to use the same formula. If that changes, just don't override this.
534    @Override
535    public int hashCode() {
536      return parent.hashCode();
537    }
538
539    @Override
540    public String toString() {
541      return parent.toString();
542    }
543  }
544
545  /**
546   * Returns {@code true} if {@code object} is an {@code ImmutableIntArray} containing the same
547   * values as this one, in the same order.
548   */
549  @Override
550  public boolean equals(@Nullable Object object) {
551    if (object == this) {
552      return true;
553    }
554    if (!(object instanceof ImmutableIntArray)) {
555      return false;
556    }
557    ImmutableIntArray that = (ImmutableIntArray) object;
558    if (this.length() != that.length()) {
559      return false;
560    }
561    for (int i = 0; i < length(); i++) {
562      if (this.get(i) != that.get(i)) {
563        return false;
564      }
565    }
566    return true;
567  }
568
569  /** Returns an unspecified hash code for the contents of this immutable array. */
570  @Override
571  public int hashCode() {
572    int hash = 1;
573    for (int i = start; i < end; i++) {
574      hash *= 31;
575      hash += Ints.hashCode(array[i]);
576    }
577    return hash;
578  }
579
580  /**
581   * Returns a string representation of this array in the same form as {@link
582   * Arrays#toString(int[])}, for example {@code "[1, 2, 3]"}.
583   */
584  @Override
585  public String toString() {
586    if (isEmpty()) {
587      return "[]";
588    }
589    StringBuilder builder = new StringBuilder(length() * 5); // rough estimate is fine
590    builder.append('[').append(array[start]);
591
592    for (int i = start + 1; i < end; i++) {
593      builder.append(", ").append(array[i]);
594    }
595    builder.append(']');
596    return builder.toString();
597  }
598
599  /**
600   * Returns an immutable array containing the same values as {@code this} array. This is logically
601   * a no-op, and in some circumstances {@code this} itself is returned. However, if this instance
602   * is a {@link #subArray} view of a larger array, this method will copy only the appropriate range
603   * of values, resulting in an equivalent array with a smaller memory footprint.
604   */
605  public ImmutableIntArray trimmed() {
606    return isPartialView() ? new ImmutableIntArray(toArray()) : this;
607  }
608
609  private boolean isPartialView() {
610    return start > 0 || end < array.length;
611  }
612
613  Object writeReplace() {
614    return trimmed();
615  }
616
617  Object readResolve() {
618    return isEmpty() ? EMPTY : this;
619  }
620}