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 javax.annotation.CheckForNull;
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>, third
045 *       edition, Item 17).
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
091@ElementTypesAreNonnullByDefault
092public final class ImmutableIntArray implements Serializable {
093  private static final ImmutableIntArray EMPTY = new ImmutableIntArray(new int[0]);
094
095  /** Returns the empty array. */
096  public static ImmutableIntArray of() {
097    return EMPTY;
098  }
099
100  /** Returns an immutable array containing a single value. */
101  public static ImmutableIntArray of(int e0) {
102    return new ImmutableIntArray(new int[] {e0});
103  }
104
105  /** Returns an immutable array containing the given values, in order. */
106  public static ImmutableIntArray of(int e0, int e1) {
107    return new ImmutableIntArray(new int[] {e0, e1});
108  }
109
110  /** Returns an immutable array containing the given values, in order. */
111  public static ImmutableIntArray of(int e0, int e1, int e2) {
112    return new ImmutableIntArray(new int[] {e0, e1, e2});
113  }
114
115  /** Returns an immutable array containing the given values, in order. */
116  public static ImmutableIntArray of(int e0, int e1, int e2, int e3) {
117    return new ImmutableIntArray(new int[] {e0, e1, e2, e3});
118  }
119
120  /** Returns an immutable array containing the given values, in order. */
121  public static ImmutableIntArray of(int e0, int e1, int e2, int e3, int e4) {
122    return new ImmutableIntArray(new int[] {e0, e1, e2, e3, e4});
123  }
124
125  /** Returns an immutable array containing the given values, in order. */
126  public static ImmutableIntArray of(int e0, int e1, int e2, int e3, int e4, int e5) {
127    return new ImmutableIntArray(new int[] {e0, e1, e2, e3, e4, e5});
128  }
129
130  // TODO(kevinb): go up to 11?
131
132  /**
133   * Returns an immutable array containing the given values, in order.
134   *
135   * <p>The array {@code rest} must not be longer than {@code Integer.MAX_VALUE - 1}.
136   */
137  // Use (first, rest) so that `of(someIntArray)` won't compile (they should use copyOf), which is
138  // okay since we have to copy the just-created array anyway.
139  public static ImmutableIntArray of(int first, int... rest) {
140    checkArgument(
141        rest.length <= Integer.MAX_VALUE - 1, "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        array = Arrays.copyOf(array, expandedCapacity(array.length, newCount));
296      }
297    }
298
299    // Unfortunately this is pasted from ImmutableCollection.Builder.
300    private static int expandedCapacity(int oldCapacity, int minCapacity) {
301      if (minCapacity < 0) {
302        throw new AssertionError("cannot store more than MAX_VALUE elements");
303      }
304      // careful of overflow!
305      int newCapacity = oldCapacity + (oldCapacity >> 1) + 1;
306      if (newCapacity < minCapacity) {
307        newCapacity = Integer.highestOneBit(minCapacity - 1) << 1;
308      }
309      if (newCapacity < 0) {
310        newCapacity = Integer.MAX_VALUE; // guaranteed to be >= newCapacity
311      }
312      return newCapacity;
313    }
314
315    /**
316     * Returns a new immutable array. The builder can continue to be used after this call, to append
317     * more values and build again.
318     *
319     * <p><b>Performance note:</b> the returned array is backed by the same array as the builder, so
320     * no data is copied as part of this step, but this may occupy more memory than strictly
321     * necessary. To copy the data to a right-sized backing array, use {@code .build().trimmed()}.
322     */
323    @CheckReturnValue
324    public ImmutableIntArray build() {
325      return count == 0 ? EMPTY : new ImmutableIntArray(array, 0, count);
326    }
327  }
328
329  // Instance stuff here
330
331  // The array is never mutated after storing in this field and the construction strategies ensure
332  // it doesn't escape this class
333  @SuppressWarnings("Immutable")
334  private final int[] array;
335
336  /*
337   * TODO(kevinb): evaluate the trade-offs of going bimorphic to save these two fields from most
338   * instances. Note that the instances that would get smaller are the right set to care about
339   * optimizing, because the rest have the option of calling `trimmed`.
340   */
341
342  private final transient int start; // it happens that we only serialize instances where this is 0
343  private final int end; // exclusive
344
345  private ImmutableIntArray(int[] array) {
346    this(array, 0, array.length);
347  }
348
349  private ImmutableIntArray(int[] array, int start, int end) {
350    this.array = array;
351    this.start = start;
352    this.end = end;
353  }
354
355  /** Returns the number of values in this array. */
356  public int length() {
357    return end - start;
358  }
359
360  /** Returns {@code true} if there are no values in this array ({@link #length} is zero). */
361  public boolean isEmpty() {
362    return end == start;
363  }
364
365  /**
366   * Returns the {@code int} value present at the given index.
367   *
368   * @throws IndexOutOfBoundsException if {@code index} is negative, or greater than or equal to
369   *     {@link #length}
370   */
371  public int get(int index) {
372    Preconditions.checkElementIndex(index, length());
373    return array[start + index];
374  }
375
376  /**
377   * Returns the smallest index for which {@link #get} returns {@code target}, or {@code -1} if no
378   * such index exists. Equivalent to {@code asList().indexOf(target)}.
379   */
380  public int indexOf(int target) {
381    for (int i = start; i < end; i++) {
382      if (array[i] == target) {
383        return i - start;
384      }
385    }
386    return -1;
387  }
388
389  /**
390   * Returns the largest index for which {@link #get} returns {@code target}, or {@code -1} if no
391   * such index exists. Equivalent to {@code asList().lastIndexOf(target)}.
392   */
393  public int lastIndexOf(int target) {
394    for (int i = end - 1; i >= start; i--) {
395      if (array[i] == target) {
396        return i - start;
397      }
398    }
399    return -1;
400  }
401
402  /**
403   * Returns {@code true} if {@code target} is present at any index in this array. Equivalent to
404   * {@code asList().contains(target)}.
405   */
406  public boolean contains(int target) {
407    return indexOf(target) >= 0;
408  }
409
410  /** Invokes {@code consumer} for each value contained in this array, in order. */
411  public void forEach(IntConsumer consumer) {
412    checkNotNull(consumer);
413    for (int i = start; i < end; i++) {
414      consumer.accept(array[i]);
415    }
416  }
417
418  /** Returns a stream over the values in this array, in order. */
419  public IntStream stream() {
420    return Arrays.stream(array, start, end);
421  }
422
423  /** Returns a new, mutable copy of this array's values, as a primitive {@code int[]}. */
424  public int[] toArray() {
425    return Arrays.copyOfRange(array, start, end);
426  }
427
428  /**
429   * Returns a new immutable array containing the values in the specified range.
430   *
431   * <p><b>Performance note:</b> The returned array has the same full memory footprint as this one
432   * does (no actual copying is performed). To reduce memory usage, use {@code subArray(start,
433   * end).trimmed()}.
434   */
435  public ImmutableIntArray subArray(int startIndex, int endIndex) {
436    Preconditions.checkPositionIndexes(startIndex, endIndex, length());
437    return startIndex == endIndex
438        ? EMPTY
439        : new ImmutableIntArray(array, start + startIndex, start + endIndex);
440  }
441
442  private Spliterator.OfInt spliterator() {
443    return Spliterators.spliterator(array, start, end, Spliterator.IMMUTABLE | Spliterator.ORDERED);
444  }
445
446  /**
447   * Returns an immutable <i>view</i> of this array's values as a {@code List}; note that {@code
448   * int} values are boxed into {@link Integer} instances on demand, which can be very expensive.
449   * The returned list should be used once and discarded. For any usages beyond that, pass the
450   * returned list to {@link com.google.common.collect.ImmutableList#copyOf(Collection)
451   * ImmutableList.copyOf} and use that list instead.
452   */
453  public List<Integer> asList() {
454    /*
455     * Typically we cache this kind of thing, but much repeated use of this view is a performance
456     * anti-pattern anyway. If we cache, then everyone pays a price in memory footprint even if
457     * they never use this method.
458     */
459    return new AsList(this);
460  }
461
462  static class AsList extends AbstractList<Integer> implements RandomAccess, Serializable {
463    private final ImmutableIntArray parent;
464
465    private AsList(ImmutableIntArray parent) {
466      this.parent = parent;
467    }
468
469    // inherit: isEmpty, containsAll, toArray x2, iterator, listIterator, stream, forEach, mutations
470
471    @Override
472    public int size() {
473      return parent.length();
474    }
475
476    @Override
477    public Integer get(int index) {
478      return parent.get(index);
479    }
480
481    @Override
482    public boolean contains(@CheckForNull Object target) {
483      return indexOf(target) >= 0;
484    }
485
486    @Override
487    public int indexOf(@CheckForNull Object target) {
488      return target instanceof Integer ? parent.indexOf((Integer) target) : -1;
489    }
490
491    @Override
492    public int lastIndexOf(@CheckForNull Object target) {
493      return target instanceof Integer ? parent.lastIndexOf((Integer) target) : -1;
494    }
495
496    @Override
497    public List<Integer> subList(int fromIndex, int toIndex) {
498      return parent.subArray(fromIndex, toIndex).asList();
499    }
500
501    // The default List spliterator is not efficiently splittable
502    @Override
503    public Spliterator<Integer> spliterator() {
504      return parent.spliterator();
505    }
506
507    @Override
508    public boolean equals(@CheckForNull Object object) {
509      if (object instanceof AsList) {
510        AsList that = (AsList) object;
511        return this.parent.equals(that.parent);
512      }
513      // We could delegate to super now but it would still box too much
514      if (!(object instanceof List)) {
515        return false;
516      }
517      List<?> that = (List<?>) object;
518      if (this.size() != that.size()) {
519        return false;
520      }
521      int i = parent.start;
522      // Since `that` is very likely RandomAccess we could avoid allocating this iterator...
523      for (Object element : that) {
524        if (!(element instanceof Integer) || parent.array[i++] != (Integer) element) {
525          return false;
526        }
527      }
528      return true;
529    }
530
531    // Because we happen to use the same formula. If that changes, just don't override this.
532    @Override
533    public int hashCode() {
534      return parent.hashCode();
535    }
536
537    @Override
538    public String toString() {
539      return parent.toString();
540    }
541  }
542
543  /**
544   * Returns {@code true} if {@code object} is an {@code ImmutableIntArray} containing the same
545   * values as this one, in the same order.
546   */
547  @Override
548  public boolean equals(@CheckForNull Object object) {
549    if (object == this) {
550      return true;
551    }
552    if (!(object instanceof ImmutableIntArray)) {
553      return false;
554    }
555    ImmutableIntArray that = (ImmutableIntArray) object;
556    if (this.length() != that.length()) {
557      return false;
558    }
559    for (int i = 0; i < length(); i++) {
560      if (this.get(i) != that.get(i)) {
561        return false;
562      }
563    }
564    return true;
565  }
566
567  /** Returns an unspecified hash code for the contents of this immutable array. */
568  @Override
569  public int hashCode() {
570    int hash = 1;
571    for (int i = start; i < end; i++) {
572      hash *= 31;
573      hash += Ints.hashCode(array[i]);
574    }
575    return hash;
576  }
577
578  /**
579   * Returns a string representation of this array in the same form as {@link
580   * Arrays#toString(int[])}, for example {@code "[1, 2, 3]"}.
581   */
582  @Override
583  public String toString() {
584    if (isEmpty()) {
585      return "[]";
586    }
587    StringBuilder builder = new StringBuilder(length() * 5); // rough estimate is fine
588    builder.append('[').append(array[start]);
589
590    for (int i = start + 1; i < end; i++) {
591      builder.append(", ").append(array[i]);
592    }
593    builder.append(']');
594    return builder.toString();
595  }
596
597  /**
598   * Returns an immutable array containing the same values as {@code this} array. This is logically
599   * a no-op, and in some circumstances {@code this} itself is returned. However, if this instance
600   * is a {@link #subArray} view of a larger array, this method will copy only the appropriate range
601   * of values, resulting in an equivalent array with a smaller memory footprint.
602   */
603  public ImmutableIntArray trimmed() {
604    return isPartialView() ? new ImmutableIntArray(toArray()) : this;
605  }
606
607  private boolean isPartialView() {
608    return start > 0 || end < array.length;
609  }
610
611  Object writeReplace() {
612    return trimmed();
613  }
614
615  Object readResolve() {
616    return isEmpty() ? EMPTY : this;
617  }
618}