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.DoubleConsumer;
035import java.util.stream.DoubleStream;
036import javax.annotation.CheckForNull;
037
038/**
039 * An immutable array of {@code double} values, with an API resembling {@link List}.
040 *
041 * <p>Advantages compared to {@code double[]}:
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 Doubles} 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.getBarDoubles().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 double[]}:
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 double[]} (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 * <Double>}:
070 *
071 * <ul>
072 *   <li>Improved memory compactness and locality.
073 *   <li>Can be queried without allocating garbage.
074 *   <li>Access to {@code DoubleStream} features (like {@link DoubleStream#sum}) using {@code
075 *       stream()} instead of the awkward {@code stream().mapToDouble(v -> v)}.
076 * </ul>
077 *
078 * <p>Disadvantages compared to {@code ImmutableList<Double>}:
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 ImmutableDoubleArray implements Serializable {
093  private static final ImmutableDoubleArray EMPTY = new ImmutableDoubleArray(new double[0]);
094
095  /** Returns the empty array. */
096  public static ImmutableDoubleArray of() {
097    return EMPTY;
098  }
099
100  /** Returns an immutable array containing a single value. */
101  public static ImmutableDoubleArray of(double e0) {
102    return new ImmutableDoubleArray(new double[] {e0});
103  }
104
105  /** Returns an immutable array containing the given values, in order. */
106  public static ImmutableDoubleArray of(double e0, double e1) {
107    return new ImmutableDoubleArray(new double[] {e0, e1});
108  }
109
110  /** Returns an immutable array containing the given values, in order. */
111  public static ImmutableDoubleArray of(double e0, double e1, double e2) {
112    return new ImmutableDoubleArray(new double[] {e0, e1, e2});
113  }
114
115  /** Returns an immutable array containing the given values, in order. */
116  public static ImmutableDoubleArray of(double e0, double e1, double e2, double e3) {
117    return new ImmutableDoubleArray(new double[] {e0, e1, e2, e3});
118  }
119
120  /** Returns an immutable array containing the given values, in order. */
121  public static ImmutableDoubleArray of(double e0, double e1, double e2, double e3, double e4) {
122    return new ImmutableDoubleArray(new double[] {e0, e1, e2, e3, e4});
123  }
124
125  /** Returns an immutable array containing the given values, in order. */
126  public static ImmutableDoubleArray of(
127      double e0, double e1, double e2, double e3, double e4, double e5) {
128    return new ImmutableDoubleArray(new double[] {e0, e1, e2, e3, e4, e5});
129  }
130
131  // TODO(kevinb): go up to 11?
132
133  /**
134   * Returns an immutable array containing the given values, in order.
135   *
136   * <p>The array {@code rest} must not be longer than {@code Integer.MAX_VALUE - 1}.
137   */
138  // Use (first, rest) so that `of(someDoubleArray)` won't compile (they should use copyOf), which
139  // is okay since we have to copy the just-created array anyway.
140  public static ImmutableDoubleArray of(double first, double... rest) {
141    checkArgument(
142        rest.length <= Integer.MAX_VALUE - 1, "the total number of elements must fit in an int");
143    double[] array = new double[rest.length + 1];
144    array[0] = first;
145    System.arraycopy(rest, 0, array, 1, rest.length);
146    return new ImmutableDoubleArray(array);
147  }
148
149  /** Returns an immutable array containing the given values, in order. */
150  public static ImmutableDoubleArray copyOf(double[] values) {
151    return values.length == 0
152        ? EMPTY
153        : new ImmutableDoubleArray(Arrays.copyOf(values, values.length));
154  }
155
156  /** Returns an immutable array containing the given values, in order. */
157  public static ImmutableDoubleArray copyOf(Collection<Double> values) {
158    return values.isEmpty() ? EMPTY : new ImmutableDoubleArray(Doubles.toArray(values));
159  }
160
161  /**
162   * Returns an immutable array containing the given values, in order.
163   *
164   * <p><b>Performance note:</b> this method delegates to {@link #copyOf(Collection)} if {@code
165   * values} is a {@link Collection}. Otherwise it creates a {@link #builder} and uses {@link
166   * Builder#addAll(Iterable)}, with all the performance implications associated with that.
167   */
168  public static ImmutableDoubleArray copyOf(Iterable<Double> values) {
169    if (values instanceof Collection) {
170      return copyOf((Collection<Double>) values);
171    }
172    return builder().addAll(values).build();
173  }
174
175  /** Returns an immutable array containing all the values from {@code stream}, in order. */
176  public static ImmutableDoubleArray copyOf(DoubleStream stream) {
177    // Note this uses very different growth behavior from copyOf(Iterable) and the builder.
178    double[] array = stream.toArray();
179    return (array.length == 0) ? EMPTY : new ImmutableDoubleArray(array);
180  }
181
182  /**
183   * Returns a new, empty builder for {@link ImmutableDoubleArray} instances, sized to hold up to
184   * {@code initialCapacity} values without resizing. The returned builder is not thread-safe.
185   *
186   * <p><b>Performance note:</b> When feasible, {@code initialCapacity} should be the exact number
187   * of values that will be added, if that knowledge is readily available. It is better to guess a
188   * value slightly too high than slightly too low. If the value is not exact, the {@link
189   * ImmutableDoubleArray} that is built will very likely occupy more memory than strictly
190   * necessary; to trim memory usage, build using {@code builder.build().trimmed()}.
191   */
192  public static Builder builder(int initialCapacity) {
193    checkArgument(initialCapacity >= 0, "Invalid initialCapacity: %s", initialCapacity);
194    return new Builder(initialCapacity);
195  }
196
197  /**
198   * Returns a new, empty builder for {@link ImmutableDoubleArray} instances, with a default initial
199   * capacity. The returned builder is not thread-safe.
200   *
201   * <p><b>Performance note:</b> The {@link ImmutableDoubleArray} that is built will very likely
202   * occupy more memory than necessary; to trim memory usage, build using {@code
203   * builder.build().trimmed()}.
204   */
205  public static Builder builder() {
206    return new Builder(10);
207  }
208
209  /**
210   * A builder for {@link ImmutableDoubleArray} instances; obtained using {@link
211   * ImmutableDoubleArray#builder}.
212   */
213  @CanIgnoreReturnValue
214  public static final class Builder {
215    private double[] array;
216    private int count = 0; // <= array.length
217
218    Builder(int initialCapacity) {
219      array = new double[initialCapacity];
220    }
221
222    /**
223     * Appends {@code value} to the end of the values the built {@link ImmutableDoubleArray} will
224     * contain.
225     */
226    public Builder add(double value) {
227      ensureRoomFor(1);
228      array[count] = value;
229      count += 1;
230      return this;
231    }
232
233    /**
234     * Appends {@code values}, in order, to the end of the values the built {@link
235     * ImmutableDoubleArray} will contain.
236     */
237    public Builder addAll(double[] values) {
238      ensureRoomFor(values.length);
239      System.arraycopy(values, 0, array, count, values.length);
240      count += values.length;
241      return this;
242    }
243
244    /**
245     * Appends {@code values}, in order, to the end of the values the built {@link
246     * ImmutableDoubleArray} will contain.
247     */
248    public Builder addAll(Iterable<Double> values) {
249      if (values instanceof Collection) {
250        return addAll((Collection<Double>) values);
251      }
252      for (Double value : values) {
253        add(value);
254      }
255      return this;
256    }
257
258    /**
259     * Appends {@code values}, in order, to the end of the values the built {@link
260     * ImmutableDoubleArray} will contain.
261     */
262    public Builder addAll(Collection<Double> values) {
263      ensureRoomFor(values.size());
264      for (Double value : values) {
265        array[count++] = value;
266      }
267      return this;
268    }
269
270    /**
271     * Appends all values from {@code stream}, in order, to the end of the values the built {@link
272     * ImmutableDoubleArray} will contain.
273     */
274    public Builder addAll(DoubleStream stream) {
275      Spliterator.OfDouble spliterator = stream.spliterator();
276      long size = spliterator.getExactSizeIfKnown();
277      if (size > 0) { // known *and* nonempty
278        ensureRoomFor(Ints.saturatedCast(size));
279      }
280      spliterator.forEachRemaining((DoubleConsumer) this::add);
281      return this;
282    }
283
284    /**
285     * Appends {@code values}, in order, to the end of the values the built {@link
286     * ImmutableDoubleArray} will contain.
287     */
288    public Builder addAll(ImmutableDoubleArray values) {
289      ensureRoomFor(values.length());
290      System.arraycopy(values.array, values.start, array, count, values.length());
291      count += values.length();
292      return this;
293    }
294
295    private void ensureRoomFor(int numberToAdd) {
296      int newCount = count + numberToAdd; // TODO(kevinb): check overflow now?
297      if (newCount > array.length) {
298        array = Arrays.copyOf(array, expandedCapacity(array.length, newCount));
299      }
300    }
301
302    // Unfortunately this is pasted from ImmutableCollection.Builder.
303    private static int expandedCapacity(int oldCapacity, int minCapacity) {
304      if (minCapacity < 0) {
305        throw new AssertionError("cannot store more than MAX_VALUE elements");
306      }
307      // careful of overflow!
308      int newCapacity = oldCapacity + (oldCapacity >> 1) + 1;
309      if (newCapacity < minCapacity) {
310        newCapacity = Integer.highestOneBit(minCapacity - 1) << 1;
311      }
312      if (newCapacity < 0) {
313        newCapacity = Integer.MAX_VALUE; // guaranteed to be >= newCapacity
314      }
315      return newCapacity;
316    }
317
318    /**
319     * Returns a new immutable array. The builder can continue to be used after this call, to append
320     * more values and build again.
321     *
322     * <p><b>Performance note:</b> the returned array is backed by the same array as the builder, so
323     * no data is copied as part of this step, but this may occupy more memory than strictly
324     * necessary. To copy the data to a right-sized backing array, use {@code .build().trimmed()}.
325     */
326    @CheckReturnValue
327    public ImmutableDoubleArray build() {
328      return count == 0 ? EMPTY : new ImmutableDoubleArray(array, 0, count);
329    }
330  }
331
332  // Instance stuff here
333
334  // The array is never mutated after storing in this field and the construction strategies ensure
335  // it doesn't escape this class
336  @SuppressWarnings("Immutable")
337  private final double[] array;
338
339  /*
340   * TODO(kevinb): evaluate the trade-offs of going bimorphic to save these two fields from most
341   * instances. Note that the instances that would get smaller are the right set to care about
342   * optimizing, because the rest have the option of calling `trimmed`.
343   */
344
345  private final transient int start; // it happens that we only serialize instances where this is 0
346  private final int end; // exclusive
347
348  private ImmutableDoubleArray(double[] array) {
349    this(array, 0, array.length);
350  }
351
352  private ImmutableDoubleArray(double[] array, int start, int end) {
353    this.array = array;
354    this.start = start;
355    this.end = end;
356  }
357
358  /** Returns the number of values in this array. */
359  public int length() {
360    return end - start;
361  }
362
363  /** Returns {@code true} if there are no values in this array ({@link #length} is zero). */
364  public boolean isEmpty() {
365    return end == start;
366  }
367
368  /**
369   * Returns the {@code double} value present at the given index.
370   *
371   * @throws IndexOutOfBoundsException if {@code index} is negative, or greater than or equal to
372   *     {@link #length}
373   */
374  public double get(int index) {
375    Preconditions.checkElementIndex(index, length());
376    return array[start + index];
377  }
378
379  /**
380   * Returns the smallest index for which {@link #get} returns {@code target}, or {@code -1} if no
381   * such index exists. Values are compared as if by {@link Double#equals}. Equivalent to {@code
382   * asList().indexOf(target)}.
383   */
384  public int indexOf(double target) {
385    for (int i = start; i < end; i++) {
386      if (areEqual(array[i], target)) {
387        return i - start;
388      }
389    }
390    return -1;
391  }
392
393  /**
394   * Returns the largest index for which {@link #get} returns {@code target}, or {@code -1} if no
395   * such index exists. Values are compared as if by {@link Double#equals}. Equivalent to {@code
396   * asList().lastIndexOf(target)}.
397   */
398  public int lastIndexOf(double target) {
399    for (int i = end - 1; i >= start; i--) {
400      if (areEqual(array[i], target)) {
401        return i - start;
402      }
403    }
404    return -1;
405  }
406
407  /**
408   * Returns {@code true} if {@code target} is present at any index in this array. Values are
409   * compared as if by {@link Double#equals}. Equivalent to {@code asList().contains(target)}.
410   */
411  public boolean contains(double target) {
412    return indexOf(target) >= 0;
413  }
414
415  /** Invokes {@code consumer} for each value contained in this array, in order. */
416  public void forEach(DoubleConsumer consumer) {
417    checkNotNull(consumer);
418    for (int i = start; i < end; i++) {
419      consumer.accept(array[i]);
420    }
421  }
422
423  /** Returns a stream over the values in this array, in order. */
424  public DoubleStream stream() {
425    return Arrays.stream(array, start, end);
426  }
427
428  /** Returns a new, mutable copy of this array's values, as a primitive {@code double[]}. */
429  public double[] toArray() {
430    return Arrays.copyOfRange(array, start, end);
431  }
432
433  /**
434   * Returns a new immutable array containing the values in the specified range.
435   *
436   * <p><b>Performance note:</b> The returned array has the same full memory footprint as this one
437   * does (no actual copying is performed). To reduce memory usage, use {@code subArray(start,
438   * end).trimmed()}.
439   */
440  public ImmutableDoubleArray subArray(int startIndex, int endIndex) {
441    Preconditions.checkPositionIndexes(startIndex, endIndex, length());
442    return startIndex == endIndex
443        ? EMPTY
444        : new ImmutableDoubleArray(array, start + startIndex, start + endIndex);
445  }
446
447  private Spliterator.OfDouble spliterator() {
448    return Spliterators.spliterator(array, start, end, Spliterator.IMMUTABLE | Spliterator.ORDERED);
449  }
450
451  /**
452   * Returns an immutable <i>view</i> of this array's values as a {@code List}; note that {@code
453   * double} values are boxed into {@link Double} instances on demand, which can be very expensive.
454   * The returned list should be used once and discarded. For any usages beyond that, pass the
455   * returned list to {@link com.google.common.collect.ImmutableList#copyOf(Collection)
456   * ImmutableList.copyOf} and use that list instead.
457   */
458  public List<Double> asList() {
459    /*
460     * Typically we cache this kind of thing, but much repeated use of this view is a performance
461     * anti-pattern anyway. If we cache, then everyone pays a price in memory footprint even if
462     * they never use this method.
463     */
464    return new AsList(this);
465  }
466
467  static class AsList extends AbstractList<Double> implements RandomAccess, Serializable {
468    private final ImmutableDoubleArray parent;
469
470    private AsList(ImmutableDoubleArray parent) {
471      this.parent = parent;
472    }
473
474    // inherit: isEmpty, containsAll, toArray x2, iterator, listIterator, stream, forEach, mutations
475
476    @Override
477    public int size() {
478      return parent.length();
479    }
480
481    @Override
482    public Double get(int index) {
483      return parent.get(index);
484    }
485
486    @Override
487    public boolean contains(@CheckForNull Object target) {
488      return indexOf(target) >= 0;
489    }
490
491    @Override
492    public int indexOf(@CheckForNull Object target) {
493      return target instanceof Double ? parent.indexOf((Double) target) : -1;
494    }
495
496    @Override
497    public int lastIndexOf(@CheckForNull Object target) {
498      return target instanceof Double ? parent.lastIndexOf((Double) target) : -1;
499    }
500
501    @Override
502    public List<Double> subList(int fromIndex, int toIndex) {
503      return parent.subArray(fromIndex, toIndex).asList();
504    }
505
506    // The default List spliterator is not efficiently splittable
507    @Override
508    public Spliterator<Double> spliterator() {
509      return parent.spliterator();
510    }
511
512    @Override
513    public boolean equals(@CheckForNull Object object) {
514      if (object instanceof AsList) {
515        AsList that = (AsList) object;
516        return this.parent.equals(that.parent);
517      }
518      // We could delegate to super now but it would still box too much
519      if (!(object instanceof List)) {
520        return false;
521      }
522      List<?> that = (List<?>) object;
523      if (this.size() != that.size()) {
524        return false;
525      }
526      int i = parent.start;
527      // Since `that` is very likely RandomAccess we could avoid allocating this iterator...
528      for (Object element : that) {
529        if (!(element instanceof Double) || !areEqual(parent.array[i++], (Double) element)) {
530          return false;
531        }
532      }
533      return true;
534    }
535
536    // Because we happen to use the same formula. If that changes, just don't override this.
537    @Override
538    public int hashCode() {
539      return parent.hashCode();
540    }
541
542    @Override
543    public String toString() {
544      return parent.toString();
545    }
546  }
547
548  /**
549   * Returns {@code true} if {@code object} is an {@code ImmutableDoubleArray} containing the same
550   * values as this one, in the same order. Values are compared as if by {@link Double#equals}.
551   */
552  @Override
553  public boolean equals(@CheckForNull Object object) {
554    if (object == this) {
555      return true;
556    }
557    if (!(object instanceof ImmutableDoubleArray)) {
558      return false;
559    }
560    ImmutableDoubleArray that = (ImmutableDoubleArray) object;
561    if (this.length() != that.length()) {
562      return false;
563    }
564    for (int i = 0; i < length(); i++) {
565      if (!areEqual(this.get(i), that.get(i))) {
566        return false;
567      }
568    }
569    return true;
570  }
571
572  // Match the behavior of Double.equals()
573  private static boolean areEqual(double a, double b) {
574    return Double.doubleToLongBits(a) == Double.doubleToLongBits(b);
575  }
576
577  /** Returns an unspecified hash code for the contents of this immutable array. */
578  @Override
579  public int hashCode() {
580    int hash = 1;
581    for (int i = start; i < end; i++) {
582      hash *= 31;
583      hash += Doubles.hashCode(array[i]);
584    }
585    return hash;
586  }
587
588  /**
589   * Returns a string representation of this array in the same form as {@link
590   * Arrays#toString(double[])}, for example {@code "[1, 2, 3]"}.
591   */
592  @Override
593  public String toString() {
594    if (isEmpty()) {
595      return "[]";
596    }
597    StringBuilder builder = new StringBuilder(length() * 5); // rough estimate is fine
598    builder.append('[').append(array[start]);
599
600    for (int i = start + 1; i < end; i++) {
601      builder.append(", ").append(array[i]);
602    }
603    builder.append(']');
604    return builder.toString();
605  }
606
607  /**
608   * Returns an immutable array containing the same values as {@code this} array. This is logically
609   * a no-op, and in some circumstances {@code this} itself is returned. However, if this instance
610   * is a {@link #subArray} view of a larger array, this method will copy only the appropriate range
611   * of values, resulting in an equivalent array with a smaller memory footprint.
612   */
613  public ImmutableDoubleArray trimmed() {
614    return isPartialView() ? new ImmutableDoubleArray(toArray()) : this;
615  }
616
617  private boolean isPartialView() {
618    return start > 0 || end < array.length;
619  }
620
621  Object writeReplace() {
622    return trimmed();
623  }
624
625  Object readResolve() {
626    return isEmpty() ? EMPTY : this;
627  }
628}