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 org.checkerframework.checker.nullness.qual.Nullable;
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
091public final class ImmutableDoubleArray implements Serializable {
092  private static final ImmutableDoubleArray EMPTY = new ImmutableDoubleArray(new double[0]);
093
094  /** Returns the empty array. */
095  public static ImmutableDoubleArray of() {
096    return EMPTY;
097  }
098
099  /** Returns an immutable array containing a single value. */
100  public static ImmutableDoubleArray of(double e0) {
101    return new ImmutableDoubleArray(new double[] {e0});
102  }
103
104  /** Returns an immutable array containing the given values, in order. */
105  public static ImmutableDoubleArray of(double e0, double e1) {
106    return new ImmutableDoubleArray(new double[] {e0, e1});
107  }
108
109  /** Returns an immutable array containing the given values, in order. */
110  public static ImmutableDoubleArray of(double e0, double e1, double e2) {
111    return new ImmutableDoubleArray(new double[] {e0, e1, e2});
112  }
113
114  /** Returns an immutable array containing the given values, in order. */
115  public static ImmutableDoubleArray of(double e0, double e1, double e2, double e3) {
116    return new ImmutableDoubleArray(new double[] {e0, e1, e2, e3});
117  }
118
119  /** Returns an immutable array containing the given values, in order. */
120  public static ImmutableDoubleArray of(double e0, double e1, double e2, double e3, double e4) {
121    return new ImmutableDoubleArray(new double[] {e0, e1, e2, e3, e4});
122  }
123
124  /** Returns an immutable array containing the given values, in order. */
125  public static ImmutableDoubleArray of(
126      double e0, double e1, double e2, double e3, double e4, double e5) {
127    return new ImmutableDoubleArray(new double[] {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(someDoubleArray)` won't compile (they should use copyOf), which
138  // is okay since we have to copy the just-created array anyway.
139  public static ImmutableDoubleArray of(double first, double... rest) {
140    checkArgument(
141        rest.length <= Integer.MAX_VALUE - 1, "the total number of elements must fit in an int");
142    double[] array = new double[rest.length + 1];
143    array[0] = first;
144    System.arraycopy(rest, 0, array, 1, rest.length);
145    return new ImmutableDoubleArray(array);
146  }
147
148  /** Returns an immutable array containing the given values, in order. */
149  public static ImmutableDoubleArray copyOf(double[] values) {
150    return values.length == 0
151        ? EMPTY
152        : new ImmutableDoubleArray(Arrays.copyOf(values, values.length));
153  }
154
155  /** Returns an immutable array containing the given values, in order. */
156  public static ImmutableDoubleArray copyOf(Collection<Double> values) {
157    return values.isEmpty() ? EMPTY : new ImmutableDoubleArray(Doubles.toArray(values));
158  }
159
160  /**
161   * Returns an immutable array containing the given values, in order.
162   *
163   * <p><b>Performance note:</b> this method delegates to {@link #copyOf(Collection)} if {@code
164   * values} is a {@link Collection}. Otherwise it creates a {@link #builder} and uses {@link
165   * Builder#addAll(Iterable)}, with all the performance implications associated with that.
166   */
167  public static ImmutableDoubleArray copyOf(Iterable<Double> values) {
168    if (values instanceof Collection) {
169      return copyOf((Collection<Double>) values);
170    }
171    return builder().addAll(values).build();
172  }
173
174  /** Returns an immutable array containing all the values from {@code stream}, in order. */
175  public static ImmutableDoubleArray copyOf(DoubleStream stream) {
176    // Note this uses very different growth behavior from copyOf(Iterable) and the builder.
177    double[] array = stream.toArray();
178    return (array.length == 0) ? EMPTY : new ImmutableDoubleArray(array);
179  }
180
181  /**
182   * Returns a new, empty builder for {@link ImmutableDoubleArray} instances, sized to hold up to
183   * {@code initialCapacity} values without resizing. The returned builder is not thread-safe.
184   *
185   * <p><b>Performance note:</b> When feasible, {@code initialCapacity} should be the exact number
186   * of values that will be added, if that knowledge is readily available. It is better to guess a
187   * value slightly too high than slightly too low. If the value is not exact, the {@link
188   * ImmutableDoubleArray} that is built will very likely occupy more memory than strictly
189   * necessary; to trim memory usage, build using {@code builder.build().trimmed()}.
190   */
191  public static Builder builder(int initialCapacity) {
192    checkArgument(initialCapacity >= 0, "Invalid initialCapacity: %s", initialCapacity);
193    return new Builder(initialCapacity);
194  }
195
196  /**
197   * Returns a new, empty builder for {@link ImmutableDoubleArray} instances, with a default initial
198   * capacity. The returned builder is not thread-safe.
199   *
200   * <p><b>Performance note:</b> The {@link ImmutableDoubleArray} that is built will very likely
201   * occupy more memory than necessary; to trim memory usage, build using {@code
202   * builder.build().trimmed()}.
203   */
204  public static Builder builder() {
205    return new Builder(10);
206  }
207
208  /**
209   * A builder for {@link ImmutableDoubleArray} instances; obtained using {@link
210   * ImmutableDoubleArray#builder}.
211   */
212  @CanIgnoreReturnValue
213  public static final class Builder {
214    private double[] array;
215    private int count = 0; // <= array.length
216
217    Builder(int initialCapacity) {
218      array = new double[initialCapacity];
219    }
220
221    /**
222     * Appends {@code value} to the end of the values the built {@link ImmutableDoubleArray} will
223     * contain.
224     */
225    public Builder add(double value) {
226      ensureRoomFor(1);
227      array[count] = value;
228      count += 1;
229      return this;
230    }
231
232    /**
233     * Appends {@code values}, in order, to the end of the values the built {@link
234     * ImmutableDoubleArray} will contain.
235     */
236    public Builder addAll(double[] values) {
237      ensureRoomFor(values.length);
238      System.arraycopy(values, 0, array, count, values.length);
239      count += values.length;
240      return this;
241    }
242
243    /**
244     * Appends {@code values}, in order, to the end of the values the built {@link
245     * ImmutableDoubleArray} will contain.
246     */
247    public Builder addAll(Iterable<Double> values) {
248      if (values instanceof Collection) {
249        return addAll((Collection<Double>) values);
250      }
251      for (Double value : values) {
252        add(value);
253      }
254      return this;
255    }
256
257    /**
258     * Appends {@code values}, in order, to the end of the values the built {@link
259     * ImmutableDoubleArray} will contain.
260     */
261    public Builder addAll(Collection<Double> values) {
262      ensureRoomFor(values.size());
263      for (Double value : values) {
264        array[count++] = value;
265      }
266      return this;
267    }
268
269    /**
270     * Appends all values from {@code stream}, in order, to the end of the values the built {@link
271     * ImmutableDoubleArray} will contain.
272     */
273    public Builder addAll(DoubleStream stream) {
274      Spliterator.OfDouble spliterator = stream.spliterator();
275      long size = spliterator.getExactSizeIfKnown();
276      if (size > 0) { // known *and* nonempty
277        ensureRoomFor(Ints.saturatedCast(size));
278      }
279      spliterator.forEachRemaining((DoubleConsumer) this::add);
280      return this;
281    }
282
283    /**
284     * Appends {@code values}, in order, to the end of the values the built {@link
285     * ImmutableDoubleArray} will contain.
286     */
287    public Builder addAll(ImmutableDoubleArray values) {
288      ensureRoomFor(values.length());
289      System.arraycopy(values.array, values.start, array, count, values.length());
290      count += values.length();
291      return this;
292    }
293
294    private void ensureRoomFor(int numberToAdd) {
295      int newCount = count + numberToAdd; // TODO(kevinb): check overflow now?
296      if (newCount > array.length) {
297        double[] newArray = new double[expandedCapacity(array.length, newCount)];
298        System.arraycopy(array, 0, newArray, 0, count);
299        this.array = newArray;
300      }
301    }
302
303    // Unfortunately this is pasted from ImmutableCollection.Builder.
304    private static int expandedCapacity(int oldCapacity, int minCapacity) {
305      if (minCapacity < 0) {
306        throw new AssertionError("cannot store more than MAX_VALUE elements");
307      }
308      // careful of overflow!
309      int newCapacity = oldCapacity + (oldCapacity >> 1) + 1;
310      if (newCapacity < minCapacity) {
311        newCapacity = Integer.highestOneBit(minCapacity - 1) << 1;
312      }
313      if (newCapacity < 0) {
314        newCapacity = Integer.MAX_VALUE; // guaranteed to be >= newCapacity
315      }
316      return newCapacity;
317    }
318
319    /**
320     * Returns a new immutable array. The builder can continue to be used after this call, to append
321     * more values and build again.
322     *
323     * <p><b>Performance note:</b> the returned array is backed by the same array as the builder, so
324     * no data is copied as part of this step, but this may occupy more memory than strictly
325     * necessary. To copy the data to a right-sized backing array, use {@code .build().trimmed()}.
326     */
327    @CheckReturnValue
328    public ImmutableDoubleArray build() {
329      return count == 0 ? EMPTY : new ImmutableDoubleArray(array, 0, count);
330    }
331  }
332
333  // Instance stuff here
334
335  // The array is never mutated after storing in this field and the construction strategies ensure
336  // it doesn't escape this class
337  @SuppressWarnings("Immutable")
338  private final double[] array;
339
340  /*
341   * TODO(kevinb): evaluate the trade-offs of going bimorphic to save these two fields from most
342   * instances. Note that the instances that would get smaller are the right set to care about
343   * optimizing, because the rest have the option of calling `trimmed`.
344   */
345
346  private final transient int start; // it happens that we only serialize instances where this is 0
347  private final int end; // exclusive
348
349  private ImmutableDoubleArray(double[] array) {
350    this(array, 0, array.length);
351  }
352
353  private ImmutableDoubleArray(double[] array, int start, int end) {
354    this.array = array;
355    this.start = start;
356    this.end = end;
357  }
358
359  /** Returns the number of values in this array. */
360  public int length() {
361    return end - start;
362  }
363
364  /** Returns {@code true} if there are no values in this array ({@link #length} is zero). */
365  public boolean isEmpty() {
366    return end == start;
367  }
368
369  /**
370   * Returns the {@code double} value present at the given index.
371   *
372   * @throws IndexOutOfBoundsException if {@code index} is negative, or greater than or equal to
373   *     {@link #length}
374   */
375  public double get(int index) {
376    Preconditions.checkElementIndex(index, length());
377    return array[start + index];
378  }
379
380  /**
381   * Returns the smallest index for which {@link #get} returns {@code target}, or {@code -1} if no
382   * such index exists. Values are compared as if by {@link Double#equals}. Equivalent to {@code
383   * asList().indexOf(target)}.
384   */
385  public int indexOf(double target) {
386    for (int i = start; i < end; i++) {
387      if (areEqual(array[i], target)) {
388        return i - start;
389      }
390    }
391    return -1;
392  }
393
394  /**
395   * Returns the largest index for which {@link #get} returns {@code target}, or {@code -1} if no
396   * such index exists. Values are compared as if by {@link Double#equals}. Equivalent to {@code
397   * asList().lastIndexOf(target)}.
398   */
399  public int lastIndexOf(double target) {
400    for (int i = end - 1; i >= start; i--) {
401      if (areEqual(array[i], target)) {
402        return i - start;
403      }
404    }
405    return -1;
406  }
407
408  /**
409   * Returns {@code true} if {@code target} is present at any index in this array. Values are
410   * compared as if by {@link Double#equals}. Equivalent to {@code asList().contains(target)}.
411   */
412  public boolean contains(double target) {
413    return indexOf(target) >= 0;
414  }
415
416  /** Invokes {@code consumer} for each value contained in this array, in order. */
417  public void forEach(DoubleConsumer consumer) {
418    checkNotNull(consumer);
419    for (int i = start; i < end; i++) {
420      consumer.accept(array[i]);
421    }
422  }
423
424  /** Returns a stream over the values in this array, in order. */
425  public DoubleStream stream() {
426    return Arrays.stream(array, start, end);
427  }
428
429  /** Returns a new, mutable copy of this array's values, as a primitive {@code double[]}. */
430  public double[] toArray() {
431    return Arrays.copyOfRange(array, start, end);
432  }
433
434  /**
435   * Returns a new immutable array containing the values in the specified range.
436   *
437   * <p><b>Performance note:</b> The returned array has the same full memory footprint as this one
438   * does (no actual copying is performed). To reduce memory usage, use {@code subArray(start,
439   * end).trimmed()}.
440   */
441  public ImmutableDoubleArray subArray(int startIndex, int endIndex) {
442    Preconditions.checkPositionIndexes(startIndex, endIndex, length());
443    return startIndex == endIndex
444        ? EMPTY
445        : new ImmutableDoubleArray(array, start + startIndex, start + endIndex);
446  }
447
448  private Spliterator.OfDouble spliterator() {
449    return Spliterators.spliterator(array, start, end, Spliterator.IMMUTABLE | Spliterator.ORDERED);
450  }
451
452  /**
453   * Returns an immutable <i>view</i> of this array's values as a {@code List}; note that {@code
454   * double} values are boxed into {@link Double} instances on demand, which can be very expensive.
455   * The returned list should be used once and discarded. For any usages beyond that, pass the
456   * returned list to {@link com.google.common.collect.ImmutableList#copyOf(Collection)
457   * ImmutableList.copyOf} and use that list instead.
458   */
459  public List<Double> asList() {
460    /*
461     * Typically we cache this kind of thing, but much repeated use of this view is a performance
462     * anti-pattern anyway. If we cache, then everyone pays a price in memory footprint even if
463     * they never use this method.
464     */
465    return new AsList(this);
466  }
467
468  static class AsList extends AbstractList<Double> implements RandomAccess, Serializable {
469    private final ImmutableDoubleArray parent;
470
471    private AsList(ImmutableDoubleArray parent) {
472      this.parent = parent;
473    }
474
475    // inherit: isEmpty, containsAll, toArray x2, iterator, listIterator, stream, forEach, mutations
476
477    @Override
478    public int size() {
479      return parent.length();
480    }
481
482    @Override
483    public Double get(int index) {
484      return parent.get(index);
485    }
486
487    @Override
488    public boolean contains(Object target) {
489      return indexOf(target) >= 0;
490    }
491
492    @Override
493    public int indexOf(Object target) {
494      return target instanceof Double ? parent.indexOf((Double) target) : -1;
495    }
496
497    @Override
498    public int lastIndexOf(Object target) {
499      return target instanceof Double ? parent.lastIndexOf((Double) target) : -1;
500    }
501
502    @Override
503    public List<Double> subList(int fromIndex, int toIndex) {
504      return parent.subArray(fromIndex, toIndex).asList();
505    }
506
507    // The default List spliterator is not efficiently splittable
508    @Override
509    public Spliterator<Double> spliterator() {
510      return parent.spliterator();
511    }
512
513    @Override
514    public boolean equals(@Nullable Object object) {
515      if (object instanceof AsList) {
516        AsList that = (AsList) object;
517        return this.parent.equals(that.parent);
518      }
519      // We could delegate to super now but it would still box too much
520      if (!(object instanceof List)) {
521        return false;
522      }
523      List<?> that = (List<?>) object;
524      if (this.size() != that.size()) {
525        return false;
526      }
527      int i = parent.start;
528      // Since `that` is very likely RandomAccess we could avoid allocating this iterator...
529      for (Object element : that) {
530        if (!(element instanceof Double) || !areEqual(parent.array[i++], (Double) element)) {
531          return false;
532        }
533      }
534      return true;
535    }
536
537    // Because we happen to use the same formula. If that changes, just don't override this.
538    @Override
539    public int hashCode() {
540      return parent.hashCode();
541    }
542
543    @Override
544    public String toString() {
545      return parent.toString();
546    }
547  }
548
549  /**
550   * Returns {@code true} if {@code object} is an {@code ImmutableDoubleArray} containing the same
551   * values as this one, in the same order. Values are compared as if by {@link Double#equals}.
552   */
553  @Override
554  public boolean equals(@Nullable Object object) {
555    if (object == this) {
556      return true;
557    }
558    if (!(object instanceof ImmutableDoubleArray)) {
559      return false;
560    }
561    ImmutableDoubleArray that = (ImmutableDoubleArray) object;
562    if (this.length() != that.length()) {
563      return false;
564    }
565    for (int i = 0; i < length(); i++) {
566      if (!areEqual(this.get(i), that.get(i))) {
567        return false;
568      }
569    }
570    return true;
571  }
572
573  // Match the behavior of Double.equals()
574  private static boolean areEqual(double a, double b) {
575    return Double.doubleToLongBits(a) == Double.doubleToLongBits(b);
576  }
577
578  /** Returns an unspecified hash code for the contents of this immutable array. */
579  @Override
580  public int hashCode() {
581    int hash = 1;
582    for (int i = start; i < end; i++) {
583      hash *= 31;
584      hash += Doubles.hashCode(array[i]);
585    }
586    return hash;
587  }
588
589  /**
590   * Returns a string representation of this array in the same form as {@link
591   * Arrays#toString(double[])}, for example {@code "[1, 2, 3]"}.
592   */
593  @Override
594  public String toString() {
595    if (isEmpty()) {
596      return "[]";
597    }
598    StringBuilder builder = new StringBuilder(length() * 5); // rough estimate is fine
599    builder.append('[').append(array[start]);
600
601    for (int i = start + 1; i < end; i++) {
602      builder.append(", ").append(array[i]);
603    }
604    builder.append(']');
605    return builder.toString();
606  }
607
608  /**
609   * Returns an immutable array containing the same values as {@code this} array. This is logically
610   * a no-op, and in some circumstances {@code this} itself is returned. However, if this instance
611   * is a {@link #subArray} view of a larger array, this method will copy only the appropriate range
612   * of values, resulting in an equivalent array with a smaller memory footprint.
613   */
614  public ImmutableDoubleArray trimmed() {
615    return isPartialView() ? new ImmutableDoubleArray(toArray()) : this;
616  }
617
618  private boolean isPartialView() {
619    return start > 0 || end < array.length;
620  }
621
622  Object writeReplace() {
623    return trimmed();
624  }
625
626  Object readResolve() {
627    return isEmpty() ? EMPTY : this;
628  }
629}