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.Immutable;
025import java.io.Serializable;
026import java.util.AbstractList;
027import java.util.Arrays;
028import java.util.Collection;
029import java.util.List;
030import java.util.RandomAccess;
031import java.util.Spliterator;
032import java.util.Spliterators;
033import java.util.function.DoubleConsumer;
034import java.util.stream.DoubleStream;
035import javax.annotation.CheckReturnValue;
036import javax.annotation.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>, 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 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  /** Returns an immutable array containing the given values, in order. */
133  // Use (first, rest) so that `of(someDoubleArray)` won't compile (they should use copyOf), which
134  // is okay since we have to copy the just-created array anyway.
135  public static ImmutableDoubleArray of(double first, double... rest) {
136    double[] array = new double[rest.length + 1];
137    array[0] = first;
138    System.arraycopy(rest, 0, array, 1, rest.length);
139    return new ImmutableDoubleArray(array);
140  }
141
142  /** Returns an immutable array containing the given values, in order. */
143  public static ImmutableDoubleArray copyOf(double[] values) {
144    return values.length == 0
145        ? EMPTY
146        : new ImmutableDoubleArray(Arrays.copyOf(values, values.length));
147  }
148
149  /** Returns an immutable array containing the given values, in order. */
150  public static ImmutableDoubleArray copyOf(Collection<Double> values) {
151    return values.isEmpty() ? EMPTY : new ImmutableDoubleArray(Doubles.toArray(values));
152  }
153
154  /**
155   * Returns an immutable array containing the given values, in order.
156   *
157   * <p><b>Performance note:</b> this method delegates to {@link #copyOf(Collection)} if {@code
158   * values} is a {@link Collection}. Otherwise it creates a {@link #builder} and uses {@link
159   * Builder#addAll(Iterable)}, with all the performance implications associated with that.
160   */
161  public static ImmutableDoubleArray copyOf(Iterable<Double> values) {
162    if (values instanceof Collection) {
163      return copyOf((Collection<Double>) values);
164    }
165    return builder().addAll(values).build();
166  }
167
168  /** Returns an immutable array containing all the values from {@code stream}, in order. */
169  public static ImmutableDoubleArray copyOf(DoubleStream stream) {
170    // Note this uses very different growth behavior from copyOf(Iterable) and the builder.
171    double[] array = stream.toArray();
172    return (array.length == 0) ? EMPTY : new ImmutableDoubleArray(array);
173  }
174
175  /**
176   * Returns a new, empty builder for {@link ImmutableDoubleArray} instances, sized to hold up to
177   * {@code initialCapacity} values without resizing. The returned builder is not thread-safe.
178   *
179   * <p><b>Performance note:</b> When feasible, {@code initialCapacity} should be the exact number
180   * of values that will be added, if that knowledge is readily available. It is better to guess a
181   * value slightly too high than slightly too low. If the value is not exact, the {@link
182   * ImmutableDoubleArray} that is built will very likely occupy more memory than strictly
183   * necessary; to trim memory usage, build using {@code builder.build().trimmed()}.
184   */
185  public static Builder builder(int initialCapacity) {
186    checkArgument(initialCapacity >= 0, "Invalid initialCapacity: %s", initialCapacity);
187    return new Builder(initialCapacity);
188  }
189
190  /**
191   * Returns a new, empty builder for {@link ImmutableDoubleArray} instances, with a default initial
192   * capacity. The returned builder is not thread-safe.
193   *
194   * <p><b>Performance note:</b> The {@link ImmutableDoubleArray} that is built will very likely
195   * occupy more memory than necessary; to trim memory usage, build using {@code
196   * builder.build().trimmed()}.
197   */
198  public static Builder builder() {
199    return new Builder(10);
200  }
201
202  /**
203   * A builder for {@link ImmutableDoubleArray} instances; obtained using {@link
204   * ImmutableDoubleArray#builder}.
205   */
206  @CanIgnoreReturnValue
207  public static final class Builder {
208    private double[] array;
209    private int count = 0; // <= array.length
210
211    Builder(int initialCapacity) {
212      array = new double[initialCapacity];
213    }
214
215    /**
216     * Appends {@code value} to the end of the values the built {@link ImmutableDoubleArray} will
217     * contain.
218     */
219    public Builder add(double value) {
220      ensureRoomFor(1);
221      array[count] = value;
222      count += 1;
223      return this;
224    }
225
226    /**
227     * Appends {@code values}, in order, to the end of the values the built {@link
228     * ImmutableDoubleArray} will contain.
229     */
230    public Builder addAll(double[] values) {
231      ensureRoomFor(values.length);
232      System.arraycopy(values, 0, array, count, values.length);
233      count += values.length;
234      return this;
235    }
236
237    /**
238     * Appends {@code values}, in order, to the end of the values the built {@link
239     * ImmutableDoubleArray} will contain.
240     */
241    public Builder addAll(Iterable<Double> values) {
242      if (values instanceof Collection) {
243        return addAll((Collection<Double>) values);
244      }
245      for (Double value : values) {
246        add(value);
247      }
248      return this;
249    }
250
251    /**
252     * Appends {@code values}, in order, to the end of the values the built {@link
253     * ImmutableDoubleArray} will contain.
254     */
255    public Builder addAll(Collection<Double> values) {
256      ensureRoomFor(values.size());
257      for (Double value : values) {
258        array[count++] = value;
259      }
260      return this;
261    }
262
263    /**
264     * Appends all values from {@code stream}, in order, to the end of the values the built {@link
265     * ImmutableDoubleArray} will contain.
266     */
267    public Builder addAll(DoubleStream stream) {
268      Spliterator.OfDouble spliterator = stream.spliterator();
269      long size = spliterator.getExactSizeIfKnown();
270      if (size > 0) { // known *and* nonempty
271        ensureRoomFor(Ints.saturatedCast(size));
272      }
273      spliterator.forEachRemaining((DoubleConsumer) this::add);
274      return this;
275    }
276
277    /**
278     * Appends {@code values}, in order, to the end of the values the built {@link
279     * ImmutableDoubleArray} will contain.
280     */
281    public Builder addAll(ImmutableDoubleArray values) {
282      ensureRoomFor(values.length());
283      System.arraycopy(values.array, values.start, array, count, values.length());
284      count += values.length();
285      return this;
286    }
287
288    private void ensureRoomFor(int numberToAdd) {
289      int newCount = count + numberToAdd; // TODO(kevinb): check overflow now?
290      if (newCount > array.length) {
291        double[] newArray = new double[expandedCapacity(array.length, newCount)];
292        System.arraycopy(array, 0, newArray, 0, count);
293        this.array = newArray;
294      }
295    }
296
297    // Unfortunately this is pasted from ImmutableCollection.Builder.
298    private static int expandedCapacity(int oldCapacity, int minCapacity) {
299      if (minCapacity < 0) {
300        throw new AssertionError("cannot store more than MAX_VALUE elements");
301      }
302      // careful of overflow!
303      int newCapacity = oldCapacity + (oldCapacity >> 1) + 1;
304      if (newCapacity < minCapacity) {
305        newCapacity = Integer.highestOneBit(minCapacity - 1) << 1;
306      }
307      if (newCapacity < 0) {
308        newCapacity = Integer.MAX_VALUE; // guaranteed to be >= newCapacity
309      }
310      return newCapacity;
311    }
312
313    /**
314     * Returns a new immutable array. The builder can continue to be used after this call, to append
315     * more values and build again.
316     *
317     * <p><b>Performance note:</b> the returned array is backed by the same array as the builder, so
318     * no data is copied as part of this step, but this may occupy more memory than strictly
319     * necessary. To copy the data to a right-sized backing array, use {@code .build().trimmed()}.
320     */
321    @CheckReturnValue
322    public ImmutableDoubleArray build() {
323      return count == 0 ? EMPTY : new ImmutableDoubleArray(array, 0, count);
324    }
325  }
326
327  // Instance stuff here
328
329  // The array is never mutated after storing in this field and the construction strategies ensure
330  // it doesn't escape this class
331  @SuppressWarnings("Immutable")
332  private final double[] array;
333
334  /*
335   * TODO(kevinb): evaluate the trade-offs of going bimorphic to save these two fields from most
336   * instances. Note that the instances that would get smaller are the right set to care about
337   * optimizing, because the rest have the option of calling `trimmed`.
338   */
339
340  private final transient int start; // it happens that we only serialize instances where this is 0
341  private final int end; // exclusive
342
343  private ImmutableDoubleArray(double[] array) {
344    this(array, 0, array.length);
345  }
346
347  private ImmutableDoubleArray(double[] array, int start, int end) {
348    this.array = array;
349    this.start = start;
350    this.end = end;
351  }
352
353  /** Returns the number of values in this array. */
354  public int length() {
355    return end - start;
356  }
357
358  /** Returns {@code true} if there are no values in this array ({@link #length} is zero). */
359  public boolean isEmpty() {
360    return end == start;
361  }
362
363  /**
364   * Returns the {@code double} value present at the given index.
365   *
366   * @throws IndexOutOfBoundsException if {@code index} is negative, or greater than or equal to
367   *     {@link #length}
368   */
369  public double get(int index) {
370    Preconditions.checkElementIndex(index, length());
371    return array[start + index];
372  }
373
374  /**
375   * Returns the smallest index for which {@link #get} returns {@code target}, or {@code -1} if no
376   * such index exists. Values are compared as if by {@link Double#equals}. Equivalent to {@code
377   * asList().indexOf(target)}.
378   */
379  public int indexOf(double target) {
380    for (int i = start; i < end; i++) {
381      if (areEqual(array[i], target)) {
382        return i - start;
383      }
384    }
385    return -1;
386  }
387
388  /**
389   * Returns the largest index for which {@link #get} returns {@code target}, or {@code -1} if no
390   * such index exists. Values are compared as if by {@link Double#equals}. Equivalent to {@code
391   * asList().lastIndexOf(target)}.
392   */
393  public int lastIndexOf(double target) {
394    for (int i = end - 1; i >= start; i--) {
395      if (areEqual(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. Values are
404   * compared as if by {@link Double#equals}. Equivalent to {@code asList().contains(target)}.
405   */
406  public boolean contains(double 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(DoubleConsumer 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 DoubleStream 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 double[]}. */
424  public double[] 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 ImmutableDoubleArray subArray(int startIndex, int endIndex) {
436    Preconditions.checkPositionIndexes(startIndex, endIndex, length());
437    return startIndex == endIndex
438        ? EMPTY
439        : new ImmutableDoubleArray(array, start + startIndex, start + endIndex);
440  }
441
442  private Spliterator.OfDouble 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   * double} values are boxed into {@link Double} 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<Double> 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<Double> implements RandomAccess, Serializable {
463    private final ImmutableDoubleArray parent;
464
465    private AsList(ImmutableDoubleArray 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 Double get(int index) {
478      return parent.get(index);
479    }
480
481    @Override
482    public boolean contains(Object target) {
483      return indexOf(target) >= 0;
484    }
485
486    @Override
487    public int indexOf(Object target) {
488      return target instanceof Double ? parent.indexOf((Double) target) : -1;
489    }
490
491    @Override
492    public int lastIndexOf(Object target) {
493      return target instanceof Double ? parent.lastIndexOf((Double) target) : -1;
494    }
495
496    @Override
497    public List<Double> 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<Double> spliterator() {
504      return parent.spliterator();
505    }
506
507    @Override
508    public boolean equals(@Nullable 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 Double) || !areEqual(parent.array[i++], (Double) 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 ImmutableDoubleArray} containing the same
545   * values as this one, in the same order. Values are compared as if by {@link Double#equals}.
546   */
547  @Override
548  public boolean equals(@Nullable Object object) {
549    if (object == this) {
550      return true;
551    }
552    if (!(object instanceof ImmutableDoubleArray)) {
553      return false;
554    }
555    ImmutableDoubleArray that = (ImmutableDoubleArray) object;
556    if (this.length() != that.length()) {
557      return false;
558    }
559    for (int i = 0; i < length(); i++) {
560      if (!areEqual(this.get(i), that.get(i))) {
561        return false;
562      }
563    }
564    return true;
565  }
566
567  // Match the behavior of Double.equals()
568  private static boolean areEqual(double a, double b) {
569    return Double.doubleToLongBits(a) == Double.doubleToLongBits(b);
570  }
571
572  /** Returns an unspecified hash code for the contents of this immutable array. */
573  @Override
574  public int hashCode() {
575    int hash = 1;
576    for (int i = start; i < end; i++) {
577      hash *= 31;
578      hash += Doubles.hashCode(array[i]);
579    }
580    return hash;
581  }
582
583  /**
584   * Returns a string representation of this array in the same form as {@link
585   * Arrays#toString(double[])}, for example {@code "[1, 2, 3]"}.
586   */
587  @Override
588  public String toString() {
589    if (isEmpty()) {
590      return "[]";
591    }
592    StringBuilder builder = new StringBuilder(length() * 5); // rough estimate is fine
593    builder.append('[').append(array[start]);
594
595    for (int i = start + 1; i < end; i++) {
596      builder.append(", ").append(array[i]);
597    }
598    builder.append(']');
599    return builder.toString();
600  }
601
602  /**
603   * Returns an immutable array containing the same values as {@code this} array. This is logically
604   * a no-op, and in some circumstances {@code this} itself is returned. However, if this instance
605   * is a {@link #subArray} view of a larger array, this method will copy only the appropriate range
606   * of values, resulting in an equivalent array with a smaller memory footprint.
607   */
608  public ImmutableDoubleArray trimmed() {
609    return isPartialView() ? new ImmutableDoubleArray(toArray()) : this;
610  }
611
612  private boolean isPartialView() {
613    return start > 0 || end < array.length;
614  }
615
616  Object writeReplace() {
617    return trimmed();
618  }
619
620  Object readResolve() {
621    return isEmpty() ? EMPTY : this;
622  }
623}