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.LongConsumer;
035import java.util.stream.LongStream;
036import org.checkerframework.checker.nullness.qual.Nullable;
037
038/**
039 * An immutable array of {@code long} values, with an API resembling {@link List}.
040 *
041 * <p>Advantages compared to {@code long[]}:
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 Longs} 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.getBarLongs().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 long[]}:
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 long[]} (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 * <Long>}:
070 *
071 * <ul>
072 *   <li>Improved memory compactness and locality.
073 *   <li>Can be queried without allocating garbage.
074 *   <li>Access to {@code LongStream} features (like {@link LongStream#sum}) using {@code stream()}
075 *       instead of the awkward {@code stream().mapToLong(v -> v)}.
076 * </ul>
077 *
078 * <p>Disadvantages compared to {@code ImmutableList<Long>}:
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 ImmutableLongArray implements Serializable {
092  private static final ImmutableLongArray EMPTY = new ImmutableLongArray(new long[0]);
093
094  /** Returns the empty array. */
095  public static ImmutableLongArray of() {
096    return EMPTY;
097  }
098
099  /** Returns an immutable array containing a single value. */
100  public static ImmutableLongArray of(long e0) {
101    return new ImmutableLongArray(new long[] {e0});
102  }
103
104  /** Returns an immutable array containing the given values, in order. */
105  public static ImmutableLongArray of(long e0, long e1) {
106    return new ImmutableLongArray(new long[] {e0, e1});
107  }
108
109  /** Returns an immutable array containing the given values, in order. */
110  public static ImmutableLongArray of(long e0, long e1, long e2) {
111    return new ImmutableLongArray(new long[] {e0, e1, e2});
112  }
113
114  /** Returns an immutable array containing the given values, in order. */
115  public static ImmutableLongArray of(long e0, long e1, long e2, long e3) {
116    return new ImmutableLongArray(new long[] {e0, e1, e2, e3});
117  }
118
119  /** Returns an immutable array containing the given values, in order. */
120  public static ImmutableLongArray of(long e0, long e1, long e2, long e3, long e4) {
121    return new ImmutableLongArray(new long[] {e0, e1, e2, e3, e4});
122  }
123
124  /** Returns an immutable array containing the given values, in order. */
125  public static ImmutableLongArray of(long e0, long e1, long e2, long e3, long e4, long e5) {
126    return new ImmutableLongArray(new long[] {e0, e1, e2, e3, e4, e5});
127  }
128
129  // TODO(kevinb): go up to 11?
130
131  /**
132   * Returns an immutable array containing the given values, in order.
133   *
134   * <p>The array {@code rest} must not be longer than {@code Integer.MAX_VALUE - 1}.
135   */
136  // Use (first, rest) so that `of(someLongArray)` won't compile (they should use copyOf), which is
137  // okay since we have to copy the just-created array anyway.
138  public static ImmutableLongArray of(long first, long... rest) {
139    checkArgument(
140        rest.length <= Integer.MAX_VALUE - 1,
141        "the total number of elements must fit in an int");
142    long[] array = new long[rest.length + 1];
143    array[0] = first;
144    System.arraycopy(rest, 0, array, 1, rest.length);
145    return new ImmutableLongArray(array);
146  }
147
148  /** Returns an immutable array containing the given values, in order. */
149  public static ImmutableLongArray copyOf(long[] values) {
150    return values.length == 0
151        ? EMPTY
152        : new ImmutableLongArray(Arrays.copyOf(values, values.length));
153  }
154
155  /** Returns an immutable array containing the given values, in order. */
156  public static ImmutableLongArray copyOf(Collection<Long> values) {
157    return values.isEmpty() ? EMPTY : new ImmutableLongArray(Longs.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 ImmutableLongArray copyOf(Iterable<Long> values) {
168    if (values instanceof Collection) {
169      return copyOf((Collection<Long>) 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 ImmutableLongArray copyOf(LongStream stream) {
176    // Note this uses very different growth behavior from copyOf(Iterable) and the builder.
177    long[] array = stream.toArray();
178    return (array.length == 0) ? EMPTY : new ImmutableLongArray(array);
179  }
180
181  /**
182   * Returns a new, empty builder for {@link ImmutableLongArray} 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   * ImmutableLongArray} that is built will very likely occupy more memory than strictly necessary;
189   * 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 ImmutableLongArray} instances, with a default initial
198   * capacity. The returned builder is not thread-safe.
199   *
200   * <p><b>Performance note:</b> The {@link ImmutableLongArray} 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 ImmutableLongArray} instances; obtained using {@link
210   * ImmutableLongArray#builder}.
211   */
212  @CanIgnoreReturnValue
213  public static final class Builder {
214    private long[] array;
215    private int count = 0; // <= array.length
216
217    Builder(int initialCapacity) {
218      array = new long[initialCapacity];
219    }
220
221    /**
222     * Appends {@code value} to the end of the values the built {@link ImmutableLongArray} will
223     * contain.
224     */
225    public Builder add(long 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     * ImmutableLongArray} will contain.
235     */
236    public Builder addAll(long[] 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     * ImmutableLongArray} will contain.
246     */
247    public Builder addAll(Iterable<Long> values) {
248      if (values instanceof Collection) {
249        return addAll((Collection<Long>) values);
250      }
251      for (Long 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     * ImmutableLongArray} will contain.
260     */
261    public Builder addAll(Collection<Long> values) {
262      ensureRoomFor(values.size());
263      for (Long 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     * ImmutableLongArray} will contain.
272     */
273    public Builder addAll(LongStream stream) {
274      Spliterator.OfLong spliterator = stream.spliterator();
275      long size = spliterator.getExactSizeIfKnown();
276      if (size > 0) { // known *and* nonempty
277        ensureRoomFor(Ints.saturatedCast(size));
278      }
279      spliterator.forEachRemaining((LongConsumer) this::add);
280      return this;
281    }
282
283    /**
284     * Appends {@code values}, in order, to the end of the values the built {@link
285     * ImmutableLongArray} will contain.
286     */
287    public Builder addAll(ImmutableLongArray 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        long[] newArray = new long[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 ImmutableLongArray build() {
329      return count == 0 ? EMPTY : new ImmutableLongArray(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 long[] 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 ImmutableLongArray(long[] array) {
350    this(array, 0, array.length);
351  }
352
353  private ImmutableLongArray(long[] 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 long} 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 long 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. Equivalent to {@code asList().indexOf(target)}.
383   */
384  public int indexOf(long target) {
385    for (int i = start; i < end; i++) {
386      if (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. Equivalent to {@code asList().lastIndexOf(target)}.
396   */
397  public int lastIndexOf(long target) {
398    for (int i = end - 1; i >= start; i--) {
399      if (array[i] == target) {
400        return i - start;
401      }
402    }
403    return -1;
404  }
405
406  /**
407   * Returns {@code true} if {@code target} is present at any index in this array. Equivalent to
408   * {@code asList().contains(target)}.
409   */
410  public boolean contains(long target) {
411    return indexOf(target) >= 0;
412  }
413
414  /** Invokes {@code consumer} for each value contained in this array, in order. */
415  public void forEach(LongConsumer consumer) {
416    checkNotNull(consumer);
417    for (int i = start; i < end; i++) {
418      consumer.accept(array[i]);
419    }
420  }
421
422  /** Returns a stream over the values in this array, in order. */
423  public LongStream stream() {
424    return Arrays.stream(array, start, end);
425  }
426
427  /** Returns a new, mutable copy of this array's values, as a primitive {@code long[]}. */
428  public long[] toArray() {
429    return Arrays.copyOfRange(array, start, end);
430  }
431
432  /**
433   * Returns a new immutable array containing the values in the specified range.
434   *
435   * <p><b>Performance note:</b> The returned array has the same full memory footprint as this one
436   * does (no actual copying is performed). To reduce memory usage, use {@code subArray(start,
437   * end).trimmed()}.
438   */
439  public ImmutableLongArray subArray(int startIndex, int endIndex) {
440    Preconditions.checkPositionIndexes(startIndex, endIndex, length());
441    return startIndex == endIndex
442        ? EMPTY
443        : new ImmutableLongArray(array, start + startIndex, start + endIndex);
444  }
445
446  private Spliterator.OfLong spliterator() {
447    return Spliterators.spliterator(array, start, end, Spliterator.IMMUTABLE | Spliterator.ORDERED);
448  }
449
450  /**
451   * Returns an immutable <i>view</i> of this array's values as a {@code List}; note that {@code
452   * long} values are boxed into {@link Long} instances on demand, which can be very expensive. The
453   * returned list should be used once and discarded. For any usages beyond that, pass the returned
454   * list to {@link com.google.common.collect.ImmutableList#copyOf(Collection) ImmutableList.copyOf}
455   * and use that list instead.
456   */
457  public List<Long> asList() {
458    /*
459     * Typically we cache this kind of thing, but much repeated use of this view is a performance
460     * anti-pattern anyway. If we cache, then everyone pays a price in memory footprint even if
461     * they never use this method.
462     */
463    return new AsList(this);
464  }
465
466  static class AsList extends AbstractList<Long> implements RandomAccess, Serializable {
467    private final ImmutableLongArray parent;
468
469    private AsList(ImmutableLongArray parent) {
470      this.parent = parent;
471    }
472
473    // inherit: isEmpty, containsAll, toArray x2, iterator, listIterator, stream, forEach, mutations
474
475    @Override
476    public int size() {
477      return parent.length();
478    }
479
480    @Override
481    public Long get(int index) {
482      return parent.get(index);
483    }
484
485    @Override
486    public boolean contains(Object target) {
487      return indexOf(target) >= 0;
488    }
489
490    @Override
491    public int indexOf(Object target) {
492      return target instanceof Long ? parent.indexOf((Long) target) : -1;
493    }
494
495    @Override
496    public int lastIndexOf(Object target) {
497      return target instanceof Long ? parent.lastIndexOf((Long) target) : -1;
498    }
499
500    @Override
501    public List<Long> subList(int fromIndex, int toIndex) {
502      return parent.subArray(fromIndex, toIndex).asList();
503    }
504
505    // The default List spliterator is not efficiently splittable
506    @Override
507    public Spliterator<Long> spliterator() {
508      return parent.spliterator();
509    }
510
511    @Override
512    public boolean equals(@Nullable Object object) {
513      if (object instanceof AsList) {
514        AsList that = (AsList) object;
515        return this.parent.equals(that.parent);
516      }
517      // We could delegate to super now but it would still box too much
518      if (!(object instanceof List)) {
519        return false;
520      }
521      List<?> that = (List<?>) object;
522      if (this.size() != that.size()) {
523        return false;
524      }
525      int i = parent.start;
526      // Since `that` is very likely RandomAccess we could avoid allocating this iterator...
527      for (Object element : that) {
528        if (!(element instanceof Long) || parent.array[i++] != (Long) element) {
529          return false;
530        }
531      }
532      return true;
533    }
534
535    // Because we happen to use the same formula. If that changes, just don't override this.
536    @Override
537    public int hashCode() {
538      return parent.hashCode();
539    }
540
541    @Override
542    public String toString() {
543      return parent.toString();
544    }
545  }
546
547  /**
548   * Returns {@code true} if {@code object} is an {@code ImmutableLongArray} containing the same
549   * values as this one, in the same order.
550   */
551  @Override
552  public boolean equals(@Nullable Object object) {
553    if (object == this) {
554      return true;
555    }
556    if (!(object instanceof ImmutableLongArray)) {
557      return false;
558    }
559    ImmutableLongArray that = (ImmutableLongArray) object;
560    if (this.length() != that.length()) {
561      return false;
562    }
563    for (int i = 0; i < length(); i++) {
564      if (this.get(i) != that.get(i)) {
565        return false;
566      }
567    }
568    return true;
569  }
570
571  /** Returns an unspecified hash code for the contents of this immutable array. */
572  @Override
573  public int hashCode() {
574    int hash = 1;
575    for (int i = start; i < end; i++) {
576      hash *= 31;
577      hash += Longs.hashCode(array[i]);
578    }
579    return hash;
580  }
581
582  /**
583   * Returns a string representation of this array in the same form as {@link
584   * Arrays#toString(long[])}, for example {@code "[1, 2, 3]"}.
585   */
586  @Override
587  public String toString() {
588    if (isEmpty()) {
589      return "[]";
590    }
591    StringBuilder builder = new StringBuilder(length() * 5); // rough estimate is fine
592    builder.append('[').append(array[start]);
593
594    for (int i = start + 1; i < end; i++) {
595      builder.append(", ").append(array[i]);
596    }
597    builder.append(']');
598    return builder.toString();
599  }
600
601  /**
602   * Returns an immutable array containing the same values as {@code this} array. This is logically
603   * a no-op, and in some circumstances {@code this} itself is returned. However, if this instance
604   * is a {@link #subArray} view of a larger array, this method will copy only the appropriate range
605   * of values, resulting in an equivalent array with a smaller memory footprint.
606   */
607  public ImmutableLongArray trimmed() {
608    return isPartialView() ? new ImmutableLongArray(toArray()) : this;
609  }
610
611  private boolean isPartialView() {
612    return start > 0 || end < array.length;
613  }
614
615  Object writeReplace() {
616    return trimmed();
617  }
618
619  Object readResolve() {
620    return isEmpty() ? EMPTY : this;
621  }
622}