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;
018
019import com.google.common.annotations.Beta;
020import com.google.common.annotations.GwtCompatible;
021import com.google.common.base.Preconditions;
022import com.google.errorprone.annotations.CanIgnoreReturnValue;
023import com.google.errorprone.annotations.CheckReturnValue;
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 org.checkerframework.checker.nullness.compatqual.NullableDecl;
032
033/**
034 * An immutable array of {@code long} values, with an API resembling {@link List}.
035 *
036 * <p>Advantages compared to {@code long[]}:
037 *
038 * <ul>
039 *   <li>All the many well-known advantages of immutability (read <i>Effective Java</i>, third
040 *       edition, Item 17).
041 *   <li>Has the value-based (not identity-based) {@link #equals}, {@link #hashCode}, and {@link
042 *       #toString} behavior you expect.
043 *   <li>Offers useful operations beyond just {@code get} and {@code length}, so you don't have to
044 *       hunt through classes like {@link Arrays} and {@link Longs} for them.
045 *   <li>Supports a copy-free {@link #subArray} view, so methods that accept this type don't need to
046 *       add overloads that accept start and end indexes.
047 *   <li>Access to all collection-based utilities via {@link #asList} (though at the cost of
048 *       allocating garbage).
049 * </ul>
050 *
051 * <p>Disadvantages compared to {@code long[]}:
052 *
053 * <ul>
054 *   <li>Memory footprint has a fixed overhead (about 24 bytes per instance).
055 *   <li><i>Some</i> construction use cases force the data to be copied (though several construction
056 *       APIs are offered that don't).
057 *   <li>Can't be passed directly to methods that expect {@code long[]} (though the most common
058 *       utilities do have replacements here).
059 *   <li>Dependency on {@code com.google.common} / Guava.
060 * </ul>
061 *
062 * <p>Advantages compared to {@link com.google.common.collect.ImmutableList ImmutableList}{@code
063 * <Long>}:
064 *
065 * <ul>
066 *   <li>Improved memory compactness and locality.
067 *   <li>Can be queried without allocating garbage.
068 * </ul>
069 *
070 * <p>Disadvantages compared to {@code ImmutableList<Long>}:
071 *
072 * <ul>
073 *   <li>Can't be passed directly to methods that expect {@code Iterable}, {@code Collection}, or
074 *       {@code List} (though the most common utilities do have replacements here, and there is a
075 *       lazy {@link #asList} view).
076 * </ul>
077 *
078 * @since 22.0
079 */
080@Beta
081@GwtCompatible
082@Immutable
083public final class ImmutableLongArray implements Serializable {
084  private static final ImmutableLongArray EMPTY = new ImmutableLongArray(new long[0]);
085
086  /** Returns the empty array. */
087  public static ImmutableLongArray of() {
088    return EMPTY;
089  }
090
091  /** Returns an immutable array containing a single value. */
092  public static ImmutableLongArray of(long e0) {
093    return new ImmutableLongArray(new long[] {e0});
094  }
095
096  /** Returns an immutable array containing the given values, in order. */
097  public static ImmutableLongArray of(long e0, long e1) {
098    return new ImmutableLongArray(new long[] {e0, e1});
099  }
100
101  /** Returns an immutable array containing the given values, in order. */
102  public static ImmutableLongArray of(long e0, long e1, long e2) {
103    return new ImmutableLongArray(new long[] {e0, e1, e2});
104  }
105
106  /** Returns an immutable array containing the given values, in order. */
107  public static ImmutableLongArray of(long e0, long e1, long e2, long e3) {
108    return new ImmutableLongArray(new long[] {e0, e1, e2, e3});
109  }
110
111  /** Returns an immutable array containing the given values, in order. */
112  public static ImmutableLongArray of(long e0, long e1, long e2, long e3, long e4) {
113    return new ImmutableLongArray(new long[] {e0, e1, e2, e3, e4});
114  }
115
116  /** Returns an immutable array containing the given values, in order. */
117  public static ImmutableLongArray of(long e0, long e1, long e2, long e3, long e4, long e5) {
118    return new ImmutableLongArray(new long[] {e0, e1, e2, e3, e4, e5});
119  }
120
121  // TODO(kevinb): go up to 11?
122
123  /**
124   * Returns an immutable array containing the given values, in order.
125   *
126   * <p>The array {@code rest} must not be longer than {@code Integer.MAX_VALUE - 1}.
127   */
128  // Use (first, rest) so that `of(someLongArray)` won't compile (they should use copyOf), which is
129  // okay since we have to copy the just-created array anyway.
130  public static ImmutableLongArray of(long first, long... rest) {
131    checkArgument(
132        rest.length <= Integer.MAX_VALUE - 1, "the total number of elements must fit in an int");
133    long[] array = new long[rest.length + 1];
134    array[0] = first;
135    System.arraycopy(rest, 0, array, 1, rest.length);
136    return new ImmutableLongArray(array);
137  }
138
139  /** Returns an immutable array containing the given values, in order. */
140  public static ImmutableLongArray copyOf(long[] values) {
141    return values.length == 0
142        ? EMPTY
143        : new ImmutableLongArray(Arrays.copyOf(values, values.length));
144  }
145
146  /** Returns an immutable array containing the given values, in order. */
147  public static ImmutableLongArray copyOf(Collection<Long> values) {
148    return values.isEmpty() ? EMPTY : new ImmutableLongArray(Longs.toArray(values));
149  }
150
151  /**
152   * Returns an immutable array containing the given values, in order.
153   *
154   * <p><b>Performance note:</b> this method delegates to {@link #copyOf(Collection)} if {@code
155   * values} is a {@link Collection}. Otherwise it creates a {@link #builder} and uses {@link
156   * Builder#addAll(Iterable)}, with all the performance implications associated with that.
157   */
158  public static ImmutableLongArray copyOf(Iterable<Long> values) {
159    if (values instanceof Collection) {
160      return copyOf((Collection<Long>) values);
161    }
162    return builder().addAll(values).build();
163  }
164
165  /**
166   * Returns a new, empty builder for {@link ImmutableLongArray} instances, sized to hold up to
167   * {@code initialCapacity} values without resizing. The returned builder is not thread-safe.
168   *
169   * <p><b>Performance note:</b> When feasible, {@code initialCapacity} should be the exact number
170   * of values that will be added, if that knowledge is readily available. It is better to guess a
171   * value slightly too high than slightly too low. If the value is not exact, the {@link
172   * ImmutableLongArray} that is built will very likely occupy more memory than strictly necessary;
173   * to trim memory usage, build using {@code builder.build().trimmed()}.
174   */
175  public static Builder builder(int initialCapacity) {
176    checkArgument(initialCapacity >= 0, "Invalid initialCapacity: %s", initialCapacity);
177    return new Builder(initialCapacity);
178  }
179
180  /**
181   * Returns a new, empty builder for {@link ImmutableLongArray} instances, with a default initial
182   * capacity. The returned builder is not thread-safe.
183   *
184   * <p><b>Performance note:</b> The {@link ImmutableLongArray} that is built will very likely
185   * occupy more memory than necessary; to trim memory usage, build using {@code
186   * builder.build().trimmed()}.
187   */
188  public static Builder builder() {
189    return new Builder(10);
190  }
191
192  /**
193   * A builder for {@link ImmutableLongArray} instances; obtained using {@link
194   * ImmutableLongArray#builder}.
195   */
196  @CanIgnoreReturnValue
197  public static final class Builder {
198    private long[] array;
199    private int count = 0; // <= array.length
200
201    Builder(int initialCapacity) {
202      array = new long[initialCapacity];
203    }
204
205    /**
206     * Appends {@code value} to the end of the values the built {@link ImmutableLongArray} will
207     * contain.
208     */
209    public Builder add(long value) {
210      ensureRoomFor(1);
211      array[count] = value;
212      count += 1;
213      return this;
214    }
215
216    /**
217     * Appends {@code values}, in order, to the end of the values the built {@link
218     * ImmutableLongArray} will contain.
219     */
220    public Builder addAll(long[] values) {
221      ensureRoomFor(values.length);
222      System.arraycopy(values, 0, array, count, values.length);
223      count += values.length;
224      return this;
225    }
226
227    /**
228     * Appends {@code values}, in order, to the end of the values the built {@link
229     * ImmutableLongArray} will contain.
230     */
231    public Builder addAll(Iterable<Long> values) {
232      if (values instanceof Collection) {
233        return addAll((Collection<Long>) values);
234      }
235      for (Long value : values) {
236        add(value);
237      }
238      return this;
239    }
240
241    /**
242     * Appends {@code values}, in order, to the end of the values the built {@link
243     * ImmutableLongArray} will contain.
244     */
245    public Builder addAll(Collection<Long> values) {
246      ensureRoomFor(values.size());
247      for (Long value : values) {
248        array[count++] = value;
249      }
250      return this;
251    }
252
253    /**
254     * Appends {@code values}, in order, to the end of the values the built {@link
255     * ImmutableLongArray} will contain.
256     */
257    public Builder addAll(ImmutableLongArray values) {
258      ensureRoomFor(values.length());
259      System.arraycopy(values.array, values.start, array, count, values.length());
260      count += values.length();
261      return this;
262    }
263
264    private void ensureRoomFor(int numberToAdd) {
265      int newCount = count + numberToAdd; // TODO(kevinb): check overflow now?
266      if (newCount > array.length) {
267        array = Arrays.copyOf(array, expandedCapacity(array.length, newCount));
268      }
269    }
270
271    // Unfortunately this is pasted from ImmutableCollection.Builder.
272    private static int expandedCapacity(int oldCapacity, int minCapacity) {
273      if (minCapacity < 0) {
274        throw new AssertionError("cannot store more than MAX_VALUE elements");
275      }
276      // careful of overflow!
277      int newCapacity = oldCapacity + (oldCapacity >> 1) + 1;
278      if (newCapacity < minCapacity) {
279        newCapacity = Integer.highestOneBit(minCapacity - 1) << 1;
280      }
281      if (newCapacity < 0) {
282        newCapacity = Integer.MAX_VALUE; // guaranteed to be >= newCapacity
283      }
284      return newCapacity;
285    }
286
287    /**
288     * Returns a new immutable array. The builder can continue to be used after this call, to append
289     * more values and build again.
290     *
291     * <p><b>Performance note:</b> the returned array is backed by the same array as the builder, so
292     * no data is copied as part of this step, but this may occupy more memory than strictly
293     * necessary. To copy the data to a right-sized backing array, use {@code .build().trimmed()}.
294     */
295    @CheckReturnValue
296    public ImmutableLongArray build() {
297      return count == 0 ? EMPTY : new ImmutableLongArray(array, 0, count);
298    }
299  }
300
301  // Instance stuff here
302
303  // The array is never mutated after storing in this field and the construction strategies ensure
304  // it doesn't escape this class
305  @SuppressWarnings("Immutable")
306  private final long[] array;
307
308  /*
309   * TODO(kevinb): evaluate the trade-offs of going bimorphic to save these two fields from most
310   * instances. Note that the instances that would get smaller are the right set to care about
311   * optimizing, because the rest have the option of calling `trimmed`.
312   */
313
314  private final transient int start; // it happens that we only serialize instances where this is 0
315  private final int end; // exclusive
316
317  private ImmutableLongArray(long[] array) {
318    this(array, 0, array.length);
319  }
320
321  private ImmutableLongArray(long[] array, int start, int end) {
322    this.array = array;
323    this.start = start;
324    this.end = end;
325  }
326
327  /** Returns the number of values in this array. */
328  public int length() {
329    return end - start;
330  }
331
332  /** Returns {@code true} if there are no values in this array ({@link #length} is zero). */
333  public boolean isEmpty() {
334    return end == start;
335  }
336
337  /**
338   * Returns the {@code long} value present at the given index.
339   *
340   * @throws IndexOutOfBoundsException if {@code index} is negative, or greater than or equal to
341   *     {@link #length}
342   */
343  public long get(int index) {
344    Preconditions.checkElementIndex(index, length());
345    return array[start + index];
346  }
347
348  /**
349   * Returns the smallest index for which {@link #get} returns {@code target}, or {@code -1} if no
350   * such index exists. Equivalent to {@code asList().indexOf(target)}.
351   */
352  public int indexOf(long target) {
353    for (int i = start; i < end; i++) {
354      if (array[i] == target) {
355        return i - start;
356      }
357    }
358    return -1;
359  }
360
361  /**
362   * Returns the largest index for which {@link #get} returns {@code target}, or {@code -1} if no
363   * such index exists. Equivalent to {@code asList().lastIndexOf(target)}.
364   */
365  public int lastIndexOf(long target) {
366    for (int i = end - 1; i >= start; i--) {
367      if (array[i] == target) {
368        return i - start;
369      }
370    }
371    return -1;
372  }
373
374  /**
375   * Returns {@code true} if {@code target} is present at any index in this array. Equivalent to
376   * {@code asList().contains(target)}.
377   */
378  public boolean contains(long target) {
379    return indexOf(target) >= 0;
380  }
381
382  /** Returns a new, mutable copy of this array's values, as a primitive {@code long[]}. */
383  public long[] toArray() {
384    return Arrays.copyOfRange(array, start, end);
385  }
386
387  /**
388   * Returns a new immutable array containing the values in the specified range.
389   *
390   * <p><b>Performance note:</b> The returned array has the same full memory footprint as this one
391   * does (no actual copying is performed). To reduce memory usage, use {@code subArray(start,
392   * end).trimmed()}.
393   */
394  public ImmutableLongArray subArray(int startIndex, int endIndex) {
395    Preconditions.checkPositionIndexes(startIndex, endIndex, length());
396    return startIndex == endIndex
397        ? EMPTY
398        : new ImmutableLongArray(array, start + startIndex, start + endIndex);
399  }
400
401  /**
402   * Returns an immutable <i>view</i> of this array's values as a {@code List}; note that {@code
403   * long} values are boxed into {@link Long} instances on demand, which can be very expensive. The
404   * returned list should be used once and discarded. For any usages beyond that, pass the returned
405   * list to {@link com.google.common.collect.ImmutableList#copyOf(Collection) ImmutableList.copyOf}
406   * and use that list instead.
407   */
408  public List<Long> asList() {
409    /*
410     * Typically we cache this kind of thing, but much repeated use of this view is a performance
411     * anti-pattern anyway. If we cache, then everyone pays a price in memory footprint even if
412     * they never use this method.
413     */
414    return new AsList(this);
415  }
416
417  static class AsList extends AbstractList<Long> implements RandomAccess, Serializable {
418    private final ImmutableLongArray parent;
419
420    private AsList(ImmutableLongArray parent) {
421      this.parent = parent;
422    }
423
424    // inherit: isEmpty, containsAll, toArray x2, iterator, listIterator, mutations
425
426    @Override
427    public int size() {
428      return parent.length();
429    }
430
431    @Override
432    public Long get(int index) {
433      return parent.get(index);
434    }
435
436    @Override
437    public boolean contains(Object target) {
438      return indexOf(target) >= 0;
439    }
440
441    @Override
442    public int indexOf(Object target) {
443      return target instanceof Long ? parent.indexOf((Long) target) : -1;
444    }
445
446    @Override
447    public int lastIndexOf(Object target) {
448      return target instanceof Long ? parent.lastIndexOf((Long) target) : -1;
449    }
450
451    @Override
452    public List<Long> subList(int fromIndex, int toIndex) {
453      return parent.subArray(fromIndex, toIndex).asList();
454    }
455
456    @Override
457    public boolean equals(@NullableDecl Object object) {
458      if (object instanceof AsList) {
459        AsList that = (AsList) object;
460        return this.parent.equals(that.parent);
461      }
462      // We could delegate to super now but it would still box too much
463      if (!(object instanceof List)) {
464        return false;
465      }
466      List<?> that = (List<?>) object;
467      if (this.size() != that.size()) {
468        return false;
469      }
470      int i = parent.start;
471      // Since `that` is very likely RandomAccess we could avoid allocating this iterator...
472      for (Object element : that) {
473        if (!(element instanceof Long) || parent.array[i++] != (Long) element) {
474          return false;
475        }
476      }
477      return true;
478    }
479
480    // Because we happen to use the same formula. If that changes, just don't override this.
481    @Override
482    public int hashCode() {
483      return parent.hashCode();
484    }
485
486    @Override
487    public String toString() {
488      return parent.toString();
489    }
490  }
491
492  /**
493   * Returns {@code true} if {@code object} is an {@code ImmutableLongArray} containing the same
494   * values as this one, in the same order.
495   */
496  @Override
497  public boolean equals(@NullableDecl Object object) {
498    if (object == this) {
499      return true;
500    }
501    if (!(object instanceof ImmutableLongArray)) {
502      return false;
503    }
504    ImmutableLongArray that = (ImmutableLongArray) object;
505    if (this.length() != that.length()) {
506      return false;
507    }
508    for (int i = 0; i < length(); i++) {
509      if (this.get(i) != that.get(i)) {
510        return false;
511      }
512    }
513    return true;
514  }
515
516  /** Returns an unspecified hash code for the contents of this immutable array. */
517  @Override
518  public int hashCode() {
519    int hash = 1;
520    for (int i = start; i < end; i++) {
521      hash *= 31;
522      hash += Longs.hashCode(array[i]);
523    }
524    return hash;
525  }
526
527  /**
528   * Returns a string representation of this array in the same form as {@link
529   * Arrays#toString(long[])}, for example {@code "[1, 2, 3]"}.
530   */
531  @Override
532  public String toString() {
533    if (isEmpty()) {
534      return "[]";
535    }
536    StringBuilder builder = new StringBuilder(length() * 5); // rough estimate is fine
537    builder.append('[').append(array[start]);
538
539    for (int i = start + 1; i < end; i++) {
540      builder.append(", ").append(array[i]);
541    }
542    builder.append(']');
543    return builder.toString();
544  }
545
546  /**
547   * Returns an immutable array containing the same values as {@code this} array. This is logically
548   * a no-op, and in some circumstances {@code this} itself is returned. However, if this instance
549   * is a {@link #subArray} view of a larger array, this method will copy only the appropriate range
550   * of values, resulting in an equivalent array with a smaller memory footprint.
551   */
552  public ImmutableLongArray trimmed() {
553    return isPartialView() ? new ImmutableLongArray(toArray()) : this;
554  }
555
556  private boolean isPartialView() {
557    return start > 0 || end < array.length;
558  }
559
560  Object writeReplace() {
561    return trimmed();
562  }
563
564  Object readResolve() {
565    return isEmpty() ? EMPTY : this;
566  }
567}