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.Immutable;
024import java.io.Serializable;
025import java.util.AbstractList;
026import java.util.Arrays;
027import java.util.Collection;
028import java.util.List;
029import java.util.RandomAccess;
030import javax.annotation.CheckReturnValue;
031import javax.annotation.Nullable;
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>, second
040 *       edition, Item 15).
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  /** Returns an immutable array containing the given values, in order. */
124  // Use (first, rest) so that `of(someLongArray)` won't compile (they should use copyOf), which is
125  // okay since we have to copy the just-created array anyway.
126  public static ImmutableLongArray of(long first, long... rest) {
127    long[] array = new long[rest.length + 1];
128    array[0] = first;
129    System.arraycopy(rest, 0, array, 1, rest.length);
130    return new ImmutableLongArray(array);
131  }
132
133  /** Returns an immutable array containing the given values, in order. */
134  public static ImmutableLongArray copyOf(long[] values) {
135    return values.length == 0
136        ? EMPTY
137        : new ImmutableLongArray(Arrays.copyOf(values, values.length));
138  }
139
140  /** Returns an immutable array containing the given values, in order. */
141  public static ImmutableLongArray copyOf(Collection<Long> values) {
142    return values.isEmpty() ? EMPTY : new ImmutableLongArray(Longs.toArray(values));
143  }
144
145  /**
146   * Returns an immutable array containing the given values, in order.
147   *
148   * <p><b>Performance note:</b> this method delegates to {@link #copyOf(Collection)} if {@code
149   * values} is a {@link Collection}. Otherwise it creates a {@link #builder} and uses {@link
150   * Builder#addAll(Iterable)}, with all the performance implications associated with that.
151   */
152  public static ImmutableLongArray copyOf(Iterable<Long> values) {
153    if (values instanceof Collection) {
154      return copyOf((Collection<Long>) values);
155    }
156    return builder().addAll(values).build();
157  }
158
159  /**
160   * Returns a new, empty builder for {@link ImmutableLongArray} instances, sized to hold up to
161   * {@code initialCapacity} values without resizing. The returned builder is not thread-safe.
162   *
163   * <p><b>Performance note:</b> When feasible, {@code initialCapacity} should be the exact number
164   * of values that will be added, if that knowledge is readily available. It is better to guess a
165   * value slightly too high than slightly too low. If the value is not exact, the {@link
166   * ImmutableLongArray} that is built will very likely occupy more memory than strictly necessary;
167   * to trim memory usage, build using {@code builder.build().trimmed()}.
168   */
169  public static Builder builder(int initialCapacity) {
170    checkArgument(initialCapacity >= 0, "Invalid initialCapacity: %s", initialCapacity);
171    return new Builder(initialCapacity);
172  }
173
174  /**
175   * Returns a new, empty builder for {@link ImmutableLongArray} instances, with a default initial
176   * capacity. The returned builder is not thread-safe.
177   *
178   * <p><b>Performance note:</b> The {@link ImmutableLongArray} that is built will very likely
179   * occupy more memory than necessary; to trim memory usage, build using {@code
180   * builder.build().trimmed()}.
181   */
182  public static Builder builder() {
183    return new Builder(10);
184  }
185
186  /**
187   * A builder for {@link ImmutableLongArray} instances; obtained using {@link
188   * ImmutableLongArray#builder}.
189   */
190  @CanIgnoreReturnValue
191  public static final class Builder {
192    private long[] array;
193    private int count = 0; // <= array.length
194
195    Builder(int initialCapacity) {
196      array = new long[initialCapacity];
197    }
198
199    /**
200     * Appends {@code value} to the end of the values the built {@link ImmutableLongArray} will
201     * contain.
202     */
203    public Builder add(long value) {
204      ensureRoomFor(1);
205      array[count] = value;
206      count += 1;
207      return this;
208    }
209
210    /**
211     * Appends {@code values}, in order, to the end of the values the built {@link
212     * ImmutableLongArray} will contain.
213     */
214    public Builder addAll(long[] values) {
215      ensureRoomFor(values.length);
216      System.arraycopy(values, 0, array, count, values.length);
217      count += values.length;
218      return this;
219    }
220
221    /**
222     * Appends {@code values}, in order, to the end of the values the built {@link
223     * ImmutableLongArray} will contain.
224     */
225    public Builder addAll(Iterable<Long> values) {
226      if (values instanceof Collection) {
227        return addAll((Collection<Long>) values);
228      }
229      for (Long value : values) {
230        add(value);
231      }
232      return this;
233    }
234
235    /**
236     * Appends {@code values}, in order, to the end of the values the built {@link
237     * ImmutableLongArray} will contain.
238     */
239    public Builder addAll(Collection<Long> values) {
240      ensureRoomFor(values.size());
241      for (Long value : values) {
242        array[count++] = value;
243      }
244      return this;
245    }
246
247    /**
248     * Appends {@code values}, in order, to the end of the values the built {@link
249     * ImmutableLongArray} will contain.
250     */
251    public Builder addAll(ImmutableLongArray values) {
252      ensureRoomFor(values.length());
253      System.arraycopy(values.array, values.start, array, count, values.length());
254      count += values.length();
255      return this;
256    }
257
258    private void ensureRoomFor(int numberToAdd) {
259      int newCount = count + numberToAdd; // TODO(kevinb): check overflow now?
260      if (newCount > array.length) {
261        long[] newArray = new long[expandedCapacity(array.length, newCount)];
262        System.arraycopy(array, 0, newArray, 0, count);
263        this.array = newArray;
264      }
265    }
266
267    // Unfortunately this is pasted from ImmutableCollection.Builder.
268    private static int expandedCapacity(int oldCapacity, int minCapacity) {
269      if (minCapacity < 0) {
270        throw new AssertionError("cannot store more than MAX_VALUE elements");
271      }
272      // careful of overflow!
273      int newCapacity = oldCapacity + (oldCapacity >> 1) + 1;
274      if (newCapacity < minCapacity) {
275        newCapacity = Integer.highestOneBit(minCapacity - 1) << 1;
276      }
277      if (newCapacity < 0) {
278        newCapacity = Integer.MAX_VALUE; // guaranteed to be >= newCapacity
279      }
280      return newCapacity;
281    }
282
283    /**
284     * Returns a new immutable array. The builder can continue to be used after this call, to append
285     * more values and build again.
286     *
287     * <p><b>Performance note:</b> the returned array is backed by the same array as the builder, so
288     * no data is copied as part of this step, but this may occupy more memory than strictly
289     * necessary. To copy the data to a right-sized backing array, use {@code .build().trimmed()}.
290     */
291    @CheckReturnValue
292    public ImmutableLongArray build() {
293      return count == 0 ? EMPTY : new ImmutableLongArray(array, 0, count);
294    }
295  }
296
297  // Instance stuff here
298
299  // The array is never mutated after storing in this field and the construction strategies ensure
300  // it doesn't escape this class
301  @SuppressWarnings("Immutable")
302  private final long[] array;
303
304  /*
305   * TODO(kevinb): evaluate the trade-offs of going bimorphic to save these two fields from most
306   * instances. Note that the instances that would get smaller are the right set to care about
307   * optimizing, because the rest have the option of calling `trimmed`.
308   */
309
310  private final transient int start; // it happens that we only serialize instances where this is 0
311  private final int end; // exclusive
312
313  private ImmutableLongArray(long[] array) {
314    this(array, 0, array.length);
315  }
316
317  private ImmutableLongArray(long[] array, int start, int end) {
318    this.array = array;
319    this.start = start;
320    this.end = end;
321  }
322
323  /** Returns the number of values in this array. */
324  public int length() {
325    return end - start;
326  }
327
328  /** Returns {@code true} if there are no values in this array ({@link #length} is zero). */
329  public boolean isEmpty() {
330    return end == start;
331  }
332
333  /**
334   * Returns the {@code long} value present at the given index.
335   *
336   * @throws IndexOutOfBoundsException if {@code index} is negative, or greater than or equal to
337   *     {@link #length}
338   */
339  public long get(int index) {
340    Preconditions.checkElementIndex(index, length());
341    return array[start + index];
342  }
343
344  /**
345   * Returns the smallest index for which {@link #get} returns {@code target}, or {@code -1} if no
346   * such index exists. Equivalent to {@code asList().indexOf(target)}.
347   */
348  public int indexOf(long target) {
349    for (int i = start; i < end; i++) {
350      if (array[i] == target) {
351        return i - start;
352      }
353    }
354    return -1;
355  }
356
357  /**
358   * Returns the largest index for which {@link #get} returns {@code target}, or {@code -1} if no
359   * such index exists. Equivalent to {@code asList().lastIndexOf(target)}.
360   */
361  public int lastIndexOf(long target) {
362    for (int i = end - 1; i >= start; i--) {
363      if (array[i] == target) {
364        return i - start;
365      }
366    }
367    return -1;
368  }
369
370  /**
371   * Returns {@code true} if {@code target} is present at any index in this array. Equivalent to
372   * {@code asList().contains(target)}.
373   */
374  public boolean contains(long target) {
375    return indexOf(target) >= 0;
376  }
377
378  /** Returns a new, mutable copy of this array's values, as a primitive {@code long[]}. */
379  public long[] toArray() {
380    return Arrays.copyOfRange(array, start, end);
381  }
382
383  /**
384   * Returns a new immutable array containing the values in the specified range.
385   *
386   * <p><b>Performance note:</b> The returned array has the same full memory footprint as this one
387   * does (no actual copying is performed). To reduce memory usage, use {@code subArray(start,
388   * end).trimmed()}.
389   */
390  public ImmutableLongArray subArray(int startIndex, int endIndex) {
391    Preconditions.checkPositionIndexes(startIndex, endIndex, length());
392    return startIndex == endIndex
393        ? EMPTY
394        : new ImmutableLongArray(array, start + startIndex, start + endIndex);
395  }
396
397  /**
398   * Returns an immutable <i>view</i> of this array's values as a {@code List}; note that {@code
399   * long} values are boxed into {@link Long} instances on demand, which can be very expensive. The
400   * returned list should be used once and discarded. For any usages beyond that, pass the returned
401   * list to {@link com.google.common.collect.ImmutableList#copyOf(Collection) ImmutableList.copyOf}
402   * and use that list instead.
403   */
404  public List<Long> asList() {
405    /*
406     * Typically we cache this kind of thing, but much repeated use of this view is a performance
407     * anti-pattern anyway. If we cache, then everyone pays a price in memory footprint even if
408     * they never use this method.
409     */
410    return new AsList(this);
411  }
412
413  static class AsList extends AbstractList<Long> implements RandomAccess, Serializable {
414    private final ImmutableLongArray parent;
415
416    private AsList(ImmutableLongArray parent) {
417      this.parent = parent;
418    }
419
420    // inherit: isEmpty, containsAll, toArray x2, iterator, listIterator, mutations
421
422    @Override
423    public int size() {
424      return parent.length();
425    }
426
427    @Override
428    public Long get(int index) {
429      return parent.get(index);
430    }
431
432    @Override
433    public boolean contains(Object target) {
434      return indexOf(target) >= 0;
435    }
436
437    @Override
438    public int indexOf(Object target) {
439      return target instanceof Long ? parent.indexOf((Long) target) : -1;
440    }
441
442    @Override
443    public int lastIndexOf(Object target) {
444      return target instanceof Long ? parent.lastIndexOf((Long) target) : -1;
445    }
446
447    @Override
448    public List<Long> subList(int fromIndex, int toIndex) {
449      return parent.subArray(fromIndex, toIndex).asList();
450    }
451
452    @Override
453    public boolean equals(@Nullable Object object) {
454      if (object instanceof AsList) {
455        AsList that = (AsList) object;
456        return this.parent.equals(that.parent);
457      }
458      // We could delegate to super now but it would still box too much
459      if (!(object instanceof List)) {
460        return false;
461      }
462      List<?> that = (List<?>) object;
463      if (this.size() != that.size()) {
464        return false;
465      }
466      int i = parent.start;
467      // Since `that` is very likely RandomAccess we could avoid allocating this iterator...
468      for (Object element : that) {
469        if (!(element instanceof Long) || parent.array[i++] != (Long) element) {
470          return false;
471        }
472      }
473      return true;
474    }
475
476    // Because we happen to use the same formula. If that changes, just don't override this.
477    @Override
478    public int hashCode() {
479      return parent.hashCode();
480    }
481
482    @Override
483    public String toString() {
484      return parent.toString();
485    }
486  }
487
488  /**
489   * Returns {@code true} if {@code object} is an {@code ImmutableLongArray} containing the same
490   * values as this one, in the same order.
491   */
492  @Override
493  public boolean equals(@Nullable Object object) {
494    if (object == this) {
495      return true;
496    }
497    if (!(object instanceof ImmutableLongArray)) {
498      return false;
499    }
500    ImmutableLongArray that = (ImmutableLongArray) object;
501    if (this.length() != that.length()) {
502      return false;
503    }
504    for (int i = 0; i < length(); i++) {
505      if (this.get(i) != that.get(i)) {
506        return false;
507      }
508    }
509    return true;
510  }
511
512  /** Returns an unspecified hash code for the contents of this immutable array. */
513  @Override
514  public int hashCode() {
515    int hash = 1;
516    for (int i = start; i < end; i++) {
517      hash *= 31;
518      hash += Longs.hashCode(array[i]);
519    }
520    return hash;
521  }
522
523  /**
524   * Returns a string representation of this array in the same form as {@link
525   * Arrays#toString(long[])}, for example {@code "[1, 2, 3]"}.
526   */
527  @Override
528  public String toString() {
529    if (isEmpty()) {
530      return "[]";
531    }
532    StringBuilder builder = new StringBuilder(length() * 5); // rough estimate is fine
533    builder.append('[').append(array[start]);
534
535    for (int i = start + 1; i < end; i++) {
536      builder.append(", ").append(array[i]);
537    }
538    builder.append(']');
539    return builder.toString();
540  }
541
542  /**
543   * Returns an immutable array containing the same values as {@code this} array. This is logically
544   * a no-op, and in some circumstances {@code this} itself is returned. However, if this instance
545   * is a {@link #subArray} view of a larger array, this method will copy only the appropriate range
546   * of values, resulting in an equivalent array with a smaller memory footprint.
547   */
548  public ImmutableLongArray trimmed() {
549    return isPartialView() ? new ImmutableLongArray(toArray()) : this;
550  }
551
552  private boolean isPartialView() {
553    return start > 0 || end < array.length;
554  }
555
556  Object writeReplace() {
557    return trimmed();
558  }
559
560  Object readResolve() {
561    return isEmpty() ? EMPTY : this;
562  }
563}