001/*
002 * Copyright (C) 2007 The Guava Authors
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of the License at
007 *
008 * http://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 */
016
017package com.google.common.collect;
018
019import static com.google.common.base.Preconditions.checkArgument;
020import static com.google.common.base.Preconditions.checkElementIndex;
021import static com.google.common.base.Preconditions.checkNotNull;
022import static com.google.common.base.Preconditions.checkPositionIndex;
023import static com.google.common.base.Preconditions.checkPositionIndexes;
024import static com.google.common.collect.CollectPreconditions.checkNonnegative;
025import static com.google.common.collect.ObjectArrays.checkElementsNotNull;
026import static com.google.common.collect.RegularImmutableList.EMPTY;
027
028import com.google.common.annotations.Beta;
029import com.google.common.annotations.GwtCompatible;
030import com.google.common.annotations.J2ktIncompatible;
031import com.google.errorprone.annotations.CanIgnoreReturnValue;
032import com.google.errorprone.annotations.DoNotCall;
033import com.google.errorprone.annotations.InlineMe;
034import java.io.InvalidObjectException;
035import java.io.ObjectInputStream;
036import java.io.Serializable;
037import java.util.Arrays;
038import java.util.Collection;
039import java.util.Collections;
040import java.util.Comparator;
041import java.util.Iterator;
042import java.util.List;
043import java.util.RandomAccess;
044import javax.annotation.CheckForNull;
045import org.checkerframework.checker.nullness.qual.Nullable;
046
047/**
048 * A {@link List} whose contents will never change, with many other important properties detailed at
049 * {@link ImmutableCollection}.
050 *
051 * <p>See the Guava User Guide article on <a href=
052 * "https://github.com/google/guava/wiki/ImmutableCollectionsExplained">immutable collections</a>.
053 *
054 * @see ImmutableMap
055 * @see ImmutableSet
056 * @author Kevin Bourrillion
057 * @since 2.0
058 */
059@GwtCompatible(serializable = true, emulated = true)
060@SuppressWarnings("serial") // we're overriding default serialization
061@ElementTypesAreNonnullByDefault
062public abstract class ImmutableList<E> extends ImmutableCollection<E>
063    implements List<E>, RandomAccess {
064  /**
065   * Returns the empty immutable list. This list behaves and performs comparably to {@link
066   * Collections#emptyList}, and is preferable mainly for consistency and maintainability of your
067   * code.
068   *
069   * <p><b>Performance note:</b> the instance returned is a singleton.
070   */
071  // Casting to any type is safe because the list will never hold any elements.
072  @SuppressWarnings("unchecked")
073  public static <E> ImmutableList<E> of() {
074    return (ImmutableList<E>) EMPTY;
075  }
076
077  /**
078   * Returns an immutable list containing a single element. This list behaves and performs
079   * comparably to {@link Collections#singletonList}, but will not accept a null element. It is
080   * preferable mainly for consistency and maintainability of your code.
081   *
082   * @throws NullPointerException if {@code element} is null
083   */
084  public static <E> ImmutableList<E> of(E element) {
085    return construct(element);
086  }
087
088  /**
089   * Returns an immutable list containing the given elements, in order.
090   *
091   * @throws NullPointerException if any element is null
092   */
093  public static <E> ImmutableList<E> of(E e1, E e2) {
094    return construct(e1, e2);
095  }
096
097  /**
098   * Returns an immutable list containing the given elements, in order.
099   *
100   * @throws NullPointerException if any element is null
101   */
102  public static <E> ImmutableList<E> of(E e1, E e2, E e3) {
103    return construct(e1, e2, e3);
104  }
105
106  /**
107   * Returns an immutable list containing the given elements, in order.
108   *
109   * @throws NullPointerException if any element is null
110   */
111  public static <E> ImmutableList<E> of(E e1, E e2, E e3, E e4) {
112    return construct(e1, e2, e3, e4);
113  }
114
115  /**
116   * Returns an immutable list containing the given elements, in order.
117   *
118   * @throws NullPointerException if any element is null
119   */
120  public static <E> ImmutableList<E> of(E e1, E e2, E e3, E e4, E e5) {
121    return construct(e1, e2, e3, e4, e5);
122  }
123
124  /**
125   * Returns an immutable list containing the given elements, in order.
126   *
127   * @throws NullPointerException if any element is null
128   */
129  public static <E> ImmutableList<E> of(E e1, E e2, E e3, E e4, E e5, E e6) {
130    return construct(e1, e2, e3, e4, e5, e6);
131  }
132
133  /**
134   * Returns an immutable list containing the given elements, in order.
135   *
136   * @throws NullPointerException if any element is null
137   */
138  public static <E> ImmutableList<E> of(E e1, E e2, E e3, E e4, E e5, E e6, E e7) {
139    return construct(e1, e2, e3, e4, e5, e6, e7);
140  }
141
142  /**
143   * Returns an immutable list containing the given elements, in order.
144   *
145   * @throws NullPointerException if any element is null
146   */
147  public static <E> ImmutableList<E> of(E e1, E e2, E e3, E e4, E e5, E e6, E e7, E e8) {
148    return construct(e1, e2, e3, e4, e5, e6, e7, e8);
149  }
150
151  /**
152   * Returns an immutable list containing the given elements, in order.
153   *
154   * @throws NullPointerException if any element is null
155   */
156  public static <E> ImmutableList<E> of(E e1, E e2, E e3, E e4, E e5, E e6, E e7, E e8, E e9) {
157    return construct(e1, e2, e3, e4, e5, e6, e7, e8, e9);
158  }
159
160  /**
161   * Returns an immutable list containing the given elements, in order.
162   *
163   * @throws NullPointerException if any element is null
164   */
165  public static <E> ImmutableList<E> of(
166      E e1, E e2, E e3, E e4, E e5, E e6, E e7, E e8, E e9, E e10) {
167    return construct(e1, e2, e3, e4, e5, e6, e7, e8, e9, e10);
168  }
169
170  /**
171   * Returns an immutable list containing the given elements, in order.
172   *
173   * @throws NullPointerException if any element is null
174   */
175  public static <E> ImmutableList<E> of(
176      E e1, E e2, E e3, E e4, E e5, E e6, E e7, E e8, E e9, E e10, E e11) {
177    return construct(e1, e2, e3, e4, e5, e6, e7, e8, e9, e10, e11);
178  }
179
180  // These go up to eleven. After that, you just get the varargs form, and
181  // whatever warnings might come along with it. :(
182
183  /**
184   * Returns an immutable list containing the given elements, in order.
185   *
186   * <p>The array {@code others} must not be longer than {@code Integer.MAX_VALUE - 12}.
187   *
188   * @throws NullPointerException if any element is null
189   * @since 3.0 (source-compatible since 2.0)
190   */
191  @SafeVarargs // For Eclipse. For internal javac we have disabled this pointless type of warning.
192  public static <E> ImmutableList<E> of(
193      E e1, E e2, E e3, E e4, E e5, E e6, E e7, E e8, E e9, E e10, E e11, E e12, E... others) {
194    checkArgument(
195        others.length <= Integer.MAX_VALUE - 12, "the total number of elements must fit in an int");
196    Object[] array = new Object[12 + others.length];
197    array[0] = e1;
198    array[1] = e2;
199    array[2] = e3;
200    array[3] = e4;
201    array[4] = e5;
202    array[5] = e6;
203    array[6] = e7;
204    array[7] = e8;
205    array[8] = e9;
206    array[9] = e10;
207    array[10] = e11;
208    array[11] = e12;
209    System.arraycopy(others, 0, array, 12, others.length);
210    return construct(array);
211  }
212
213  /**
214   * Returns an immutable list containing the given elements, in order. If {@code elements} is a
215   * {@link Collection}, this method behaves exactly as {@link #copyOf(Collection)}; otherwise, it
216   * behaves exactly as {@code copyOf(elements.iterator()}.
217   *
218   * @throws NullPointerException if {@code elements} contains a null element
219   */
220  public static <E> ImmutableList<E> copyOf(Iterable<? extends E> elements) {
221    checkNotNull(elements); // TODO(kevinb): is this here only for GWT?
222    return (elements instanceof Collection)
223        ? copyOf((Collection<? extends E>) elements)
224        : copyOf(elements.iterator());
225  }
226
227  /**
228   * Returns an immutable list containing the given elements, in order.
229   *
230   * <p>Despite the method name, this method attempts to avoid actually copying the data when it is
231   * safe to do so. The exact circumstances under which a copy will or will not be performed are
232   * undocumented and subject to change.
233   *
234   * <p>Note that if {@code list} is a {@code List<String>}, then {@code ImmutableList.copyOf(list)}
235   * returns an {@code ImmutableList<String>} containing each of the strings in {@code list}, while
236   * ImmutableList.of(list)} returns an {@code ImmutableList<List<String>>} containing one element
237   * (the given list itself).
238   *
239   * <p>This method is safe to use even when {@code elements} is a synchronized or concurrent
240   * collection that is currently being modified by another thread.
241   *
242   * @throws NullPointerException if {@code elements} contains a null element
243   */
244  public static <E> ImmutableList<E> copyOf(Collection<? extends E> elements) {
245    if (elements instanceof ImmutableCollection) {
246      @SuppressWarnings("unchecked") // all supported methods are covariant
247      ImmutableList<E> list = ((ImmutableCollection<E>) elements).asList();
248      return list.isPartialView() ? ImmutableList.<E>asImmutableList(list.toArray()) : list;
249    }
250    return construct(elements.toArray());
251  }
252
253  /**
254   * Returns an immutable list containing the given elements, in order.
255   *
256   * @throws NullPointerException if {@code elements} contains a null element
257   */
258  public static <E> ImmutableList<E> copyOf(Iterator<? extends E> elements) {
259    // We special-case for 0 or 1 elements, but going further is madness.
260    if (!elements.hasNext()) {
261      return of();
262    }
263    E first = elements.next();
264    if (!elements.hasNext()) {
265      return of(first);
266    } else {
267      return new ImmutableList.Builder<E>().add(first).addAll(elements).build();
268    }
269  }
270
271  /**
272   * Returns an immutable list containing the given elements, in order.
273   *
274   * @throws NullPointerException if {@code elements} contains a null element
275   * @since 3.0
276   */
277  public static <E> ImmutableList<E> copyOf(E[] elements) {
278    return (elements.length == 0)
279        ? ImmutableList.<E>of()
280        : ImmutableList.<E>construct(elements.clone());
281  }
282
283  /**
284   * Returns an immutable list containing the given elements, sorted according to their natural
285   * order. The sorting algorithm used is stable, so elements that compare as equal will stay in the
286   * order in which they appear in the input.
287   *
288   * <p>If your data has no duplicates, or you wish to deduplicate elements, use {@code
289   * ImmutableSortedSet.copyOf(elements)}; if you want a {@code List} you can use its {@code
290   * asList()} view.
291   *
292   * <p><b>Java 8 users:</b> If you want to convert a {@link java.util.stream.Stream} to a sorted
293   * {@code ImmutableList}, use {@code stream.sorted().collect(toImmutableList())}.
294   *
295   * @throws NullPointerException if any element in the input is null
296   * @since 21.0
297   */
298  public static <E extends Comparable<? super E>> ImmutableList<E> sortedCopyOf(
299      Iterable<? extends E> elements) {
300    Comparable<?>[] array = Iterables.toArray(elements, new Comparable<?>[0]);
301    checkElementsNotNull((Object[]) array);
302    Arrays.sort(array);
303    return asImmutableList(array);
304  }
305
306  /**
307   * Returns an immutable list containing the given elements, in sorted order relative to the
308   * specified comparator. The sorting algorithm used is stable, so elements that compare as equal
309   * will stay in the order in which they appear in the input.
310   *
311   * <p>If your data has no duplicates, or you wish to deduplicate elements, use {@code
312   * ImmutableSortedSet.copyOf(comparator, elements)}; if you want a {@code List} you can use its
313   * {@code asList()} view.
314   *
315   * <p><b>Java 8 users:</b> If you want to convert a {@link java.util.stream.Stream} to a sorted
316   * {@code ImmutableList}, use {@code stream.sorted(comparator).collect(toImmutableList())}.
317   *
318   * @throws NullPointerException if any element in the input is null
319   * @since 21.0
320   */
321  public static <E> ImmutableList<E> sortedCopyOf(
322      Comparator<? super E> comparator, Iterable<? extends E> elements) {
323    checkNotNull(comparator);
324    @SuppressWarnings("unchecked") // all supported methods are covariant
325    E[] array = (E[]) Iterables.toArray(elements);
326    checkElementsNotNull(array);
327    Arrays.sort(array, comparator);
328    return asImmutableList(array);
329  }
330
331  /** Views the array as an immutable list. Checks for nulls; does not copy. */
332  private static <E> ImmutableList<E> construct(Object... elements) {
333    return asImmutableList(checkElementsNotNull(elements));
334  }
335
336  /**
337   * Views the array as an immutable list. Does not check for nulls; does not copy.
338   *
339   * <p>The array must be internally created.
340   */
341  static <E> ImmutableList<E> asImmutableList(Object[] elements) {
342    return asImmutableList(elements, elements.length);
343  }
344
345  /** Views the array as an immutable list. Does not check for nulls. */
346  static <E> ImmutableList<E> asImmutableList(@Nullable Object[] elements, int length) {
347    if (length == 0) {
348      return of();
349    }
350    return new RegularImmutableList<E>(elements, length);
351  }
352
353  ImmutableList() {}
354
355  // This declaration is needed to make List.iterator() and
356  // ImmutableCollection.iterator() consistent.
357  @Override
358  public UnmodifiableIterator<E> iterator() {
359    return listIterator();
360  }
361
362  @Override
363  public UnmodifiableListIterator<E> listIterator() {
364    return listIterator(0);
365  }
366
367  @SuppressWarnings("unchecked")
368  @Override
369  public UnmodifiableListIterator<E> listIterator(int index) {
370    checkPositionIndex(index, size());
371    if (isEmpty()) {
372      return (UnmodifiableListIterator<E>) EMPTY_ITR;
373    } else {
374      return new Itr<E>(this, index);
375    }
376  }
377
378  /** A singleton implementation of iterator() for the empty ImmutableList. */
379  private static final UnmodifiableListIterator<Object> EMPTY_ITR =
380      new Itr<Object>(RegularImmutableList.EMPTY, 0);
381
382  static class Itr<E> extends AbstractIndexedListIterator<E> {
383    private final ImmutableList<E> list;
384
385    Itr(ImmutableList<E> list, int index) {
386      super(list.size(), index);
387      this.list = list;
388    }
389
390    @Override
391    protected E get(int index) {
392      return list.get(index);
393    }
394  }
395
396  @Override
397  public int indexOf(@CheckForNull Object object) {
398    return (object == null) ? -1 : Lists.indexOfImpl(this, object);
399  }
400
401  @Override
402  public int lastIndexOf(@CheckForNull Object object) {
403    return (object == null) ? -1 : Lists.lastIndexOfImpl(this, object);
404  }
405
406  @Override
407  public boolean contains(@CheckForNull Object object) {
408    return indexOf(object) >= 0;
409  }
410
411  // constrain the return type to ImmutableList<E>
412
413  /**
414   * Returns an immutable list of the elements between the specified {@code fromIndex}, inclusive,
415   * and {@code toIndex}, exclusive. (If {@code fromIndex} and {@code toIndex} are equal, the empty
416   * immutable list is returned.)
417   */
418  @Override
419  public ImmutableList<E> subList(int fromIndex, int toIndex) {
420    checkPositionIndexes(fromIndex, toIndex, size());
421    int length = toIndex - fromIndex;
422    if (length == size()) {
423      return this;
424    } else if (length == 0) {
425      return of();
426    } else {
427      return subListUnchecked(fromIndex, toIndex);
428    }
429  }
430
431  /**
432   * Called by the default implementation of {@link #subList} when {@code toIndex - fromIndex > 1},
433   * after index validation has already been performed.
434   */
435  ImmutableList<E> subListUnchecked(int fromIndex, int toIndex) {
436    return new SubList(fromIndex, toIndex - fromIndex);
437  }
438
439  class SubList extends ImmutableList<E> {
440    final transient int offset;
441    final transient int length;
442
443    SubList(int offset, int length) {
444      this.offset = offset;
445      this.length = length;
446    }
447
448    @Override
449    public int size() {
450      return length;
451    }
452
453    @Override
454    @CheckForNull
455    @Nullable
456    Object[] internalArray() {
457      return ImmutableList.this.internalArray();
458    }
459
460    @Override
461    int internalArrayStart() {
462      return ImmutableList.this.internalArrayStart() + offset;
463    }
464
465    @Override
466    int internalArrayEnd() {
467      return ImmutableList.this.internalArrayStart() + offset + length;
468    }
469
470    @Override
471    public E get(int index) {
472      checkElementIndex(index, length);
473      return ImmutableList.this.get(index + offset);
474    }
475
476    @Override
477    public ImmutableList<E> subList(int fromIndex, int toIndex) {
478      checkPositionIndexes(fromIndex, toIndex, length);
479      return ImmutableList.this.subList(fromIndex + offset, toIndex + offset);
480    }
481
482    @Override
483    boolean isPartialView() {
484      return true;
485    }
486  }
487
488  /**
489   * Guaranteed to throw an exception and leave the list unmodified.
490   *
491   * @throws UnsupportedOperationException always
492   * @deprecated Unsupported operation.
493   */
494  @CanIgnoreReturnValue
495  @Deprecated
496  @Override
497  @DoNotCall("Always throws UnsupportedOperationException")
498  public final boolean addAll(int index, Collection<? extends E> newElements) {
499    throw new UnsupportedOperationException();
500  }
501
502  /**
503   * Guaranteed to throw an exception and leave the list unmodified.
504   *
505   * @throws UnsupportedOperationException always
506   * @deprecated Unsupported operation.
507   */
508  @CanIgnoreReturnValue
509  @Deprecated
510  @Override
511  @DoNotCall("Always throws UnsupportedOperationException")
512  public final E set(int index, E element) {
513    throw new UnsupportedOperationException();
514  }
515
516  /**
517   * Guaranteed to throw an exception and leave the list unmodified.
518   *
519   * @throws UnsupportedOperationException always
520   * @deprecated Unsupported operation.
521   */
522  @Deprecated
523  @Override
524  @DoNotCall("Always throws UnsupportedOperationException")
525  public final void add(int index, E element) {
526    throw new UnsupportedOperationException();
527  }
528
529  /**
530   * Guaranteed to throw an exception and leave the list unmodified.
531   *
532   * @throws UnsupportedOperationException always
533   * @deprecated Unsupported operation.
534   */
535  @CanIgnoreReturnValue
536  @Deprecated
537  @Override
538  @DoNotCall("Always throws UnsupportedOperationException")
539  public final E remove(int index) {
540    throw new UnsupportedOperationException();
541  }
542
543  /**
544   * Returns this list instance.
545   *
546   * @since 2.0
547   * @deprecated There is no reason to use this; it always returns {@code this}.
548   */
549  @InlineMe(replacement = "this")
550  @Deprecated
551  @Override
552  public final ImmutableList<E> asList() {
553    return this;
554  }
555
556  @Override
557  int copyIntoArray(@Nullable Object[] dst, int offset) {
558    // this loop is faster for RandomAccess instances, which ImmutableLists are
559    int size = size();
560    for (int i = 0; i < size; i++) {
561      dst[offset + i] = get(i);
562    }
563    return offset + size;
564  }
565
566  /**
567   * Returns a view of this immutable list in reverse order. For example, {@code ImmutableList.of(1,
568   * 2, 3).reverse()} is equivalent to {@code ImmutableList.of(3, 2, 1)}.
569   *
570   * @return a view of this immutable list in reverse order
571   * @since 7.0
572   */
573  public ImmutableList<E> reverse() {
574    return (size() <= 1) ? this : new ReverseImmutableList<E>(this);
575  }
576
577  private static class ReverseImmutableList<E> extends ImmutableList<E> {
578    private final transient ImmutableList<E> forwardList;
579
580    ReverseImmutableList(ImmutableList<E> backingList) {
581      this.forwardList = backingList;
582    }
583
584    private int reverseIndex(int index) {
585      return (size() - 1) - index;
586    }
587
588    private int reversePosition(int index) {
589      return size() - index;
590    }
591
592    @Override
593    public ImmutableList<E> reverse() {
594      return forwardList;
595    }
596
597    @Override
598    public boolean contains(@CheckForNull Object object) {
599      return forwardList.contains(object);
600    }
601
602    @Override
603    public int indexOf(@CheckForNull Object object) {
604      int index = forwardList.lastIndexOf(object);
605      return (index >= 0) ? reverseIndex(index) : -1;
606    }
607
608    @Override
609    public int lastIndexOf(@CheckForNull Object object) {
610      int index = forwardList.indexOf(object);
611      return (index >= 0) ? reverseIndex(index) : -1;
612    }
613
614    @Override
615    public ImmutableList<E> subList(int fromIndex, int toIndex) {
616      checkPositionIndexes(fromIndex, toIndex, size());
617      return forwardList.subList(reversePosition(toIndex), reversePosition(fromIndex)).reverse();
618    }
619
620    @Override
621    public E get(int index) {
622      checkElementIndex(index, size());
623      return forwardList.get(reverseIndex(index));
624    }
625
626    @Override
627    public int size() {
628      return forwardList.size();
629    }
630
631    @Override
632    boolean isPartialView() {
633      return forwardList.isPartialView();
634    }
635  }
636
637  @Override
638  public boolean equals(@CheckForNull Object obj) {
639    return Lists.equalsImpl(this, obj);
640  }
641
642  @Override
643  public int hashCode() {
644    int hashCode = 1;
645    int n = size();
646    for (int i = 0; i < n; i++) {
647      hashCode = 31 * hashCode + get(i).hashCode();
648
649      hashCode = ~~hashCode;
650      // needed to deal with GWT integer overflow
651    }
652    return hashCode;
653  }
654
655  /*
656   * Serializes ImmutableLists as their logical contents. This ensures that
657   * implementation types do not leak into the serialized representation.
658   */
659  @J2ktIncompatible // serialization
660  static class SerializedForm implements Serializable {
661    final Object[] elements;
662
663    SerializedForm(Object[] elements) {
664      this.elements = elements;
665    }
666
667    Object readResolve() {
668      return copyOf(elements);
669    }
670
671    private static final long serialVersionUID = 0;
672  }
673
674  @J2ktIncompatible // serialization
675  private void readObject(ObjectInputStream stream) throws InvalidObjectException {
676    throw new InvalidObjectException("Use SerializedForm");
677  }
678
679  @Override
680  @J2ktIncompatible // serialization
681  Object writeReplace() {
682    return new SerializedForm(toArray());
683  }
684
685  /**
686   * Returns a new builder. The generated builder is equivalent to the builder created by the {@link
687   * Builder} constructor.
688   */
689  public static <E> Builder<E> builder() {
690    return new Builder<E>();
691  }
692
693  /**
694   * Returns a new builder, expecting the specified number of elements to be added.
695   *
696   * <p>If {@code expectedSize} is exactly the number of elements added to the builder before {@link
697   * Builder#build} is called, the builder is likely to perform better than an unsized {@link
698   * #builder()} would have.
699   *
700   * <p>It is not specified if any performance benefits apply if {@code expectedSize} is close to,
701   * but not exactly, the number of elements added to the builder.
702   *
703   * @since 23.1
704   */
705  @Beta
706  public static <E> Builder<E> builderWithExpectedSize(int expectedSize) {
707    checkNonnegative(expectedSize, "expectedSize");
708    return new ImmutableList.Builder<E>(expectedSize);
709  }
710
711  /**
712   * A builder for creating immutable list instances, especially {@code public static final} lists
713   * ("constant lists"). Example:
714   *
715   * <pre>{@code
716   * public static final ImmutableList<Color> GOOGLE_COLORS
717   *     = new ImmutableList.Builder<Color>()
718   *         .addAll(WEBSAFE_COLORS)
719   *         .add(new Color(0, 191, 255))
720   *         .build();
721   * }</pre>
722   *
723   * <p>Elements appear in the resulting list in the same order they were added to the builder.
724   *
725   * <p>Builder instances can be reused; it is safe to call {@link #build} multiple times to build
726   * multiple lists in series. Each new list contains all the elements of the ones created before
727   * it.
728   *
729   * @since 2.0
730   */
731  public static final class Builder<E> extends ImmutableCollection.ArrayBasedBuilder<E> {
732    /**
733     * Creates a new builder. The returned builder is equivalent to the builder generated by {@link
734     * ImmutableList#builder}.
735     */
736    public Builder() {
737      this(DEFAULT_INITIAL_CAPACITY);
738    }
739
740    Builder(int capacity) {
741      super(capacity);
742    }
743
744    /**
745     * Adds {@code element} to the {@code ImmutableList}.
746     *
747     * @param element the element to add
748     * @return this {@code Builder} object
749     * @throws NullPointerException if {@code element} is null
750     */
751    @CanIgnoreReturnValue
752    @Override
753    public Builder<E> add(E element) {
754      super.add(element);
755      return this;
756    }
757
758    /**
759     * Adds each element of {@code elements} to the {@code ImmutableList}.
760     *
761     * @param elements the {@code Iterable} to add to the {@code ImmutableList}
762     * @return this {@code Builder} object
763     * @throws NullPointerException if {@code elements} is null or contains a null element
764     */
765    @CanIgnoreReturnValue
766    @Override
767    public Builder<E> add(E... elements) {
768      super.add(elements);
769      return this;
770    }
771
772    /**
773     * Adds each element of {@code elements} to the {@code ImmutableList}.
774     *
775     * @param elements the {@code Iterable} to add to the {@code ImmutableList}
776     * @return this {@code Builder} object
777     * @throws NullPointerException if {@code elements} is null or contains a null element
778     */
779    @CanIgnoreReturnValue
780    @Override
781    public Builder<E> addAll(Iterable<? extends E> elements) {
782      super.addAll(elements);
783      return this;
784    }
785
786    /**
787     * Adds each element of {@code elements} to the {@code ImmutableList}.
788     *
789     * @param elements the {@code Iterator} to add to the {@code ImmutableList}
790     * @return this {@code Builder} object
791     * @throws NullPointerException if {@code elements} is null or contains a null element
792     */
793    @CanIgnoreReturnValue
794    @Override
795    public Builder<E> addAll(Iterator<? extends E> elements) {
796      super.addAll(elements);
797      return this;
798    }
799
800    @CanIgnoreReturnValue
801    Builder<E> combine(Builder<E> other) {
802      addAll(other.contents, other.size);
803      return this;
804    }
805
806    /**
807     * Returns a newly-created {@code ImmutableList} based on the contents of the {@code Builder}.
808     */
809    @Override
810    public ImmutableList<E> build() {
811      forceCopy = true;
812      return asImmutableList(contents, size);
813    }
814  }
815}