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.checkPositionIndexes; 023import static com.google.common.collect.CollectPreconditions.checkNonnegative; 024import static com.google.common.collect.ObjectArrays.checkElementsNotNull; 025import static com.google.common.collect.RegularImmutableList.EMPTY; 026import static java.util.Objects.requireNonNull; 027 028import com.google.common.annotations.Beta; 029import com.google.common.annotations.GwtCompatible; 030import com.google.common.annotations.VisibleForTesting; 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 java.util.Spliterator; 045import java.util.function.Consumer; 046import java.util.function.UnaryOperator; 047import java.util.stream.Collector; 048import javax.annotation.CheckForNull; 049import org.checkerframework.checker.nullness.qual.Nullable; 050 051/** 052 * A {@link List} whose contents will never change, with many other important properties detailed at 053 * {@link ImmutableCollection}. 054 * 055 * <p>See the Guava User Guide article on <a href= 056 * "https://github.com/google/guava/wiki/ImmutableCollectionsExplained">immutable collections</a>. 057 * 058 * @see ImmutableMap 059 * @see ImmutableSet 060 * @author Kevin Bourrillion 061 * @since 2.0 062 */ 063@GwtCompatible(serializable = true, emulated = true) 064@SuppressWarnings("serial") // we're overriding default serialization 065@ElementTypesAreNonnullByDefault 066public abstract class ImmutableList<E> extends ImmutableCollection<E> 067 implements List<E>, RandomAccess { 068 069 /** 070 * Returns a {@code Collector} that accumulates the input elements into a new {@code 071 * ImmutableList}, in encounter order. 072 * 073 * @since 21.0 074 */ 075 public static <E> Collector<E, ?, ImmutableList<E>> toImmutableList() { 076 return CollectCollectors.toImmutableList(); 077 } 078 079 /** 080 * Returns the empty immutable list. This list behaves and performs comparably to {@link 081 * Collections#emptyList}, and is preferable mainly for consistency and maintainability of your 082 * code. 083 * 084 * <p><b>Performance note:</b> the instance returned is a singleton. 085 */ 086 // Casting to any type is safe because the list will never hold any elements. 087 @SuppressWarnings("unchecked") 088 public static <E> ImmutableList<E> of() { 089 return (ImmutableList<E>) EMPTY; 090 } 091 092 /** 093 * Returns an immutable list containing a single element. This list behaves and performs 094 * comparably to {@link Collections#singletonList}, but will not accept a null element. It is 095 * preferable mainly for consistency and maintainability of your code. 096 * 097 * @throws NullPointerException if {@code element} is null 098 */ 099 public static <E> ImmutableList<E> of(E element) { 100 return new SingletonImmutableList<E>(element); 101 } 102 103 /** 104 * Returns an immutable list containing the given elements, in order. 105 * 106 * @throws NullPointerException if any element is null 107 */ 108 public static <E> ImmutableList<E> of(E e1, E e2) { 109 return construct(e1, e2); 110 } 111 112 /** 113 * Returns an immutable list containing the given elements, in order. 114 * 115 * @throws NullPointerException if any element is null 116 */ 117 public static <E> ImmutableList<E> of(E e1, E e2, E e3) { 118 return construct(e1, e2, e3); 119 } 120 121 /** 122 * Returns an immutable list containing the given elements, in order. 123 * 124 * @throws NullPointerException if any element is null 125 */ 126 public static <E> ImmutableList<E> of(E e1, E e2, E e3, E e4) { 127 return construct(e1, e2, e3, e4); 128 } 129 130 /** 131 * Returns an immutable list containing the given elements, in order. 132 * 133 * @throws NullPointerException if any element is null 134 */ 135 public static <E> ImmutableList<E> of(E e1, E e2, E e3, E e4, E e5) { 136 return construct(e1, e2, e3, e4, e5); 137 } 138 139 /** 140 * Returns an immutable list containing the given elements, in order. 141 * 142 * @throws NullPointerException if any element is null 143 */ 144 public static <E> ImmutableList<E> of(E e1, E e2, E e3, E e4, E e5, E e6) { 145 return construct(e1, e2, e3, e4, e5, e6); 146 } 147 148 /** 149 * Returns an immutable list containing the given elements, in order. 150 * 151 * @throws NullPointerException if any element is null 152 */ 153 public static <E> ImmutableList<E> of(E e1, E e2, E e3, E e4, E e5, E e6, E e7) { 154 return construct(e1, e2, e3, e4, e5, e6, e7); 155 } 156 157 /** 158 * Returns an immutable list containing the given elements, in order. 159 * 160 * @throws NullPointerException if any element is null 161 */ 162 public static <E> ImmutableList<E> of(E e1, E e2, E e3, E e4, E e5, E e6, E e7, E e8) { 163 return construct(e1, e2, e3, e4, e5, e6, e7, e8); 164 } 165 166 /** 167 * Returns an immutable list containing the given elements, in order. 168 * 169 * @throws NullPointerException if any element is null 170 */ 171 public static <E> ImmutableList<E> of(E e1, E e2, E e3, E e4, E e5, E e6, E e7, E e8, E e9) { 172 return construct(e1, e2, e3, e4, e5, e6, e7, e8, e9); 173 } 174 175 /** 176 * Returns an immutable list containing the given elements, in order. 177 * 178 * @throws NullPointerException if any element is null 179 */ 180 public static <E> ImmutableList<E> of( 181 E e1, E e2, E e3, E e4, E e5, E e6, E e7, E e8, E e9, E e10) { 182 return construct(e1, e2, e3, e4, e5, e6, e7, e8, e9, e10); 183 } 184 185 /** 186 * Returns an immutable list containing the given elements, in order. 187 * 188 * @throws NullPointerException if any element is null 189 */ 190 public static <E> ImmutableList<E> of( 191 E e1, E e2, E e3, E e4, E e5, E e6, E e7, E e8, E e9, E e10, E e11) { 192 return construct(e1, e2, e3, e4, e5, e6, e7, e8, e9, e10, e11); 193 } 194 195 // These go up to eleven. After that, you just get the varargs form, and 196 // whatever warnings might come along with it. :( 197 198 /** 199 * Returns an immutable list containing the given elements, in order. 200 * 201 * <p>The array {@code others} must not be longer than {@code Integer.MAX_VALUE - 12}. 202 * 203 * @throws NullPointerException if any element is null 204 * @since 3.0 (source-compatible since 2.0) 205 */ 206 @SafeVarargs // For Eclipse. For internal javac we have disabled this pointless type of warning. 207 public static <E> ImmutableList<E> of( 208 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) { 209 checkArgument( 210 others.length <= Integer.MAX_VALUE - 12, "the total number of elements must fit in an int"); 211 Object[] array = new Object[12 + others.length]; 212 array[0] = e1; 213 array[1] = e2; 214 array[2] = e3; 215 array[3] = e4; 216 array[4] = e5; 217 array[5] = e6; 218 array[6] = e7; 219 array[7] = e8; 220 array[8] = e9; 221 array[9] = e10; 222 array[10] = e11; 223 array[11] = e12; 224 System.arraycopy(others, 0, array, 12, others.length); 225 return construct(array); 226 } 227 228 /** 229 * Returns an immutable list containing the given elements, in order. If {@code elements} is a 230 * {@link Collection}, this method behaves exactly as {@link #copyOf(Collection)}; otherwise, it 231 * behaves exactly as {@code copyOf(elements.iterator()}. 232 * 233 * @throws NullPointerException if {@code elements} contains a null element 234 */ 235 public static <E> ImmutableList<E> copyOf(Iterable<? extends E> elements) { 236 checkNotNull(elements); // TODO(kevinb): is this here only for GWT? 237 return (elements instanceof Collection) 238 ? copyOf((Collection<? extends E>) elements) 239 : copyOf(elements.iterator()); 240 } 241 242 /** 243 * Returns an immutable list containing the given elements, in order. 244 * 245 * <p>Despite the method name, this method attempts to avoid actually copying the data when it is 246 * safe to do so. The exact circumstances under which a copy will or will not be performed are 247 * undocumented and subject to change. 248 * 249 * <p>Note that if {@code list} is a {@code List<String>}, then {@code ImmutableList.copyOf(list)} 250 * returns an {@code ImmutableList<String>} containing each of the strings in {@code list}, while 251 * ImmutableList.of(list)} returns an {@code ImmutableList<List<String>>} containing one element 252 * (the given list itself). 253 * 254 * <p>This method is safe to use even when {@code elements} is a synchronized or concurrent 255 * collection that is currently being modified by another thread. 256 * 257 * @throws NullPointerException if {@code elements} contains a null element 258 */ 259 public static <E> ImmutableList<E> copyOf(Collection<? extends E> elements) { 260 if (elements instanceof ImmutableCollection) { 261 @SuppressWarnings("unchecked") // all supported methods are covariant 262 ImmutableList<E> list = ((ImmutableCollection<E>) elements).asList(); 263 return list.isPartialView() ? ImmutableList.<E>asImmutableList(list.toArray()) : list; 264 } 265 return construct(elements.toArray()); 266 } 267 268 /** 269 * Returns an immutable list containing the given elements, in order. 270 * 271 * @throws NullPointerException if {@code elements} contains a null element 272 */ 273 public static <E> ImmutableList<E> copyOf(Iterator<? extends E> elements) { 274 // We special-case for 0 or 1 elements, but going further is madness. 275 if (!elements.hasNext()) { 276 return of(); 277 } 278 E first = elements.next(); 279 if (!elements.hasNext()) { 280 return of(first); 281 } else { 282 return new ImmutableList.Builder<E>().add(first).addAll(elements).build(); 283 } 284 } 285 286 /** 287 * Returns an immutable list containing the given elements, in order. 288 * 289 * @throws NullPointerException if {@code elements} contains a null element 290 * @since 3.0 291 */ 292 public static <E> ImmutableList<E> copyOf(E[] elements) { 293 switch (elements.length) { 294 case 0: 295 return of(); 296 case 1: 297 return of(elements[0]); 298 default: 299 return construct(elements.clone()); 300 } 301 } 302 303 /** 304 * Returns an immutable list containing the given elements, sorted according to their natural 305 * order. The sorting algorithm used is stable, so elements that compare as equal will stay in the 306 * order in which they appear in the input. 307 * 308 * <p>If your data has no duplicates, or you wish to deduplicate elements, use {@code 309 * ImmutableSortedSet.copyOf(elements)}; if you want a {@code List} you can use its {@code 310 * asList()} view. 311 * 312 * <p><b>Java 8 users:</b> If you want to convert a {@link java.util.stream.Stream} to a sorted 313 * {@code ImmutableList}, use {@code stream.sorted().collect(toImmutableList())}. 314 * 315 * @throws NullPointerException if any element in the input is null 316 * @since 21.0 317 */ 318 public static <E extends Comparable<? super E>> ImmutableList<E> sortedCopyOf( 319 Iterable<? extends E> elements) { 320 Comparable<?>[] array = Iterables.toArray(elements, new Comparable<?>[0]); 321 checkElementsNotNull((Object[]) array); 322 Arrays.sort(array); 323 return asImmutableList(array); 324 } 325 326 /** 327 * Returns an immutable list containing the given elements, in sorted order relative to the 328 * specified comparator. The sorting algorithm used is stable, so elements that compare as equal 329 * will stay in the order in which they appear in the input. 330 * 331 * <p>If your data has no duplicates, or you wish to deduplicate elements, use {@code 332 * ImmutableSortedSet.copyOf(comparator, elements)}; if you want a {@code List} you can use its 333 * {@code asList()} view. 334 * 335 * <p><b>Java 8 users:</b> If you want to convert a {@link java.util.stream.Stream} to a sorted 336 * {@code ImmutableList}, use {@code stream.sorted(comparator).collect(toImmutableList())}. 337 * 338 * @throws NullPointerException if any element in the input is null 339 * @since 21.0 340 */ 341 public static <E> ImmutableList<E> sortedCopyOf( 342 Comparator<? super E> comparator, Iterable<? extends E> elements) { 343 checkNotNull(comparator); 344 @SuppressWarnings("unchecked") // all supported methods are covariant 345 E[] array = (E[]) Iterables.toArray(elements); 346 checkElementsNotNull(array); 347 Arrays.sort(array, comparator); 348 return asImmutableList(array); 349 } 350 351 /** Views the array as an immutable list. Checks for nulls; does not copy. */ 352 private static <E> ImmutableList<E> construct(Object... elements) { 353 return asImmutableList(checkElementsNotNull(elements)); 354 } 355 356 /** 357 * Views the array as an immutable list. Does not check for nulls; does not copy. 358 * 359 * <p>The array must be internally created. 360 */ 361 static <E> ImmutableList<E> asImmutableList(Object[] elements) { 362 return asImmutableList(elements, elements.length); 363 } 364 365 /** 366 * Views the array as an immutable list. Copies if the specified range does not cover the complete 367 * array. Does not check for nulls. 368 */ 369 static <E> ImmutableList<E> asImmutableList(@Nullable Object[] elements, int length) { 370 switch (length) { 371 case 0: 372 return of(); 373 case 1: 374 /* 375 * requireNonNull is safe because the callers promise to put non-null objects in the first 376 * `length` array elements. 377 */ 378 @SuppressWarnings("unchecked") // our callers put only E instances into the array 379 E onlyElement = (E) requireNonNull(elements[0]); 380 return of(onlyElement); 381 default: 382 /* 383 * The suppression is safe because the callers promise to put non-null objects in the first 384 * `length` array elements. 385 */ 386 @SuppressWarnings("nullness") 387 Object[] elementsWithoutTrailingNulls = 388 length < elements.length ? Arrays.copyOf(elements, length) : elements; 389 return new RegularImmutableList<E>(elementsWithoutTrailingNulls); 390 } 391 } 392 393 ImmutableList() {} 394 395 // This declaration is needed to make List.iterator() and 396 // ImmutableCollection.iterator() consistent. 397 @Override 398 public UnmodifiableIterator<E> iterator() { 399 return listIterator(); 400 } 401 402 @Override 403 public UnmodifiableListIterator<E> listIterator() { 404 return listIterator(0); 405 } 406 407 @Override 408 public UnmodifiableListIterator<E> listIterator(int index) { 409 return new AbstractIndexedListIterator<E>(size(), index) { 410 @Override 411 protected E get(int index) { 412 return ImmutableList.this.get(index); 413 } 414 }; 415 } 416 417 @Override 418 public void forEach(Consumer<? super E> consumer) { 419 checkNotNull(consumer); 420 int n = size(); 421 for (int i = 0; i < n; i++) { 422 consumer.accept(get(i)); 423 } 424 } 425 426 @Override 427 public int indexOf(@CheckForNull Object object) { 428 return (object == null) ? -1 : Lists.indexOfImpl(this, object); 429 } 430 431 @Override 432 public int lastIndexOf(@CheckForNull Object object) { 433 return (object == null) ? -1 : Lists.lastIndexOfImpl(this, object); 434 } 435 436 @Override 437 public boolean contains(@CheckForNull Object object) { 438 return indexOf(object) >= 0; 439 } 440 441 // constrain the return type to ImmutableList<E> 442 443 /** 444 * Returns an immutable list of the elements between the specified {@code fromIndex}, inclusive, 445 * and {@code toIndex}, exclusive. (If {@code fromIndex} and {@code toIndex} are equal, the empty 446 * immutable list is returned.) 447 */ 448 @Override 449 public ImmutableList<E> subList(int fromIndex, int toIndex) { 450 checkPositionIndexes(fromIndex, toIndex, size()); 451 int length = toIndex - fromIndex; 452 if (length == size()) { 453 return this; 454 } else if (length == 0) { 455 return of(); 456 } else if (length == 1) { 457 return of(get(fromIndex)); 458 } else { 459 return subListUnchecked(fromIndex, toIndex); 460 } 461 } 462 463 /** 464 * Called by the default implementation of {@link #subList} when {@code toIndex - fromIndex > 1}, 465 * after index validation has already been performed. 466 */ 467 ImmutableList<E> subListUnchecked(int fromIndex, int toIndex) { 468 return new SubList(fromIndex, toIndex - fromIndex); 469 } 470 471 class SubList extends ImmutableList<E> { 472 final transient int offset; 473 final transient int length; 474 475 SubList(int offset, int length) { 476 this.offset = offset; 477 this.length = length; 478 } 479 480 @Override 481 public int size() { 482 return length; 483 } 484 485 @Override 486 public E get(int index) { 487 checkElementIndex(index, length); 488 return ImmutableList.this.get(index + offset); 489 } 490 491 @Override 492 public ImmutableList<E> subList(int fromIndex, int toIndex) { 493 checkPositionIndexes(fromIndex, toIndex, length); 494 return ImmutableList.this.subList(fromIndex + offset, toIndex + offset); 495 } 496 497 @Override 498 boolean isPartialView() { 499 return true; 500 } 501 } 502 503 /** 504 * Guaranteed to throw an exception and leave the list unmodified. 505 * 506 * @throws UnsupportedOperationException always 507 * @deprecated Unsupported operation. 508 */ 509 @CanIgnoreReturnValue 510 @Deprecated 511 @Override 512 @DoNotCall("Always throws UnsupportedOperationException") 513 public final boolean addAll(int index, Collection<? extends E> newElements) { 514 throw new UnsupportedOperationException(); 515 } 516 517 /** 518 * Guaranteed to throw an exception and leave the list unmodified. 519 * 520 * @throws UnsupportedOperationException always 521 * @deprecated Unsupported operation. 522 */ 523 @CanIgnoreReturnValue 524 @Deprecated 525 @Override 526 @DoNotCall("Always throws UnsupportedOperationException") 527 public final E set(int index, E element) { 528 throw new UnsupportedOperationException(); 529 } 530 531 /** 532 * Guaranteed to throw an exception and leave the list unmodified. 533 * 534 * @throws UnsupportedOperationException always 535 * @deprecated Unsupported operation. 536 */ 537 @Deprecated 538 @Override 539 @DoNotCall("Always throws UnsupportedOperationException") 540 public final void add(int index, E element) { 541 throw new UnsupportedOperationException(); 542 } 543 544 /** 545 * Guaranteed to throw an exception and leave the list unmodified. 546 * 547 * @throws UnsupportedOperationException always 548 * @deprecated Unsupported operation. 549 */ 550 @CanIgnoreReturnValue 551 @Deprecated 552 @Override 553 @DoNotCall("Always throws UnsupportedOperationException") 554 public final E remove(int index) { 555 throw new UnsupportedOperationException(); 556 } 557 558 /** 559 * Guaranteed to throw an exception and leave the list unmodified. 560 * 561 * @throws UnsupportedOperationException always 562 * @deprecated Unsupported operation. 563 */ 564 @Deprecated 565 @Override 566 @DoNotCall("Always throws UnsupportedOperationException") 567 public final void replaceAll(UnaryOperator<E> operator) { 568 throw new UnsupportedOperationException(); 569 } 570 571 /** 572 * Guaranteed to throw an exception and leave the list unmodified. 573 * 574 * @throws UnsupportedOperationException always 575 * @deprecated Unsupported operation. 576 */ 577 @Deprecated 578 @Override 579 @DoNotCall("Always throws UnsupportedOperationException") 580 public final void sort(Comparator<? super E> c) { 581 throw new UnsupportedOperationException(); 582 } 583 584 /** 585 * Returns this list instance. 586 * 587 * @since 2.0 588 * @deprecated There is no reason to use this; it always returns {@code this}. 589 */ 590 @InlineMe(replacement = "this") 591 @Deprecated 592 @Override 593 public final ImmutableList<E> asList() { 594 return this; 595 } 596 597 @Override 598 public Spliterator<E> spliterator() { 599 return CollectSpliterators.indexed(size(), SPLITERATOR_CHARACTERISTICS, this::get); 600 } 601 602 @Override 603 int copyIntoArray(@Nullable Object[] dst, int offset) { 604 // this loop is faster for RandomAccess instances, which ImmutableLists are 605 int size = size(); 606 for (int i = 0; i < size; i++) { 607 dst[offset + i] = get(i); 608 } 609 return offset + size; 610 } 611 612 /** 613 * Returns a view of this immutable list in reverse order. For example, {@code ImmutableList.of(1, 614 * 2, 3).reverse()} is equivalent to {@code ImmutableList.of(3, 2, 1)}. 615 * 616 * @return a view of this immutable list in reverse order 617 * @since 7.0 618 */ 619 public ImmutableList<E> reverse() { 620 return (size() <= 1) ? this : new ReverseImmutableList<E>(this); 621 } 622 623 private static class ReverseImmutableList<E> extends ImmutableList<E> { 624 private final transient ImmutableList<E> forwardList; 625 626 ReverseImmutableList(ImmutableList<E> backingList) { 627 this.forwardList = backingList; 628 } 629 630 private int reverseIndex(int index) { 631 return (size() - 1) - index; 632 } 633 634 private int reversePosition(int index) { 635 return size() - index; 636 } 637 638 @Override 639 public ImmutableList<E> reverse() { 640 return forwardList; 641 } 642 643 @Override 644 public boolean contains(@CheckForNull Object object) { 645 return forwardList.contains(object); 646 } 647 648 @Override 649 public int indexOf(@CheckForNull Object object) { 650 int index = forwardList.lastIndexOf(object); 651 return (index >= 0) ? reverseIndex(index) : -1; 652 } 653 654 @Override 655 public int lastIndexOf(@CheckForNull Object object) { 656 int index = forwardList.indexOf(object); 657 return (index >= 0) ? reverseIndex(index) : -1; 658 } 659 660 @Override 661 public ImmutableList<E> subList(int fromIndex, int toIndex) { 662 checkPositionIndexes(fromIndex, toIndex, size()); 663 return forwardList.subList(reversePosition(toIndex), reversePosition(fromIndex)).reverse(); 664 } 665 666 @Override 667 public E get(int index) { 668 checkElementIndex(index, size()); 669 return forwardList.get(reverseIndex(index)); 670 } 671 672 @Override 673 public int size() { 674 return forwardList.size(); 675 } 676 677 @Override 678 boolean isPartialView() { 679 return forwardList.isPartialView(); 680 } 681 } 682 683 @Override 684 public boolean equals(@CheckForNull Object obj) { 685 return Lists.equalsImpl(this, obj); 686 } 687 688 @Override 689 public int hashCode() { 690 int hashCode = 1; 691 int n = size(); 692 for (int i = 0; i < n; i++) { 693 hashCode = 31 * hashCode + get(i).hashCode(); 694 695 hashCode = ~~hashCode; 696 // needed to deal with GWT integer overflow 697 } 698 return hashCode; 699 } 700 701 /* 702 * Serializes ImmutableLists as their logical contents. This ensures that 703 * implementation types do not leak into the serialized representation. 704 */ 705 static class SerializedForm implements Serializable { 706 final Object[] elements; 707 708 SerializedForm(Object[] elements) { 709 this.elements = elements; 710 } 711 712 Object readResolve() { 713 return copyOf(elements); 714 } 715 716 private static final long serialVersionUID = 0; 717 } 718 719 private void readObject(ObjectInputStream stream) throws InvalidObjectException { 720 throw new InvalidObjectException("Use SerializedForm"); 721 } 722 723 @Override 724 Object writeReplace() { 725 return new SerializedForm(toArray()); 726 } 727 728 /** 729 * Returns a new builder. The generated builder is equivalent to the builder created by the {@link 730 * Builder} constructor. 731 */ 732 public static <E> Builder<E> builder() { 733 return new Builder<E>(); 734 } 735 736 /** 737 * Returns a new builder, expecting the specified number of elements to be added. 738 * 739 * <p>If {@code expectedSize} is exactly the number of elements added to the builder before {@link 740 * Builder#build} is called, the builder is likely to perform better than an unsized {@link 741 * #builder()} would have. 742 * 743 * <p>It is not specified if any performance benefits apply if {@code expectedSize} is close to, 744 * but not exactly, the number of elements added to the builder. 745 * 746 * @since 23.1 747 */ 748 @Beta 749 public static <E> Builder<E> builderWithExpectedSize(int expectedSize) { 750 checkNonnegative(expectedSize, "expectedSize"); 751 return new ImmutableList.Builder<E>(expectedSize); 752 } 753 754 /** 755 * A builder for creating immutable list instances, especially {@code public static final} lists 756 * ("constant lists"). Example: 757 * 758 * <pre>{@code 759 * public static final ImmutableList<Color> GOOGLE_COLORS 760 * = new ImmutableList.Builder<Color>() 761 * .addAll(WEBSAFE_COLORS) 762 * .add(new Color(0, 191, 255)) 763 * .build(); 764 * }</pre> 765 * 766 * <p>Elements appear in the resulting list in the same order they were added to the builder. 767 * 768 * <p>Builder instances can be reused; it is safe to call {@link #build} multiple times to build 769 * multiple lists in series. Each new list contains all the elements of the ones created before 770 * it. 771 * 772 * @since 2.0 773 */ 774 public static final class Builder<E> extends ImmutableCollection.Builder<E> { 775 // The first `size` elements are non-null. 776 @VisibleForTesting @Nullable Object[] contents; 777 private int size; 778 private boolean forceCopy; 779 780 /** 781 * Creates a new builder. The returned builder is equivalent to the builder generated by {@link 782 * ImmutableList#builder}. 783 */ 784 public Builder() { 785 this(DEFAULT_INITIAL_CAPACITY); 786 } 787 788 Builder(int capacity) { 789 this.contents = new @Nullable Object[capacity]; 790 this.size = 0; 791 } 792 793 private void getReadyToExpandTo(int minCapacity) { 794 if (contents.length < minCapacity) { 795 this.contents = Arrays.copyOf(contents, expandedCapacity(contents.length, minCapacity)); 796 forceCopy = false; 797 } else if (forceCopy) { 798 contents = Arrays.copyOf(contents, contents.length); 799 forceCopy = false; 800 } 801 } 802 803 /** 804 * Adds {@code element} to the {@code ImmutableList}. 805 * 806 * @param element the element to add 807 * @return this {@code Builder} object 808 * @throws NullPointerException if {@code element} is null 809 */ 810 @CanIgnoreReturnValue 811 @Override 812 public Builder<E> add(E element) { 813 checkNotNull(element); 814 getReadyToExpandTo(size + 1); 815 contents[size++] = element; 816 return this; 817 } 818 819 /** 820 * Adds each element of {@code elements} to the {@code ImmutableList}. 821 * 822 * @param elements the {@code Iterable} to add to the {@code ImmutableList} 823 * @return this {@code Builder} object 824 * @throws NullPointerException if {@code elements} is null or contains a null element 825 */ 826 @CanIgnoreReturnValue 827 @Override 828 public Builder<E> add(E... elements) { 829 checkElementsNotNull(elements); 830 add(elements, elements.length); 831 return this; 832 } 833 834 private void add(@Nullable Object[] elements, int n) { 835 getReadyToExpandTo(size + n); 836 /* 837 * The following call is not statically checked, since arraycopy accepts plain Object for its 838 * parameters. If it were statically checked, the checker would still be OK with it, since 839 * we're copying into a `contents` array whose type allows it to contain nulls. Still, it's 840 * worth noting that we promise not to put nulls into the array in the first `size` elements. 841 * We uphold that promise here because our callers promise that `elements` will not contain 842 * nulls in its first `n` elements. 843 */ 844 System.arraycopy(elements, 0, contents, size, n); 845 size += n; 846 } 847 848 /** 849 * Adds each element of {@code elements} to the {@code ImmutableList}. 850 * 851 * @param elements the {@code Iterable} to add to the {@code ImmutableList} 852 * @return this {@code Builder} object 853 * @throws NullPointerException if {@code elements} is null or contains a null element 854 */ 855 @CanIgnoreReturnValue 856 @Override 857 public Builder<E> addAll(Iterable<? extends E> elements) { 858 checkNotNull(elements); 859 if (elements instanceof Collection) { 860 Collection<?> collection = (Collection<?>) elements; 861 getReadyToExpandTo(size + collection.size()); 862 if (collection instanceof ImmutableCollection) { 863 ImmutableCollection<?> immutableCollection = (ImmutableCollection<?>) collection; 864 size = immutableCollection.copyIntoArray(contents, size); 865 return this; 866 } 867 } 868 super.addAll(elements); 869 return this; 870 } 871 872 /** 873 * Adds each element of {@code elements} to the {@code ImmutableList}. 874 * 875 * @param elements the {@code Iterator} to add to the {@code ImmutableList} 876 * @return this {@code Builder} object 877 * @throws NullPointerException if {@code elements} is null or contains a null element 878 */ 879 @CanIgnoreReturnValue 880 @Override 881 public Builder<E> addAll(Iterator<? extends E> elements) { 882 super.addAll(elements); 883 return this; 884 } 885 886 @CanIgnoreReturnValue 887 Builder<E> combine(Builder<E> builder) { 888 checkNotNull(builder); 889 add(builder.contents, builder.size); 890 return this; 891 } 892 893 /** 894 * Returns a newly-created {@code ImmutableList} based on the contents of the {@code Builder}. 895 */ 896 @Override 897 public ImmutableList<E> build() { 898 forceCopy = true; 899 return asImmutableList(contents, size); 900 } 901 } 902}