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.checkElementIndex; 020import static com.google.common.base.Preconditions.checkNotNull; 021import static com.google.common.base.Preconditions.checkPositionIndexes; 022import static com.google.common.collect.ObjectArrays.arraysCopyOf; 023import static com.google.common.collect.ObjectArrays.checkElementsNotNull; 024import static com.google.common.collect.RegularImmutableList.EMPTY; 025 026import com.google.common.annotations.GwtCompatible; 027 028import java.io.InvalidObjectException; 029import java.io.ObjectInputStream; 030import java.io.Serializable; 031import java.util.Collection; 032import java.util.Collections; 033import java.util.Iterator; 034import java.util.List; 035import java.util.RandomAccess; 036 037import javax.annotation.Nullable; 038 039/** 040 * A {@link List} whose contents will never change, with many other important properties detailed at 041 * {@link ImmutableCollection}. 042 * 043 * <p>See the Guava User Guide article on <a href= 044 * "https://github.com/google/guava/wiki/ImmutableCollectionsExplained"> 045 * immutable collections</a>. 046 * 047 * @see ImmutableMap 048 * @see ImmutableSet 049 * @author Kevin Bourrillion 050 * @since 2.0 051 */ 052@GwtCompatible(serializable = true, emulated = true) 053@SuppressWarnings("serial") // we're overriding default serialization 054public abstract class ImmutableList<E> extends ImmutableCollection<E> 055 implements List<E>, RandomAccess { 056 /** 057 * Returns the empty immutable list. This set behaves and performs comparably 058 * to {@link Collections#emptyList}, and is preferable mainly for consistency 059 * and maintainability of your code. 060 */ 061 // Casting to any type is safe because the list will never hold any elements. 062 @SuppressWarnings("unchecked") 063 public static <E> ImmutableList<E> of() { 064 return (ImmutableList<E>) EMPTY; 065 } 066 067 /** 068 * Returns an immutable list containing a single element. This list behaves 069 * and performs comparably to {@link Collections#singleton}, but will not 070 * accept a null element. It is preferable mainly for consistency and 071 * maintainability of your code. 072 * 073 * @throws NullPointerException if {@code element} is null 074 */ 075 public static <E> ImmutableList<E> of(E element) { 076 return new SingletonImmutableList<E>(element); 077 } 078 079 /** 080 * Returns an immutable list containing the given elements, in order. 081 * 082 * @throws NullPointerException if any element is null 083 */ 084 public static <E> ImmutableList<E> of(E e1, E e2) { 085 return construct(e1, e2); 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, E e3) { 094 return construct(e1, e2, e3); 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, E e4) { 103 return construct(e1, e2, e3, e4); 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, E e5) { 112 return construct(e1, e2, e3, e4, e5); 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, E e6) { 121 return construct(e1, e2, e3, e4, e5, e6); 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, E e7) { 130 return construct(e1, e2, e3, e4, e5, e6, e7); 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, E e8) { 139 return construct(e1, e2, e3, e4, e5, e6, e7, e8); 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, E e9) { 148 return construct(e1, e2, e3, e4, e5, e6, e7, e8, e9); 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( 157 E e1, E e2, E e3, E e4, E e5, E e6, E e7, E e8, E e9, E e10) { 158 return construct(e1, e2, e3, e4, e5, e6, e7, e8, e9, e10); 159 } 160 161 /** 162 * Returns an immutable list containing the given elements, in order. 163 * 164 * @throws NullPointerException if any element is null 165 */ 166 public static <E> ImmutableList<E> of( 167 E e1, E e2, E e3, E e4, E e5, E e6, E e7, E e8, E e9, E e10, E e11) { 168 return construct(e1, e2, e3, e4, e5, e6, e7, e8, e9, e10, e11); 169 } 170 171 // These go up to eleven. After that, you just get the varargs form, and 172 // whatever warnings might come along with it. :( 173 174 /** 175 * Returns an immutable list containing the given elements, in order. 176 * 177 * @throws NullPointerException if any element is null 178 * @since 3.0 (source-compatible since 2.0) 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, E e11, E e12, E... others) { 182 Object[] array = new Object[12 + others.length]; 183 array[0] = e1; 184 array[1] = e2; 185 array[2] = e3; 186 array[3] = e4; 187 array[4] = e5; 188 array[5] = e6; 189 array[6] = e7; 190 array[7] = e8; 191 array[8] = e9; 192 array[9] = e10; 193 array[10] = e11; 194 array[11] = e12; 195 System.arraycopy(others, 0, array, 12, others.length); 196 return construct(array); 197 } 198 199 /** 200 * Returns an immutable list containing the given elements, in order. If 201 * {@code elements} is a {@link Collection}, this method behaves exactly as 202 * {@link #copyOf(Collection)}; otherwise, it behaves exactly as {@code 203 * copyOf(elements.iterator()}. 204 * 205 * @throws NullPointerException if any of {@code elements} is null 206 */ 207 public static <E> ImmutableList<E> copyOf(Iterable<? extends E> elements) { 208 checkNotNull(elements); // TODO(kevinb): is this here only for GWT? 209 return (elements instanceof Collection) 210 ? copyOf((Collection<? extends E>) elements) 211 : copyOf(elements.iterator()); 212 } 213 214 /** 215 * Returns an immutable list containing the given elements, in order. 216 * 217 * <p>Despite the method name, this method attempts to avoid actually copying 218 * the data when it is safe to do so. The exact circumstances under which a 219 * copy will or will not be performed are undocumented and subject to change. 220 * 221 * <p>Note that if {@code list} is a {@code List<String>}, then {@code 222 * ImmutableList.copyOf(list)} returns an {@code ImmutableList<String>} 223 * containing each of the strings in {@code list}, while 224 * ImmutableList.of(list)} returns an {@code ImmutableList<List<String>>} 225 * containing one element (the given list itself). 226 * 227 * <p>This method is safe to use even when {@code elements} is a synchronized 228 * or concurrent collection that is currently being modified by another 229 * thread. 230 * 231 * @throws NullPointerException if any of {@code elements} is null 232 */ 233 public static <E> ImmutableList<E> copyOf(Collection<? extends E> elements) { 234 if (elements instanceof ImmutableCollection) { 235 @SuppressWarnings("unchecked") // all supported methods are covariant 236 ImmutableList<E> list = ((ImmutableCollection<E>) elements).asList(); 237 return list.isPartialView() 238 ? ImmutableList.<E>asImmutableList(list.toArray()) 239 : list; 240 } 241 return construct(elements.toArray()); 242 } 243 244 /** 245 * Returns an immutable list containing the given elements, in order. 246 * 247 * @throws NullPointerException if any of {@code elements} is null 248 */ 249 public static <E> ImmutableList<E> copyOf(Iterator<? extends E> elements) { 250 // We special-case for 0 or 1 elements, but going further is madness. 251 if (!elements.hasNext()) { 252 return of(); 253 } 254 E first = elements.next(); 255 if (!elements.hasNext()) { 256 return of(first); 257 } else { 258 return new ImmutableList.Builder<E>() 259 .add(first) 260 .addAll(elements) 261 .build(); 262 } 263 } 264 265 /** 266 * Returns an immutable list containing the given elements, in order. 267 * 268 * @throws NullPointerException if any of {@code elements} is null 269 * @since 3.0 270 */ 271 public static <E> ImmutableList<E> copyOf(E[] elements) { 272 switch (elements.length) { 273 case 0: 274 return ImmutableList.of(); 275 case 1: 276 return new SingletonImmutableList<E>(elements[0]); 277 default: 278 return new RegularImmutableList<E>(checkElementsNotNull(elements.clone())); 279 } 280 } 281 282 /** 283 * Views the array as an immutable list. Checks for nulls; does not copy. 284 */ 285 private static <E> ImmutableList<E> construct(Object... elements) { 286 return asImmutableList(checkElementsNotNull(elements)); 287 } 288 289 /** 290 * Views the array as an immutable list. Does not check for nulls; does not copy. 291 * 292 * <p>The array must be internally created. 293 */ 294 static <E> ImmutableList<E> asImmutableList(Object[] elements) { 295 return asImmutableList(elements, elements.length); 296 } 297 298 /** 299 * Views the array as an immutable list. Copies if the specified range does not cover the complete 300 * array. Does not check for nulls. 301 */ 302 static <E> ImmutableList<E> asImmutableList(Object[] elements, int length) { 303 switch (length) { 304 case 0: 305 return of(); 306 case 1: 307 @SuppressWarnings("unchecked") // collection had only Es in it 308 ImmutableList<E> list = new SingletonImmutableList<E>((E) elements[0]); 309 return list; 310 default: 311 if (length < elements.length) { 312 elements = arraysCopyOf(elements, length); 313 } 314 return new RegularImmutableList<E>(elements); 315 } 316 } 317 318 ImmutableList() {} 319 320 // This declaration is needed to make List.iterator() and 321 // ImmutableCollection.iterator() consistent. 322 @Override 323 public UnmodifiableIterator<E> iterator() { 324 return listIterator(); 325 } 326 327 @Override 328 public UnmodifiableListIterator<E> listIterator() { 329 return listIterator(0); 330 } 331 332 @Override 333 public UnmodifiableListIterator<E> listIterator(int index) { 334 return new AbstractIndexedListIterator<E>(size(), index) { 335 @Override 336 protected E get(int index) { 337 return ImmutableList.this.get(index); 338 } 339 }; 340 } 341 342 @Override 343 public int indexOf(@Nullable Object object) { 344 return (object == null) ? -1 : Lists.indexOfImpl(this, object); 345 } 346 347 @Override 348 public int lastIndexOf(@Nullable Object object) { 349 return (object == null) ? -1 : Lists.lastIndexOfImpl(this, object); 350 } 351 352 @Override 353 public boolean contains(@Nullable Object object) { 354 return indexOf(object) >= 0; 355 } 356 357 // constrain the return type to ImmutableList<E> 358 359 /** 360 * Returns an immutable list of the elements between the specified {@code 361 * fromIndex}, inclusive, and {@code toIndex}, exclusive. (If {@code 362 * fromIndex} and {@code toIndex} are equal, the empty immutable list is 363 * returned.) 364 */ 365 @Override 366 public ImmutableList<E> subList(int fromIndex, int toIndex) { 367 checkPositionIndexes(fromIndex, toIndex, size()); 368 int length = toIndex - fromIndex; 369 if (length == size()) { 370 return this; 371 } 372 switch (length) { 373 case 0: 374 return of(); 375 case 1: 376 return of(get(fromIndex)); 377 default: 378 return subListUnchecked(fromIndex, toIndex); 379 } 380 } 381 382 /** 383 * Called by the default implementation of {@link #subList} when {@code 384 * toIndex - fromIndex > 1}, after index validation has already been 385 * performed. 386 */ 387 ImmutableList<E> subListUnchecked(int fromIndex, int toIndex) { 388 return new SubList(fromIndex, toIndex - fromIndex); 389 } 390 391 class SubList extends ImmutableList<E> { 392 final transient int offset; 393 final transient int length; 394 395 SubList(int offset, int length) { 396 this.offset = offset; 397 this.length = length; 398 } 399 400 @Override 401 public int size() { 402 return length; 403 } 404 405 @Override 406 public E get(int index) { 407 checkElementIndex(index, length); 408 return ImmutableList.this.get(index + offset); 409 } 410 411 @Override 412 public ImmutableList<E> subList(int fromIndex, int toIndex) { 413 checkPositionIndexes(fromIndex, toIndex, length); 414 return ImmutableList.this.subList(fromIndex + offset, toIndex + offset); 415 } 416 417 @Override 418 boolean isPartialView() { 419 return true; 420 } 421 } 422 423 /** 424 * Guaranteed to throw an exception and leave the list unmodified. 425 * 426 * @throws UnsupportedOperationException always 427 * @deprecated Unsupported operation. 428 */ 429 @Deprecated 430 @Override 431 public final boolean addAll(int index, Collection<? extends E> newElements) { 432 throw new UnsupportedOperationException(); 433 } 434 435 /** 436 * Guaranteed to throw an exception and leave the list unmodified. 437 * 438 * @throws UnsupportedOperationException always 439 * @deprecated Unsupported operation. 440 */ 441 @Deprecated 442 @Override 443 public final E set(int index, E element) { 444 throw new UnsupportedOperationException(); 445 } 446 447 /** 448 * Guaranteed to throw an exception and leave the list unmodified. 449 * 450 * @throws UnsupportedOperationException always 451 * @deprecated Unsupported operation. 452 */ 453 @Deprecated 454 @Override 455 public final void add(int index, E element) { 456 throw new UnsupportedOperationException(); 457 } 458 459 /** 460 * Guaranteed to throw an exception and leave the list unmodified. 461 * 462 * @throws UnsupportedOperationException always 463 * @deprecated Unsupported operation. 464 */ 465 @Deprecated 466 @Override 467 public final E remove(int index) { 468 throw new UnsupportedOperationException(); 469 } 470 471 /** 472 * Returns this list instance. 473 * 474 * @since 2.0 475 */ 476 @Override 477 public final ImmutableList<E> asList() { 478 return this; 479 } 480 481 @Override 482 int copyIntoArray(Object[] dst, int offset) { 483 // this loop is faster for RandomAccess instances, which ImmutableLists are 484 int size = size(); 485 for (int i = 0; i < size; i++) { 486 dst[offset + i] = get(i); 487 } 488 return offset + size; 489 } 490 491 /** 492 * Returns a view of this immutable list in reverse order. For example, {@code 493 * ImmutableList.of(1, 2, 3).reverse()} is equivalent to {@code 494 * ImmutableList.of(3, 2, 1)}. 495 * 496 * @return a view of this immutable list in reverse order 497 * @since 7.0 498 */ 499 public ImmutableList<E> reverse() { 500 return (size() <= 1) ? this : new ReverseImmutableList<E>(this); 501 } 502 503 private static class ReverseImmutableList<E> extends ImmutableList<E> { 504 private final transient ImmutableList<E> forwardList; 505 506 ReverseImmutableList(ImmutableList<E> backingList) { 507 this.forwardList = backingList; 508 } 509 510 private int reverseIndex(int index) { 511 return (size() - 1) - index; 512 } 513 514 private int reversePosition(int index) { 515 return size() - index; 516 } 517 518 @Override 519 public ImmutableList<E> reverse() { 520 return forwardList; 521 } 522 523 @Override 524 public boolean contains(@Nullable Object object) { 525 return forwardList.contains(object); 526 } 527 528 @Override 529 public int indexOf(@Nullable Object object) { 530 int index = forwardList.lastIndexOf(object); 531 return (index >= 0) ? reverseIndex(index) : -1; 532 } 533 534 @Override 535 public int lastIndexOf(@Nullable Object object) { 536 int index = forwardList.indexOf(object); 537 return (index >= 0) ? reverseIndex(index) : -1; 538 } 539 540 @Override 541 public ImmutableList<E> subList(int fromIndex, int toIndex) { 542 checkPositionIndexes(fromIndex, toIndex, size()); 543 return forwardList 544 .subList(reversePosition(toIndex), reversePosition(fromIndex)) 545 .reverse(); 546 } 547 548 @Override 549 public E get(int index) { 550 checkElementIndex(index, size()); 551 return forwardList.get(reverseIndex(index)); 552 } 553 554 @Override 555 public int size() { 556 return forwardList.size(); 557 } 558 559 @Override 560 boolean isPartialView() { 561 return forwardList.isPartialView(); 562 } 563 } 564 565 @Override 566 public boolean equals(@Nullable Object obj) { 567 return Lists.equalsImpl(this, obj); 568 } 569 570 @Override 571 public int hashCode() { 572 int hashCode = 1; 573 int n = size(); 574 for (int i = 0; i < n; i++) { 575 hashCode = 31 * hashCode + get(i).hashCode(); 576 577 hashCode = ~~hashCode; 578 // needed to deal with GWT integer overflow 579 } 580 return hashCode; 581 } 582 583 /* 584 * Serializes ImmutableLists as their logical contents. This ensures that 585 * implementation types do not leak into the serialized representation. 586 */ 587 static class SerializedForm implements Serializable { 588 final Object[] elements; 589 590 SerializedForm(Object[] elements) { 591 this.elements = elements; 592 } 593 594 Object readResolve() { 595 return copyOf(elements); 596 } 597 598 private static final long serialVersionUID = 0; 599 } 600 601 private void readObject(ObjectInputStream stream) throws InvalidObjectException { 602 throw new InvalidObjectException("Use SerializedForm"); 603 } 604 605 @Override 606 Object writeReplace() { 607 return new SerializedForm(toArray()); 608 } 609 610 /** 611 * Returns a new builder. The generated builder is equivalent to the builder 612 * created by the {@link Builder} constructor. 613 */ 614 public static <E> Builder<E> builder() { 615 return new Builder<E>(); 616 } 617 618 /** 619 * A builder for creating immutable list instances, especially {@code public 620 * static final} lists ("constant lists"). Example: <pre> {@code 621 * 622 * public static final ImmutableList<Color> GOOGLE_COLORS 623 * = new ImmutableList.Builder<Color>() 624 * .addAll(WEBSAFE_COLORS) 625 * .add(new Color(0, 191, 255)) 626 * .build();}</pre> 627 * 628 * <p>Builder instances can be reused; it is safe to call {@link #build} multiple 629 * times to build multiple lists in series. Each new list contains all the 630 * elements of the ones created before it. 631 * 632 * @since 2.0 633 */ 634 public static final class Builder<E> extends ImmutableCollection.ArrayBasedBuilder<E> { 635 /** 636 * Creates a new builder. The returned builder is equivalent to the builder 637 * generated by {@link ImmutableList#builder}. 638 */ 639 public Builder() { 640 this(DEFAULT_INITIAL_CAPACITY); 641 } 642 643 // TODO(lowasser): consider exposing this 644 Builder(int capacity) { 645 super(capacity); 646 } 647 648 /** 649 * Adds {@code element} to the {@code ImmutableList}. 650 * 651 * @param element the element to add 652 * @return this {@code Builder} object 653 * @throws NullPointerException if {@code element} is null 654 */ 655 @Override 656 public Builder<E> add(E element) { 657 super.add(element); 658 return this; 659 } 660 661 /** 662 * Adds each element of {@code elements} to the {@code ImmutableList}. 663 * 664 * @param elements the {@code Iterable} to add to the {@code ImmutableList} 665 * @return this {@code Builder} object 666 * @throws NullPointerException if {@code elements} is null or contains a 667 * null element 668 */ 669 @Override 670 public Builder<E> addAll(Iterable<? extends E> elements) { 671 super.addAll(elements); 672 return this; 673 } 674 675 /** 676 * Adds each element of {@code elements} to the {@code ImmutableList}. 677 * 678 * @param elements the {@code Iterable} to add to the {@code ImmutableList} 679 * @return this {@code Builder} object 680 * @throws NullPointerException if {@code elements} is null or contains a 681 * null element 682 */ 683 @Override 684 public Builder<E> add(E... elements) { 685 super.add(elements); 686 return this; 687 } 688 689 /** 690 * Adds each element of {@code elements} to the {@code ImmutableList}. 691 * 692 * @param elements the {@code Iterable} to add to the {@code ImmutableList} 693 * @return this {@code Builder} object 694 * @throws NullPointerException if {@code elements} is null or contains a 695 * null element 696 */ 697 @Override 698 public Builder<E> addAll(Iterator<? extends E> elements) { 699 super.addAll(elements); 700 return this; 701 } 702 703 /** 704 * Returns a newly-created {@code ImmutableList} based on the contents of 705 * the {@code Builder}. 706 */ 707 @Override 708 public ImmutableList<E> build() { 709 return asImmutableList(contents, size); 710 } 711 } 712}