001/* 002 * Copyright (C) 2008 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.collect; 016 017import static com.google.common.base.Preconditions.checkNotNull; 018 019import com.google.common.annotations.GwtCompatible; 020import com.google.common.annotations.GwtIncompatible; 021import com.google.common.base.Function; 022import com.google.common.base.Joiner; 023import com.google.common.base.Optional; 024import com.google.common.base.Predicate; 025import com.google.errorprone.annotations.CanIgnoreReturnValue; 026import com.google.errorprone.annotations.InlineMe; 027import java.util.Arrays; 028import java.util.Collection; 029import java.util.Collections; 030import java.util.Comparator; 031import java.util.Iterator; 032import java.util.List; 033import java.util.SortedSet; 034import java.util.stream.Stream; 035import javax.annotation.CheckForNull; 036import org.checkerframework.checker.nullness.qual.NonNull; 037import org.checkerframework.checker.nullness.qual.Nullable; 038 039/** 040 * A discouraged (but not deprecated) precursor to Java's superior {@link Stream} library. 041 * 042 * <p>The following types of methods are provided: 043 * 044 * <ul> 045 * <li>chaining methods which return a new {@code FluentIterable} based in some way on the 046 * contents of the current one (for example {@link #transform}) 047 * <li>element extraction methods which facilitate the retrieval of certain elements (for example 048 * {@link #last}) 049 * <li>query methods which answer questions about the {@code FluentIterable}'s contents (for 050 * example {@link #anyMatch}) 051 * <li>conversion methods which copy the {@code FluentIterable}'s contents into a new collection 052 * or array (for example {@link #toList}) 053 * </ul> 054 * 055 * <p>Several lesser-used features are currently available only as static methods on the {@link 056 * Iterables} class. 057 * 058 * <p><a id="streams"></a> 059 * 060 * <h3>Comparison to streams</h3> 061 * 062 * <p>{@link Stream} is similar to this class, but generally more powerful, and certainly more 063 * standard. Key differences include: 064 * 065 * <ul> 066 * <li>A stream is <i>single-use</i>; it becomes invalid as soon as any "terminal operation" such 067 * as {@code findFirst()} or {@code iterator()} is invoked. (Even though {@code Stream} 068 * contains all the right method <i>signatures</i> to implement {@link Iterable}, it does not 069 * actually do so, to avoid implying repeat-iterability.) {@code FluentIterable}, on the other 070 * hand, is multiple-use, and does implement {@link Iterable}. 071 * <li>Streams offer many features not found here, including {@code min/max}, {@code distinct}, 072 * {@code reduce}, {@code sorted}, the very powerful {@code collect}, and built-in support for 073 * parallelizing stream operations. 074 * <li>{@code FluentIterable} contains several features not available on {@code Stream}, which are 075 * noted in the method descriptions below. 076 * <li>Streams include primitive-specialized variants such as {@code IntStream}, the use of which 077 * is strongly recommended. 078 * <li>Streams are standard Java, not requiring a third-party dependency. 079 * </ul> 080 * 081 * <h3>Example</h3> 082 * 083 * <p>Here is an example that accepts a list from a database call, filters it based on a predicate, 084 * transforms it by invoking {@code toString()} on each element, and returns the first 10 elements 085 * as a {@code List}: 086 * 087 * <pre>{@code 088 * ImmutableList<String> results = 089 * FluentIterable.from(database.getClientList()) 090 * .filter(Client::isActiveInLastMonth) 091 * .transform(Object::toString) 092 * .limit(10) 093 * .toList(); 094 * }</pre> 095 * 096 * The approximate stream equivalent is: 097 * 098 * <pre>{@code 099 * List<String> results = 100 * database.getClientList() 101 * .stream() 102 * .filter(Client::isActiveInLastMonth) 103 * .map(Object::toString) 104 * .limit(10) 105 * .collect(Collectors.toList()); 106 * }</pre> 107 * 108 * @author Marcin Mikosik 109 * @since 12.0 110 */ 111@GwtCompatible(emulated = true) 112@ElementTypesAreNonnullByDefault 113public abstract class FluentIterable<E extends @Nullable Object> implements Iterable<E> { 114 // We store 'iterable' and use it instead of 'this' to allow Iterables to perform instanceof 115 // checks on the _original_ iterable when FluentIterable.from is used. 116 // To avoid a self retain cycle under j2objc, we store Optional.absent() instead of 117 // Optional.of(this). To access the delegate iterable, call #getDelegate(), which converts to 118 // absent() back to 'this'. 119 private final Optional<Iterable<E>> iterableDelegate; 120 121 /** Constructor for use by subclasses. */ 122 protected FluentIterable() { 123 this.iterableDelegate = Optional.absent(); 124 } 125 126 FluentIterable(Iterable<E> iterable) { 127 this.iterableDelegate = Optional.of(iterable); 128 } 129 130 private Iterable<E> getDelegate() { 131 return iterableDelegate.or(this); 132 } 133 134 /** 135 * Returns a fluent iterable that wraps {@code iterable}, or {@code iterable} itself if it is 136 * already a {@code FluentIterable}. 137 * 138 * <p><b>{@code Stream} equivalent:</b> {@link Collection#stream} if {@code iterable} is a {@link 139 * Collection}; {@link Streams#stream(Iterable)} otherwise. 140 */ 141 public static <E extends @Nullable Object> FluentIterable<E> from(final Iterable<E> iterable) { 142 return (iterable instanceof FluentIterable) 143 ? (FluentIterable<E>) iterable 144 : new FluentIterable<E>(iterable) { 145 @Override 146 public Iterator<E> iterator() { 147 return iterable.iterator(); 148 } 149 }; 150 } 151 152 /** 153 * Returns a fluent iterable containing {@code elements} in the specified order. 154 * 155 * <p>The returned iterable is an unmodifiable view of the input array. 156 * 157 * <p><b>{@code Stream} equivalent:</b> {@link java.util.stream.Stream#of(Object[]) 158 * Stream.of(T...)}. 159 * 160 * @since 20.0 (since 18.0 as an overload of {@code of}) 161 */ 162 public static <E extends @Nullable Object> FluentIterable<E> from(E[] elements) { 163 return from(Arrays.asList(elements)); 164 } 165 166 /** 167 * Construct a fluent iterable from another fluent iterable. This is obviously never necessary, 168 * but is intended to help call out cases where one migration from {@code Iterable} to {@code 169 * FluentIterable} has obviated the need to explicitly convert to a {@code FluentIterable}. 170 * 171 * @deprecated instances of {@code FluentIterable} don't need to be converted to {@code 172 * FluentIterable} 173 */ 174 @Deprecated 175 @InlineMe( 176 replacement = "checkNotNull(iterable)", 177 staticImports = {"com.google.common.base.Preconditions.checkNotNull"}) 178 public static <E extends @Nullable Object> FluentIterable<E> from(FluentIterable<E> iterable) { 179 return checkNotNull(iterable); 180 } 181 182 /** 183 * Returns a fluent iterable that combines two iterables. The returned iterable has an iterator 184 * that traverses the elements in {@code a}, followed by the elements in {@code b}. The source 185 * iterators are not polled until necessary. 186 * 187 * <p>The returned iterable's iterator supports {@code remove()} when the corresponding input 188 * iterator supports it. 189 * 190 * <p><b>{@code Stream} equivalent:</b> {@link Stream#concat}. 191 * 192 * @since 20.0 193 */ 194 public static <T extends @Nullable Object> FluentIterable<T> concat( 195 Iterable<? extends T> a, Iterable<? extends T> b) { 196 return concatNoDefensiveCopy(a, b); 197 } 198 199 /** 200 * Returns a fluent iterable that combines three iterables. The returned iterable has an iterator 201 * that traverses the elements in {@code a}, followed by the elements in {@code b}, followed by 202 * the elements in {@code c}. The source iterators are not polled until necessary. 203 * 204 * <p>The returned iterable's iterator supports {@code remove()} when the corresponding input 205 * iterator supports it. 206 * 207 * <p><b>{@code Stream} equivalent:</b> use nested calls to {@link Stream#concat}, or see the 208 * advice in {@link #concat(Iterable...)}. 209 * 210 * @since 20.0 211 */ 212 public static <T extends @Nullable Object> FluentIterable<T> concat( 213 Iterable<? extends T> a, Iterable<? extends T> b, Iterable<? extends T> c) { 214 return concatNoDefensiveCopy(a, b, c); 215 } 216 217 /** 218 * Returns a fluent iterable that combines four iterables. The returned iterable has an iterator 219 * that traverses the elements in {@code a}, followed by the elements in {@code b}, followed by 220 * the elements in {@code c}, followed by the elements in {@code d}. The source iterators are not 221 * polled until necessary. 222 * 223 * <p>The returned iterable's iterator supports {@code remove()} when the corresponding input 224 * iterator supports it. 225 * 226 * <p><b>{@code Stream} equivalent:</b> use nested calls to {@link Stream#concat}, or see the 227 * advice in {@link #concat(Iterable...)}. 228 * 229 * @since 20.0 230 */ 231 public static <T extends @Nullable Object> FluentIterable<T> concat( 232 Iterable<? extends T> a, 233 Iterable<? extends T> b, 234 Iterable<? extends T> c, 235 Iterable<? extends T> d) { 236 return concatNoDefensiveCopy(a, b, c, d); 237 } 238 239 /** 240 * Returns a fluent iterable that combines several iterables. The returned iterable has an 241 * iterator that traverses the elements of each iterable in {@code inputs}. The input iterators 242 * are not polled until necessary. 243 * 244 * <p>The returned iterable's iterator supports {@code remove()} when the corresponding input 245 * iterator supports it. 246 * 247 * <p><b>{@code Stream} equivalent:</b> to concatenate an arbitrary number of streams, use {@code 248 * Stream.of(stream1, stream2, ...).flatMap(s -> s)}. If the sources are iterables, use {@code 249 * Stream.of(iter1, iter2, ...).flatMap(Streams::stream)}. 250 * 251 * @throws NullPointerException if any of the provided iterables is {@code null} 252 * @since 20.0 253 */ 254 public static <T extends @Nullable Object> FluentIterable<T> concat( 255 Iterable<? extends T>... inputs) { 256 return concatNoDefensiveCopy(Arrays.copyOf(inputs, inputs.length)); 257 } 258 259 /** 260 * Returns a fluent iterable that combines several iterables. The returned iterable has an 261 * iterator that traverses the elements of each iterable in {@code inputs}. The input iterators 262 * are not polled until necessary. 263 * 264 * <p>The returned iterable's iterator supports {@code remove()} when the corresponding input 265 * iterator supports it. The methods of the returned iterable may throw {@code 266 * NullPointerException} if any of the input iterators is {@code null}. 267 * 268 * <p><b>{@code Stream} equivalent:</b> {@code streamOfStreams.flatMap(s -> s)} or {@code 269 * streamOfIterables.flatMap(Streams::stream)}. (See {@link Streams#stream}.) 270 * 271 * @since 20.0 272 */ 273 public static <T extends @Nullable Object> FluentIterable<T> concat( 274 final Iterable<? extends Iterable<? extends T>> inputs) { 275 checkNotNull(inputs); 276 return new FluentIterable<T>() { 277 @Override 278 public Iterator<T> iterator() { 279 return Iterators.concat(Iterators.transform(inputs.iterator(), Iterable::iterator)); 280 } 281 }; 282 } 283 284 /** Concatenates a varargs array of iterables without making a defensive copy of the array. */ 285 private static <T extends @Nullable Object> FluentIterable<T> concatNoDefensiveCopy( 286 final Iterable<? extends T>... inputs) { 287 for (Iterable<? extends T> input : inputs) { 288 checkNotNull(input); 289 } 290 return new FluentIterable<T>() { 291 @Override 292 public Iterator<T> iterator() { 293 return Iterators.concat( 294 /* lazily generate the iterators on each input only as needed */ 295 new AbstractIndexedListIterator<Iterator<? extends T>>(inputs.length) { 296 @Override 297 public Iterator<? extends T> get(int i) { 298 return inputs[i].iterator(); 299 } 300 }); 301 } 302 }; 303 } 304 305 /** 306 * Returns a fluent iterable containing no elements. 307 * 308 * <p><b>{@code Stream} equivalent:</b> {@link Stream#empty}. 309 * 310 * @since 20.0 311 */ 312 public static <E extends @Nullable Object> FluentIterable<E> of() { 313 return FluentIterable.from(Collections.<E>emptyList()); 314 } 315 316 /** 317 * Returns a fluent iterable containing the specified elements in order. 318 * 319 * <p><b>{@code Stream} equivalent:</b> {@link java.util.stream.Stream#of(Object[]) 320 * Stream.of(T...)}. 321 * 322 * @since 20.0 323 */ 324 public static <E extends @Nullable Object> FluentIterable<E> of( 325 @ParametricNullness E element, E... elements) { 326 return from(Lists.asList(element, elements)); 327 } 328 329 /** 330 * Returns a string representation of this fluent iterable, with the format {@code [e1, e2, ..., 331 * en]}. 332 * 333 * <p><b>{@code Stream} equivalent:</b> {@code stream.collect(Collectors.joining(", ", "[", "]"))} 334 * or (less efficiently) {@code stream.collect(Collectors.toList()).toString()}. 335 */ 336 @Override 337 public String toString() { 338 return Iterables.toString(getDelegate()); 339 } 340 341 /** 342 * Returns the number of elements in this fluent iterable. 343 * 344 * <p><b>{@code Stream} equivalent:</b> {@link Stream#count}. 345 */ 346 public final int size() { 347 return Iterables.size(getDelegate()); 348 } 349 350 /** 351 * Returns {@code true} if this fluent iterable contains any object for which {@code 352 * equals(target)} is true. 353 * 354 * <p><b>{@code Stream} equivalent:</b> {@code stream.anyMatch(Predicate.isEqual(target))}. 355 */ 356 public final boolean contains(@CheckForNull Object target) { 357 return Iterables.contains(getDelegate(), target); 358 } 359 360 /** 361 * Returns a fluent iterable whose {@code Iterator} cycles indefinitely over the elements of this 362 * fluent iterable. 363 * 364 * <p>That iterator supports {@code remove()} if {@code iterable.iterator()} does. After {@code 365 * remove()} is called, subsequent cycles omit the removed element, which is no longer in this 366 * fluent iterable. The iterator's {@code hasNext()} method returns {@code true} until this fluent 367 * iterable is empty. 368 * 369 * <p><b>Warning:</b> Typical uses of the resulting iterator may produce an infinite loop. You 370 * should use an explicit {@code break} or be certain that you will eventually remove all the 371 * elements. 372 * 373 * <p><b>{@code Stream} equivalent:</b> if the source iterable has only a single element {@code 374 * e}, use {@code Stream.generate(() -> e)}. Otherwise, collect your stream into a collection and 375 * use {@code Stream.generate(() -> collection).flatMap(Collection::stream)}. 376 */ 377 public final FluentIterable<E> cycle() { 378 return from(Iterables.cycle(getDelegate())); 379 } 380 381 /** 382 * Returns a fluent iterable whose iterators traverse first the elements of this fluent iterable, 383 * followed by those of {@code other}. The iterators are not polled until necessary. 384 * 385 * <p>The returned iterable's {@code Iterator} supports {@code remove()} when the corresponding 386 * {@code Iterator} supports it. 387 * 388 * <p><b>{@code Stream} equivalent:</b> {@link Stream#concat}. 389 * 390 * @since 18.0 391 */ 392 public final FluentIterable<E> append(Iterable<? extends E> other) { 393 return FluentIterable.concat(getDelegate(), other); 394 } 395 396 /** 397 * Returns a fluent iterable whose iterators traverse first the elements of this fluent iterable, 398 * followed by {@code elements}. 399 * 400 * <p><b>{@code Stream} equivalent:</b> {@code Stream.concat(thisStream, Stream.of(elements))}. 401 * 402 * @since 18.0 403 */ 404 public final FluentIterable<E> append(E... elements) { 405 return FluentIterable.concat(getDelegate(), Arrays.asList(elements)); 406 } 407 408 /** 409 * Returns the elements from this fluent iterable that satisfy a predicate. The resulting fluent 410 * iterable's iterator does not support {@code remove()}. 411 * 412 * <p><b>{@code Stream} equivalent:</b> {@link Stream#filter} (same). 413 */ 414 public final FluentIterable<E> filter(Predicate<? super E> predicate) { 415 return from(Iterables.filter(getDelegate(), predicate)); 416 } 417 418 /** 419 * Returns the elements from this fluent iterable that are instances of class {@code type}. 420 * 421 * <p><b>{@code Stream} equivalent:</b> {@code stream.filter(type::isInstance).map(type::cast)}. 422 * This does perform a little more work than necessary, so another option is to insert an 423 * unchecked cast at some later point: 424 * 425 * <pre> 426 * {@code @SuppressWarnings("unchecked") // safe because of ::isInstance check 427 * ImmutableList<NewType> result = 428 * (ImmutableList) stream.filter(NewType.class::isInstance).collect(toImmutableList());} 429 * </pre> 430 */ 431 @GwtIncompatible // Class.isInstance 432 public final <T> FluentIterable<T> filter(Class<T> type) { 433 return from(Iterables.filter(getDelegate(), type)); 434 } 435 436 /** 437 * Returns {@code true} if any element in this fluent iterable satisfies the predicate. 438 * 439 * <p><b>{@code Stream} equivalent:</b> {@link Stream#anyMatch} (same). 440 */ 441 public final boolean anyMatch(Predicate<? super E> predicate) { 442 return Iterables.any(getDelegate(), predicate); 443 } 444 445 /** 446 * Returns {@code true} if every element in this fluent iterable satisfies the predicate. If this 447 * fluent iterable is empty, {@code true} is returned. 448 * 449 * <p><b>{@code Stream} equivalent:</b> {@link Stream#allMatch} (same). 450 */ 451 public final boolean allMatch(Predicate<? super E> predicate) { 452 return Iterables.all(getDelegate(), predicate); 453 } 454 455 /** 456 * Returns an {@link Optional} containing the first element in this fluent iterable that satisfies 457 * the given predicate, if such an element exists. 458 * 459 * <p><b>Warning:</b> avoid using a {@code predicate} that matches {@code null}. If {@code null} 460 * is matched in this fluent iterable, a {@link NullPointerException} will be thrown. 461 * 462 * <p><b>{@code Stream} equivalent:</b> {@code stream.filter(predicate).findFirst()}. 463 */ 464 @SuppressWarnings("nullness") // Unsafe, but we can't do much about it now. 465 public final Optional<@NonNull E> firstMatch(Predicate<? super E> predicate) { 466 return Iterables.<E>tryFind((Iterable<@NonNull E>) getDelegate(), predicate); 467 } 468 469 /** 470 * Returns a fluent iterable that applies {@code function} to each element of this fluent 471 * iterable. 472 * 473 * <p>The returned fluent iterable's iterator supports {@code remove()} if this iterable's 474 * iterator does. After a successful {@code remove()} call, this fluent iterable no longer 475 * contains the corresponding element. 476 * 477 * <p><b>{@code Stream} equivalent:</b> {@link Stream#map}. 478 */ 479 public final <T extends @Nullable Object> FluentIterable<T> transform( 480 Function<? super E, T> function) { 481 return from(Iterables.transform(getDelegate(), function)); 482 } 483 484 /** 485 * Applies {@code function} to each element of this fluent iterable and returns a fluent iterable 486 * with the concatenated combination of results. {@code function} returns an Iterable of results. 487 * 488 * <p>The returned fluent iterable's iterator supports {@code remove()} if this function-returned 489 * iterables' iterator does. After a successful {@code remove()} call, the returned fluent 490 * iterable no longer contains the corresponding element. 491 * 492 * <p><b>{@code Stream} equivalent:</b> {@link Stream#flatMap} (using a function that produces 493 * streams, not iterables). 494 * 495 * @since 13.0 (required {@code Function<E, Iterable<T>>} until 14.0) 496 */ 497 public <T extends @Nullable Object> FluentIterable<T> transformAndConcat( 498 Function<? super E, ? extends Iterable<? extends T>> function) { 499 return FluentIterable.concat(transform(function)); 500 } 501 502 /** 503 * Returns an {@link Optional} containing the first element in this fluent iterable. If the 504 * iterable is empty, {@code Optional.absent()} is returned. 505 * 506 * <p><b>{@code Stream} equivalent:</b> if the goal is to obtain any element, {@link 507 * Stream#findAny}; if it must specifically be the <i>first</i> element, {@code Stream#findFirst}. 508 * 509 * @throws NullPointerException if the first element is null; if this is a possibility, use {@code 510 * iterator().next()} or {@link Iterables#getFirst} instead. 511 */ 512 @SuppressWarnings("nullness") // Unsafe, but we can't do much about it now. 513 public final Optional<@NonNull E> first() { 514 Iterator<E> iterator = getDelegate().iterator(); 515 return iterator.hasNext() ? Optional.of(iterator.next()) : Optional.absent(); 516 } 517 518 /** 519 * Returns an {@link Optional} containing the last element in this fluent iterable. If the 520 * iterable is empty, {@code Optional.absent()} is returned. If the underlying {@code iterable} is 521 * a {@link List} with {@link java.util.RandomAccess} support, then this operation is guaranteed 522 * to be {@code O(1)}. 523 * 524 * <p><b>{@code Stream} equivalent:</b> {@code stream.reduce((a, b) -> b)}. 525 * 526 * @throws NullPointerException if the last element is null; if this is a possibility, use {@link 527 * Iterables#getLast} instead. 528 */ 529 @SuppressWarnings("nullness") // Unsafe, but we can't do much about it now. 530 public final Optional<@NonNull E> last() { 531 // Iterables#getLast was inlined here so we don't have to throw/catch a NSEE 532 533 // TODO(kevinb): Support a concurrently modified collection? 534 Iterable<E> iterable = getDelegate(); 535 if (iterable instanceof List) { 536 List<E> list = (List<E>) iterable; 537 if (list.isEmpty()) { 538 return Optional.absent(); 539 } 540 return Optional.of(list.get(list.size() - 1)); 541 } 542 Iterator<E> iterator = iterable.iterator(); 543 if (!iterator.hasNext()) { 544 return Optional.absent(); 545 } 546 547 /* 548 * TODO(kevinb): consider whether this "optimization" is worthwhile. Users with SortedSets tend 549 * to know they are SortedSets and probably would not call this method. 550 */ 551 if (iterable instanceof SortedSet) { 552 SortedSet<E> sortedSet = (SortedSet<E>) iterable; 553 return Optional.of(sortedSet.last()); 554 } 555 556 while (true) { 557 E current = iterator.next(); 558 if (!iterator.hasNext()) { 559 return Optional.of(current); 560 } 561 } 562 } 563 564 /** 565 * Returns a view of this fluent iterable that skips its first {@code numberToSkip} elements. If 566 * this fluent iterable contains fewer than {@code numberToSkip} elements, the returned fluent 567 * iterable skips all of its elements. 568 * 569 * <p>Modifications to this fluent iterable before a call to {@code iterator()} are reflected in 570 * the returned fluent iterable. That is, the iterator skips the first {@code numberToSkip} 571 * elements that exist when the iterator is created, not when {@code skip()} is called. 572 * 573 * <p>The returned fluent iterable's iterator supports {@code remove()} if the {@code Iterator} of 574 * this fluent iterable supports it. Note that it is <i>not</i> possible to delete the last 575 * skipped element by immediately calling {@code remove()} on the returned fluent iterable's 576 * iterator, as the {@code Iterator} contract states that a call to {@code * remove()} before a 577 * call to {@code next()} will throw an {@link IllegalStateException}. 578 * 579 * <p><b>{@code Stream} equivalent:</b> {@link Stream#skip} (same). 580 */ 581 public final FluentIterable<E> skip(int numberToSkip) { 582 return from(Iterables.skip(getDelegate(), numberToSkip)); 583 } 584 585 /** 586 * Creates a fluent iterable with the first {@code size} elements of this fluent iterable. If this 587 * fluent iterable does not contain that many elements, the returned fluent iterable will have the 588 * same behavior as this fluent iterable. The returned fluent iterable's iterator supports {@code 589 * remove()} if this fluent iterable's iterator does. 590 * 591 * <p><b>{@code Stream} equivalent:</b> {@link Stream#limit} (same). 592 * 593 * @param maxSize the maximum number of elements in the returned fluent iterable 594 * @throws IllegalArgumentException if {@code size} is negative 595 */ 596 public final FluentIterable<E> limit(int maxSize) { 597 return from(Iterables.limit(getDelegate(), maxSize)); 598 } 599 600 /** 601 * Determines whether this fluent iterable is empty. 602 * 603 * <p><b>{@code Stream} equivalent:</b> {@code !stream.findAny().isPresent()}. 604 */ 605 public final boolean isEmpty() { 606 return !getDelegate().iterator().hasNext(); 607 } 608 609 /** 610 * Returns an {@code ImmutableList} containing all of the elements from this fluent iterable in 611 * proper sequence. 612 * 613 * <p><b>{@code Stream} equivalent:</b> pass {@link ImmutableList#toImmutableList} to {@code 614 * stream.collect()}. 615 * 616 * @throws NullPointerException if any element is {@code null} 617 * @since 14.0 (since 12.0 as {@code toImmutableList()}). 618 */ 619 @SuppressWarnings("nullness") // Unsafe, but we can't do much about it now. 620 public final ImmutableList<@NonNull E> toList() { 621 return ImmutableList.copyOf((Iterable<@NonNull E>) getDelegate()); 622 } 623 624 /** 625 * Returns an {@code ImmutableList} containing all of the elements from this {@code 626 * FluentIterable} in the order specified by {@code comparator}. To produce an {@code 627 * ImmutableList} sorted by its natural ordering, use {@code toSortedList(Ordering.natural())}. 628 * 629 * <p><b>{@code Stream} equivalent:</b> pass {@link ImmutableList#toImmutableList} to {@code 630 * stream.sorted(comparator).collect()}. 631 * 632 * @param comparator the function by which to sort list elements 633 * @throws NullPointerException if any element of this iterable is {@code null} 634 * @since 14.0 (since 13.0 as {@code toSortedImmutableList()}). 635 */ 636 @SuppressWarnings("nullness") // Unsafe, but we can't do much about it now. 637 public final ImmutableList<@NonNull E> toSortedList(Comparator<? super E> comparator) { 638 return Ordering.from(comparator).immutableSortedCopy((Iterable<@NonNull E>) getDelegate()); 639 } 640 641 /** 642 * Returns an {@code ImmutableSet} containing all of the elements from this fluent iterable with 643 * duplicates removed. 644 * 645 * <p><b>{@code Stream} equivalent:</b> pass {@link ImmutableSet#toImmutableSet} to {@code 646 * stream.collect()}. 647 * 648 * @throws NullPointerException if any element is {@code null} 649 * @since 14.0 (since 12.0 as {@code toImmutableSet()}). 650 */ 651 @SuppressWarnings("nullness") // Unsafe, but we can't do much about it now. 652 public final ImmutableSet<@NonNull E> toSet() { 653 return ImmutableSet.copyOf((Iterable<@NonNull E>) getDelegate()); 654 } 655 656 /** 657 * Returns an {@code ImmutableSortedSet} containing all of the elements from this {@code 658 * FluentIterable} in the order specified by {@code comparator}, with duplicates (determined by 659 * {@code comparator.compare(x, y) == 0}) removed. To produce an {@code ImmutableSortedSet} sorted 660 * by its natural ordering, use {@code toSortedSet(Ordering.natural())}. 661 * 662 * <p><b>{@code Stream} equivalent:</b> pass {@link ImmutableSortedSet#toImmutableSortedSet} to 663 * {@code stream.collect()}. 664 * 665 * @param comparator the function by which to sort set elements 666 * @throws NullPointerException if any element of this iterable is {@code null} 667 * @since 14.0 (since 12.0 as {@code toImmutableSortedSet()}). 668 */ 669 @SuppressWarnings("nullness") // Unsafe, but we can't do much about it now. 670 public final ImmutableSortedSet<@NonNull E> toSortedSet(Comparator<? super E> comparator) { 671 return ImmutableSortedSet.copyOf(comparator, (Iterable<@NonNull E>) getDelegate()); 672 } 673 674 /** 675 * Returns an {@code ImmutableMultiset} containing all of the elements from this fluent iterable. 676 * 677 * <p><b>{@code Stream} equivalent:</b> pass {@link ImmutableMultiset#toImmutableMultiset} to 678 * {@code stream.collect()}. 679 * 680 * @throws NullPointerException if any element is null 681 * @since 19.0 682 */ 683 @SuppressWarnings("nullness") // Unsafe, but we can't do much about it now. 684 public final ImmutableMultiset<@NonNull E> toMultiset() { 685 return ImmutableMultiset.copyOf((Iterable<@NonNull E>) getDelegate()); 686 } 687 688 /** 689 * Returns an immutable map whose keys are the distinct elements of this {@code FluentIterable} 690 * and whose value for each key was computed by {@code valueFunction}. The map's iteration order 691 * is the order of the first appearance of each key in this iterable. 692 * 693 * <p>When there are multiple instances of a key in this iterable, it is unspecified whether 694 * {@code valueFunction} will be applied to more than one instance of that key and, if it is, 695 * which result will be mapped to that key in the returned map. 696 * 697 * <p><b>{@code Stream} equivalent:</b> {@code stream.collect(ImmutableMap.toImmutableMap(k -> k, 698 * valueFunction))}. 699 * 700 * @throws NullPointerException if any element of this iterable is {@code null}, or if {@code 701 * valueFunction} produces {@code null} for any key 702 * @since 14.0 703 */ 704 @SuppressWarnings("nullness") // Unsafe, but we can't do much about it now. 705 public final <V> ImmutableMap<@NonNull E, V> toMap(Function<? super E, V> valueFunction) { 706 return Maps.toMap((Iterable<@NonNull E>) getDelegate(), valueFunction); 707 } 708 709 /** 710 * Creates an index {@code ImmutableListMultimap} that contains the results of applying a 711 * specified function to each item in this {@code FluentIterable} of values. Each element of this 712 * iterable will be stored as a value in the resulting multimap, yielding a multimap with the same 713 * size as this iterable. The key used to store that value in the multimap will be the result of 714 * calling the function on that value. The resulting multimap is created as an immutable snapshot. 715 * In the returned multimap, keys appear in the order they are first encountered, and the values 716 * corresponding to each key appear in the same order as they are encountered. 717 * 718 * <p><b>{@code Stream} equivalent:</b> {@code stream.collect(Collectors.groupingBy(keyFunction))} 719 * behaves similarly, but returns a mutable {@code Map<K, List<E>>} instead, and may not preserve 720 * the order of entries. 721 * 722 * @param keyFunction the function used to produce the key for each value 723 * @throws NullPointerException if any element of this iterable is {@code null}, or if {@code 724 * keyFunction} produces {@code null} for any key 725 * @since 14.0 726 */ 727 @SuppressWarnings("nullness") // Unsafe, but we can't do much about it now. 728 public final <K> ImmutableListMultimap<K, @NonNull E> index(Function<? super E, K> keyFunction) { 729 return Multimaps.index((Iterable<@NonNull E>) getDelegate(), keyFunction); 730 } 731 732 /** 733 * Returns a map with the contents of this {@code FluentIterable} as its {@code values}, indexed 734 * by keys derived from those values. In other words, each input value produces an entry in the 735 * map whose key is the result of applying {@code keyFunction} to that value. These entries appear 736 * in the same order as they appeared in this fluent iterable. Example usage: 737 * 738 * <pre>{@code 739 * Color red = new Color("red", 255, 0, 0); 740 * ... 741 * FluentIterable<Color> allColors = FluentIterable.from(ImmutableSet.of(red, green, blue)); 742 * 743 * Map<String, Color> colorForName = allColors.uniqueIndex(toStringFunction()); 744 * assertThat(colorForName).containsEntry("red", red); 745 * }</pre> 746 * 747 * <p>If your index may associate multiple values with each key, use {@link #index(Function) 748 * index}. 749 * 750 * <p><b>{@code Stream} equivalent:</b> {@code 751 * stream.collect(ImmutableMap.toImmutableMap(keyFunction, v -> v))}. 752 * 753 * @param keyFunction the function used to produce the key for each value 754 * @return a map mapping the result of evaluating the function {@code keyFunction} on each value 755 * in this fluent iterable to that value 756 * @throws IllegalArgumentException if {@code keyFunction} produces the same key for more than one 757 * value in this fluent iterable 758 * @throws NullPointerException if any element of this iterable is {@code null}, or if {@code 759 * keyFunction} produces {@code null} for any key 760 * @since 14.0 761 */ 762 @SuppressWarnings("nullness") // Unsafe, but we can't do much about it now. 763 public final <K> ImmutableMap<K, @NonNull E> uniqueIndex(Function<? super E, K> keyFunction) { 764 return Maps.uniqueIndex((Iterable<@NonNull E>) getDelegate(), keyFunction); 765 } 766 767 /** 768 * Returns an array containing all of the elements from this fluent iterable in iteration order. 769 * 770 * <p><b>{@code Stream} equivalent:</b> if an object array is acceptable, use {@code 771 * stream.toArray()}; if {@code type} is a class literal such as {@code MyType.class}, use {@code 772 * stream.toArray(MyType[]::new)}. Otherwise use {@code stream.toArray( len -> (E[]) 773 * Array.newInstance(type, len))}. 774 * 775 * @param type the type of the elements 776 * @return a newly-allocated array into which all the elements of this fluent iterable have been 777 * copied 778 */ 779 @GwtIncompatible // Array.newArray(Class, int) 780 public final @Nullable E[] toArray(Class<@NonNull E> type) { 781 return Iterables.toArray(getDelegate(), type); 782 } 783 784 /** 785 * Copies all the elements from this fluent iterable to {@code collection}. This is equivalent to 786 * calling {@code Iterables.addAll(collection, this)}. 787 * 788 * <p><b>{@code Stream} equivalent:</b> {@code stream.forEachOrdered(collection::add)} or {@code 789 * stream.forEach(collection::add)}. 790 * 791 * @param collection the collection to copy elements to 792 * @return {@code collection}, for convenience 793 * @since 14.0 794 */ 795 @CanIgnoreReturnValue 796 public final <C extends Collection<? super E>> C copyInto(C collection) { 797 checkNotNull(collection); 798 Iterable<E> iterable = getDelegate(); 799 if (iterable instanceof Collection) { 800 collection.addAll((Collection<E>) iterable); 801 } else { 802 for (E item : iterable) { 803 collection.add(item); 804 } 805 } 806 return collection; 807 } 808 809 /** 810 * Returns a {@link String} containing all of the elements of this fluent iterable joined with 811 * {@code joiner}. 812 * 813 * <p><b>{@code Stream} equivalent:</b> {@code joiner.join(stream.iterator())}, or, if you are not 814 * using any optional {@code Joiner} features, {@code 815 * stream.collect(Collectors.joining(delimiter)}. 816 * 817 * @since 18.0 818 */ 819 public final String join(Joiner joiner) { 820 return joiner.join(this); 821 } 822 823 /** 824 * Returns the element at the specified position in this fluent iterable. 825 * 826 * <p><b>{@code Stream} equivalent:</b> {@code stream.skip(position).findFirst().get()} (but note 827 * that this throws different exception types, and throws an exception if {@code null} would be 828 * returned). 829 * 830 * @param position position of the element to return 831 * @return the element at the specified position in this fluent iterable 832 * @throws IndexOutOfBoundsException if {@code position} is negative or greater than or equal to 833 * the size of this fluent iterable 834 */ 835 @ParametricNullness 836 public final E get(int position) { 837 return Iterables.get(getDelegate(), position); 838 } 839 840 /** 841 * Returns a stream of this fluent iterable's contents (similar to calling {@link 842 * Collection#stream} on a collection). 843 * 844 * <p><b>Note:</b> the earlier in the chain you can switch to {@code Stream} usage (ideally not 845 * going through {@code FluentIterable} at all), the more performant and idiomatic your code will 846 * be. This method is a transitional aid, to be used only when really necessary. 847 * 848 * @since 21.0 849 */ 850 public final Stream<E> stream() { 851 return Streams.stream(getDelegate()); 852 } 853 854 /** Function that transforms {@code Iterable<E>} into a fluent iterable. */ 855 private static class FromIterableFunction<E extends @Nullable Object> 856 implements Function<Iterable<E>, FluentIterable<E>> { 857 @Override 858 public FluentIterable<E> apply(Iterable<E> fromObject) { 859 return FluentIterable.from(fromObject); 860 } 861 } 862}