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 @SafeVarargs 255 public static <T extends @Nullable Object> FluentIterable<T> concat( 256 Iterable<? extends T>... inputs) { 257 return concatNoDefensiveCopy(Arrays.copyOf(inputs, inputs.length)); 258 } 259 260 /** 261 * Returns a fluent iterable that combines several iterables. The returned iterable has an 262 * iterator that traverses the elements of each iterable in {@code inputs}. The input iterators 263 * are not polled until necessary. 264 * 265 * <p>The returned iterable's iterator supports {@code remove()} when the corresponding input 266 * iterator supports it. The methods of the returned iterable may throw {@code 267 * NullPointerException} if any of the input iterators is {@code null}. 268 * 269 * <p><b>{@code Stream} equivalent:</b> {@code streamOfStreams.flatMap(s -> s)} or {@code 270 * streamOfIterables.flatMap(Streams::stream)}. (See {@link Streams#stream}.) 271 * 272 * @since 20.0 273 */ 274 public static <T extends @Nullable Object> FluentIterable<T> concat( 275 final Iterable<? extends Iterable<? extends T>> inputs) { 276 checkNotNull(inputs); 277 return new FluentIterable<T>() { 278 @Override 279 public Iterator<T> iterator() { 280 return Iterators.concat(Iterators.transform(inputs.iterator(), Iterable::iterator)); 281 } 282 }; 283 } 284 285 /** Concatenates a varargs array of iterables without making a defensive copy of the array. */ 286 private static <T extends @Nullable Object> FluentIterable<T> concatNoDefensiveCopy( 287 final Iterable<? extends T>... inputs) { 288 for (Iterable<? extends T> input : inputs) { 289 checkNotNull(input); 290 } 291 return new FluentIterable<T>() { 292 @Override 293 public Iterator<T> iterator() { 294 return Iterators.concat( 295 /* lazily generate the iterators on each input only as needed */ 296 new AbstractIndexedListIterator<Iterator<? extends T>>(inputs.length) { 297 @Override 298 public Iterator<? extends T> get(int i) { 299 return inputs[i].iterator(); 300 } 301 }); 302 } 303 }; 304 } 305 306 /** 307 * Returns a fluent iterable containing no elements. 308 * 309 * <p><b>{@code Stream} equivalent:</b> {@link Stream#empty}. 310 * 311 * @since 20.0 312 */ 313 public static <E extends @Nullable Object> FluentIterable<E> of() { 314 return FluentIterable.from(Collections.<E>emptyList()); 315 } 316 317 /** 318 * Returns a fluent iterable containing the specified elements in order. 319 * 320 * <p><b>{@code Stream} equivalent:</b> {@link java.util.stream.Stream#of(Object[]) 321 * Stream.of(T...)}. 322 * 323 * @since 20.0 324 */ 325 public static <E extends @Nullable Object> FluentIterable<E> of( 326 @ParametricNullness E element, E... elements) { 327 return from(Lists.asList(element, elements)); 328 } 329 330 /** 331 * Returns a string representation of this fluent iterable, with the format {@code [e1, e2, ..., 332 * en]}. 333 * 334 * <p><b>{@code Stream} equivalent:</b> {@code stream.collect(Collectors.joining(", ", "[", "]"))} 335 * or (less efficiently) {@code stream.collect(Collectors.toList()).toString()}. 336 */ 337 @Override 338 public String toString() { 339 return Iterables.toString(getDelegate()); 340 } 341 342 /** 343 * Returns the number of elements in this fluent iterable. 344 * 345 * <p><b>{@code Stream} equivalent:</b> {@link Stream#count}. 346 */ 347 public final int size() { 348 return Iterables.size(getDelegate()); 349 } 350 351 /** 352 * Returns {@code true} if this fluent iterable contains any object for which {@code 353 * equals(target)} is true. 354 * 355 * <p><b>{@code Stream} equivalent:</b> {@code stream.anyMatch(Predicate.isEqual(target))}. 356 */ 357 public final boolean contains(@CheckForNull Object target) { 358 return Iterables.contains(getDelegate(), target); 359 } 360 361 /** 362 * Returns a fluent iterable whose {@code Iterator} cycles indefinitely over the elements of this 363 * fluent iterable. 364 * 365 * <p>That iterator supports {@code remove()} if {@code iterable.iterator()} does. After {@code 366 * remove()} is called, subsequent cycles omit the removed element, which is no longer in this 367 * fluent iterable. The iterator's {@code hasNext()} method returns {@code true} until this fluent 368 * iterable is empty. 369 * 370 * <p><b>Warning:</b> Typical uses of the resulting iterator may produce an infinite loop. You 371 * should use an explicit {@code break} or be certain that you will eventually remove all the 372 * elements. 373 * 374 * <p><b>{@code Stream} equivalent:</b> if the source iterable has only a single element {@code 375 * e}, use {@code Stream.generate(() -> e)}. Otherwise, collect your stream into a collection and 376 * use {@code Stream.generate(() -> collection).flatMap(Collection::stream)}. 377 */ 378 public final FluentIterable<E> cycle() { 379 return from(Iterables.cycle(getDelegate())); 380 } 381 382 /** 383 * Returns a fluent iterable whose iterators traverse first the elements of this fluent iterable, 384 * followed by those of {@code other}. The iterators are not polled until necessary. 385 * 386 * <p>The returned iterable's {@code Iterator} supports {@code remove()} when the corresponding 387 * {@code Iterator} supports it. 388 * 389 * <p><b>{@code Stream} equivalent:</b> {@link Stream#concat}. 390 * 391 * @since 18.0 392 */ 393 public final FluentIterable<E> append(Iterable<? extends E> other) { 394 return FluentIterable.concat(getDelegate(), other); 395 } 396 397 /** 398 * Returns a fluent iterable whose iterators traverse first the elements of this fluent iterable, 399 * followed by {@code elements}. 400 * 401 * <p><b>{@code Stream} equivalent:</b> {@code Stream.concat(thisStream, Stream.of(elements))}. 402 * 403 * @since 18.0 404 */ 405 public final FluentIterable<E> append(E... elements) { 406 return FluentIterable.concat(getDelegate(), Arrays.asList(elements)); 407 } 408 409 /** 410 * Returns the elements from this fluent iterable that satisfy a predicate. The resulting fluent 411 * iterable's iterator does not support {@code remove()}. 412 * 413 * <p><b>{@code Stream} equivalent:</b> {@link Stream#filter} (same). 414 */ 415 public final FluentIterable<E> filter(Predicate<? super E> predicate) { 416 return from(Iterables.filter(getDelegate(), predicate)); 417 } 418 419 /** 420 * Returns the elements from this fluent iterable that are instances of class {@code type}. 421 * 422 * <p><b>{@code Stream} equivalent:</b> {@code stream.filter(type::isInstance).map(type::cast)}. 423 * This does perform a little more work than necessary, so another option is to insert an 424 * unchecked cast at some later point: 425 * 426 * <pre> 427 * {@code @SuppressWarnings("unchecked") // safe because of ::isInstance check 428 * ImmutableList<NewType> result = 429 * (ImmutableList) stream.filter(NewType.class::isInstance).collect(toImmutableList());} 430 * </pre> 431 */ 432 @GwtIncompatible // Class.isInstance 433 public final <T> FluentIterable<T> filter(Class<T> type) { 434 return from(Iterables.filter(getDelegate(), type)); 435 } 436 437 /** 438 * Returns {@code true} if any element in this fluent iterable satisfies the predicate. 439 * 440 * <p><b>{@code Stream} equivalent:</b> {@link Stream#anyMatch} (same). 441 */ 442 public final boolean anyMatch(Predicate<? super E> predicate) { 443 return Iterables.any(getDelegate(), predicate); 444 } 445 446 /** 447 * Returns {@code true} if every element in this fluent iterable satisfies the predicate. If this 448 * fluent iterable is empty, {@code true} is returned. 449 * 450 * <p><b>{@code Stream} equivalent:</b> {@link Stream#allMatch} (same). 451 */ 452 public final boolean allMatch(Predicate<? super E> predicate) { 453 return Iterables.all(getDelegate(), predicate); 454 } 455 456 /** 457 * Returns an {@link Optional} containing the first element in this fluent iterable that satisfies 458 * the given predicate, if such an element exists. 459 * 460 * <p><b>Warning:</b> avoid using a {@code predicate} that matches {@code null}. If {@code null} 461 * is matched in this fluent iterable, a {@link NullPointerException} will be thrown. 462 * 463 * <p><b>{@code Stream} equivalent:</b> {@code stream.filter(predicate).findFirst()}. 464 */ 465 @SuppressWarnings("nullness") // Unsafe, but we can't do much about it now. 466 public final Optional<@NonNull E> firstMatch(Predicate<? super E> predicate) { 467 return Iterables.<E>tryFind((Iterable<@NonNull E>) getDelegate(), predicate); 468 } 469 470 /** 471 * Returns a fluent iterable that applies {@code function} to each element of this fluent 472 * iterable. 473 * 474 * <p>The returned fluent iterable's iterator supports {@code remove()} if this iterable's 475 * iterator does. After a successful {@code remove()} call, this fluent iterable no longer 476 * contains the corresponding element. 477 * 478 * <p><b>{@code Stream} equivalent:</b> {@link Stream#map}. 479 */ 480 public final <T extends @Nullable Object> FluentIterable<T> transform( 481 Function<? super E, T> function) { 482 return from(Iterables.transform(getDelegate(), function)); 483 } 484 485 /** 486 * Applies {@code function} to each element of this fluent iterable and returns a fluent iterable 487 * with the concatenated combination of results. {@code function} returns an Iterable of results. 488 * 489 * <p>The returned fluent iterable's iterator supports {@code remove()} if this function-returned 490 * iterables' iterator does. After a successful {@code remove()} call, the returned fluent 491 * iterable no longer contains the corresponding element. 492 * 493 * <p><b>{@code Stream} equivalent:</b> {@link Stream#flatMap} (using a function that produces 494 * streams, not iterables). 495 * 496 * @since 13.0 (required {@code Function<E, Iterable<T>>} until 14.0) 497 */ 498 public <T extends @Nullable Object> FluentIterable<T> transformAndConcat( 499 Function<? super E, ? extends Iterable<? extends T>> function) { 500 return FluentIterable.concat(transform(function)); 501 } 502 503 /** 504 * Returns an {@link Optional} containing the first element in this fluent iterable. If the 505 * iterable is empty, {@code Optional.absent()} is returned. 506 * 507 * <p><b>{@code Stream} equivalent:</b> if the goal is to obtain any element, {@link 508 * Stream#findAny}; if it must specifically be the <i>first</i> element, {@code Stream#findFirst}. 509 * 510 * @throws NullPointerException if the first element is null; if this is a possibility, use {@code 511 * iterator().next()} or {@link Iterables#getFirst} instead. 512 */ 513 @SuppressWarnings("nullness") // Unsafe, but we can't do much about it now. 514 public final Optional<@NonNull E> first() { 515 Iterator<E> iterator = getDelegate().iterator(); 516 return iterator.hasNext() ? Optional.of(iterator.next()) : Optional.absent(); 517 } 518 519 /** 520 * Returns an {@link Optional} containing the last element in this fluent iterable. If the 521 * iterable is empty, {@code Optional.absent()} is returned. If the underlying {@code iterable} is 522 * a {@link List} with {@link java.util.RandomAccess} support, then this operation is guaranteed 523 * to be {@code O(1)}. 524 * 525 * <p><b>{@code Stream} equivalent:</b> {@code stream.reduce((a, b) -> b)}. 526 * 527 * @throws NullPointerException if the last element is null; if this is a possibility, use {@link 528 * Iterables#getLast} instead. 529 */ 530 @SuppressWarnings("nullness") // Unsafe, but we can't do much about it now. 531 public final Optional<@NonNull E> last() { 532 // Iterables#getLast was inlined here so we don't have to throw/catch a NSEE 533 534 // TODO(kevinb): Support a concurrently modified collection? 535 Iterable<E> iterable = getDelegate(); 536 if (iterable instanceof List) { 537 List<E> list = (List<E>) iterable; 538 if (list.isEmpty()) { 539 return Optional.absent(); 540 } 541 return Optional.of(list.get(list.size() - 1)); 542 } 543 Iterator<E> iterator = iterable.iterator(); 544 if (!iterator.hasNext()) { 545 return Optional.absent(); 546 } 547 548 /* 549 * TODO(kevinb): consider whether this "optimization" is worthwhile. Users with SortedSets tend 550 * to know they are SortedSets and probably would not call this method. 551 */ 552 if (iterable instanceof SortedSet) { 553 SortedSet<E> sortedSet = (SortedSet<E>) iterable; 554 return Optional.of(sortedSet.last()); 555 } 556 557 while (true) { 558 E current = iterator.next(); 559 if (!iterator.hasNext()) { 560 return Optional.of(current); 561 } 562 } 563 } 564 565 /** 566 * Returns a view of this fluent iterable that skips its first {@code numberToSkip} elements. If 567 * this fluent iterable contains fewer than {@code numberToSkip} elements, the returned fluent 568 * iterable skips all of its elements. 569 * 570 * <p>Modifications to this fluent iterable before a call to {@code iterator()} are reflected in 571 * the returned fluent iterable. That is, the iterator skips the first {@code numberToSkip} 572 * elements that exist when the iterator is created, not when {@code skip()} is called. 573 * 574 * <p>The returned fluent iterable's iterator supports {@code remove()} if the {@code Iterator} of 575 * this fluent iterable supports it. Note that it is <i>not</i> possible to delete the last 576 * skipped element by immediately calling {@code remove()} on the returned fluent iterable's 577 * iterator, as the {@code Iterator} contract states that a call to {@code * remove()} before a 578 * call to {@code next()} will throw an {@link IllegalStateException}. 579 * 580 * <p><b>{@code Stream} equivalent:</b> {@link Stream#skip} (same). 581 */ 582 public final FluentIterable<E> skip(int numberToSkip) { 583 return from(Iterables.skip(getDelegate(), numberToSkip)); 584 } 585 586 /** 587 * Creates a fluent iterable with the first {@code size} elements of this fluent iterable. If this 588 * fluent iterable does not contain that many elements, the returned fluent iterable will have the 589 * same behavior as this fluent iterable. The returned fluent iterable's iterator supports {@code 590 * remove()} if this fluent iterable's iterator does. 591 * 592 * <p><b>{@code Stream} equivalent:</b> {@link Stream#limit} (same). 593 * 594 * @param maxSize the maximum number of elements in the returned fluent iterable 595 * @throws IllegalArgumentException if {@code size} is negative 596 */ 597 public final FluentIterable<E> limit(int maxSize) { 598 return from(Iterables.limit(getDelegate(), maxSize)); 599 } 600 601 /** 602 * Determines whether this fluent iterable is empty. 603 * 604 * <p><b>{@code Stream} equivalent:</b> {@code !stream.findAny().isPresent()}. 605 */ 606 public final boolean isEmpty() { 607 return !getDelegate().iterator().hasNext(); 608 } 609 610 /** 611 * Returns an {@code ImmutableList} containing all of the elements from this fluent iterable in 612 * proper sequence. 613 * 614 * <p><b>{@code Stream} equivalent:</b> pass {@link ImmutableList#toImmutableList} to {@code 615 * stream.collect()}. 616 * 617 * @throws NullPointerException if any element is {@code null} 618 * @since 14.0 (since 12.0 as {@code toImmutableList()}). 619 */ 620 @SuppressWarnings("nullness") // Unsafe, but we can't do much about it now. 621 public final ImmutableList<@NonNull E> toList() { 622 return ImmutableList.copyOf((Iterable<@NonNull E>) getDelegate()); 623 } 624 625 /** 626 * Returns an {@code ImmutableList} containing all of the elements from this {@code 627 * FluentIterable} in the order specified by {@code comparator}. To produce an {@code 628 * ImmutableList} sorted by its natural ordering, use {@code toSortedList(Ordering.natural())}. 629 * 630 * <p><b>{@code Stream} equivalent:</b> pass {@link ImmutableList#toImmutableList} to {@code 631 * stream.sorted(comparator).collect()}. 632 * 633 * @param comparator the function by which to sort list elements 634 * @throws NullPointerException if any element of this iterable is {@code null} 635 * @since 14.0 (since 13.0 as {@code toSortedImmutableList()}). 636 */ 637 @SuppressWarnings("nullness") // Unsafe, but we can't do much about it now. 638 public final ImmutableList<@NonNull E> toSortedList(Comparator<? super E> comparator) { 639 return Ordering.from(comparator).immutableSortedCopy((Iterable<@NonNull E>) getDelegate()); 640 } 641 642 /** 643 * Returns an {@code ImmutableSet} containing all of the elements from this fluent iterable with 644 * duplicates removed. 645 * 646 * <p><b>{@code Stream} equivalent:</b> pass {@link ImmutableSet#toImmutableSet} to {@code 647 * stream.collect()}. 648 * 649 * @throws NullPointerException if any element is {@code null} 650 * @since 14.0 (since 12.0 as {@code toImmutableSet()}). 651 */ 652 @SuppressWarnings("nullness") // Unsafe, but we can't do much about it now. 653 public final ImmutableSet<@NonNull E> toSet() { 654 return ImmutableSet.copyOf((Iterable<@NonNull E>) getDelegate()); 655 } 656 657 /** 658 * Returns an {@code ImmutableSortedSet} containing all of the elements from this {@code 659 * FluentIterable} in the order specified by {@code comparator}, with duplicates (determined by 660 * {@code comparator.compare(x, y) == 0}) removed. To produce an {@code ImmutableSortedSet} sorted 661 * by its natural ordering, use {@code toSortedSet(Ordering.natural())}. 662 * 663 * <p><b>{@code Stream} equivalent:</b> pass {@link ImmutableSortedSet#toImmutableSortedSet} to 664 * {@code stream.collect()}. 665 * 666 * @param comparator the function by which to sort set elements 667 * @throws NullPointerException if any element of this iterable is {@code null} 668 * @since 14.0 (since 12.0 as {@code toImmutableSortedSet()}). 669 */ 670 @SuppressWarnings("nullness") // Unsafe, but we can't do much about it now. 671 public final ImmutableSortedSet<@NonNull E> toSortedSet(Comparator<? super E> comparator) { 672 return ImmutableSortedSet.copyOf(comparator, (Iterable<@NonNull E>) getDelegate()); 673 } 674 675 /** 676 * Returns an {@code ImmutableMultiset} containing all of the elements from this fluent iterable. 677 * 678 * <p><b>{@code Stream} equivalent:</b> pass {@link ImmutableMultiset#toImmutableMultiset} to 679 * {@code stream.collect()}. 680 * 681 * @throws NullPointerException if any element is null 682 * @since 19.0 683 */ 684 @SuppressWarnings("nullness") // Unsafe, but we can't do much about it now. 685 public final ImmutableMultiset<@NonNull E> toMultiset() { 686 return ImmutableMultiset.copyOf((Iterable<@NonNull E>) getDelegate()); 687 } 688 689 /** 690 * Returns an immutable map whose keys are the distinct elements of this {@code FluentIterable} 691 * and whose value for each key was computed by {@code valueFunction}. The map's iteration order 692 * is the order of the first appearance of each key in this iterable. 693 * 694 * <p>When there are multiple instances of a key in this iterable, it is unspecified whether 695 * {@code valueFunction} will be applied to more than one instance of that key and, if it is, 696 * which result will be mapped to that key in the returned map. 697 * 698 * <p><b>{@code Stream} equivalent:</b> {@code stream.collect(ImmutableMap.toImmutableMap(k -> k, 699 * valueFunction))}. 700 * 701 * @throws NullPointerException if any element of this iterable is {@code null}, or if {@code 702 * valueFunction} produces {@code null} for any key 703 * @since 14.0 704 */ 705 @SuppressWarnings("nullness") // Unsafe, but we can't do much about it now. 706 public final <V> ImmutableMap<@NonNull E, V> toMap(Function<? super E, V> valueFunction) { 707 return Maps.toMap((Iterable<@NonNull E>) getDelegate(), valueFunction); 708 } 709 710 /** 711 * Creates an index {@code ImmutableListMultimap} that contains the results of applying a 712 * specified function to each item in this {@code FluentIterable} of values. Each element of this 713 * iterable will be stored as a value in the resulting multimap, yielding a multimap with the same 714 * size as this iterable. The key used to store that value in the multimap will be the result of 715 * calling the function on that value. The resulting multimap is created as an immutable snapshot. 716 * In the returned multimap, keys appear in the order they are first encountered, and the values 717 * corresponding to each key appear in the same order as they are encountered. 718 * 719 * <p><b>{@code Stream} equivalent:</b> {@code stream.collect(Collectors.groupingBy(keyFunction))} 720 * behaves similarly, but returns a mutable {@code Map<K, List<E>>} instead, and may not preserve 721 * the order of entries. 722 * 723 * @param keyFunction the function used to produce the key for each value 724 * @throws NullPointerException if any element of this iterable is {@code null}, or if {@code 725 * keyFunction} produces {@code null} for any key 726 * @since 14.0 727 */ 728 @SuppressWarnings("nullness") // Unsafe, but we can't do much about it now. 729 public final <K> ImmutableListMultimap<K, @NonNull E> index(Function<? super E, K> keyFunction) { 730 return Multimaps.index((Iterable<@NonNull E>) getDelegate(), keyFunction); 731 } 732 733 /** 734 * Returns a map with the contents of this {@code FluentIterable} as its {@code values}, indexed 735 * by keys derived from those values. In other words, each input value produces an entry in the 736 * map whose key is the result of applying {@code keyFunction} to that value. These entries appear 737 * in the same order as they appeared in this fluent iterable. Example usage: 738 * 739 * <pre>{@code 740 * Color red = new Color("red", 255, 0, 0); 741 * ... 742 * FluentIterable<Color> allColors = FluentIterable.from(ImmutableSet.of(red, green, blue)); 743 * 744 * Map<String, Color> colorForName = allColors.uniqueIndex(toStringFunction()); 745 * assertThat(colorForName).containsEntry("red", red); 746 * }</pre> 747 * 748 * <p>If your index may associate multiple values with each key, use {@link #index(Function) 749 * index}. 750 * 751 * <p><b>{@code Stream} equivalent:</b> {@code 752 * stream.collect(ImmutableMap.toImmutableMap(keyFunction, v -> v))}. 753 * 754 * @param keyFunction the function used to produce the key for each value 755 * @return a map mapping the result of evaluating the function {@code keyFunction} on each value 756 * in this fluent iterable to that value 757 * @throws IllegalArgumentException if {@code keyFunction} produces the same key for more than one 758 * value in this fluent iterable 759 * @throws NullPointerException if any element of this iterable is {@code null}, or if {@code 760 * keyFunction} produces {@code null} for any key 761 * @since 14.0 762 */ 763 @SuppressWarnings("nullness") // Unsafe, but we can't do much about it now. 764 public final <K> ImmutableMap<K, @NonNull E> uniqueIndex(Function<? super E, K> keyFunction) { 765 return Maps.uniqueIndex((Iterable<@NonNull E>) getDelegate(), keyFunction); 766 } 767 768 /** 769 * Returns an array containing all of the elements from this fluent iterable in iteration order. 770 * 771 * <p><b>{@code Stream} equivalent:</b> if an object array is acceptable, use {@code 772 * stream.toArray()}; if {@code type} is a class literal such as {@code MyType.class}, use {@code 773 * stream.toArray(MyType[]::new)}. Otherwise use {@code stream.toArray( len -> (E[]) 774 * Array.newInstance(type, len))}. 775 * 776 * @param type the type of the elements 777 * @return a newly-allocated array into which all the elements of this fluent iterable have been 778 * copied 779 */ 780 @GwtIncompatible // Array.newArray(Class, int) 781 public final E[] toArray(Class<@NonNull E> type) { 782 return Iterables.<E>toArray(getDelegate(), type); 783 } 784 785 /** 786 * Copies all the elements from this fluent iterable to {@code collection}. This is equivalent to 787 * calling {@code Iterables.addAll(collection, this)}. 788 * 789 * <p><b>{@code Stream} equivalent:</b> {@code stream.forEachOrdered(collection::add)} or {@code 790 * stream.forEach(collection::add)}. 791 * 792 * @param collection the collection to copy elements to 793 * @return {@code collection}, for convenience 794 * @since 14.0 795 */ 796 @CanIgnoreReturnValue 797 public final <C extends Collection<? super E>> C copyInto(C collection) { 798 checkNotNull(collection); 799 Iterable<E> iterable = getDelegate(); 800 if (iterable instanceof Collection) { 801 collection.addAll((Collection<E>) iterable); 802 } else { 803 for (E item : iterable) { 804 collection.add(item); 805 } 806 } 807 return collection; 808 } 809 810 /** 811 * Returns a {@link String} containing all of the elements of this fluent iterable joined with 812 * {@code joiner}. 813 * 814 * <p><b>{@code Stream} equivalent:</b> {@code joiner.join(stream.iterator())}, or, if you are not 815 * using any optional {@code Joiner} features, {@code 816 * stream.collect(Collectors.joining(delimiter)}. 817 * 818 * @since 18.0 819 */ 820 public final String join(Joiner joiner) { 821 return joiner.join(this); 822 } 823 824 /** 825 * Returns the element at the specified position in this fluent iterable. 826 * 827 * <p><b>{@code Stream} equivalent:</b> {@code stream.skip(position).findFirst().get()} (but note 828 * that this throws different exception types, and throws an exception if {@code null} would be 829 * returned). 830 * 831 * @param position position of the element to return 832 * @return the element at the specified position in this fluent iterable 833 * @throws IndexOutOfBoundsException if {@code position} is negative or greater than or equal to 834 * the size of this fluent iterable 835 */ 836 @ParametricNullness 837 public final E get(int position) { 838 return Iterables.get(getDelegate(), position); 839 } 840 841 /** 842 * Returns a stream of this fluent iterable's contents (similar to calling {@link 843 * Collection#stream} on a collection). 844 * 845 * <p><b>Note:</b> the earlier in the chain you can switch to {@code Stream} usage (ideally not 846 * going through {@code FluentIterable} at all), the more performant and idiomatic your code will 847 * be. This method is a transitional aid, to be used only when really necessary. 848 * 849 * @since 21.0 850 */ 851 public final Stream<E> stream() { 852 return Streams.stream(getDelegate()); 853 } 854 855 /** Function that transforms {@code Iterable<E>} into a fluent iterable. */ 856 private static class FromIterableFunction<E extends @Nullable Object> 857 implements Function<Iterable<E>, FluentIterable<E>> { 858 @Override 859 public FluentIterable<E> apply(Iterable<E> fromObject) { 860 return FluentIterable.from(fromObject); 861 } 862 } 863}