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 javax.annotation.CheckForNull; 035import org.checkerframework.checker.nullness.qual.NonNull; 036import org.checkerframework.checker.nullness.qual.Nullable; 037 038/** 039 * An expanded {@code Iterable} API, providing functionality similar to Java 8's powerful <a href= 040 * "https://docs.oracle.com/javase/8/docs/api/java/util/stream/package-summary.html#package.description" 041 * >streams library</a> in a slightly different way. 042 * 043 * <p>The following types of methods are provided: 044 * 045 * <ul> 046 * <li>chaining methods which return a new {@code FluentIterable} based in some way on the 047 * contents of the current one (for example {@link #transform}) 048 * <li>element extraction methods which facilitate the retrieval of certain elements (for example 049 * {@link #last}) 050 * <li>query methods which answer questions about the {@code FluentIterable}'s contents (for 051 * example {@link #anyMatch}) 052 * <li>conversion methods which copy the {@code FluentIterable}'s contents into a new collection 053 * or array (for example {@link #toList}) 054 * </ul> 055 * 056 * <p>Several lesser-used features are currently available only as static methods on the {@link 057 * Iterables} class. 058 * 059 * <p><a id="streams"></a> 060 * 061 * <h3>Comparison to streams</h3> 062 * 063 * <p>Starting with Java 8, the core Java class libraries provide a new "Streams" library (in {@code 064 * java.util.stream}), which is similar to {@code FluentIterable} but generally more powerful. Key 065 * differences include: 066 * 067 * <ul> 068 * <li>A stream is <i>single-use</i>; it becomes invalid as soon as any "terminal operation" such 069 * as {@code findFirst()} or {@code iterator()} is invoked. (Even though {@code Stream} 070 * contains all the right method <i>signatures</i> to implement {@link Iterable}, it does not 071 * actually do so, to avoid implying repeat-iterability.) {@code FluentIterable}, on the other 072 * hand, is multiple-use, and does implement {@link Iterable}. 073 * <li>Streams offer many features not found here, including {@code min/max}, {@code distinct}, 074 * {@code reduce}, {@code sorted}, the very powerful {@code collect}, and built-in support for 075 * parallelizing stream operations. 076 * <li>{@code FluentIterable} contains several features not available on {@code Stream}, which are 077 * noted in the method descriptions below. 078 * <li>Streams include primitive-specialized variants such as {@code IntStream}, the use of which 079 * is strongly recommended. 080 * <li>Streams are standard Java, not requiring a third-party dependency (but do render your code 081 * incompatible with Java 7 and earlier). 082 * </ul> 083 * 084 * <h3>Example</h3> 085 * 086 * <p>Here is an example that accepts a list from a database call, filters it based on a predicate, 087 * transforms it by invoking {@code toString()} on each element, and returns the first 10 elements 088 * as a {@code List}: 089 * 090 * <pre>{@code 091 * ImmutableList<String> results = 092 * FluentIterable.from(database.getClientList()) 093 * .filter(Client::isActiveInLastMonth) 094 * .transform(Object::toString) 095 * .limit(10) 096 * .toList(); 097 * }</pre> 098 * 099 * The approximate stream equivalent is: 100 * 101 * <pre>{@code 102 * List<String> results = 103 * database.getClientList() 104 * .stream() 105 * .filter(Client::isActiveInLastMonth) 106 * .map(Object::toString) 107 * .limit(10) 108 * .collect(Collectors.toList()); 109 * }</pre> 110 * 111 * @author Marcin Mikosik 112 * @since 12.0 113 */ 114@GwtCompatible(emulated = true) 115@ElementTypesAreNonnullByDefault 116public abstract class FluentIterable<E extends @Nullable Object> implements Iterable<E> { 117 // We store 'iterable' and use it instead of 'this' to allow Iterables to perform instanceof 118 // checks on the _original_ iterable when FluentIterable.from is used. 119 // To avoid a self retain cycle under j2objc, we store Optional.absent() instead of 120 // Optional.of(this). To access the delegate iterable, call #getDelegate(), which converts to 121 // absent() back to 'this'. 122 private final Optional<Iterable<E>> iterableDelegate; 123 124 /** Constructor for use by subclasses. */ 125 protected FluentIterable() { 126 this.iterableDelegate = Optional.absent(); 127 } 128 129 FluentIterable(Iterable<E> iterable) { 130 this.iterableDelegate = Optional.of(iterable); 131 } 132 133 private Iterable<E> getDelegate() { 134 return iterableDelegate.or(this); 135 } 136 137 /** 138 * Returns a fluent iterable that wraps {@code iterable}, or {@code iterable} itself if it is 139 * already a {@code FluentIterable}. 140 * 141 * <p><b>{@code Stream} equivalent:</b> {@code iterable.stream()} if {@code iterable} is a {@link 142 * Collection}; {@code StreamSupport.stream(iterable.spliterator(), false)} otherwise. 143 */ 144 public static <E extends @Nullable Object> FluentIterable<E> from(final Iterable<E> iterable) { 145 return (iterable instanceof FluentIterable) 146 ? (FluentIterable<E>) iterable 147 : new FluentIterable<E>(iterable) { 148 @Override 149 public Iterator<E> iterator() { 150 return iterable.iterator(); 151 } 152 }; 153 } 154 155 /** 156 * Returns a fluent iterable containing {@code elements} in the specified order. 157 * 158 * <p>The returned iterable is an unmodifiable view of the input array. 159 * 160 * <p><b>{@code Stream} equivalent:</b> {@link java.util.stream.Stream#of(Object[]) 161 * Stream.of(T...)}. 162 * 163 * @since 20.0 (since 18.0 as an overload of {@code of}) 164 */ 165 public static <E extends @Nullable Object> FluentIterable<E> from(E[] elements) { 166 return from(Arrays.asList(elements)); 167 } 168 169 /** 170 * Construct a fluent iterable from another fluent iterable. This is obviously never necessary, 171 * but is intended to help call out cases where one migration from {@code Iterable} to {@code 172 * FluentIterable} has obviated the need to explicitly convert to a {@code FluentIterable}. 173 * 174 * @deprecated instances of {@code FluentIterable} don't need to be converted to {@code 175 * FluentIterable} 176 */ 177 @Deprecated 178 @InlineMe( 179 replacement = "checkNotNull(iterable)", 180 staticImports = {"com.google.common.base.Preconditions.checkNotNull"}) 181 public static <E extends @Nullable Object> FluentIterable<E> from(FluentIterable<E> iterable) { 182 return checkNotNull(iterable); 183 } 184 185 /** 186 * Returns a fluent iterable that combines two iterables. The returned iterable has an iterator 187 * that traverses the elements in {@code a}, followed by the elements in {@code b}. The source 188 * iterators are not polled until necessary. 189 * 190 * <p>The returned iterable's iterator supports {@code remove()} when the corresponding input 191 * iterator supports it. 192 * 193 * <p><b>{@code Stream} equivalent:</b> {@link Stream#concat}. 194 * 195 * @since 20.0 196 */ 197 public static <T extends @Nullable Object> FluentIterable<T> concat( 198 Iterable<? extends T> a, Iterable<? extends T> b) { 199 return concatNoDefensiveCopy(a, b); 200 } 201 202 /** 203 * Returns a fluent iterable that combines three iterables. The returned iterable has an iterator 204 * that traverses the elements in {@code a}, followed by the elements in {@code b}, followed by 205 * the elements in {@code c}. The source iterators are not polled until necessary. 206 * 207 * <p>The returned iterable's iterator supports {@code remove()} when the corresponding input 208 * iterator supports it. 209 * 210 * <p><b>{@code Stream} equivalent:</b> use nested calls to {@link Stream#concat}, or see the 211 * advice in {@link #concat(Iterable...)}. 212 * 213 * @since 20.0 214 */ 215 public static <T extends @Nullable Object> FluentIterable<T> concat( 216 Iterable<? extends T> a, Iterable<? extends T> b, Iterable<? extends T> c) { 217 return concatNoDefensiveCopy(a, b, c); 218 } 219 220 /** 221 * Returns a fluent iterable that combines four iterables. The returned iterable has an iterator 222 * that traverses the elements in {@code a}, followed by the elements in {@code b}, followed by 223 * the elements in {@code c}, followed by the elements in {@code d}. The source iterators are not 224 * polled until necessary. 225 * 226 * <p>The returned iterable's iterator supports {@code remove()} when the corresponding input 227 * iterator supports it. 228 * 229 * <p><b>{@code Stream} equivalent:</b> use nested calls to {@link Stream#concat}, or see the 230 * advice in {@link #concat(Iterable...)}. 231 * 232 * @since 20.0 233 */ 234 public static <T extends @Nullable Object> FluentIterable<T> concat( 235 Iterable<? extends T> a, 236 Iterable<? extends T> b, 237 Iterable<? extends T> c, 238 Iterable<? extends T> d) { 239 return concatNoDefensiveCopy(a, b, c, d); 240 } 241 242 /** 243 * Returns a fluent iterable that combines several iterables. The returned iterable has an 244 * iterator that traverses the elements of each iterable in {@code inputs}. The input iterators 245 * are not polled until necessary. 246 * 247 * <p>The returned iterable's iterator supports {@code remove()} when the corresponding input 248 * iterator supports it. 249 * 250 * <p><b>{@code Stream} equivalent:</b> to concatenate an arbitrary number of streams, use {@code 251 * Stream.of(stream1, stream2, ...).flatMap(s -> s)}. If the sources are iterables, use {@code 252 * Stream.of(iter1, iter2, ...).flatMap(Streams::stream)}. 253 * 254 * @throws NullPointerException if any of the provided iterables is {@code null} 255 * @since 20.0 256 */ 257 public static <T extends @Nullable Object> FluentIterable<T> concat( 258 Iterable<? extends T>... inputs) { 259 return concatNoDefensiveCopy(Arrays.copyOf(inputs, inputs.length)); 260 } 261 262 /** 263 * Returns a fluent iterable that combines several iterables. The returned iterable has an 264 * iterator that traverses the elements of each iterable in {@code inputs}. The input iterators 265 * are not polled until necessary. 266 * 267 * <p>The returned iterable's iterator supports {@code remove()} when the corresponding input 268 * iterator supports it. The methods of the returned iterable may throw {@code 269 * NullPointerException} if any of the input iterators is {@code null}. 270 * 271 * <p><b>{@code Stream} equivalent:</b> {@code streamOfStreams.flatMap(s -> s)} or {@code 272 * streamOfIterables.flatMap(Streams::stream)}. (See {@link Streams#stream}.) 273 * 274 * @since 20.0 275 */ 276 public static <T extends @Nullable Object> FluentIterable<T> concat( 277 final Iterable<? extends Iterable<? extends T>> inputs) { 278 checkNotNull(inputs); 279 return new FluentIterable<T>() { 280 @Override 281 public Iterator<T> iterator() { 282 return Iterators.concat(Iterators.transform(inputs.iterator(), Iterable::iterator)); 283 } 284 }; 285 } 286 287 /** Concatenates a varargs array of iterables without making a defensive copy of the array. */ 288 private static <T extends @Nullable Object> FluentIterable<T> concatNoDefensiveCopy( 289 final Iterable<? extends T>... inputs) { 290 for (Iterable<? extends T> input : inputs) { 291 checkNotNull(input); 292 } 293 return new FluentIterable<T>() { 294 @Override 295 public Iterator<T> iterator() { 296 return Iterators.concat( 297 /* lazily generate the iterators on each input only as needed */ 298 new AbstractIndexedListIterator<Iterator<? extends T>>(inputs.length) { 299 @Override 300 public Iterator<? extends T> get(int i) { 301 return inputs[i].iterator(); 302 } 303 }); 304 } 305 }; 306 } 307 308 /** 309 * Returns a fluent iterable containing no elements. 310 * 311 * <p><b>{@code Stream} equivalent:</b> {@code Stream.empty()}. 312 * 313 * @since 20.0 314 */ 315 public static <E extends @Nullable Object> FluentIterable<E> of() { 316 return FluentIterable.from(Collections.<E>emptyList()); 317 } 318 319 /** 320 * Returns a fluent iterable containing the specified elements in order. 321 * 322 * <p><b>{@code Stream} equivalent:</b> {@link java.util.stream.Stream#of(Object[]) 323 * Stream.of(T...)}. 324 * 325 * @since 20.0 326 */ 327 public static <E extends @Nullable Object> FluentIterable<E> of( 328 @ParametricNullness E element, E... elements) { 329 return from(Lists.asList(element, elements)); 330 } 331 332 /** 333 * Returns a string representation of this fluent iterable, with the format {@code [e1, e2, ..., 334 * en]}. 335 * 336 * <p><b>{@code Stream} equivalent:</b> {@code stream.collect(Collectors.joining(", ", "[", "]"))} 337 * or (less efficiently) {@code stream.collect(Collectors.toList()).toString()}. 338 */ 339 @Override 340 public String toString() { 341 return Iterables.toString(getDelegate()); 342 } 343 344 /** 345 * Returns the number of elements in this fluent iterable. 346 * 347 * <p><b>{@code Stream} equivalent:</b> {@code stream.count()}. 348 */ 349 public final int size() { 350 return Iterables.size(getDelegate()); 351 } 352 353 /** 354 * Returns {@code true} if this fluent iterable contains any object for which {@code 355 * equals(target)} is true. 356 * 357 * <p><b>{@code Stream} equivalent:</b> {@code stream.anyMatch(Predicate.isEqual(target))}. 358 */ 359 public final boolean contains(@CheckForNull Object target) { 360 return Iterables.contains(getDelegate(), target); 361 } 362 363 /** 364 * Returns a fluent iterable whose {@code Iterator} cycles indefinitely over the elements of this 365 * fluent iterable. 366 * 367 * <p>That iterator supports {@code remove()} if {@code iterable.iterator()} does. After {@code 368 * remove()} is called, subsequent cycles omit the removed element, which is no longer in this 369 * fluent iterable. The iterator's {@code hasNext()} method returns {@code true} until this fluent 370 * iterable is empty. 371 * 372 * <p><b>Warning:</b> Typical uses of the resulting iterator may produce an infinite loop. You 373 * should use an explicit {@code break} or be certain that you will eventually remove all the 374 * elements. 375 * 376 * <p><b>{@code Stream} equivalent:</b> if the source iterable has only a single element {@code 377 * e}, use {@code Stream.generate(() -> e)}. Otherwise, collect your stream into a collection and 378 * use {@code Stream.generate(() -> collection).flatMap(Collection::stream)}. 379 */ 380 public final FluentIterable<E> cycle() { 381 return from(Iterables.cycle(getDelegate())); 382 } 383 384 /** 385 * Returns a fluent iterable whose iterators traverse first the elements of this fluent iterable, 386 * followed by those of {@code other}. The iterators are not polled until necessary. 387 * 388 * <p>The returned iterable's {@code Iterator} supports {@code remove()} when the corresponding 389 * {@code Iterator} supports it. 390 * 391 * <p><b>{@code Stream} equivalent:</b> {@link Stream#concat}. 392 * 393 * @since 18.0 394 */ 395 public final FluentIterable<E> append(Iterable<? extends E> other) { 396 return FluentIterable.concat(getDelegate(), other); 397 } 398 399 /** 400 * Returns a fluent iterable whose iterators traverse first the elements of this fluent iterable, 401 * followed by {@code elements}. 402 * 403 * <p><b>{@code Stream} equivalent:</b> {@code Stream.concat(thisStream, Stream.of(elements))}. 404 * 405 * @since 18.0 406 */ 407 public final FluentIterable<E> append(E... elements) { 408 return FluentIterable.concat(getDelegate(), Arrays.asList(elements)); 409 } 410 411 /** 412 * Returns the elements from this fluent iterable that satisfy a predicate. The resulting fluent 413 * iterable's iterator does not support {@code remove()}. 414 * 415 * <p><b>{@code Stream} equivalent:</b> {@link Stream#filter} (same). 416 */ 417 public final FluentIterable<E> filter(Predicate<? super E> predicate) { 418 return from(Iterables.filter(getDelegate(), predicate)); 419 } 420 421 /** 422 * Returns the elements from this fluent iterable that are instances of class {@code type}. 423 * 424 * <p><b>{@code Stream} equivalent:</b> {@code stream.filter(type::isInstance).map(type::cast)}. 425 * This does perform a little more work than necessary, so another option is to insert an 426 * unchecked cast at some later point: 427 * 428 * <pre> 429 * {@code @SuppressWarnings("unchecked") // safe because of ::isInstance check 430 * ImmutableList<NewType> result = 431 * (ImmutableList) stream.filter(NewType.class::isInstance).collect(toImmutableList());} 432 * </pre> 433 */ 434 @GwtIncompatible // Class.isInstance 435 public final <T> FluentIterable<T> filter(Class<T> type) { 436 return from(Iterables.filter(getDelegate(), type)); 437 } 438 439 /** 440 * Returns {@code true} if any element in this fluent iterable satisfies the predicate. 441 * 442 * <p><b>{@code Stream} equivalent:</b> {@link Stream#anyMatch} (same). 443 */ 444 public final boolean anyMatch(Predicate<? super E> predicate) { 445 return Iterables.any(getDelegate(), predicate); 446 } 447 448 /** 449 * Returns {@code true} if every element in this fluent iterable satisfies the predicate. If this 450 * fluent iterable is empty, {@code true} is returned. 451 * 452 * <p><b>{@code Stream} equivalent:</b> {@link Stream#allMatch} (same). 453 */ 454 public final boolean allMatch(Predicate<? super E> predicate) { 455 return Iterables.all(getDelegate(), predicate); 456 } 457 458 /** 459 * Returns an {@link Optional} containing the first element in this fluent iterable that satisfies 460 * the given predicate, if such an element exists. 461 * 462 * <p><b>Warning:</b> avoid using a {@code predicate} that matches {@code null}. If {@code null} 463 * is matched in this fluent iterable, a {@link NullPointerException} will be thrown. 464 * 465 * <p><b>{@code Stream} equivalent:</b> {@code stream.filter(predicate).findFirst()}. 466 */ 467 @SuppressWarnings("nullness") // Unsafe, but we can't do much about it now. 468 public final Optional<@NonNull E> firstMatch(Predicate<? super E> predicate) { 469 return Iterables.<E>tryFind((Iterable<@NonNull E>) getDelegate(), predicate); 470 } 471 472 /** 473 * Returns a fluent iterable that applies {@code function} to each element of this fluent 474 * iterable. 475 * 476 * <p>The returned fluent iterable's iterator supports {@code remove()} if this iterable's 477 * iterator does. After a successful {@code remove()} call, this fluent iterable no longer 478 * contains the corresponding element. 479 * 480 * <p><b>{@code Stream} equivalent:</b> {@link Stream#map}. 481 */ 482 public final <T extends @Nullable Object> FluentIterable<T> transform( 483 Function<? super E, T> function) { 484 return from(Iterables.transform(getDelegate(), function)); 485 } 486 487 /** 488 * Applies {@code function} to each element of this fluent iterable and returns a fluent iterable 489 * with the concatenated combination of results. {@code function} returns an Iterable of results. 490 * 491 * <p>The returned fluent iterable's iterator supports {@code remove()} if this function-returned 492 * iterables' iterator does. After a successful {@code remove()} call, the returned fluent 493 * iterable no longer contains the corresponding element. 494 * 495 * <p><b>{@code Stream} equivalent:</b> {@link Stream#flatMap} (using a function that produces 496 * streams, not iterables). 497 * 498 * @since 13.0 (required {@code Function<E, Iterable<T>>} until 14.0) 499 */ 500 public <T extends @Nullable Object> FluentIterable<T> transformAndConcat( 501 Function<? super E, ? extends Iterable<? extends T>> function) { 502 return FluentIterable.concat(transform(function)); 503 } 504 505 /** 506 * Returns an {@link Optional} containing the first element in this fluent iterable. If the 507 * iterable is empty, {@code Optional.absent()} is returned. 508 * 509 * <p><b>{@code Stream} equivalent:</b> if the goal is to obtain any element, {@link 510 * Stream#findAny}; if it must specifically be the <i>first</i> element, {@code Stream#findFirst}. 511 * 512 * @throws NullPointerException if the first element is null; if this is a possibility, use {@code 513 * iterator().next()} or {@link Iterables#getFirst} instead. 514 */ 515 @SuppressWarnings("nullness") // Unsafe, but we can't do much about it now. 516 public final Optional<@NonNull E> first() { 517 Iterator<E> iterator = getDelegate().iterator(); 518 return iterator.hasNext() ? Optional.of(iterator.next()) : Optional.absent(); 519 } 520 521 /** 522 * Returns an {@link Optional} containing the last element in this fluent iterable. If the 523 * iterable is empty, {@code Optional.absent()} is returned. If the underlying {@code iterable} is 524 * a {@link List} with {@link java.util.RandomAccess} support, then this operation is guaranteed 525 * to be {@code O(1)}. 526 * 527 * <p><b>{@code Stream} equivalent:</b> {@code stream.reduce((a, b) -> b)}. 528 * 529 * @throws NullPointerException if the last element is null; if this is a possibility, use {@link 530 * Iterables#getLast} instead. 531 */ 532 @SuppressWarnings("nullness") // Unsafe, but we can't do much about it now. 533 public final Optional<@NonNull E> last() { 534 // Iterables#getLast was inlined here so we don't have to throw/catch a NSEE 535 536 // TODO(kevinb): Support a concurrently modified collection? 537 Iterable<E> iterable = getDelegate(); 538 if (iterable instanceof List) { 539 List<E> list = (List<E>) iterable; 540 if (list.isEmpty()) { 541 return Optional.absent(); 542 } 543 return Optional.of(list.get(list.size() - 1)); 544 } 545 Iterator<E> iterator = iterable.iterator(); 546 if (!iterator.hasNext()) { 547 return Optional.absent(); 548 } 549 550 /* 551 * TODO(kevinb): consider whether this "optimization" is worthwhile. Users with SortedSets tend 552 * to know they are SortedSets and probably would not call this method. 553 */ 554 if (iterable instanceof SortedSet) { 555 SortedSet<E> sortedSet = (SortedSet<E>) iterable; 556 return Optional.of(sortedSet.last()); 557 } 558 559 while (true) { 560 E current = iterator.next(); 561 if (!iterator.hasNext()) { 562 return Optional.of(current); 563 } 564 } 565 } 566 567 /** 568 * Returns a view of this fluent iterable that skips its first {@code numberToSkip} elements. If 569 * this fluent iterable contains fewer than {@code numberToSkip} elements, the returned fluent 570 * iterable skips all of its elements. 571 * 572 * <p>Modifications to this fluent iterable before a call to {@code iterator()} are reflected in 573 * the returned fluent iterable. That is, the iterator skips the first {@code numberToSkip} 574 * elements that exist when the iterator is created, not when {@code skip()} is called. 575 * 576 * <p>The returned fluent iterable's iterator supports {@code remove()} if the {@code Iterator} of 577 * this fluent iterable supports it. Note that it is <i>not</i> possible to delete the last 578 * skipped element by immediately calling {@code remove()} on the returned fluent iterable's 579 * iterator, as the {@code Iterator} contract states that a call to {@code * remove()} before a 580 * call to {@code next()} will throw an {@link IllegalStateException}. 581 * 582 * <p><b>{@code Stream} equivalent:</b> {@link Stream#skip} (same). 583 */ 584 public final FluentIterable<E> skip(int numberToSkip) { 585 return from(Iterables.skip(getDelegate(), numberToSkip)); 586 } 587 588 /** 589 * Creates a fluent iterable with the first {@code size} elements of this fluent iterable. If this 590 * fluent iterable does not contain that many elements, the returned fluent iterable will have the 591 * same behavior as this fluent iterable. The returned fluent iterable's iterator supports {@code 592 * remove()} if this fluent iterable's iterator does. 593 * 594 * <p><b>{@code Stream} equivalent:</b> {@link Stream#limit} (same). 595 * 596 * @param maxSize the maximum number of elements in the returned fluent iterable 597 * @throws IllegalArgumentException if {@code size} is negative 598 */ 599 public final FluentIterable<E> limit(int maxSize) { 600 return from(Iterables.limit(getDelegate(), maxSize)); 601 } 602 603 /** 604 * Determines whether this fluent iterable is empty. 605 * 606 * <p><b>{@code Stream} equivalent:</b> {@code !stream.findAny().isPresent()}. 607 */ 608 public final boolean isEmpty() { 609 return !getDelegate().iterator().hasNext(); 610 } 611 612 /** 613 * Returns an {@code ImmutableList} containing all of the elements from this fluent iterable in 614 * proper sequence. 615 * 616 * <p><b>{@code Stream} equivalent:</b> {@code ImmutableList.copyOf(stream.iterator())}, or pass 617 * {@link ImmutableList#toImmutableList} to {@code stream.collect()}. 618 * 619 * @throws NullPointerException if any element is {@code null} 620 * @since 14.0 (since 12.0 as {@code toImmutableList()}). 621 */ 622 @SuppressWarnings("nullness") // Unsafe, but we can't do much about it now. 623 public final ImmutableList<@NonNull E> toList() { 624 return ImmutableList.copyOf((Iterable<@NonNull E>) getDelegate()); 625 } 626 627 /** 628 * Returns an {@code ImmutableList} containing all of the elements from this {@code 629 * FluentIterable} in the order specified by {@code comparator}. To produce an {@code 630 * ImmutableList} sorted by its natural ordering, use {@code toSortedList(Ordering.natural())}. 631 * 632 * <p><b>{@code Stream} equivalent:</b> {@code 633 * ImmutableList.copyOf(stream.sorted(comparator).iterator())}, or pass {@link 634 * ImmutableList#toImmutableList} to {@code stream.sorted(comparator).collect()}. 635 * 636 * @param comparator the function by which to sort list elements 637 * @throws NullPointerException if any element of this iterable is {@code null} 638 * @since 14.0 (since 13.0 as {@code toSortedImmutableList()}). 639 */ 640 @SuppressWarnings("nullness") // Unsafe, but we can't do much about it now. 641 public final ImmutableList<@NonNull E> toSortedList(Comparator<? super E> comparator) { 642 return Ordering.from(comparator).immutableSortedCopy((Iterable<@NonNull E>) getDelegate()); 643 } 644 645 /** 646 * Returns an {@code ImmutableSet} containing all of the elements from this fluent iterable with 647 * duplicates removed. 648 * 649 * <p><b>{@code Stream} equivalent:</b> {@code ImmutableSet.copyOf(stream.iterator())}, or pass 650 * {@link ImmutableSet#toImmutableSet} to {@code stream.collect()}. 651 * 652 * @throws NullPointerException if any element is {@code null} 653 * @since 14.0 (since 12.0 as {@code toImmutableSet()}). 654 */ 655 @SuppressWarnings("nullness") // Unsafe, but we can't do much about it now. 656 public final ImmutableSet<@NonNull E> toSet() { 657 return ImmutableSet.copyOf((Iterable<@NonNull E>) getDelegate()); 658 } 659 660 /** 661 * Returns an {@code ImmutableSortedSet} containing all of the elements from this {@code 662 * FluentIterable} in the order specified by {@code comparator}, with duplicates (determined by 663 * {@code comparator.compare(x, y) == 0}) removed. To produce an {@code ImmutableSortedSet} sorted 664 * by its natural ordering, use {@code toSortedSet(Ordering.natural())}. 665 * 666 * <p><b>{@code Stream} equivalent:</b> {@code ImmutableSortedSet.copyOf(comparator, 667 * stream.iterator())}, or pass {@link ImmutableSortedSet#toImmutableSortedSet} to {@code 668 * stream.collect()}. 669 * 670 * @param comparator the function by which to sort set elements 671 * @throws NullPointerException if any element of this iterable is {@code null} 672 * @since 14.0 (since 12.0 as {@code toImmutableSortedSet()}). 673 */ 674 @SuppressWarnings("nullness") // Unsafe, but we can't do much about it now. 675 public final ImmutableSortedSet<@NonNull E> toSortedSet(Comparator<? super E> comparator) { 676 return ImmutableSortedSet.copyOf(comparator, (Iterable<@NonNull E>) getDelegate()); 677 } 678 679 /** 680 * Returns an {@code ImmutableMultiset} containing all of the elements from this fluent iterable. 681 * 682 * <p><b>{@code Stream} equivalent:</b> {@code ImmutableMultiset.copyOf(stream.iterator())}, or 683 * pass {@link ImmutableMultiset#toImmutableMultiset} to {@code stream.collect()}. 684 * 685 * @throws NullPointerException if any element is null 686 * @since 19.0 687 */ 688 @SuppressWarnings("nullness") // Unsafe, but we can't do much about it now. 689 public final ImmutableMultiset<@NonNull E> toMultiset() { 690 return ImmutableMultiset.copyOf((Iterable<@NonNull E>) getDelegate()); 691 } 692 693 /** 694 * Returns an immutable map whose keys are the distinct elements of this {@code FluentIterable} 695 * and whose value for each key was computed by {@code valueFunction}. The map's iteration order 696 * is the order of the first appearance of each key in this iterable. 697 * 698 * <p>When there are multiple instances of a key in this iterable, it is unspecified whether 699 * {@code valueFunction} will be applied to more than one instance of that key and, if it is, 700 * which result will be mapped to that key in the returned map. 701 * 702 * <p><b>{@code Stream} equivalent:</b> use {@code stream.collect(ImmutableMap.toImmutableMap(k -> 703 * k, valueFunction))}. {@code ImmutableMap.copyOf(stream.collect(Collectors.toMap(k -> k, 704 * valueFunction)))} behaves similarly, but may not preserve the order of entries. 705 * 706 * @throws NullPointerException if any element of this iterable is {@code null}, or if {@code 707 * valueFunction} produces {@code null} for any key 708 * @since 14.0 709 */ 710 @SuppressWarnings("nullness") // Unsafe, but we can't do much about it now. 711 public final <V> ImmutableMap<@NonNull E, V> toMap(Function<? super E, V> valueFunction) { 712 return Maps.toMap((Iterable<@NonNull E>) getDelegate(), valueFunction); 713 } 714 715 /** 716 * Creates an index {@code ImmutableListMultimap} that contains the results of applying a 717 * specified function to each item in this {@code FluentIterable} of values. Each element of this 718 * iterable will be stored as a value in the resulting multimap, yielding a multimap with the same 719 * size as this iterable. The key used to store that value in the multimap will be the result of 720 * calling the function on that value. The resulting multimap is created as an immutable snapshot. 721 * In the returned multimap, keys appear in the order they are first encountered, and the values 722 * corresponding to each key appear in the same order as they are encountered. 723 * 724 * <p><b>{@code Stream} equivalent:</b> {@code stream.collect(Collectors.groupingBy(keyFunction))} 725 * behaves similarly, but returns a mutable {@code Map<K, List<E>>} instead, and may not preserve 726 * the order of entries. 727 * 728 * @param keyFunction the function used to produce the key for each value 729 * @throws NullPointerException if any element of this iterable is {@code null}, or if {@code 730 * keyFunction} produces {@code null} for any key 731 * @since 14.0 732 */ 733 @SuppressWarnings("nullness") // Unsafe, but we can't do much about it now. 734 public final <K> ImmutableListMultimap<K, @NonNull E> index(Function<? super E, K> keyFunction) { 735 return Multimaps.index((Iterable<@NonNull E>) getDelegate(), keyFunction); 736 } 737 738 /** 739 * Returns a map with the contents of this {@code FluentIterable} as its {@code values}, indexed 740 * by keys derived from those values. In other words, each input value produces an entry in the 741 * map whose key is the result of applying {@code keyFunction} to that value. These entries appear 742 * in the same order as they appeared in this fluent iterable. Example usage: 743 * 744 * <pre>{@code 745 * Color red = new Color("red", 255, 0, 0); 746 * ... 747 * FluentIterable<Color> allColors = FluentIterable.from(ImmutableSet.of(red, green, blue)); 748 * 749 * Map<String, Color> colorForName = allColors.uniqueIndex(toStringFunction()); 750 * assertThat(colorForName).containsEntry("red", red); 751 * }</pre> 752 * 753 * <p>If your index may associate multiple values with each key, use {@link #index(Function) 754 * index}. 755 * 756 * <p><b>{@code Stream} equivalent:</b> use {@code 757 * stream.collect(ImmutableMap.toImmutableMap(keyFunction, v -> v))}. {@code 758 * ImmutableMap.copyOf(stream.collect(Collectors.toMap(keyFunction, v -> v)))}, but be aware that 759 * this may not preserve the order of entries. 760 * 761 * @param keyFunction the function used to produce the key for each value 762 * @return a map mapping the result of evaluating the function {@code keyFunction} on each value 763 * in this fluent iterable to that value 764 * @throws IllegalArgumentException if {@code keyFunction} produces the same key for more than one 765 * value in this fluent iterable 766 * @throws NullPointerException if any element of this iterable is {@code null}, or if {@code 767 * keyFunction} produces {@code null} for any key 768 * @since 14.0 769 */ 770 @SuppressWarnings("nullness") // Unsafe, but we can't do much about it now. 771 public final <K> ImmutableMap<K, @NonNull E> uniqueIndex(Function<? super E, K> keyFunction) { 772 return Maps.uniqueIndex((Iterable<@NonNull E>) getDelegate(), keyFunction); 773 } 774 775 /** 776 * Returns an array containing all of the elements from this fluent iterable in iteration order. 777 * 778 * <p><b>{@code Stream} equivalent:</b> if an object array is acceptable, use {@code 779 * stream.toArray()}; if {@code type} is a class literal such as {@code MyType.class}, use {@code 780 * stream.toArray(MyType[]::new)}. Otherwise use {@code stream.toArray( len -> (E[]) 781 * Array.newInstance(type, len))}. 782 * 783 * @param type the type of the elements 784 * @return a newly-allocated array into which all the elements of this fluent iterable have been 785 * copied 786 */ 787 @GwtIncompatible // Array.newArray(Class, int) 788 public final E[] toArray(Class<@NonNull E> type) { 789 return Iterables.<E>toArray(getDelegate(), type); 790 } 791 792 /** 793 * Copies all the elements from this fluent iterable to {@code collection}. This is equivalent to 794 * calling {@code Iterables.addAll(collection, this)}. 795 * 796 * <p><b>{@code Stream} equivalent:</b> {@code stream.forEachOrdered(collection::add)} or {@code 797 * stream.forEach(collection::add)}. 798 * 799 * @param collection the collection to copy elements to 800 * @return {@code collection}, for convenience 801 * @since 14.0 802 */ 803 @CanIgnoreReturnValue 804 public final <C extends Collection<? super E>> C copyInto(C collection) { 805 checkNotNull(collection); 806 Iterable<E> iterable = getDelegate(); 807 if (iterable instanceof Collection) { 808 collection.addAll((Collection<E>) iterable); 809 } else { 810 for (E item : iterable) { 811 collection.add(item); 812 } 813 } 814 return collection; 815 } 816 817 /** 818 * Returns a {@link String} containing all of the elements of this fluent iterable joined with 819 * {@code joiner}. 820 * 821 * <p><b>{@code Stream} equivalent:</b> {@code joiner.join(stream.iterator())}, or, if you are not 822 * using any optional {@code Joiner} features, {@code 823 * stream.collect(Collectors.joining(delimiter)}. 824 * 825 * @since 18.0 826 */ 827 public final String join(Joiner joiner) { 828 return joiner.join(this); 829 } 830 831 /** 832 * Returns the element at the specified position in this fluent iterable. 833 * 834 * <p><b>{@code Stream} equivalent:</b> {@code stream.skip(position).findFirst().get()} (but note 835 * that this throws different exception types, and throws an exception if {@code null} would be 836 * returned). 837 * 838 * @param position position of the element to return 839 * @return the element at the specified position in this fluent iterable 840 * @throws IndexOutOfBoundsException if {@code position} is negative or greater than or equal to 841 * the size of this fluent iterable 842 */ 843 @ParametricNullness 844 public final E get(int position) { 845 return Iterables.get(getDelegate(), position); 846 } 847 848 /** Function that transforms {@code Iterable<E>} into a fluent iterable. */ 849 private static class FromIterableFunction<E extends @Nullable Object> 850 implements Function<Iterable<E>, FluentIterable<E>> { 851 @Override 852 public FluentIterable<E> apply(Iterable<E> fromObject) { 853 return FluentIterable.from(fromObject); 854 } 855 } 856}