/* * Copyright (C) 2008 The Guava Authors * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package com.google.common.collect; import static com.google.common.base.Preconditions.checkNotNull; import com.google.common.annotations.Beta; import com.google.common.annotations.GwtCompatible; import com.google.common.annotations.GwtIncompatible; import com.google.common.base.Function; import com.google.common.base.Optional; import com.google.common.base.Predicate; import java.util.Collection; import java.util.Comparator; import java.util.Iterator; import java.util.List; import java.util.SortedSet; import javax.annotation.Nullable; /** * {@code FluentIterable} provides a rich interface for manipulating {@code Iterable}s in a chained * fashion. A {@code FluentIterable} can be created from an {@code Iterable}, or from a set of * elements. The following types of methods are provided on {@code FluentIterable}: * <ul> * <li>chained methods which return a new {@code FluentIterable} based in some way on the contents * of the current one (for example {@link #transform}) * <li>conversion methods which copy the {@code FluentIterable}'s contents into a new collection or * array (for example {@link #toList}) * <li>element extraction methods which facilitate the retrieval of certain elements (for example * {@link #last}) * <li>query methods which answer questions about the {@code FluentIterable}'s contents (for example * {@link #anyMatch}) * </ul> * * <p>Here is an example that merges the lists returned by two separate database calls, transforms * it by invoking {@code toString()} on each element, and returns the first 10 elements as an * {@code ImmutableList}: <pre> {@code * * FluentIterable * .from(database.getClientList()) * .filter(activeInLastMonth()) * .transform(Functions.toStringFunction()) * .limit(10) * .toList();}</pre> * * Anything which can be done using {@code FluentIterable} could be done in a different fashion * (often with {@link Iterables}), however the use of {@code FluentIterable} makes many sets of * operations significantly more concise. * * @author Marcin Mikosik * @since 12.0 */ @Beta @GwtCompatible(emulated = true) public abstract class FluentIterable<E> implements Iterable<E> { // We store 'iterable' and use it instead of 'this' to allow Iterables to perform instanceof // checks on the _original_ iterable when FluentIterable.from is used. private final Iterable<E> iterable; /** Constructor for use by subclasses. */ protected FluentIterable() { this.iterable = this; } FluentIterable(Iterable<E> iterable) { this.iterable = checkNotNull(iterable); } /** * Returns a fluent iterable that wraps {@code iterable}, or {@code iterable} itself if it * is already a {@code FluentIterable}. */ public static <E> FluentIterable<E> from(final Iterable<E> iterable) { return (iterable instanceof FluentIterable) ? (FluentIterable<E>) iterable : new FluentIterable<E>(iterable) { @Override public Iterator<E> iterator() { return iterable.iterator(); } }; } /** * Construct a fluent iterable from another fluent iterable. This is obviously never necessary, * but is intended to help call out cases where one migration from {@code Iterable} to * {@code FluentIterable} has obviated the need to explicitly convert to a {@code FluentIterable}. * * @deprecated instances of {@code FluentIterable} don't need to be converted to * {@code FluentIterable} */ @Deprecated public static <E> FluentIterable<E> from(FluentIterable<E> iterable) { return checkNotNull(iterable); } /** * Returns a string representation of this fluent iterable, with the format * {@code [e1, e2, ..., en]}. */ @Override public String toString() { return Iterables.toString(iterable); } /** * Returns the number of elements in this fluent iterable. */ public final int size() { return Iterables.size(iterable); } /** * Returns {@code true} if this fluent iterable contains any object for which * {@code equals(element)} is true. */ public final boolean contains(@Nullable Object element) { return Iterables.contains(iterable, element); } /** * Returns a fluent iterable whose {@code Iterator} cycles indefinitely over the elements of * this fluent iterable. * * <p>That iterator supports {@code remove()} if {@code iterable.iterator()} does. After * {@code remove()} is called, subsequent cycles omit the removed element, which is no longer in * this fluent iterable. The iterator's {@code hasNext()} method returns {@code true} until * this fluent iterable is empty. * * <p><b>Warning:</b> Typical uses of the resulting iterator may produce an infinite loop. You * should use an explicit {@code break} or be certain that you will eventually remove all the * elements. */ public final FluentIterable<E> cycle() { return from(Iterables.cycle(iterable)); } /** * Returns the elements from this fluent iterable that satisfy a predicate. The * resulting fluent iterable's iterator does not support {@code remove()}. */ public final FluentIterable<E> filter(Predicate<? super E> predicate) { return from(Iterables.filter(iterable, predicate)); } /** * Returns the elements from this fluent iterable that are instances of class {@code type}. * * @param type the type of elements desired */ @GwtIncompatible("Class.isInstance") public final <T> FluentIterable<T> filter(Class<T> type) { return from(Iterables.filter(iterable, type)); } /** * Returns {@code true} if any element in this fluent iterable satisfies the predicate. */ public final boolean anyMatch(Predicate<? super E> predicate) { return Iterables.any(iterable, predicate); } /** * Returns {@code true} if every element in this fluent iterable satisfies the predicate. * If this fluent iterable is empty, {@code true} is returned. */ public final boolean allMatch(Predicate<? super E> predicate) { return Iterables.all(iterable, predicate); } /** * Returns an {@link Optional} containing the first element in this fluent iterable that * satisfies the given predicate, if such an element exists. * * <p><b>Warning:</b> avoid using a {@code predicate} that matches {@code null}. If {@code null} * is matched in this fluent iterable, a {@link NullPointerException} will be thrown. */ public final Optional<E> firstMatch(Predicate<? super E> predicate) { return Iterables.tryFind(iterable, predicate); } /** * Returns a fluent iterable that applies {@code function} to each element of this * fluent iterable. * * <p>The returned fluent iterable's iterator supports {@code remove()} if this iterable's * iterator does. After a successful {@code remove()} call, this fluent iterable no longer * contains the corresponding element. */ public final <T> FluentIterable<T> transform(Function<? super E, T> function) { return from(Iterables.transform(iterable, function)); } /** * Applies {@code function} to each element of this fluent iterable and returns * a fluent iterable with the concatenated combination of results. {@code function} * returns an Iterable of results. * * <p>The returned fluent iterable's iterator supports {@code remove()} if this * function-returned iterables' iterator does. After a successful {@code remove()} call, * the returned fluent iterable no longer contains the corresponding element. * * @since 13.0 */ public <T> FluentIterable<T> transformAndConcat( Function<? super E, ? extends Iterable<T>> function) { return from(Iterables.concat(transform(function))); } /** * Returns an {@link Optional} containing the first element in this fluent iterable. * If the iterable is empty, {@code Optional.absent()} is returned. * * @throws NullPointerException if the first element is null; if this is a possibility, use * {@code iterator().next()} or {@link Iterables#getFirst} instead. */ public final Optional<E> first() { Iterator<E> iterator = iterable.iterator(); return iterator.hasNext() ? Optional.of(iterator.next()) : Optional.<E>absent(); } /** * Returns an {@link Optional} containing the last element in this fluent iterable. * If the iterable is empty, {@code Optional.absent()} is returned. * * @throws NullPointerException if the last element is null; if this is a possibility, use * {@link Iterables#getLast} instead. */ public final Optional<E> last() { // Iterables#getLast was inlined here so we don't have to throw/catch a NSEE // TODO(kevinb): Support a concurrently modified collection? if (iterable instanceof List) { List<E> list = (List<E>) iterable; if (list.isEmpty()) { return Optional.absent(); } return Optional.of(list.get(list.size() - 1)); } Iterator<E> iterator = iterable.iterator(); if (!iterator.hasNext()) { return Optional.absent(); } /* * TODO(kevinb): consider whether this "optimization" is worthwhile. Users * with SortedSets tend to know they are SortedSets and probably would not * call this method. */ if (iterable instanceof SortedSet) { SortedSet<E> sortedSet = (SortedSet<E>) iterable; return Optional.of(sortedSet.last()); } while (true) { E current = iterator.next(); if (!iterator.hasNext()) { return Optional.of(current); } } } /** * Returns a view of this fluent iterable that skips its first {@code numberToSkip} * elements. If this fluent iterable contains fewer than {@code numberToSkip} elements, * the returned fluent iterable skips all of its elements. * * <p>Modifications to this fluent iterable before a call to {@code iterator()} are * reflected in the returned fluent iterable. That is, the its iterator skips the first * {@code numberToSkip} elements that exist when the iterator is created, not when {@code skip()} * is called. * * <p>The returned fluent iterable's iterator supports {@code remove()} if the * {@code Iterator} of this fluent iterable supports it. Note that it is <i>not</i> * possible to delete the last skipped element by immediately calling {@code remove()} on the * returned fluent iterable's iterator, as the {@code Iterator} contract states that a call * to {@code * remove()} before a call to {@code next()} will throw an * {@link IllegalStateException}. */ public final FluentIterable<E> skip(int numberToSkip) { return from(Iterables.skip(iterable, numberToSkip)); } /** * Creates a fluent iterable with the first {@code size} elements of this * fluent iterable. If this fluent iterable does not contain that many elements, * the returned fluent iterable will have the same behavior as this fluent iterable. * The returned fluent iterable's iterator supports {@code remove()} if this * fluent iterable's iterator does. * * @param size the maximum number of elements in the returned fluent iterable * @throws IllegalArgumentException if {@code size} is negative */ public final FluentIterable<E> limit(int size) { return from(Iterables.limit(iterable, size)); } /** * Determines whether this fluent iterable is empty. */ public final boolean isEmpty() { return !iterable.iterator().hasNext(); } /** * Returns an {@code ImmutableList} containing all of the elements from this fluent iterable in * proper sequence. * * @since 14.0 (since 12.0 as {@code toImmutableList()}). */ public final ImmutableList<E> toList() { return ImmutableList.copyOf(iterable); } /** * Returns an {@code ImmutableList} containing all of the elements from this {@code * FluentIterable} in the order specified by {@code comparator}. To produce an {@code * ImmutableList} sorted by its natural ordering, use {@code toSortedList(Ordering.natural())}. * * @param comparator the function by which to sort list elements * @throws NullPointerException if any element is null * @since 14.0 (since 13.0 as {@code toSortedImmutableList()}). */ public final ImmutableList<E> toSortedList(Comparator<? super E> comparator) { return Ordering.from(comparator).immutableSortedCopy(iterable); } /** * Returns an {@code ImmutableSet} containing all of the elements from this fluent iterable with * duplicates removed. * * @since 14.0 (since 12.0 as {@code toImmutableSet()}). */ public final ImmutableSet<E> toSet() { return ImmutableSet.copyOf(iterable); } /** * Returns an {@code ImmutableSortedSet} containing all of the elements from this {@code * FluentIterable} in the order specified by {@code comparator}, with duplicates (determined by * {@code comparator.compare(x, y) == 0}) removed. To produce an {@code ImmutableSortedSet} sorted * by its natural ordering, use {@code toSortedSet(Ordering.natural())}. * * @param comparator the function by which to sort set elements * @throws NullPointerException if any element is null * @since 14.0 (since 12.0 as {@code toImmutableSortedSet()}). */ public final ImmutableSortedSet<E> toSortedSet(Comparator<? super E> comparator) { return ImmutableSortedSet.copyOf(comparator, iterable); } /** * Returns an {@code ImmutableList} containing all of the elements from this * fluent iterable in proper sequence. * * @deprecated Use {@link #toList()} instead. This method is scheduled for removal in Guava 15.0. */ @Deprecated public final ImmutableList<E> toImmutableList() { return toList(); } /** * Returns an {@code ImmutableList} containing all of the elements from this * {@code FluentIterable} in the order specified by {@code comparator}. To produce an * {@code ImmutableList} sorted by its natural ordering, use * {@code toSortedImmutableList(Ordering.natural())}. * * @param comparator the function by which to sort list elements * @throws NullPointerException if any element is null * @since 13.0 * @deprecated Use {@link #toSortedList(Comparator)} instead. This method is scheduled for removal * in Guava 15.0. */ @Deprecated public final ImmutableList<E> toSortedImmutableList(Comparator<? super E> comparator) { return toSortedList(comparator); } /** * Returns an {@code ImmutableSet} containing all of the elements from this * fluent iterable with duplicates removed. * * @deprecated Use {@link #toSet()} instead. This method is scheduled for removal in Guava 15.0. */ @Deprecated public final ImmutableSet<E> toImmutableSet() { return toSet(); } /** * Returns an {@code ImmutableSortedSet} containing all of the elements from this * {@code FluentIterable} in the order specified by {@code comparator}, with duplicates * (determined by {@code comparator.compare(x, y) == 0}) removed. To produce an * {@code ImmutableSortedSet} sorted by its natural ordering, use * {@code toImmutableSortedSet(Ordering.natural())}. * * @param comparator the function by which to sort set elements * @throws NullPointerException if any element is null * @deprecated Use {@link #toSortedSet(Comparator)} instead. This method is scheduled for removal * in Guava 15.0. */ @Deprecated public final ImmutableSortedSet<E> toImmutableSortedSet(Comparator<? super E> comparator) { return toSortedSet(comparator); } /** * Returns an array containing all of the elements from this fluent iterable in iteration order. * * @param type the type of the elements * @return a newly-allocated array into which all the elements of this fluent iterable have * been copied */ @GwtIncompatible("Array.newArray(Class, int)") public final E[] toArray(Class<E> type) { return Iterables.toArray(iterable, type); } /** * Copies all the elements from this fluent iterable to {@code collection}. This is equivalent to * calling {@code Iterables.addAll(collection, this)}. * * @param collection the collection to copy elements to * @return {@code collection}, for convenience * @since 14.0 */ public final <C extends Collection<? super E>> C copyInto(C collection) { checkNotNull(collection); if (iterable instanceof Collection) { collection.addAll(Collections2.cast(iterable)); } else { for (E item : iterable) { collection.add(item); } } return collection; } /** * Returns the element at the specified position in this fluent iterable. * * @param position position of the element to return * @return the element at the specified position in this fluent iterable * @throws IndexOutOfBoundsException if {@code position} is negative or greater than or equal to * the size of this fluent iterable */ public final E get(int position) { return Iterables.get(iterable, position); } /** * Function that transforms {@code Iterable<E>} into a fluent iterable. */ private static class FromIterableFunction<E> implements Function<Iterable<E>, FluentIterable<E>> { @Override public FluentIterable<E> apply(Iterable<E> fromObject) { return FluentIterable.from(fromObject); } } }