com.google.common.collect.FluentIterable Maven / Gradle / Ivy
/*
* 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.Joiner;
import com.google.common.base.Optional;
import com.google.common.base.Predicate;
import java.util.Arrays;
import java.util.Collection;
import java.util.Comparator;
import java.util.Iterator;
import java.util.List;
import java.util.SortedSet;
import javax.annotation.CheckReturnValue;
import javax.annotation.Nullable;
/**
* An expanded {@code Iterable} API, providing functionality similar to Java 8's powerful streams library in a slightly different way.
*
* The following types of methods are provided:
*
*
* - chaining methods which return a new {@code FluentIterable} based in some way on the contents
* of the current one (for example {@link #transform})
*
- element extraction methods which facilitate the retrieval of certain elements (for example
* {@link #last})
*
- query methods which answer questions about the {@code FluentIterable}'s contents (for example
* {@link #anyMatch})
*
- conversion methods which copy the {@code FluentIterable}'s contents into a new collection or
* array (for example {@link #toList})
*
*
* Several lesser-used features are currently available only as static methods on the {@link
* Iterables} class.
*
*
*
Comparison to streams
*
* Starting with Java 8, the core Java class libraries provide a new "Streams" library (in {@code
* java.util.stream}), which is similar to {@code FluentIterable} but generally more powerful. Key
* differences include:
*
*
* - A stream is single-use; it becomes invalid as soon as any "terminal operation" such as
* {@code findFirst()} or {@code iterator()} is invoked. (Even though {@code Stream} contains
* all the right method signatures to implement {@link Iterable}, it does not actually
* do so, to avoid implying repeat-iterability.) {@code FluentIterable}, on the other hand, is
* multiple-use, and does implement {@link Iterable}.
*
- Streams offer many features not found here, including {@code min/max}, {@code
* distinct}, {@code reduce}, {@code sorted}, the very powerful {@code collect}, and built-in
* support for parallelizing stream operations.
*
- {@code FluentIterable} contains several features not available on {@code Stream}, which are
* noted in the method descriptions below.
*
- Streams include primitive-specialized variants such as {@code IntStream}, the use of which is
* strongly recommended.
*
- Streams are standard Java, not requiring a third-party dependency (but do render your code
* incompatible with Java 7 and earlier).
*
*
* Example
*
* Here is an example that accepts a list from a database call, filters it based on a predicate,
* transforms it by invoking {@code toString()} on each element, and returns the first 10 elements
* as a {@code List}:
{@code
*
* List results =
* FluentIterable.from(database.getClientList())
* .filter(activeInLastMonthPredicate)
* .transform(Functions.toStringFunction())
* .limit(10)
* .toList();}
*
* The approximate stream equivalent is: {@code
*
* List results =
* database.getClientList()
* .stream()
* .filter(activeInLastMonthPredicate)
* .map(Functions.toStringFunction())
* .limit(10)
* .collect(Collectors.toList());}
*
* @author Marcin Mikosik
* @since 12.0
*/
@GwtCompatible(emulated = true)
public abstract class FluentIterable implements Iterable {
// 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 iterable;
/** Constructor for use by subclasses. */
protected FluentIterable() {
this.iterable = this;
}
FluentIterable(Iterable iterable) {
this.iterable = checkNotNull(iterable);
}
/**
* Returns a fluent iterable that wraps {@code iterable}, or {@code iterable} itself if it
* is already a {@code FluentIterable}.
*
* {@code Stream} equivalent: {@code iterable.stream()} if {@code iterable} is a
* {@link Collection}; {@code StreamSupport.stream(iterable.spliterator(), false)} otherwise.
*/
@CheckReturnValue
public static FluentIterable from(final Iterable iterable) {
return (iterable instanceof FluentIterable)
? (FluentIterable) iterable
: new FluentIterable(iterable) {
@Override
public Iterator 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
@CheckReturnValue
public static FluentIterable from(FluentIterable iterable) {
return checkNotNull(iterable);
}
/**
* Returns a fluent iterable containing {@code elements} in the specified order.
*
* {@code Stream} equivalent: {@code Stream.of(elements)} or {@code
* Arrays.stream(elements)}.
*
* @since 18.0
*/
@Beta
@CheckReturnValue
public static FluentIterable of(E[] elements) {
return from(Lists.newArrayList(elements));
}
/**
* Returns a string representation of this fluent iterable, with the format
* {@code [e1, e2, ..., en]}.
*
* {@code Stream} equivalent: {@code stream.collect(Collectors.joining(", ", "[", "]"))}
* or (less efficiently) {@code collect(Collectors.toList()).toString()}.
*/
@Override
@CheckReturnValue
public String toString() {
return Iterables.toString(iterable);
}
/**
* Returns the number of elements in this fluent iterable.
*
*
{@code Stream} equivalent: {@code stream.count()}.
*/
@CheckReturnValue
public final int size() {
return Iterables.size(iterable);
}
/**
* Returns {@code true} if this fluent iterable contains any object for which
* {@code equals(target)} is true.
*
*
{@code Stream} equivalent: {@code stream.anyMatch(Predicate.isEqual(target))}.
*/
@CheckReturnValue
public final boolean contains(@Nullable Object target) {
return Iterables.contains(iterable, target);
}
/**
* Returns a fluent iterable whose {@code Iterator} cycles indefinitely over the elements of
* this fluent iterable.
*
*
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.
*
*
Warning: 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.
*
*
{@code Stream} equivalent: if the source iterable has only a single element {@code
* element}, use {@code Stream.generate(() -> element)}. Otherwise, if the source iterable has
* a {@code stream} method (for example, if it is a {@link Collection}), use
* {@code Stream.generate(iterable::stream).flatMap(s -> s)}.
*/
@CheckReturnValue
public final FluentIterable cycle() {
return from(Iterables.cycle(iterable));
}
/**
* Returns a fluent iterable whose iterators traverse first the elements of this fluent iterable,
* followed by those of {@code other}. The iterators are not polled until necessary.
*
* The returned iterable's {@code Iterator} supports {@code remove()} when the corresponding
* {@code Iterator} supports it.
*
*
{@code Stream} equivalent: {@code Stream.concat(thisStream, otherStream)}.
*
* @since 18.0
*/
@Beta
@CheckReturnValue
public final FluentIterable append(Iterable other) {
return from(Iterables.concat(iterable, other));
}
/**
* Returns a fluent iterable whose iterators traverse first the elements of this fluent iterable,
* followed by {@code elements}.
*
* {@code Stream} equivalent: {@code Stream.concat(thisStream, Stream.of(elements))}.
*
* @since 18.0
*/
@Beta
@CheckReturnValue
public final FluentIterable append(E... elements) {
return from(Iterables.concat(iterable, Arrays.asList(elements)));
}
/**
* Returns the elements from this fluent iterable that satisfy a predicate. The
* resulting fluent iterable's iterator does not support {@code remove()}.
*
* {@code Stream} equivalent: {@code stream.filter(predicate)} (same).
*/
@CheckReturnValue
public final FluentIterable filter(Predicate 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
*
* {@code Stream} equivalent:
{@code
*
* @SuppressWarnings("unchecked") // safe by runtime check
* Stream result = (Stream) stream.filter(type::isInstance);}
*
* ... or if {@code type} is a class literal {@code MyType.class}, {@code
*
* @SuppressWarnings("unchecked") // safe by runtime check
* Stream result = (Stream) stream.filter(e -> e instanceof MyType);}
*/
@GwtIncompatible("Class.isInstance")
@CheckReturnValue
public final FluentIterable filter(Class type) {
return from(Iterables.filter(iterable, type));
}
/**
* Returns {@code true} if any element in this fluent iterable satisfies the predicate.
*
* {@code Stream} equivalent: {@code stream.anyMatch(predicate)} (same).
*/
@CheckReturnValue
public final boolean anyMatch(Predicate 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.
*
*
{@code Stream} equivalent: {@code stream.allMatch(predicate)} (same).
*/
@CheckReturnValue
public final boolean allMatch(Predicate 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.
*
*
Warning: avoid using a {@code predicate} that matches {@code null}. If {@code null}
* is matched in this fluent iterable, a {@link NullPointerException} will be thrown.
*
*
{@code Stream} equivalent: {@code stream.filter(predicate).findFirst()}.
*/
@CheckReturnValue
public final Optional firstMatch(Predicate predicate) {
return Iterables.tryFind(iterable, predicate);
}
/**
* Returns a fluent iterable that applies {@code function} to each element of this
* fluent iterable.
*
* 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.
*
*
{@code Stream} equivalent: {@code stream.map(function)}.
*/
@CheckReturnValue
public final FluentIterable transform(Function 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.
*
* 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.
*
*
{@code Stream} equivalent: {@code stream.flatMap(function)} (using a function that
* produces streams, not iterables).
*
* @since 13.0 (required {@code Function>} until 14.0)
*/
@CheckReturnValue
public FluentIterable transformAndConcat(
Function> 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.
*
* {@code Stream} equivalent: if the goal is to obtain any element, {@code
* stream.findAny()}; if it must specifically be the first element, {@code
* stream.findFirst()}.
*
* @throws NullPointerException if the first element is null; if this is a possibility, use
* {@code iterator().next()} or {@link Iterables#getFirst} instead.
*/
@CheckReturnValue
public final Optional first() {
Iterator iterator = iterable.iterator();
return iterator.hasNext() ? Optional.of(iterator.next()) : Optional.absent();
}
/**
* Returns an {@link Optional} containing the last element in this fluent iterable.
* If the iterable is empty, {@code Optional.absent()} is returned.
*
* {@code Stream} equivalent: {@code stream.reduce((a, b) -> b)}.
*
* @throws NullPointerException if the last element is null; if this is a possibility, use
* {@link Iterables#getLast} instead.
*/
@CheckReturnValue
public final Optional 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 list = (List) iterable;
if (list.isEmpty()) {
return Optional.absent();
}
return Optional.of(list.get(list.size() - 1));
}
Iterator 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 sortedSet = (SortedSet) 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.
*
* 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.
*
*
The returned fluent iterable's iterator supports {@code remove()} if the
* {@code Iterator} of this fluent iterable supports it. Note that it is not
* 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}.
*
*
{@code Stream} equivalent: {@code stream.skip(numberToSkip)} (same).
*/
@CheckReturnValue
public final FluentIterable 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.
*
* {@code Stream} equivalent: {@code stream.limit(maxSize)} (same).
*
* @param maxSize the maximum number of elements in the returned fluent iterable
* @throws IllegalArgumentException if {@code size} is negative
*/
@CheckReturnValue
public final FluentIterable limit(int maxSize) {
return from(Iterables.limit(iterable, maxSize));
}
/**
* Determines whether this fluent iterable is empty.
*
* {@code Stream} equivalent: {@code !stream.findAny().isPresent()}.
*/
@CheckReturnValue
public final boolean isEmpty() {
return !iterable.iterator().hasNext();
}
/**
* Returns an {@code ImmutableList} containing all of the elements from this fluent iterable in
* proper sequence.
*
*
{@code Stream} equivalent: {@code ImmutableList.copyOf(stream.iterator())}.
*
* @since 14.0 (since 12.0 as {@code toImmutableList()}).
*/
@CheckReturnValue
public final ImmutableList 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())}.
*
* {@code Stream} equivalent:
* {@code ImmutableList.copyOf(stream.sorted(comparator).iterator())}.
*
* @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()}).
*/
@CheckReturnValue
public final ImmutableList toSortedList(Comparator comparator) {
return Ordering.from(comparator).immutableSortedCopy(iterable);
}
/**
* Returns an {@code ImmutableSet} containing all of the elements from this fluent iterable with
* duplicates removed.
*
* {@code Stream} equivalent: {@code ImmutableSet.copyOf(stream.iterator())}.
*
* @since 14.0 (since 12.0 as {@code toImmutableSet()}).
*/
@CheckReturnValue
public final ImmutableSet 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())}.
*
* {@code Stream} equivalent:
* {@code ImmutableSortedSet.copyOf(comparator, stream.iterator())}.
*
* @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()}).
*/
@CheckReturnValue
public final ImmutableSortedSet toSortedSet(Comparator comparator) {
return ImmutableSortedSet.copyOf(comparator, iterable);
}
/**
* Returns an {@code ImmutableMultiset} containing all of the elements from this fluent iterable.
*
* {@code Stream} equivalent: {@code ImmutableMultiset.copyOf(stream.iterator())}.
*
* @since 19.0
*/
@CheckReturnValue
public final ImmutableMultiset toMultiset() {
return ImmutableMultiset.copyOf(iterable);
}
/**
* Returns an immutable map whose keys are the distinct elements of this {@code FluentIterable}
* and whose value for each key was computed by {@code valueFunction}. The map's iteration order
* is the order of the first appearance of each key in this iterable.
*
* When there are multiple instances of a key in this iterable, it is unspecified whether
* {@code valueFunction} will be applied to more than one instance of that key and, if it is,
* which result will be mapped to that key in the returned map.
*
*
{@code Stream} equivalent: {@code
* ImmutableMap.copyOf(stream.collect(Collectors.toMap(k -> k, valueFunction)))} (but note that
* this may not preserve the order of entries).
*
* @throws NullPointerException if any element of this iterable is {@code null}, or if {@code
* valueFunction} produces {@code null} for any key
* @since 14.0
*/
@CheckReturnValue
public final ImmutableMap toMap(Function valueFunction) {
return Maps.toMap(iterable, valueFunction);
}
/**
* Creates an index {@code ImmutableListMultimap} that contains the results of applying a
* specified function to each item in this {@code FluentIterable} of values. Each element of this
* iterable will be stored as a value in the resulting multimap, yielding a multimap with the same
* size as this iterable. The key used to store that value in the multimap will be the result of
* calling the function on that value. The resulting multimap is created as an immutable snapshot.
* In the returned multimap, keys appear in the order they are first encountered, and the values
* corresponding to each key appear in the same order as they are encountered.
*
* @param keyFunction the function used to produce the key for each value
* @throws NullPointerException if any of the following cases is true:
*
* - {@code keyFunction} is null
*
- An element in this fluent iterable is null
*
- {@code keyFunction} returns {@code null} for any element of this iterable
*
*
* {@code Stream} equivalent: {@code stream.collect(Collectors.groupingBy(keyFunction))}
* behaves similarly, but returns a mutable {@code Map>} instead, and may not preserve
* the order of entries).
*
* @since 14.0
*/
@CheckReturnValue
public final ImmutableListMultimap index(Function keyFunction) {
return Multimaps.index(iterable, keyFunction);
}
/**
* Returns a map with the contents of this {@code FluentIterable} as its {@code values}, indexed
* by keys derived from those values. In other words, each input value produces an entry in the
* map whose key is the result of applying {@code keyFunction} to that value. These entries appear
* in the same order as they appeared in this fluent iterable. Example usage:
* {@code
*
* Color red = new Color("red", 255, 0, 0);
* ...
* FluentIterable allColors = FluentIterable.from(ImmutableSet.of(red, green, blue));
*
* Map colorForName = allColors.uniqueIndex(toStringFunction());
* assertThat(colorForName).containsEntry("red", red);}
*
* If your index may associate multiple values with each key, use {@link #index(Function)
* index}.
*
*
{@code Stream} equivalent: {@code
* ImmutableMap.copyOf(stream.collect(Collectors.toMap(keyFunction, v -> v)))} (but note that this
* may not preserve the order of entries).
*
* @param keyFunction the function used to produce the key for each value
* @return a map mapping the result of evaluating the function {@code
* keyFunction} on each value in this fluent iterable to that value
* @throws IllegalArgumentException if {@code keyFunction} produces the same
* key for more than one value in this fluent iterable
* @throws NullPointerException if any elements of this fluent iterable is null, or
* if {@code keyFunction} produces {@code null} for any value
* @since 14.0
*/
@CheckReturnValue
public final ImmutableMap uniqueIndex(Function keyFunction) {
return Maps.uniqueIndex(iterable, keyFunction);
}
/**
* Returns an array containing all of the elements from this fluent iterable in iteration order.
*
* {@code Stream} equivalent: if an object array is acceptable, use
* {@code stream.toArray()}; if {@code type} is a class literal such as {@code MyType.class}, use
* {@code stream.toArray(MyType[]::new)}. Otherwise use {@code stream.toArray(
* len -> (E[]) Array.newInstance(type, len))}.
*
* @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)")
@CheckReturnValue
public final E[] toArray(Class 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)}.
*
* {@code Stream} equivalent: {@code stream.forEachOrdered(collection::add)} or
* {@code stream.forEach(collection::add)}.
*
* @param collection the collection to copy elements to
* @return {@code collection}, for convenience
* @since 14.0
*/
public final > 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 a {@link String} containing all of the elements of this fluent iterable joined with
* {@code joiner}.
*
* {@code Stream} equivalent: {@code joiner.join(stream.iterator())}, or, if you are not
* using any optional {@code Joiner} features,
* {@code stream.collect(Collectors.joining(delimiter)}.
*
* @since 18.0
*/
@Beta
@CheckReturnValue
public final String join(Joiner joiner) {
return joiner.join(this);
}
/**
* Returns the element at the specified position in this fluent iterable.
*
*
{@code Stream} equivalent: {@code stream.skip(position).findFirst().get()} (but note
* that this throws different exception types, and throws an exception if {@code null} would be
* returned).
*
* @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
*/
// TODO(kevinb): add @Nullable?
@CheckReturnValue
public final E get(int position) {
return Iterables.get(iterable, position);
}
/**
* Function that transforms {@code Iterable} into a fluent iterable.
*/
private static class FromIterableFunction implements Function, FluentIterable> {
@Override
public FluentIterable apply(Iterable fromObject) {
return FluentIterable.from(fromObject);
}
}
}