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