1334 lines
43 KiB
Java
1334 lines
43 KiB
Java
/*
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* Copyright (C) 2007 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.checkArgument;
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import static com.google.common.base.Preconditions.checkNotNull;
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import static com.google.common.base.Preconditions.checkState;
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import static com.google.common.base.Predicates.equalTo;
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import static com.google.common.base.Predicates.in;
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import static com.google.common.base.Predicates.instanceOf;
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import static com.google.common.base.Predicates.not;
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import static com.google.common.collect.CollectPreconditions.checkRemove;
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import java.util.Arrays;
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import java.util.Collection;
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import java.util.Collections;
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import java.util.Comparator;
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import java.util.Enumeration;
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import java.util.Iterator;
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import java.util.List;
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import java.util.ListIterator;
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import java.util.NoSuchElementException;
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import java.util.PriorityQueue;
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import java.util.Queue;
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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.Objects;
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import com.google.common.base.Optional;
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import com.google.common.base.Preconditions;
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import com.google.common.base.Predicate;
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/**
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* This class contains static utility methods that operate on or return objects
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* of type {@link Iterator}. Except as noted, each method has a corresponding
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* {@link Iterable}-based method in the {@link Iterables} class.
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*
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* <p>
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* <i>Performance notes:</i> Unless otherwise noted, all of the iterators
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* produced in this class are <i>lazy</i>, which means that they only advance
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* the backing iteration when absolutely necessary.
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*
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* <p>
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* See the Guava User Guide section on <a href=
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* "http://code.google.com/p/guava-libraries/wiki/CollectionUtilitiesExplained#Iterables">
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* {@code Iterators}</a>.
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*
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* @author Kevin Bourrillion
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* @author Jared Levy
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* @since 2.0 (imported from Google Collections Library)
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*/
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@GwtCompatible(emulated = true)
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public final class Iterators {
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private Iterators() {
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}
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static final UnmodifiableListIterator<Object> EMPTY_LIST_ITERATOR = new UnmodifiableListIterator<Object>() {
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@Override
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public boolean hasNext() {
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return false;
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}
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@Override
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public Object next() {
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throw new NoSuchElementException();
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}
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@Override
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public boolean hasPrevious() {
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return false;
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}
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@Override
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public Object previous() {
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throw new NoSuchElementException();
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}
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@Override
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public int nextIndex() {
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return 0;
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}
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@Override
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public int previousIndex() {
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return -1;
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}
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};
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/**
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* Returns the empty iterator.
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*
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* <p>
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* The {@link Iterable} equivalent of this method is {@link ImmutableSet#of()}.
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*/
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public static <T> UnmodifiableIterator<T> emptyIterator() {
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return emptyListIterator();
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}
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/**
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* Returns the empty iterator.
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*
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* <p>
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* The {@link Iterable} equivalent of this method is {@link ImmutableSet#of()}.
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*/
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// Casting to any type is safe since there are no actual elements.
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@SuppressWarnings("unchecked")
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static <T> UnmodifiableListIterator<T> emptyListIterator() {
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return (UnmodifiableListIterator<T>) EMPTY_LIST_ITERATOR;
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}
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private static final Iterator<Object> EMPTY_MODIFIABLE_ITERATOR = new Iterator<Object>() {
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@Override
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public boolean hasNext() {
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return false;
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}
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@Override
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public Object next() {
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throw new NoSuchElementException();
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}
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@Override
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public void remove() {
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checkRemove(false);
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}
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};
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/**
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* Returns the empty {@code Iterator} that throws {@link IllegalStateException}
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* instead of {@link UnsupportedOperationException} on a call to
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* {@link Iterator#remove()}.
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*/
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// Casting to any type is safe since there are no actual elements.
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@SuppressWarnings("unchecked")
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static <T> Iterator<T> emptyModifiableIterator() {
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return (Iterator<T>) EMPTY_MODIFIABLE_ITERATOR;
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}
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/** Returns an unmodifiable view of {@code iterator}. */
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public static <T> UnmodifiableIterator<T> unmodifiableIterator(final Iterator<T> iterator) {
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checkNotNull(iterator);
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if (iterator instanceof UnmodifiableIterator) {
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return (UnmodifiableIterator<T>) iterator;
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}
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return new UnmodifiableIterator<T>() {
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@Override
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public boolean hasNext() {
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return iterator.hasNext();
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}
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@Override
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public T next() {
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return iterator.next();
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}
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};
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}
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/**
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* Simply returns its argument.
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*
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* @deprecated no need to use this
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* @since 10.0
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*/
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@Deprecated
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public static <T> UnmodifiableIterator<T> unmodifiableIterator(UnmodifiableIterator<T> iterator) {
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return checkNotNull(iterator);
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}
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/**
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* Returns the number of elements remaining in {@code iterator}. The iterator
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* will be left exhausted: its {@code hasNext()} method will return
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* {@code false}.
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*/
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public static int size(Iterator<?> iterator) {
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int count = 0;
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while (iterator.hasNext()) {
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iterator.next();
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count++;
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}
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return count;
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}
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/**
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* Returns {@code true} if {@code iterator} contains {@code element}.
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*/
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public static boolean contains(Iterator<?> iterator, @Nullable Object element) {
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return any(iterator, equalTo(element));
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}
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/**
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* Traverses an iterator and removes every element that belongs to the provided
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* collection. The iterator will be left exhausted: its {@code hasNext()} method
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* will return {@code false}.
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*
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* @param removeFrom the iterator to (potentially) remove elements from
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* @param elementsToRemove the elements to remove
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* @return {@code true} if any element was removed from {@code iterator}
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*/
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public static boolean removeAll(Iterator<?> removeFrom, Collection<?> elementsToRemove) {
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return removeIf(removeFrom, in(elementsToRemove));
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}
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/**
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* Removes every element that satisfies the provided predicate from the
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* iterator. The iterator will be left exhausted: its {@code hasNext()} method
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* will return {@code false}.
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*
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* @param removeFrom the iterator to (potentially) remove elements from
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* @param predicate a predicate that determines whether an element should be
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* removed
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* @return {@code true} if any elements were removed from the iterator
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* @since 2.0
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*/
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public static <T> boolean removeIf(Iterator<T> removeFrom, Predicate<? super T> predicate) {
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checkNotNull(predicate);
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boolean modified = false;
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while (removeFrom.hasNext()) {
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if (predicate.apply(removeFrom.next())) {
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removeFrom.remove();
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modified = true;
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}
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}
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return modified;
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}
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/**
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* Traverses an iterator and removes every element that does not belong to the
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* provided collection. The iterator will be left exhausted: its
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* {@code hasNext()} method will return {@code false}.
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*
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* @param removeFrom the iterator to (potentially) remove elements from
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* @param elementsToRetain the elements to retain
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* @return {@code true} if any element was removed from {@code iterator}
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*/
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public static boolean retainAll(Iterator<?> removeFrom, Collection<?> elementsToRetain) {
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return removeIf(removeFrom, not(in(elementsToRetain)));
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}
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/**
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* Determines whether two iterators contain equal elements in the same order.
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* More specifically, this method returns {@code true} if {@code iterator1} and
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* {@code iterator2} contain the same number of elements and every element of
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* {@code iterator1} is equal to the corresponding element of {@code iterator2}.
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*
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* <p>
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* Note that this will modify the supplied iterators, since they will have been
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* advanced some number of elements forward.
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*/
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public static boolean elementsEqual(Iterator<?> iterator1, Iterator<?> iterator2) {
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while (iterator1.hasNext()) {
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if (!iterator2.hasNext()) {
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return false;
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}
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Object o1 = iterator1.next();
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Object o2 = iterator2.next();
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if (!Objects.equal(o1, o2)) {
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return false;
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}
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}
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return !iterator2.hasNext();
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}
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/**
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* Returns a string representation of {@code iterator}, with the format
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* {@code [e1, e2, ..., en]}. The iterator will be left exhausted: its
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* {@code hasNext()} method will return {@code false}.
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*/
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public static String toString(Iterator<?> iterator) {
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return Collections2.STANDARD_JOINER.appendTo(new StringBuilder().append('['), iterator).append(']').toString();
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}
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/**
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* Returns the single element contained in {@code iterator}.
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*
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* @throws NoSuchElementException if the iterator is empty
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* @throws IllegalArgumentException if the iterator contains multiple elements.
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* The state of the iterator is unspecified.
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*/
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public static <T> T getOnlyElement(Iterator<T> iterator) {
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T first = iterator.next();
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if (!iterator.hasNext()) {
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return first;
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}
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StringBuilder sb = new StringBuilder();
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sb.append("expected one element but was: <" + first);
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for (int i = 0; i < 4 && iterator.hasNext(); i++) {
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sb.append(", " + iterator.next());
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}
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if (iterator.hasNext()) {
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sb.append(", ...");
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}
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sb.append('>');
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throw new IllegalArgumentException(sb.toString());
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}
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/**
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* Returns the single element contained in {@code iterator}, or {@code
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* defaultValue} if the iterator is empty.
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*
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* @throws IllegalArgumentException if the iterator contains multiple elements.
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* The state of the iterator is unspecified.
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*/
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@Nullable
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public static <T> T getOnlyElement(Iterator<? extends T> iterator, @Nullable T defaultValue) {
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return iterator.hasNext() ? getOnlyElement(iterator) : defaultValue;
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}
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/**
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* Copies an iterator's elements into an array. The iterator will be left
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* exhausted: its {@code hasNext()} method will return {@code false}.
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*
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* @param iterator the iterator to copy
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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 the iterator
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* have been copied
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*/
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@GwtIncompatible("Array.newInstance(Class, int)")
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public static <T> T[] toArray(Iterator<? extends T> iterator, Class<T> type) {
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List<T> list = Lists.newArrayList(iterator);
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return Iterables.toArray(list, type);
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}
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/**
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* Adds all elements in {@code iterator} to {@code collection}. The iterator
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* will be left exhausted: its {@code hasNext()} method will return
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* {@code false}.
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*
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* @return {@code true} if {@code collection} was modified as a result of this
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* operation
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*/
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public static <T> boolean addAll(Collection<T> addTo, Iterator<? extends T> iterator) {
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checkNotNull(addTo);
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checkNotNull(iterator);
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boolean wasModified = false;
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while (iterator.hasNext()) {
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wasModified |= addTo.add(iterator.next());
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}
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return wasModified;
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}
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/**
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* Returns the number of elements in the specified iterator that equal the
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* specified object. The iterator will be left exhausted: its {@code hasNext()}
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* method will return {@code false}.
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*
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* @see Collections#frequency
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*/
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public static int frequency(Iterator<?> iterator, @Nullable Object element) {
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return size(filter(iterator, equalTo(element)));
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}
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/**
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* Returns an iterator that cycles indefinitely over the elements of {@code
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* iterable}.
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*
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* <p>
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* The returned iterator supports {@code remove()} if the provided iterator
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* does. After {@code remove()} is called, subsequent cycles omit the removed
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* element, which is no longer in {@code iterable}. The iterator's
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* {@code hasNext()} method returns {@code true} until {@code iterable} is
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* 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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public static <T> Iterator<T> cycle(final Iterable<T> iterable) {
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checkNotNull(iterable);
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return new Iterator<T>() {
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Iterator<T> iterator = emptyIterator();
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Iterator<T> removeFrom;
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@Override
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public boolean hasNext() {
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if (!iterator.hasNext()) {
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iterator = iterable.iterator();
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}
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return iterator.hasNext();
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}
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@Override
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public T next() {
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if (!hasNext()) {
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throw new NoSuchElementException();
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}
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removeFrom = iterator;
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return iterator.next();
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}
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@Override
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public void remove() {
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checkRemove(removeFrom != null);
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removeFrom.remove();
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removeFrom = null;
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}
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};
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}
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/**
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* Returns an iterator that cycles indefinitely over the provided elements.
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*
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* <p>
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* The returned iterator supports {@code remove()}. After {@code remove()} is
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* called, subsequent cycles omit the removed element, but {@code elements} does
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* not change. The iterator's {@code hasNext()} method returns {@code true}
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* until all of the original elements have been removed.
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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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public static <T> Iterator<T> cycle(T... elements) {
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return cycle(Lists.newArrayList(elements));
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}
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/**
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* Combines two iterators into a single iterator. The returned iterator iterates
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* across the elements in {@code a}, followed by the elements in {@code b}. The
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* source iterators are not polled until necessary.
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*
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* <p>
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* The returned iterator supports {@code remove()} when the corresponding input
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* iterator supports it.
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*
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* <p>
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* <b>Note:</b> the current implementation is not suitable for nested
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* concatenated iterators, i.e. the following should be avoided when in a loop:
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* {@code iterator = Iterators.concat(iterator, suffix);}, since iteration over
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* the resulting iterator has a cubic complexity to the depth of the nesting.
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*/
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public static <T> Iterator<T> concat(Iterator<? extends T> a, Iterator<? extends T> b) {
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return concat(ImmutableList.of(a, b).iterator());
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}
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/**
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* Combines three iterators into a single iterator. The returned iterator
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* iterates across the elements in {@code a}, followed by the elements in
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* {@code b}, followed by the elements in {@code c}. The source iterators are
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* not polled until necessary.
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*
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* <p>
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* The returned iterator supports {@code remove()} when the corresponding input
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* iterator supports it.
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*
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* <p>
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* <b>Note:</b> the current implementation is not suitable for nested
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* concatenated iterators, i.e. the following should be avoided when in a loop:
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* {@code iterator = Iterators.concat(iterator, suffix);}, since iteration over
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* the resulting iterator has a cubic complexity to the depth of the nesting.
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*/
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public static <T> Iterator<T> concat(Iterator<? extends T> a, Iterator<? extends T> b, Iterator<? extends T> c) {
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return concat(ImmutableList.of(a, b, c).iterator());
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}
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/**
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* Combines four iterators into a single iterator. The returned iterator
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* iterates across the elements in {@code a}, followed by the elements in
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* {@code b}, followed by the elements in {@code c}, followed by the elements in
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* {@code d}. The source iterators are not polled until necessary.
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*
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* <p>
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* The returned iterator supports {@code remove()} when the corresponding input
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* iterator supports it.
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*
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* <p>
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* <b>Note:</b> the current implementation is not suitable for nested
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|
* concatenated iterators, i.e. the following should be avoided when in a loop:
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* {@code iterator = Iterators.concat(iterator, suffix);}, since iteration over
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* the resulting iterator has a cubic complexity to the depth of the nesting.
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*/
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public static <T> Iterator<T> concat(Iterator<? extends T> a, Iterator<? extends T> b, Iterator<? extends T> c,
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Iterator<? extends T> d) {
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return concat(ImmutableList.of(a, b, c, d).iterator());
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}
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/**
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* Combines multiple iterators into a single iterator. The returned iterator
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* iterates across the elements of each iterator in {@code inputs}. The input
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* iterators are not polled until necessary.
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*
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* <p>
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* The returned iterator supports {@code remove()} when the corresponding input
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* iterator supports it.
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*
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* <p>
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|
* <b>Note:</b> the current implementation is not suitable for nested
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* concatenated iterators, i.e. the following should be avoided when in a loop:
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* {@code iterator = Iterators.concat(iterator, suffix);}, since iteration over
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* the resulting iterator has a cubic complexity to the depth of the nesting.
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*
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* @throws NullPointerException if any of the provided iterators is null
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*/
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public static <T> Iterator<T> concat(Iterator<? extends T>... inputs) {
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return concat(ImmutableList.copyOf(inputs).iterator());
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}
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|
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/**
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|
* Combines multiple iterators into a single iterator. The returned iterator
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|
* iterates across the elements of each iterator in {@code inputs}. The input
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* iterators are not polled until necessary.
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*
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* <p>
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* The returned iterator supports {@code remove()} when the corresponding input
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* iterator supports it. The methods of the returned iterator may throw
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* {@code NullPointerException} if any of the input iterators is null.
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*
|
|
* <p>
|
|
* <b>Note:</b> the current implementation is not suitable for nested
|
|
* concatenated iterators, i.e. the following should be avoided when in a loop:
|
|
* {@code iterator = Iterators.concat(iterator, suffix);}, since iteration over
|
|
* the resulting iterator has a cubic complexity to the depth of the nesting.
|
|
*/
|
|
public static <T> Iterator<T> concat(final Iterator<? extends Iterator<? extends T>> inputs) {
|
|
checkNotNull(inputs);
|
|
return new Iterator<T>() {
|
|
Iterator<? extends T> current = emptyIterator();
|
|
Iterator<? extends T> removeFrom;
|
|
|
|
@Override
|
|
public boolean hasNext() {
|
|
// http://code.google.com/p/google-collections/issues/detail?id=151
|
|
// current.hasNext() might be relatively expensive, worth minimizing.
|
|
boolean currentHasNext;
|
|
// checkNotNull eager for GWT
|
|
// note: it must be here & not where 'current' is assigned,
|
|
// because otherwise we'll have called inputs.next() before throwing
|
|
// the first NPE, and the next time around we'll call inputs.next()
|
|
// again, incorrectly moving beyond the error.
|
|
while (!(currentHasNext = checkNotNull(current).hasNext()) && inputs.hasNext()) {
|
|
current = inputs.next();
|
|
}
|
|
return currentHasNext;
|
|
}
|
|
|
|
@Override
|
|
public T next() {
|
|
if (!hasNext()) {
|
|
throw new NoSuchElementException();
|
|
}
|
|
removeFrom = current;
|
|
return current.next();
|
|
}
|
|
|
|
@Override
|
|
public void remove() {
|
|
checkRemove(removeFrom != null);
|
|
removeFrom.remove();
|
|
removeFrom = null;
|
|
}
|
|
};
|
|
}
|
|
|
|
/**
|
|
* Divides an iterator into unmodifiable sublists of the given size (the final
|
|
* list may be smaller). For example, partitioning an iterator containing
|
|
* {@code [a, b, c, d, e]} with a partition size of 3 yields {@code
|
|
* [[a, b, c], [d, e]]} -- an outer iterator containing two inner lists of three
|
|
* and two elements, all in the original order.
|
|
*
|
|
* <p>
|
|
* The returned lists implement {@link net.lax1dude.eaglercraft.v1_8.RandomAccess}.
|
|
*
|
|
* @param iterator the iterator to return a partitioned view of
|
|
* @param size the desired size of each partition (the last may be smaller)
|
|
* @return an iterator of immutable lists containing the elements of {@code
|
|
* iterator} divided into partitions
|
|
* @throws IllegalArgumentException if {@code size} is nonpositive
|
|
*/
|
|
public static <T> UnmodifiableIterator<List<T>> partition(Iterator<T> iterator, int size) {
|
|
return partitionImpl(iterator, size, false);
|
|
}
|
|
|
|
/**
|
|
* Divides an iterator into unmodifiable sublists of the given size, padding the
|
|
* final iterator with null values if necessary. For example, partitioning an
|
|
* iterator containing {@code [a, b, c, d, e]} with a partition size of 3 yields
|
|
* {@code [[a, b, c], [d, e, null]]} -- an outer iterator containing two inner
|
|
* lists of three elements each, all in the original order.
|
|
*
|
|
* <p>
|
|
* The returned lists implement {@link net.lax1dude.eaglercraft.v1_8.RandomAccess}.
|
|
*
|
|
* @param iterator the iterator to return a partitioned view of
|
|
* @param size the desired size of each partition
|
|
* @return an iterator of immutable lists containing the elements of {@code
|
|
* iterator} divided into partitions (the final iterable may have trailing
|
|
* null elements)
|
|
* @throws IllegalArgumentException if {@code size} is nonpositive
|
|
*/
|
|
public static <T> UnmodifiableIterator<List<T>> paddedPartition(Iterator<T> iterator, int size) {
|
|
return partitionImpl(iterator, size, true);
|
|
}
|
|
|
|
private static <T> UnmodifiableIterator<List<T>> partitionImpl(final Iterator<T> iterator, final int size,
|
|
final boolean pad) {
|
|
checkNotNull(iterator);
|
|
checkArgument(size > 0);
|
|
return new UnmodifiableIterator<List<T>>() {
|
|
@Override
|
|
public boolean hasNext() {
|
|
return iterator.hasNext();
|
|
}
|
|
|
|
@Override
|
|
public List<T> next() {
|
|
if (!hasNext()) {
|
|
throw new NoSuchElementException();
|
|
}
|
|
Object[] array = new Object[size];
|
|
int count = 0;
|
|
for (; count < size && iterator.hasNext(); count++) {
|
|
array[count] = iterator.next();
|
|
}
|
|
for (int i = count; i < size; i++) {
|
|
array[i] = null; // for GWT
|
|
}
|
|
|
|
@SuppressWarnings("unchecked") // we only put Ts in it
|
|
List<T> list = Collections.unmodifiableList((List<T>) Arrays.asList(array));
|
|
return (pad || count == size) ? list : list.subList(0, count);
|
|
}
|
|
};
|
|
}
|
|
|
|
/**
|
|
* Returns the elements of {@code unfiltered} that satisfy a predicate.
|
|
*/
|
|
public static <T> UnmodifiableIterator<T> filter(final Iterator<T> unfiltered,
|
|
final Predicate<? super T> predicate) {
|
|
checkNotNull(unfiltered);
|
|
checkNotNull(predicate);
|
|
return new AbstractIterator<T>() {
|
|
@Override
|
|
protected T computeNext() {
|
|
while (unfiltered.hasNext()) {
|
|
T element = unfiltered.next();
|
|
if (predicate.apply(element)) {
|
|
return element;
|
|
}
|
|
}
|
|
return endOfData();
|
|
}
|
|
};
|
|
}
|
|
|
|
/**
|
|
* Returns all instances of class {@code type} in {@code unfiltered}. The
|
|
* returned iterator has elements whose class is {@code type} or a subclass of
|
|
* {@code type}.
|
|
*
|
|
* @param unfiltered an iterator containing objects of any type
|
|
* @param type the type of elements desired
|
|
* @return an unmodifiable iterator containing all elements of the original
|
|
* iterator that were of the requested type
|
|
*/
|
|
@SuppressWarnings("unchecked") // can cast to <T> because non-Ts are removed
|
|
@GwtIncompatible("Class.isInstance")
|
|
public static <T> UnmodifiableIterator<T> filter(Iterator<?> unfiltered, Class<T> type) {
|
|
return (UnmodifiableIterator<T>) filter(unfiltered, instanceOf(type));
|
|
}
|
|
|
|
/**
|
|
* Returns {@code true} if one or more elements returned by {@code iterator}
|
|
* satisfy the given predicate.
|
|
*/
|
|
public static <T> boolean any(Iterator<T> iterator, Predicate<? super T> predicate) {
|
|
return indexOf(iterator, predicate) != -1;
|
|
}
|
|
|
|
/**
|
|
* Returns {@code true} if every element returned by {@code iterator} satisfies
|
|
* the given predicate. If {@code iterator} is empty, {@code true} is returned.
|
|
*/
|
|
public static <T> boolean all(Iterator<T> iterator, Predicate<? super T> predicate) {
|
|
checkNotNull(predicate);
|
|
while (iterator.hasNext()) {
|
|
T element = iterator.next();
|
|
if (!predicate.apply(element)) {
|
|
return false;
|
|
}
|
|
}
|
|
return true;
|
|
}
|
|
|
|
/**
|
|
* Returns the first element in {@code iterator} that satisfies the given
|
|
* predicate; use this method only when such an element is known to exist. If no
|
|
* such element is found, the iterator will be left exhausted: its {@code
|
|
* hasNext()} method will return {@code false}. If it is possible that <i>no</i>
|
|
* element will match, use {@link #tryFind} or
|
|
* {@link #find(Iterator, Predicate, Object)} instead.
|
|
*
|
|
* @throws NoSuchElementException if no element in {@code iterator} matches the
|
|
* given predicate
|
|
*/
|
|
public static <T> T find(Iterator<T> iterator, Predicate<? super T> predicate) {
|
|
return filter(iterator, predicate).next();
|
|
}
|
|
|
|
/**
|
|
* Returns the first element in {@code iterator} that satisfies the given
|
|
* predicate. If no such element is found, {@code defaultValue} will be returned
|
|
* from this method and the iterator will be left exhausted: its
|
|
* {@code hasNext()} method will return {@code false}. Note that this can
|
|
* usually be handled more naturally using {@code
|
|
* tryFind(iterator, predicate).or(defaultValue)}.
|
|
*
|
|
* @since 7.0
|
|
*/
|
|
@Nullable
|
|
public static <T> T find(Iterator<? extends T> iterator, Predicate<? super T> predicate, @Nullable T defaultValue) {
|
|
return getNext(filter(iterator, predicate), defaultValue);
|
|
}
|
|
|
|
/**
|
|
* Returns an {@link Optional} containing the first element in {@code
|
|
* iterator} that satisfies the given predicate, if such an element exists. If
|
|
* no such element is found, an empty {@link Optional} will be returned from
|
|
* this method and the iterator will be left exhausted: its {@code
|
|
* hasNext()} method will return {@code false}.
|
|
*
|
|
* <p>
|
|
* <b>Warning:</b> avoid using a {@code predicate} that matches {@code
|
|
* null}. If {@code null} is matched in {@code iterator}, a NullPointerException
|
|
* will be thrown.
|
|
*
|
|
* @since 11.0
|
|
*/
|
|
public static <T> Optional<T> tryFind(Iterator<T> iterator, Predicate<? super T> predicate) {
|
|
UnmodifiableIterator<T> filteredIterator = filter(iterator, predicate);
|
|
return filteredIterator.hasNext() ? Optional.of(filteredIterator.next()) : Optional.<T>absent();
|
|
}
|
|
|
|
/**
|
|
* Returns the index in {@code iterator} of the first element that satisfies the
|
|
* provided {@code predicate}, or {@code -1} if the Iterator has no such
|
|
* elements.
|
|
*
|
|
* <p>
|
|
* More formally, returns the lowest index {@code i} such that
|
|
* {@code predicate.apply(Iterators.get(iterator, i))} returns {@code true}, or
|
|
* {@code -1} if there is no such index.
|
|
*
|
|
* <p>
|
|
* If -1 is returned, the iterator will be left exhausted: its {@code hasNext()}
|
|
* method will return {@code false}. Otherwise, the iterator will be set to the
|
|
* element which satisfies the {@code predicate}.
|
|
*
|
|
* @since 2.0
|
|
*/
|
|
public static <T> int indexOf(Iterator<T> iterator, Predicate<? super T> predicate) {
|
|
checkNotNull(predicate, "predicate");
|
|
for (int i = 0; iterator.hasNext(); i++) {
|
|
T current = iterator.next();
|
|
if (predicate.apply(current)) {
|
|
return i;
|
|
}
|
|
}
|
|
return -1;
|
|
}
|
|
|
|
/**
|
|
* Returns an iterator that applies {@code function} to each element of {@code
|
|
* fromIterator}.
|
|
*
|
|
* <p>
|
|
* The returned iterator supports {@code remove()} if the provided iterator
|
|
* does. After a successful {@code remove()} call, {@code fromIterator} no
|
|
* longer contains the corresponding element.
|
|
*/
|
|
public static <F, T> Iterator<T> transform(final Iterator<F> fromIterator,
|
|
final Function<? super F, ? extends T> function) {
|
|
checkNotNull(function);
|
|
return new TransformedIterator<F, T>(fromIterator) {
|
|
@Override
|
|
T transform(F from) {
|
|
return function.apply(from);
|
|
}
|
|
};
|
|
}
|
|
|
|
/**
|
|
* Advances {@code iterator} {@code position + 1} times, returning the element
|
|
* at the {@code position}th position.
|
|
*
|
|
* @param position position of the element to return
|
|
* @return the element at the specified position in {@code iterator}
|
|
* @throws IndexOutOfBoundsException if {@code position} is negative or greater
|
|
* than or equal to the number of elements
|
|
* remaining in {@code iterator}
|
|
*/
|
|
public static <T> T get(Iterator<T> iterator, int position) {
|
|
checkNonnegative(position);
|
|
int skipped = advance(iterator, position);
|
|
if (!iterator.hasNext()) {
|
|
throw new IndexOutOfBoundsException("position (" + position
|
|
+ ") must be less than the number of elements that remained (" + skipped + ")");
|
|
}
|
|
return iterator.next();
|
|
}
|
|
|
|
static void checkNonnegative(int position) {
|
|
if (position < 0) {
|
|
throw new IndexOutOfBoundsException("position (" + position + ") must not be negative");
|
|
}
|
|
}
|
|
|
|
/**
|
|
* Advances {@code iterator} {@code position + 1} times, returning the element
|
|
* at the {@code position}th position or {@code defaultValue} otherwise.
|
|
*
|
|
* @param position position of the element to return
|
|
* @param defaultValue the default value to return if the iterator is empty or
|
|
* if {@code position} is greater than the number of
|
|
* elements remaining in {@code iterator}
|
|
* @return the element at the specified position in {@code iterator} or
|
|
* {@code defaultValue} if {@code iterator} produces fewer than
|
|
* {@code position + 1} elements.
|
|
* @throws IndexOutOfBoundsException if {@code position} is negative
|
|
* @since 4.0
|
|
*/
|
|
@Nullable
|
|
public static <T> T get(Iterator<? extends T> iterator, int position, @Nullable T defaultValue) {
|
|
checkNonnegative(position);
|
|
advance(iterator, position);
|
|
return getNext(iterator, defaultValue);
|
|
}
|
|
|
|
/**
|
|
* Returns the next element in {@code iterator} or {@code defaultValue} if the
|
|
* iterator is empty. The {@link Iterables} analog to this method is
|
|
* {@link Iterables#getFirst}.
|
|
*
|
|
* @param defaultValue the default value to return if the iterator is empty
|
|
* @return the next element of {@code iterator} or the default value
|
|
* @since 7.0
|
|
*/
|
|
@Nullable
|
|
public static <T> T getNext(Iterator<? extends T> iterator, @Nullable T defaultValue) {
|
|
return iterator.hasNext() ? iterator.next() : defaultValue;
|
|
}
|
|
|
|
/**
|
|
* Advances {@code iterator} to the end, returning the last element.
|
|
*
|
|
* @return the last element of {@code iterator}
|
|
* @throws NoSuchElementException if the iterator is empty
|
|
*/
|
|
public static <T> T getLast(Iterator<T> iterator) {
|
|
while (true) {
|
|
T current = iterator.next();
|
|
if (!iterator.hasNext()) {
|
|
return current;
|
|
}
|
|
}
|
|
}
|
|
|
|
/**
|
|
* Advances {@code iterator} to the end, returning the last element or
|
|
* {@code defaultValue} if the iterator is empty.
|
|
*
|
|
* @param defaultValue the default value to return if the iterator is empty
|
|
* @return the last element of {@code iterator}
|
|
* @since 3.0
|
|
*/
|
|
@Nullable
|
|
public static <T> T getLast(Iterator<? extends T> iterator, @Nullable T defaultValue) {
|
|
return iterator.hasNext() ? getLast(iterator) : defaultValue;
|
|
}
|
|
|
|
/**
|
|
* Calls {@code next()} on {@code iterator}, either {@code numberToAdvance}
|
|
* times or until {@code hasNext()} returns {@code false}, whichever comes
|
|
* first.
|
|
*
|
|
* @return the number of elements the iterator was advanced
|
|
* @since 13.0 (since 3.0 as {@code Iterators.skip})
|
|
*/
|
|
public static int advance(Iterator<?> iterator, int numberToAdvance) {
|
|
checkNotNull(iterator);
|
|
checkArgument(numberToAdvance >= 0, "numberToAdvance must be nonnegative");
|
|
|
|
int i;
|
|
for (i = 0; i < numberToAdvance && iterator.hasNext(); i++) {
|
|
iterator.next();
|
|
}
|
|
return i;
|
|
}
|
|
|
|
/**
|
|
* Creates an iterator returning the first {@code limitSize} elements of the
|
|
* given iterator. If the original iterator does not contain that many elements,
|
|
* the returned iterator will have the same behavior as the original iterator.
|
|
* The returned iterator supports {@code remove()} if the original iterator
|
|
* does.
|
|
*
|
|
* @param iterator the iterator to limit
|
|
* @param limitSize the maximum number of elements in the returned iterator
|
|
* @throws IllegalArgumentException if {@code limitSize} is negative
|
|
* @since 3.0
|
|
*/
|
|
public static <T> Iterator<T> limit(final Iterator<T> iterator, final int limitSize) {
|
|
checkNotNull(iterator);
|
|
checkArgument(limitSize >= 0, "limit is negative");
|
|
return new Iterator<T>() {
|
|
private int count;
|
|
|
|
@Override
|
|
public boolean hasNext() {
|
|
return count < limitSize && iterator.hasNext();
|
|
}
|
|
|
|
@Override
|
|
public T next() {
|
|
if (!hasNext()) {
|
|
throw new NoSuchElementException();
|
|
}
|
|
count++;
|
|
return iterator.next();
|
|
}
|
|
|
|
@Override
|
|
public void remove() {
|
|
iterator.remove();
|
|
}
|
|
};
|
|
}
|
|
|
|
/**
|
|
* Returns a view of the supplied {@code iterator} that removes each element
|
|
* from the supplied {@code iterator} as it is returned.
|
|
*
|
|
* <p>
|
|
* The provided iterator must support {@link Iterator#remove()} or else the
|
|
* returned iterator will fail on the first call to {@code
|
|
* next}.
|
|
*
|
|
* @param iterator the iterator to remove and return elements from
|
|
* @return an iterator that removes and returns elements from the supplied
|
|
* iterator
|
|
* @since 2.0
|
|
*/
|
|
public static <T> Iterator<T> consumingIterator(final Iterator<T> iterator) {
|
|
checkNotNull(iterator);
|
|
return new UnmodifiableIterator<T>() {
|
|
@Override
|
|
public boolean hasNext() {
|
|
return iterator.hasNext();
|
|
}
|
|
|
|
@Override
|
|
public T next() {
|
|
T next = iterator.next();
|
|
iterator.remove();
|
|
return next;
|
|
}
|
|
|
|
@Override
|
|
public String toString() {
|
|
return "Iterators.consumingIterator(...)";
|
|
}
|
|
};
|
|
}
|
|
|
|
/**
|
|
* Deletes and returns the next value from the iterator, or returns {@code null}
|
|
* if there is no such value.
|
|
*/
|
|
@Nullable
|
|
static <T> T pollNext(Iterator<T> iterator) {
|
|
if (iterator.hasNext()) {
|
|
T result = iterator.next();
|
|
iterator.remove();
|
|
return result;
|
|
} else {
|
|
return null;
|
|
}
|
|
}
|
|
|
|
// Methods only in Iterators, not in Iterables
|
|
|
|
/**
|
|
* Clears the iterator using its remove method.
|
|
*/
|
|
static void clear(Iterator<?> iterator) {
|
|
checkNotNull(iterator);
|
|
while (iterator.hasNext()) {
|
|
iterator.next();
|
|
iterator.remove();
|
|
}
|
|
}
|
|
|
|
/**
|
|
* Returns an iterator containing the elements of {@code array} in order. The
|
|
* returned iterator is a view of the array; subsequent changes to the array
|
|
* will be reflected in the iterator.
|
|
*
|
|
* <p>
|
|
* <b>Note:</b> It is often preferable to represent your data using a collection
|
|
* type, for example using {@link Arrays#asList(Object[])}, making this method
|
|
* unnecessary.
|
|
*
|
|
* <p>
|
|
* The {@code Iterable} equivalent of this method is either
|
|
* {@link Arrays#asList(Object[])}, {@link ImmutableList#copyOf(Object[])}}, or
|
|
* {@link ImmutableList#of}.
|
|
*/
|
|
public static <T> UnmodifiableIterator<T> forArray(final T... array) {
|
|
return forArray(array, 0, array.length, 0);
|
|
}
|
|
|
|
/**
|
|
* Returns a list iterator containing the elements in the specified range of
|
|
* {@code array} in order, starting at the specified index.
|
|
*
|
|
* <p>
|
|
* The {@code Iterable} equivalent of this method is {@code
|
|
* Arrays.asList(array).subList(offset, offset + length).listIterator(index)}.
|
|
*/
|
|
static <T> UnmodifiableListIterator<T> forArray(final T[] array, final int offset, int length, int index) {
|
|
checkArgument(length >= 0);
|
|
int end = offset + length;
|
|
|
|
// Technically we should give a slightly more descriptive error on overflow
|
|
Preconditions.checkPositionIndexes(offset, end, array.length);
|
|
Preconditions.checkPositionIndex(index, length);
|
|
if (length == 0) {
|
|
return emptyListIterator();
|
|
}
|
|
|
|
/*
|
|
* We can't use call the two-arg constructor with arguments (offset, end)
|
|
* because the returned Iterator is a ListIterator that may be moved back past
|
|
* the beginning of the iteration.
|
|
*/
|
|
return new AbstractIndexedListIterator<T>(length, index) {
|
|
@Override
|
|
protected T get(int index) {
|
|
return array[offset + index];
|
|
}
|
|
};
|
|
}
|
|
|
|
/**
|
|
* Returns an iterator containing only {@code value}.
|
|
*
|
|
* <p>
|
|
* The {@link Iterable} equivalent of this method is
|
|
* {@link Collections#singleton}.
|
|
*/
|
|
public static <T> UnmodifiableIterator<T> singletonIterator(@Nullable final T value) {
|
|
return new UnmodifiableIterator<T>() {
|
|
boolean done;
|
|
|
|
@Override
|
|
public boolean hasNext() {
|
|
return !done;
|
|
}
|
|
|
|
@Override
|
|
public T next() {
|
|
if (done) {
|
|
throw new NoSuchElementException();
|
|
}
|
|
done = true;
|
|
return value;
|
|
}
|
|
};
|
|
}
|
|
|
|
/**
|
|
* Adapts an {@code Enumeration} to the {@code Iterator} interface.
|
|
*
|
|
* <p>
|
|
* This method has no equivalent in {@link Iterables} because viewing an
|
|
* {@code Enumeration} as an {@code Iterable} is impossible. However, the
|
|
* contents can be <i>copied</i> into a collection using
|
|
* {@link Collections#list}.
|
|
*/
|
|
public static <T> UnmodifiableIterator<T> forEnumeration(final Enumeration<T> enumeration) {
|
|
checkNotNull(enumeration);
|
|
return new UnmodifiableIterator<T>() {
|
|
@Override
|
|
public boolean hasNext() {
|
|
return enumeration.hasMoreElements();
|
|
}
|
|
|
|
@Override
|
|
public T next() {
|
|
return enumeration.nextElement();
|
|
}
|
|
};
|
|
}
|
|
|
|
/**
|
|
* Adapts an {@code Iterator} to the {@code Enumeration} interface.
|
|
*
|
|
* <p>
|
|
* The {@code Iterable} equivalent of this method is either
|
|
* {@link Collections#enumeration} (if you have a {@link Collection}), or
|
|
* {@code Iterators.asEnumeration(collection.iterator())}.
|
|
*/
|
|
public static <T> Enumeration<T> asEnumeration(final Iterator<T> iterator) {
|
|
checkNotNull(iterator);
|
|
return new Enumeration<T>() {
|
|
@Override
|
|
public boolean hasMoreElements() {
|
|
return iterator.hasNext();
|
|
}
|
|
|
|
@Override
|
|
public T nextElement() {
|
|
return iterator.next();
|
|
}
|
|
};
|
|
}
|
|
|
|
/**
|
|
* Implementation of PeekingIterator that avoids peeking unless necessary.
|
|
*/
|
|
private static class PeekingImpl<E> implements PeekingIterator<E> {
|
|
|
|
private final Iterator<? extends E> iterator;
|
|
private boolean hasPeeked;
|
|
private E peekedElement;
|
|
|
|
public PeekingImpl(Iterator<? extends E> iterator) {
|
|
this.iterator = checkNotNull(iterator);
|
|
}
|
|
|
|
@Override
|
|
public boolean hasNext() {
|
|
return hasPeeked || iterator.hasNext();
|
|
}
|
|
|
|
@Override
|
|
public E next() {
|
|
if (!hasPeeked) {
|
|
return iterator.next();
|
|
}
|
|
E result = peekedElement;
|
|
hasPeeked = false;
|
|
peekedElement = null;
|
|
return result;
|
|
}
|
|
|
|
@Override
|
|
public void remove() {
|
|
checkState(!hasPeeked, "Can't remove after you've peeked at next");
|
|
iterator.remove();
|
|
}
|
|
|
|
@Override
|
|
public E peek() {
|
|
if (!hasPeeked) {
|
|
peekedElement = iterator.next();
|
|
hasPeeked = true;
|
|
}
|
|
return peekedElement;
|
|
}
|
|
}
|
|
|
|
/**
|
|
* Returns a {@code PeekingIterator} backed by the given iterator.
|
|
*
|
|
* <p>
|
|
* Calls to the {@code peek} method with no intervening calls to {@code
|
|
* next} do not affect the iteration, and hence return the same object each
|
|
* time. A subsequent call to {@code next} is guaranteed to return the same
|
|
* object again. For example:
|
|
*
|
|
* <pre>
|
|
* {@code
|
|
*
|
|
* PeekingIterator<String> peekingIterator =
|
|
* Iterators.peekingIterator(Iterators.forArray("a", "b"));
|
|
* String a1 = peekingIterator.peek(); // returns "a"
|
|
* String a2 = peekingIterator.peek(); // also returns "a"
|
|
* String a3 = peekingIterator.next(); // also returns "a"}
|
|
* </pre>
|
|
*
|
|
* <p>
|
|
* Any structural changes to the underlying iteration (aside from those
|
|
* performed by the iterator's own {@link PeekingIterator#remove()} method) will
|
|
* leave the iterator in an undefined state.
|
|
*
|
|
* <p>
|
|
* The returned iterator does not support removal after peeking, as explained by
|
|
* {@link PeekingIterator#remove()}.
|
|
*
|
|
* <p>
|
|
* Note: If the given iterator is already a {@code PeekingIterator}, it
|
|
* <i>might</i> be returned to the caller, although this is neither guaranteed
|
|
* to occur nor required to be consistent. For example, this method <i>might</i>
|
|
* choose to pass through recognized implementations of {@code PeekingIterator}
|
|
* when the behavior of the implementation is known to meet the contract
|
|
* guaranteed by this method.
|
|
*
|
|
* <p>
|
|
* There is no {@link Iterable} equivalent to this method, so use this method to
|
|
* wrap each individual iterator as it is generated.
|
|
*
|
|
* @param iterator the backing iterator. The {@link PeekingIterator} assumes
|
|
* ownership of this iterator, so users should cease making
|
|
* direct calls to it after calling this method.
|
|
* @return a peeking iterator backed by that iterator. Apart from the additional
|
|
* {@link PeekingIterator#peek()} method, this iterator behaves exactly
|
|
* the same as {@code iterator}.
|
|
*/
|
|
public static <T> PeekingIterator<T> peekingIterator(Iterator<? extends T> iterator) {
|
|
if (iterator instanceof PeekingImpl) {
|
|
// Safe to cast <? extends T> to <T> because PeekingImpl only uses T
|
|
// covariantly (and cannot be subclassed to add non-covariant uses).
|
|
@SuppressWarnings("unchecked")
|
|
PeekingImpl<T> peeking = (PeekingImpl<T>) iterator;
|
|
return peeking;
|
|
}
|
|
return new PeekingImpl<T>(iterator);
|
|
}
|
|
|
|
/**
|
|
* Simply returns its argument.
|
|
*
|
|
* @deprecated no need to use this
|
|
* @since 10.0
|
|
*/
|
|
@Deprecated
|
|
public static <T> PeekingIterator<T> peekingIterator(PeekingIterator<T> iterator) {
|
|
return checkNotNull(iterator);
|
|
}
|
|
|
|
/**
|
|
* Returns an iterator over the merged contents of all given {@code iterators},
|
|
* traversing every element of the input iterators. Equivalent entries will not
|
|
* be de-duplicated.
|
|
*
|
|
* <p>
|
|
* Callers must ensure that the source {@code iterators} are in non-descending
|
|
* order as this method does not sort its input.
|
|
*
|
|
* <p>
|
|
* For any equivalent elements across all {@code iterators}, it is undefined
|
|
* which element is returned first.
|
|
*
|
|
* @since 11.0
|
|
*/
|
|
@Beta
|
|
public static <T> UnmodifiableIterator<T> mergeSorted(Iterable<? extends Iterator<? extends T>> iterators,
|
|
Comparator<? super T> comparator) {
|
|
checkNotNull(iterators, "iterators");
|
|
checkNotNull(comparator, "comparator");
|
|
|
|
return new MergingIterator<T>(iterators, comparator);
|
|
}
|
|
|
|
/**
|
|
* An iterator that performs a lazy N-way merge, calculating the next value each
|
|
* time the iterator is polled. This amortizes the sorting cost over the
|
|
* iteration and requires less memory than sorting all elements at once.
|
|
*
|
|
* <p>
|
|
* Retrieving a single element takes approximately O(log(M)) time, where M is
|
|
* the number of iterators. (Retrieving all elements takes approximately
|
|
* O(N*log(M)) time, where N is the total number of elements.)
|
|
*/
|
|
private static class MergingIterator<T> extends UnmodifiableIterator<T> {
|
|
final Queue<PeekingIterator<T>> queue;
|
|
|
|
public MergingIterator(Iterable<? extends Iterator<? extends T>> iterators,
|
|
final Comparator<? super T> itemComparator) {
|
|
// A comparator that's used by the heap, allowing the heap
|
|
// to be sorted based on the top of each iterator.
|
|
Comparator<PeekingIterator<T>> heapComparator = new Comparator<PeekingIterator<T>>() {
|
|
@Override
|
|
public int compare(PeekingIterator<T> o1, PeekingIterator<T> o2) {
|
|
return itemComparator.compare(o1.peek(), o2.peek());
|
|
}
|
|
};
|
|
|
|
queue = new PriorityQueue<PeekingIterator<T>>(2, heapComparator);
|
|
|
|
for (Iterator<? extends T> iterator : iterators) {
|
|
if (iterator.hasNext()) {
|
|
queue.add(Iterators.peekingIterator(iterator));
|
|
}
|
|
}
|
|
}
|
|
|
|
@Override
|
|
public boolean hasNext() {
|
|
return !queue.isEmpty();
|
|
}
|
|
|
|
@Override
|
|
public T next() {
|
|
PeekingIterator<T> nextIter = queue.remove();
|
|
T next = nextIter.next();
|
|
if (nextIter.hasNext()) {
|
|
queue.add(nextIter);
|
|
}
|
|
return next;
|
|
}
|
|
}
|
|
|
|
/**
|
|
* Used to avoid http://bugs.sun.com/view_bug.do?bug_id=6558557
|
|
*/
|
|
static <T> ListIterator<T> cast(Iterator<T> iterator) {
|
|
return (ListIterator<T>) iterator;
|
|
}
|
|
}
|