/*
* Copyright (C) 2007 The Guava Authors
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.docx4j.com.google.common.collect;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import static org.docx4j.com.google.common.base.Preconditions.checkArgument;
import static org.docx4j.com.google.common.base.Preconditions.checkNotNull;
import static org.docx4j.com.google.common.base.Preconditions.checkState;
import java.util.ArrayDeque;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.Comparator;
import java.util.Deque;
import java.util.Enumeration;
import java.util.Iterator;
import java.util.List;
import java.util.ListIterator;
import java.util.NoSuchElementException;
import java.util.PriorityQueue;
import java.util.Queue;
import org.checkerframework.checker.nullness.qual.Nullable;
import org.docx4j.com.google.common.annotations.Beta;
import org.docx4j.com.google.common.annotations.GwtCompatible;
import org.docx4j.com.google.common.annotations.GwtIncompatible;
import org.docx4j.com.google.common.base.Function;
import org.docx4j.com.google.common.base.Objects;
import org.docx4j.com.google.common.base.Preconditions;
import org.docx4j.com.google.common.base.Predicate;
import org.docx4j.com.google.common.primitives.Ints;
/**
* This class contains static utility methods that operate on or return objects of type {@link
* Iterator}. Except as noted, each method has a corresponding {@link Iterable}-based method in the
* {@link Iterables} class.
*
* Performance notes: Unless otherwise noted, all of the iterators produced in this class
* are lazy , which means that they only advance the backing iteration when absolutely
* necessary.
*
*
See the Guava User Guide section on {@code
* Iterators} .
*
* @author Kevin Bourrillion
* @author Jared Levy
* @since 2.0
*/
@GwtCompatible(emulated = true)
public final class Iterators {
private Iterators() {}
/**
* Returns the empty iterator.
*
*
The {@link Iterable} equivalent of this method is {@link ImmutableSet#of()}.
*/
static UnmodifiableIterator emptyIterator() {
return emptyListIterator();
}
/**
* Returns the empty iterator.
*
* The {@link Iterable} equivalent of this method is {@link ImmutableSet#of()}.
*/
// Casting to any type is safe since there are no actual elements.
@SuppressWarnings("unchecked")
static UnmodifiableListIterator emptyListIterator() {
return (UnmodifiableListIterator) ArrayItr.EMPTY;
}
// /**
// * This is an enum singleton rather than an anonymous class so ProGuard can figure out it's only
// * referenced by emptyModifiableIterator().
// */
// private enum EmptyModifiableIterator implements Iterator {
// INSTANCE;
//
// @Override
// public boolean hasNext() {
// return false;
// }
//
// @Override
// public Object next() {
// throw new NoSuchElementException();
// }
//
// @Override
// public void remove() {
// checkRemove(false);
// }
// }
//
// /**
// * Returns the empty {@code Iterator} that throws {@link IllegalStateException} instead of {@link
// * UnsupportedOperationException} on a call to {@link Iterator#remove()}.
// */
// // Casting to any type is safe since there are no actual elements.
// @SuppressWarnings("unchecked")
// static Iterator emptyModifiableIterator() {
// return (Iterator) EmptyModifiableIterator.INSTANCE;
// }
/** Returns an unmodifiable view of {@code iterator}. */
public static UnmodifiableIterator unmodifiableIterator(
final Iterator iterator) {
checkNotNull(iterator);
if (iterator instanceof UnmodifiableIterator) {
@SuppressWarnings("unchecked") // Since it's unmodifiable, the covariant cast is safe
UnmodifiableIterator result = (UnmodifiableIterator) iterator;
return result;
}
return new UnmodifiableIterator() {
@Override
public boolean hasNext() {
return iterator.hasNext();
}
@Override
public T next() {
return iterator.next();
}
};
}
/**
* Simply returns its argument.
*
* @deprecated no need to use this
* @since 10.0
*/
@Deprecated
public static UnmodifiableIterator unmodifiableIterator(UnmodifiableIterator iterator) {
return checkNotNull(iterator);
}
/**
* Returns the number of elements remaining in {@code iterator}. The iterator will be left
* exhausted: its {@code hasNext()} method will return {@code false}.
*/
public static int size(Iterator iterator) {
long count = 0L;
while (iterator.hasNext()) {
iterator.next();
count++;
}
return Ints.saturatedCast(count);
}
/** Returns {@code true} if {@code iterator} contains {@code element}. */
public static boolean contains(Iterator iterator, @Nullable Object element) {
if (element == null) {
while (iterator.hasNext()) {
if (iterator.next() == null) {
return true;
}
}
} else {
while (iterator.hasNext()) {
if (element.equals(iterator.next())) {
return true;
}
}
}
return false;
}
/**
* Traverses an iterator and removes every element that belongs to the provided collection. The
* iterator will be left exhausted: its {@code hasNext()} method will return {@code false}.
*
* @param removeFrom the iterator to (potentially) remove elements from
* @param elementsToRemove the elements to remove
* @return {@code true} if any element was removed from {@code iterator}
*/
@CanIgnoreReturnValue
public static boolean removeAll(Iterator removeFrom, Collection elementsToRemove) {
checkNotNull(elementsToRemove);
boolean result = false;
while (removeFrom.hasNext()) {
if (elementsToRemove.contains(removeFrom.next())) {
removeFrom.remove();
result = true;
}
}
return result;
}
/**
* Removes every element that satisfies the provided predicate from the iterator. The iterator
* will be left exhausted: its {@code hasNext()} method will return {@code false}.
*
* @param removeFrom the iterator to (potentially) remove elements from
* @param predicate a predicate that determines whether an element should be removed
* @return {@code true} if any elements were removed from the iterator
* @since 2.0
*/
@CanIgnoreReturnValue
public static boolean removeIf(Iterator removeFrom, Predicate predicate) {
checkNotNull(predicate);
boolean modified = false;
while (removeFrom.hasNext()) {
if (predicate.apply(removeFrom.next())) {
removeFrom.remove();
modified = true;
}
}
return modified;
}
/**
* Traverses an iterator and removes every element that does not belong to the provided
* collection. The iterator will be left exhausted: its {@code hasNext()} method will return
* {@code false}.
*
* @param removeFrom the iterator to (potentially) remove elements from
* @param elementsToRetain the elements to retain
* @return {@code true} if any element was removed from {@code iterator}
*/
@CanIgnoreReturnValue
public static boolean retainAll(Iterator removeFrom, Collection elementsToRetain) {
checkNotNull(elementsToRetain);
boolean result = false;
while (removeFrom.hasNext()) {
if (!elementsToRetain.contains(removeFrom.next())) {
removeFrom.remove();
result = true;
}
}
return result;
}
/**
* Determines whether two iterators contain equal elements in the same order. More specifically,
* this method returns {@code true} if {@code iterator1} and {@code iterator2} contain the same
* number of elements and every element of {@code iterator1} is equal to the corresponding element
* of {@code iterator2}.
*
* Note that this will modify the supplied iterators, since they will have been advanced some
* number of elements forward.
*/
public static boolean elementsEqual(Iterator iterator1, Iterator iterator2) {
while (iterator1.hasNext()) {
if (!iterator2.hasNext()) {
return false;
}
Object o1 = iterator1.next();
Object o2 = iterator2.next();
if (!Objects.equal(o1, o2)) {
return false;
}
}
return !iterator2.hasNext();
}
/**
* Returns a string representation of {@code iterator}, with the format {@code [e1, e2, ..., en]}.
* The iterator will be left exhausted: its {@code hasNext()} method will return {@code false}.
*/
public static String toString(Iterator iterator) {
StringBuilder sb = new StringBuilder().append('[');
boolean first = true;
while (iterator.hasNext()) {
if (!first) {
sb.append(", ");
}
first = false;
sb.append(iterator.next());
}
return sb.append(']').toString();
}
/**
* Returns the single element contained in {@code iterator}.
*
* @throws NoSuchElementException if the iterator is empty
* @throws IllegalArgumentException if the iterator contains multiple elements. The state of the
* iterator is unspecified.
*/
public static T getOnlyElement(Iterator iterator) {
T first = iterator.next();
if (!iterator.hasNext()) {
return first;
}
StringBuilder sb = new StringBuilder().append("expected one element but was: <").append(first);
for (int i = 0; i < 4 && iterator.hasNext(); i++) {
sb.append(", ").append(iterator.next());
}
if (iterator.hasNext()) {
sb.append(", ...");
}
sb.append('>');
throw new IllegalArgumentException(sb.toString());
}
/**
* Returns the single element contained in {@code iterator}, or {@code defaultValue} if the
* iterator is empty.
*
* @throws IllegalArgumentException if the iterator contains multiple elements. The state of the
* iterator is unspecified.
*/
public static @Nullable T getOnlyElement(
Iterator iterator, @Nullable T defaultValue) {
return iterator.hasNext() ? getOnlyElement(iterator) : defaultValue;
}
// /**
// * Copies an iterator's elements into an array. The iterator will be left exhausted: its {@code
// * hasNext()} method will return {@code false}.
// *
// * @param iterator the iterator to copy
// * @param type the type of the elements
// * @return a newly-allocated array into which all the elements of the iterator have been copied
// */
// @GwtIncompatible // Array.newInstance(Class, int)
// public static T[] toArray(Iterator iterator, Class type) {
// List list = Lists.newArrayList(iterator);
// return Iterables.toArray(list, type);
// }
/**
* Adds all elements in {@code iterator} to {@code collection}. The iterator will be left
* exhausted: its {@code hasNext()} method will return {@code false}.
*
* @return {@code true} if {@code collection} was modified as a result of this operation
*/
@CanIgnoreReturnValue
public static boolean addAll(Collection addTo, Iterator iterator) {
checkNotNull(addTo);
checkNotNull(iterator);
boolean wasModified = false;
while (iterator.hasNext()) {
wasModified |= addTo.add(iterator.next());
}
return wasModified;
}
/**
* Returns the number of elements in the specified iterator that equal the specified object. The
* iterator will be left exhausted: its {@code hasNext()} method will return {@code false}.
*
* @see Collections#frequency
*/
public static int frequency(Iterator iterator, @Nullable Object element) {
int count = 0;
while (contains(iterator, element)) {
// Since it lives in the same class, we know contains gets to the element and then stops,
// though that isn't currently publicly documented.
count++;
}
return count;
}
// /**
// * Returns an iterator that cycles indefinitely over the elements of {@code iterable}.
// *
// * The returned iterator supports {@code remove()} if the provided iterator does. After {@code
// * remove()} is called, subsequent cycles omit the removed element, which is no longer in {@code
// * iterable}. The iterator's {@code hasNext()} method returns {@code true} until {@code iterable}
// * is empty.
// *
// *
Warning: Typical uses of the resulting iterator may produce an infinite loop. You
// * should use an explicit {@code break} or be certain that you will eventually remove all the
// * elements.
// */
// public static Iterator cycle(final Iterable iterable) {
// checkNotNull(iterable);
// return new Iterator() {
// Iterator iterator = emptyModifiableIterator();
//
// @Override
// public boolean hasNext() {
// /*
// * Don't store a new Iterator until we know the user can't remove() the last returned
// * element anymore. Otherwise, when we remove from the old iterator, we may be invalidating
// * the new one. The result is a ConcurrentModificationException or other bad behavior.
// *
// * (If we decide that we really, really hate allocating two Iterators per cycle instead of
// * one, we can optimistically store the new Iterator and then be willing to throw it out if
// * the user calls remove().)
// */
// return iterator.hasNext() || iterable.iterator().hasNext();
// }
//
// @Override
// public T next() {
// if (!iterator.hasNext()) {
// iterator = iterable.iterator();
// if (!iterator.hasNext()) {
// throw new NoSuchElementException();
// }
// }
// return iterator.next();
// }
//
// @Override
// public void remove() {
// iterator.remove();
// }
// };
// }
//
// /**
// * Returns an iterator that cycles indefinitely over the provided elements.
// *
// * The returned iterator supports {@code remove()}. After {@code remove()} is called,
// * subsequent cycles omit the removed element, but {@code elements} does not change. The
// * iterator's {@code hasNext()} method returns {@code true} until all of the original elements
// * have been removed.
// *
// *
Warning: Typical uses of the resulting iterator may produce an infinite loop. You
// * should use an explicit {@code break} or be certain that you will eventually remove all the
// * elements.
// */
// @SafeVarargs
// public static Iterator cycle(T... elements) {
// return cycle(Lists.newArrayList(elements));
// }
/**
* Returns an Iterator that walks the specified array, nulling out elements behind it. This can
* avoid memory leaks when an element is no longer necessary.
*
* This is mainly just to avoid the intermediate ArrayDeque in ConsumingQueueIterator.
*/
private static Iterator consumingForArray(final T... elements) {
return new UnmodifiableIterator() {
int index = 0;
@Override
public boolean hasNext() {
return index < elements.length;
}
@Override
public T next() {
if (!hasNext()) {
throw new NoSuchElementException();
}
T result = elements[index];
elements[index] = null;
index++;
return result;
}
};
}
// /**
// * Combines two iterators into a single iterator. The returned iterator iterates across the
// * elements in {@code a}, followed by the elements in {@code b}. The source iterators are not
// * polled until necessary.
// *
// * The returned iterator supports {@code remove()} when the corresponding input iterator
// * supports it.
// */
// public static Iterator concat(Iterator a, Iterator b) {
// checkNotNull(a);
// checkNotNull(b);
// return concat(consumingForArray(a, b));
// }
//
// /**
// * Combines three iterators into a single iterator. The returned iterator iterates across the
// * elements in {@code a}, followed by the elements in {@code b}, followed by the elements in
// * {@code c}. The source iterators are not polled until necessary.
// *
// * The returned iterator supports {@code remove()} when the corresponding input iterator
// * supports it.
// */
// public static Iterator concat(
// Iterator a, Iterator b, Iterator c) {
// checkNotNull(a);
// checkNotNull(b);
// checkNotNull(c);
// return concat(consumingForArray(a, b, c));
// }
//
// /**
// * Combines four iterators into a single iterator. The returned iterator iterates across the
// * elements in {@code a}, followed by the elements in {@code b}, followed by the elements in
// * {@code c}, followed by the elements in {@code d}. The source iterators are not polled until
// * necessary.
// *
// * The returned iterator supports {@code remove()} when the corresponding input iterator
// * supports it.
// */
// public static Iterator concat(
// Iterator a,
// Iterator b,
// Iterator c,
// Iterator d) {
// checkNotNull(a);
// checkNotNull(b);
// checkNotNull(c);
// checkNotNull(d);
// return concat(consumingForArray(a, b, c, d));
// }
//
// /**
// * Combines multiple iterators into a single iterator. The returned iterator iterates across the
// * elements of each iterator in {@code inputs}. The input iterators are not polled until
// * necessary.
// *
// * The returned iterator supports {@code remove()} when the corresponding input iterator
// * supports it.
// *
// * @throws NullPointerException if any of the provided iterators is null
// */
// public static Iterator concat(Iterator... inputs) {
// return concatNoDefensiveCopy(Arrays.copyOf(inputs, inputs.length));
// }
//
// /**
// * Combines multiple iterators into a single iterator. The returned iterator iterates across the
// * elements of each iterator in {@code inputs}. The input iterators are not polled until
// * necessary.
// *
// * The returned iterator supports {@code remove()} when the corresponding input iterator
// * supports it. The methods of the returned iterator may throw {@code NullPointerException} if any
// * of the input iterators is null.
// */
// public static Iterator concat(Iterator> inputs) {
// return new ConcatenatedIterator(inputs);
// }
//
// /** Concats a varargs array of iterators without making a defensive copy of the array. */
// static Iterator concatNoDefensiveCopy(Iterator... inputs) {
// for (Iterator input : checkNotNull(inputs)) {
// checkNotNull(input);
// }
// return concat(consumingForArray(inputs));
// }
/**
* 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.
*
* The returned lists implement {@link java.util.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 UnmodifiableIterator> partition(Iterator 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.
*
* The returned lists implement {@link java.util.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 UnmodifiableIterator> paddedPartition(Iterator iterator, int size) {
return partitionImpl(iterator, size, true);
}
private static UnmodifiableIterator> partitionImpl(
final Iterator iterator, final int size, final boolean pad) {
checkNotNull(iterator);
checkArgument(size > 0);
return new UnmodifiableIterator>() {
@Override
public boolean hasNext() {
return iterator.hasNext();
}
@Override
public List 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 list = Collections.unmodifiableList((List) Arrays.asList(array));
return (pad || count == size) ? list : list.subList(0, count);
}
};
}
// /**
// * Returns a view of {@code unfiltered} containing all elements that satisfy the input predicate
// * {@code retainIfTrue}.
// */
// public static UnmodifiableIterator filter(
// final Iterator unfiltered, final Predicate retainIfTrue) {
// checkNotNull(unfiltered);
// checkNotNull(retainIfTrue);
// return new AbstractIterator() {
// @Override
// protected T computeNext() {
// while (unfiltered.hasNext()) {
// T element = unfiltered.next();
// if (retainIfTrue.apply(element)) {
// return element;
// }
// }
// return endOfData();
// }
// };
// }
//
// /**
// * Returns a view of {@code unfiltered} containing all elements that are of the type {@code
// * desiredType}.
// */
// @SuppressWarnings("unchecked") // can cast to because non-Ts are removed
// @GwtIncompatible // Class.isInstance
// public static UnmodifiableIterator filter(Iterator unfiltered, Class desiredType) {
// return (UnmodifiableIterator) filter(unfiltered, instanceOf(desiredType));
// }
/**
* Returns {@code true} if one or more elements returned by {@code iterator} satisfy the given
* predicate.
*/
public static boolean any(Iterator iterator, Predicate 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 boolean all(Iterator iterator, Predicate 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 no 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 find(Iterator iterator, Predicate predicate) {
checkNotNull(iterator);
checkNotNull(predicate);
while (iterator.hasNext()) {
T t = iterator.next();
if (predicate.apply(t)) {
return t;
}
}
throw new NoSuchElementException();
}
/**
* 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
*/
public static @Nullable T find(
Iterator iterator, Predicate predicate, @Nullable T defaultValue) {
checkNotNull(iterator);
checkNotNull(predicate);
while (iterator.hasNext()) {
T t = iterator.next();
if (predicate.apply(t)) {
return t;
}
}
return 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}.
// *
// * Warning: 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 Optional tryFind(Iterator iterator, Predicate predicate) {
// checkNotNull(iterator);
// checkNotNull(predicate);
// while (iterator.hasNext()) {
// T t = iterator.next();
// if (predicate.apply(t)) {
// return Optional.of(t);
// }
// }
// return Optional.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.
*
* 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.
*
*
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 int indexOf(Iterator iterator, Predicate predicate) {
checkNotNull(predicate, "predicate");
for (int i = 0; iterator.hasNext(); i++) {
T current = iterator.next();
if (predicate.apply(current)) {
return i;
}
}
return -1;
}
// /**
// * Returns a view containing the result of applying {@code function} to each element of {@code
// * fromIterator}.
// *
// * The returned iterator supports {@code remove()} if {@code fromIterator} does. After a
// * successful {@code remove()} call, {@code fromIterator} no longer contains the corresponding
// * element.
// */
// public static Iterator transform(
// final Iterator fromIterator, final Function function) {
// checkNotNull(function);
// return new TransformedIterator(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 get(Iterator 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();
}
/**
* 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
*/
public static @Nullable T get(
Iterator iterator, int position, @Nullable T defaultValue) {
checkNonnegative(position);
advance(iterator, position);
return getNext(iterator, defaultValue);
}
static void checkNonnegative(int position) {
if (position < 0) {
throw new IndexOutOfBoundsException("position (" + position + ") must not be negative");
}
}
/**
* 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
*/
public static @Nullable T getNext(Iterator 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 getLast(Iterator 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
*/
public static @Nullable T getLast(Iterator 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})
*/
@CanIgnoreReturnValue
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;
}
/**
* Returns a view containing the first {@code limitSize} elements of {@code iterator}. If {@code
* iterator} contains fewer than {@code limitSize} elements, the returned view contains all of its
* elements. The returned iterator supports {@code remove()} if {@code 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 Iterator limit(final Iterator iterator, final int limitSize) {
checkNotNull(iterator);
checkArgument(limitSize >= 0, "limit is negative");
return new Iterator() {
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.
*
* 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 Iterator consumingIterator(final Iterator iterator) {
checkNotNull(iterator);
return new UnmodifiableIterator() {
@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.
*/
static @Nullable T pollNext(Iterator 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.
*
* Note: It is often preferable to represent your data using a collection type, for
* example using {@link Arrays#asList(Object[])}, making this method unnecessary.
*
*
The {@code Iterable} equivalent of this method is either {@link Arrays#asList(Object[])},
* {@link ImmutableList#copyOf(Object[])}}, or {@link ImmutableList#of}.
*/
@SafeVarargs
public static UnmodifiableIterator 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.
*
* The {@code Iterable} equivalent of this method is {@code
* Arrays.asList(array).subList(offset, offset + length).listIterator(index)}.
*/
static UnmodifiableListIterator 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();
}
return new ArrayItr(array, offset, length, index);
}
private static final class ArrayItr extends AbstractIndexedListIterator {
static final UnmodifiableListIterator EMPTY = new ArrayItr<>(new Object[0], 0, 0, 0);
private final T[] array;
private final int offset;
ArrayItr(T[] array, int offset, int length, int index) {
super(length, index);
this.array = array;
this.offset = offset;
}
@Override
protected T get(int index) {
return array[offset + index];
}
}
/**
* Returns an iterator containing only {@code value}.
*
* The {@link Iterable} equivalent of this method is {@link Collections#singleton}.
*/
public static UnmodifiableIterator singletonIterator(final @Nullable T value) {
return new UnmodifiableIterator() {
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.
*
* This method has no equivalent in {@link Iterables} because viewing an {@code Enumeration} as
* an {@code Iterable} is impossible. However, the contents can be copied into a collection
* using {@link Collections#list}.
*/
public static UnmodifiableIterator forEnumeration(final Enumeration enumeration) {
checkNotNull(enumeration);
return new UnmodifiableIterator() {
@Override
public boolean hasNext() {
return enumeration.hasMoreElements();
}
@Override
public T next() {
return enumeration.nextElement();
}
};
}
/**
* Adapts an {@code Iterator} to the {@code Enumeration} interface.
*
* 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 Enumeration asEnumeration(final Iterator iterator) {
checkNotNull(iterator);
return new Enumeration() {
@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 implements PeekingIterator {
//
// private final Iterator iterator;
// private boolean hasPeeked;
// private @Nullable E peekedElement;
//
// public PeekingImpl(Iterator 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.
// *
// * 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:
// *
// *
{@code
// * PeekingIterator 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"
// * }
// *
// * 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.
// *
// *
The returned iterator does not support removal after peeking, as explained by {@link
// * PeekingIterator#remove()}.
// *
// *
Note: If the given iterator is already a {@code PeekingIterator}, it might be
// * returned to the caller, although this is neither guaranteed to occur nor required to be
// * consistent. For example, this method might 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.
// *
// *
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 PeekingIterator peekingIterator(Iterator iterator) {
// if (iterator instanceof PeekingImpl) {
// // Safe to cast to because PeekingImpl only uses T
// // covariantly (and cannot be subclassed to add non-covariant uses).
// @SuppressWarnings("unchecked")
// PeekingImpl peeking = (PeekingImpl) iterator;
// return peeking;
// }
// return new PeekingImpl(iterator);
// }
//
// /**
// * Simply returns its argument.
// *
// * @deprecated no need to use this
// * @since 10.0
// */
// @Deprecated
// public static PeekingIterator peekingIterator(PeekingIterator 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.
// *
// * Callers must ensure that the source {@code iterators} are in non-descending order as this
// * method does not sort its input.
// *
// *
For any equivalent elements across all {@code iterators}, it is undefined which element is
// * returned first.
// *
// * @since 11.0
// */
// @Beta
// public static UnmodifiableIterator mergeSorted(
// Iterable> iterators, Comparator comparator) {
// checkNotNull(iterators, "iterators");
// checkNotNull(comparator, "comparator");
//
// return new MergingIterator(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.
// *
// * 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 extends UnmodifiableIterator {
// final Queue> queue;
//
// public MergingIterator(
// Iterable> iterators,
// final Comparator itemComparator) {
// // A comparator that's used by the heap, allowing the heap
// // to be sorted based on the top of each iterator.
// Comparator> heapComparator =
// new Comparator>() {
// @Override
// public int compare(PeekingIterator o1, PeekingIterator o2) {
// return itemComparator.compare(o1.peek(), o2.peek());
// }
// };
//
// queue = new PriorityQueue<>(2, heapComparator);
//
// for (Iterator iterator : iterators) {
// if (iterator.hasNext()) {
// queue.add(Iterators.peekingIterator(iterator));
// }
// }
// }
//
// @Override
// public boolean hasNext() {
// return !queue.isEmpty();
// }
//
// @Override
// public T next() {
// PeekingIterator nextIter = queue.remove();
// T next = nextIter.next();
// if (nextIter.hasNext()) {
// queue.add(nextIter);
// }
// return next;
// }
// }
//
// private static class ConcatenatedIterator implements Iterator {
// /* The last iterator to return an element. Calls to remove() go to this iterator. */
// private @Nullable Iterator toRemove;
//
// /* The iterator currently returning elements. */
// private Iterator iterator;
//
// /*
// * We track the "meta iterators," the iterators-of-iterators, below. Usually, topMetaIterator
// * is the only one in use, but if we encounter nested concatenations, we start a deque of
// * meta-iterators rather than letting the nesting get arbitrarily deep. This keeps each
// * operation O(1).
// */
//
// private Iterator> topMetaIterator;
//
// // Only becomes nonnull if we encounter nested concatenations.
// private @Nullable Deque>> metaIterators;
//
// ConcatenatedIterator(Iterator> metaIterator) {
// iterator = emptyIterator();
// topMetaIterator = checkNotNull(metaIterator);
// }
//
// // Returns a nonempty meta-iterator or, if all meta-iterators are empty, null.
// private @Nullable Iterator> getTopMetaIterator() {
// while (topMetaIterator == null || !topMetaIterator.hasNext()) {
// if (metaIterators != null && !metaIterators.isEmpty()) {
// topMetaIterator = metaIterators.removeFirst();
// } else {
// return null;
// }
// }
// return topMetaIterator;
// }
//
// @Override
// public boolean hasNext() {
// while (!checkNotNull(iterator).hasNext()) {
// // this weird checkNotNull positioning appears required by our tests, which expect
// // both hasNext and next to throw NPE if an input iterator is null.
//
// topMetaIterator = getTopMetaIterator();
// if (topMetaIterator == null) {
// return false;
// }
//
// iterator = topMetaIterator.next();
//
// if (iterator instanceof ConcatenatedIterator) {
// // Instead of taking linear time in the number of nested concatenations, unpack
// // them into the queue
// @SuppressWarnings("unchecked")
// ConcatenatedIterator topConcat = (ConcatenatedIterator) iterator;
// iterator = topConcat.iterator;
//
// // topConcat.topMetaIterator, then topConcat.metaIterators, then this.topMetaIterator,
// // then this.metaIterators
//
// if (this.metaIterators == null) {
// this.metaIterators = new ArrayDeque<>();
// }
// this.metaIterators.addFirst(this.topMetaIterator);
// if (topConcat.metaIterators != null) {
// while (!topConcat.metaIterators.isEmpty()) {
// this.metaIterators.addFirst(topConcat.metaIterators.removeLast());
// }
// }
// this.topMetaIterator = topConcat.topMetaIterator;
// }
// }
// return true;
// }
//
// @Override
// public T next() {
// if (hasNext()) {
// toRemove = iterator;
// return iterator.next();
// } else {
// throw new NoSuchElementException();
// }
// }
//
// @Override
// public void remove() {
// CollectPreconditions.checkRemove(toRemove != null);
// toRemove.remove();
// toRemove = null;
// }
// }
//
// /** Used to avoid http://bugs.sun.com/view_bug.do?bug_id=6558557 */
// static ListIterator cast(Iterator iterator) {
// return (ListIterator) iterator;
// }
}