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This artifact provides a single jar that contains all classes required to use remote EJB and JMS, including all dependencies. It is intended for use by those not using maven, maven users should just import the EJB and JMS BOM's instead (shaded JAR's cause lots of problems with maven, as it is very easy to inadvertently end up with different versions on classes on the class path).

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/*
 * 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 com.google.common.collect;

import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.base.Preconditions.checkState;
import static com.google.common.base.Predicates.instanceOf;
import static com.google.common.collect.CollectPreconditions.checkRemove;
import static com.google.common.collect.NullnessCasts.uncheckedCastNullableTToT;
import static java.util.Objects.requireNonNull;

import com.google.common.annotations.Beta;
import com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.GwtIncompatible;
import com.google.common.base.Function;
import com.google.common.base.Objects;
import com.google.common.base.Optional;
import com.google.common.base.Preconditions;
import com.google.common.base.Predicate;
import com.google.common.primitives.Ints;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
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 javax.annotation.CheckForNull;
import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * 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) @ElementTypesAreNonnullByDefault 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( 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 @ParametricNullness 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, @CheckForNull 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. */ @ParametricNullness 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. */ @ParametricNullness public static T getOnlyElement( Iterator iterator, @ParametricNullness 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) // For discussion of this signature, see the corresponding overload of *Iterables*.toArray. public static @Nullable T[] toArray(Iterator iterator, Class type) { List<@Nullable T> 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, @CheckForNull 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(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 @ParametricNullness 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 method accepts an array with element type {@code @Nullable T}, but callers must pass an * array whose contents are initially non-null. The {@code @Nullable} annotation indicates that * this method will write nulls into the array during iteration. * *

This is mainly just to avoid the intermediate ArrayDeque in ConsumingQueueIterator. */ private static > Iterator consumingForArray(@Nullable I... elements) { return new UnmodifiableIterator() { int index = 0; @Override public boolean hasNext() { return index < elements.length; } @Override public I next() { if (!hasNext()) { throw new NoSuchElementException(); } /* * requireNonNull is safe because our callers always pass non-null arguments. Each element * of the array becomes null only when we iterate past it and then clear it. */ I result = requireNonNull(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}. * *

Note: The current implementation eagerly allocates storage for {@code size} elements. * As a consequence, passing values like {@code Integer.MAX_VALUE} can lead to {@link * OutOfMemoryError}. * * @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( Iterator iterator, int size, boolean pad) { checkNotNull(iterator); checkArgument(size > 0); return new UnmodifiableIterator>() { @Override public boolean hasNext() { return iterator.hasNext(); } @Override public List<@Nullable T> next() { if (!hasNext()) { throw new NoSuchElementException(); } @SuppressWarnings("unchecked") // we only put Ts in it @Nullable T[] array = (@Nullable T[]) 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 } List<@Nullable T> list = Collections.unmodifiableList(Arrays.asList(array)); // TODO(b/192579700): Use a ternary once it no longer confuses our nullness checker. if (pad || count == size) { return list; } else { return list.subList(0, count); } } }; } /** * Returns a view of {@code unfiltered} containing all elements that satisfy the input predicate * {@code retainIfTrue}. */ public static UnmodifiableIterator filter( Iterator unfiltered, Predicate retainIfTrue) { checkNotNull(unfiltered); checkNotNull(retainIfTrue); return new AbstractIterator() { @Override @CheckForNull 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 */ @ParametricNullness 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 */ // For discussion of this signature, see the corresponding overload of *Iterables*.find. @CheckForNull public static T find( Iterator iterator, Predicate predicate, @CheckForNull 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( Iterator fromIterator, Function function) { checkNotNull(function); return new TransformedIterator(fromIterator) { @ParametricNullness @Override T transform(@ParametricNullness 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} */ @ParametricNullness 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 */ @ParametricNullness public static T get( Iterator iterator, int position, @ParametricNullness 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 */ @ParametricNullness public static T getNext( Iterator iterator, @ParametricNullness 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 */ @ParametricNullness 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 */ @ParametricNullness public static T getLast( Iterator iterator, @ParametricNullness 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( Iterator iterator, 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 @ParametricNullness 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(Iterator iterator) { checkNotNull(iterator); return new UnmodifiableIterator() { @Override public boolean hasNext() { return iterator.hasNext(); } @Override @ParametricNullness 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. */ @CheckForNull static 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(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( T[] array, 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 @ParametricNullness 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( @ParametricNullness T value) { return new UnmodifiableIterator() { boolean done; @Override public boolean hasNext() { return !done; } @Override @ParametricNullness 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}. * *

Java 9 users: use {@code enumeration.asIterator()} instead, unless it is important to * return an {@code UnmodifiableIterator} instead of a plain {@code Iterator}. */ public static UnmodifiableIterator forEnumeration( Enumeration enumeration) { checkNotNull(enumeration); return new UnmodifiableIterator() { @Override public boolean hasNext() { return enumeration.hasMoreElements(); } @Override @ParametricNullness 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(Iterator iterator) { checkNotNull(iterator); return new Enumeration() { @Override public boolean hasMoreElements() { return iterator.hasNext(); } @Override @ParametricNullness 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; @CheckForNull private E peekedElement; public PeekingImpl(Iterator iterator) { this.iterator = checkNotNull(iterator); } @Override public boolean hasNext() { return hasPeeked || iterator.hasNext(); } @Override @ParametricNullness public E next() { if (!hasPeeked) { return iterator.next(); } // The cast is safe because of the hasPeeked check. E result = uncheckedCastNullableTToT(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 @ParametricNullness public E peek() { if (!hasPeeked) { peekedElement = iterator.next(); hasPeeked = true; } // The cast is safe because of the hasPeeked check. return uncheckedCastNullableTToT(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, 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 = (PeekingIterator o1, PeekingIterator o2) -> 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 @ParametricNullness 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. */ @CheckForNull private 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). */ @CheckForNull private Iterator> topMetaIterator; // Only becomes nonnull if we encounter nested concatenations. @CheckForNull private Deque>> metaIterators; ConcatenatedIterator(Iterator> metaIterator) { iterator = emptyIterator(); topMetaIterator = checkNotNull(metaIterator); } // Returns a nonempty meta-iterator or, if all meta-iterators are empty, null. @CheckForNull private 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 @ParametricNullness public T next() { if (hasNext()) { toRemove = iterator; return iterator.next(); } else { throw new NoSuchElementException(); } } @Override public void remove() { if (toRemove == null) { throw new IllegalStateException("no calls to next() since the last call to remove()"); } 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; } }