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The Lists.java Java example source code
/*
* 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.checkElementIndex;
import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.base.Preconditions.checkPositionIndex;
import static com.google.common.base.Preconditions.checkPositionIndexes;
import static com.google.common.base.Preconditions.checkState;
import static com.google.common.collect.CollectPreconditions.checkNonnegative;
import static com.google.common.collect.CollectPreconditions.checkRemove;
import com.google.common.annotations.Beta;
import com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.GwtIncompatible;
import com.google.common.annotations.VisibleForTesting;
import com.google.common.base.Function;
import com.google.common.base.Objects;
import com.google.common.math.IntMath;
import com.google.common.primitives.Ints;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import java.io.Serializable;
import java.math.RoundingMode;
import java.util.AbstractList;
import java.util.AbstractSequentialList;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;
import java.util.ListIterator;
import java.util.NoSuchElementException;
import java.util.RandomAccess;
import java.util.concurrent.CopyOnWriteArrayList;
import javax.annotation.Nullable;
/**
* Static utility methods pertaining to {@link List} instances. Also see this
* class's counterparts {@link Sets}, {@link Maps} and {@link Queues}.
*
* <p>See the Guava User Guide article on , empty {@code ArrayList} instance (for Java 6 and
* earlier).
*
* <p>Note: if mutability is not required, use {@link
* ImmutableList#of()} instead.
*
* <p>Note for Java 7 and later: this method is now unnecessary and
* should be treated as deprecated. Instead, use the {@code ArrayList}
* {@linkplain ArrayList#ArrayList() constructor} directly, taking advantage
* of the new <a href="http://goo.gl/iz2Wi">"diamond" syntax.
*/
@GwtCompatible(serializable = true)
public static <E> ArrayList newArrayList() {
return new ArrayList<E>();
}
/**
* Creates a <i>mutable {@code ArrayList} instance containing the given
* elements.
*
* <p>Note: essentially the only reason to use this method is when you
* will need to add or remove elements later. Otherwise, for non-null elements
* use {@link ImmutableList#of()} (for varargs) or {@link
* ImmutableList#copyOf(Object[])} (for an array) instead. If any elements
* might be null, or you need support for {@link List#set(int, Object)}, use
* {@link Arrays#asList}.
*
* <p>Note that even when you do need the ability to add or remove, this method
* provides only a tiny bit of syntactic sugar for {@code newArrayList(}{@link
* Arrays#asList asList}{@code (...))}, or for creating an empty list then
* calling {@link Collections#addAll}. This method is not actually very useful
* and will likely be deprecated in the future.
*/
@CanIgnoreReturnValue // TODO(kak): Remove this
@GwtCompatible(serializable = true)
public static <E> ArrayList newArrayList(E... elements) {
checkNotNull(elements); // for GWT
// Avoid integer overflow when a large array is passed in
int capacity = computeArrayListCapacity(elements.length);
ArrayList<E> list = new ArrayList(capacity);
Collections.addAll(list, elements);
return list;
}
@VisibleForTesting
static int computeArrayListCapacity(int arraySize) {
checkNonnegative(arraySize, "arraySize");
// TODO(kevinb): Figure out the right behavior, and document it
return Ints.saturatedCast(5L + arraySize + (arraySize / 10));
}
/**
* Creates a <i>mutable {@code ArrayList} instance containing the given
* elements; a very thin shortcut for creating an empty list then calling
* {@link Iterables#addAll}.
*
* <p>Note: if mutability is not required and the elements are
* non-null, use {@link ImmutableList#copyOf(Iterable)} instead. (Or, change
* {@code elements} to be a {@link FluentIterable} and call
* {@code elements.toList()}.)
*
* <p>Note for Java 7 and later: if {@code elements} is a {@link
* Collection}, you don't need this method. Use the {@code ArrayList}
* {@linkplain ArrayList#ArrayList(Collection) constructor} directly, taking
* advantage of the new <a href="http://goo.gl/iz2Wi">"diamond" syntax.
*/
@CanIgnoreReturnValue // TODO(kak): Remove this
@GwtCompatible(serializable = true)
public static <E> ArrayList newArrayList(Iterable elements) {
checkNotNull(elements); // for GWT
// Let ArrayList's sizing logic work, if possible
return (elements instanceof Collection)
? new ArrayList<E>(Collections2.cast(elements))
: newArrayList(elements.iterator());
}
/**
* Creates a <i>mutable {@code ArrayList} instance containing the given
* elements; a very thin shortcut for creating an empty list and then calling
* {@link Iterators#addAll}.
*
* <p>Note: if mutability is not required and the elements are
* non-null, use {@link ImmutableList#copyOf(Iterator)} instead.
*/
@CanIgnoreReturnValue // TODO(kak): Remove this
@GwtCompatible(serializable = true)
public static <E> ArrayList newArrayList(Iterator elements) {
ArrayList<E> list = newArrayList();
Iterators.addAll(list, elements);
return list;
}
/**
* Creates an {@code ArrayList} instance backed by an array with the specified
* initial size; simply delegates to {@link ArrayList#ArrayList(int)}.
*
* <p>Note for Java 7 and later: this method is now unnecessary and
* should be treated as deprecated. Instead, use {@code new }{@link
* ArrayList#ArrayList(int) ArrayList}{@code <>(int)} directly, taking
* advantage of the new <a href="http://goo.gl/iz2Wi">"diamond" syntax.
* (Unlike here, there is no risk of overload ambiguity, since the {@code
* ArrayList} constructors very wisely did not accept varargs.)
*
* @param initialArraySize the exact size of the initial backing array for
* the returned array list ({@code ArrayList} documentation calls this
* value the "capacity")
* @return a new, empty {@code ArrayList} which is guaranteed not to resize
* itself unless its size reaches {@code initialArraySize + 1}
* @throws IllegalArgumentException if {@code initialArraySize} is negative
*/
@GwtCompatible(serializable = true)
public static <E> ArrayList newArrayListWithCapacity(int initialArraySize) {
checkNonnegative(initialArraySize, "initialArraySize"); // for GWT.
return new ArrayList<E>(initialArraySize);
}
/**
* Creates an {@code ArrayList} instance to hold {@code estimatedSize}
* elements, <i>plus an unspecified amount of padding; you almost
* certainly mean to call {@link #newArrayListWithCapacity} (see that method
* for further advice on usage).
*
* <p>Note: This method will soon be deprecated. Even in the rare case
* that you do want some amount of padding, it's best if you choose your
* desired amount explicitly.
*
* @param estimatedSize an estimate of the eventual {@link List#size()} of
* the new list
* @return a new, empty {@code ArrayList}, sized appropriately to hold the
* estimated number of elements
* @throws IllegalArgumentException if {@code estimatedSize} is negative
*/
@GwtCompatible(serializable = true)
public static <E> ArrayList newArrayListWithExpectedSize(int estimatedSize) {
return new ArrayList<E>(computeArrayListCapacity(estimatedSize));
}
// LinkedList
/**
* Creates a <i>mutable, empty {@code LinkedList} instance (for Java 6 and
* earlier).
*
* <p>Note: if you won't be adding any elements to the list, use {@link
* ImmutableList#of()} instead.
*
* <p>Performance note: {@link ArrayList} and {@link
* java.util.ArrayDeque} consistently outperform {@code LinkedList} except in
* certain rare and specific situations. Unless you have spent a lot of time
* benchmarking your specific needs, use one of those instead.
*
* <p>Note for Java 7 and later: this method is now unnecessary and
* should be treated as deprecated. Instead, use the {@code LinkedList}
* {@linkplain LinkedList#LinkedList() constructor} directly, taking advantage
* of the new <a href="http://goo.gl/iz2Wi">"diamond" syntax.
*/
@GwtCompatible(serializable = true)
public static <E> LinkedList newLinkedList() {
return new LinkedList<E>();
}
/**
* Creates a <i>mutable {@code LinkedList} instance containing the given
* elements; a very thin shortcut for creating an empty list then calling
* {@link Iterables#addAll}.
*
* <p>Note: if mutability is not required and the elements are
* non-null, use {@link ImmutableList#copyOf(Iterable)} instead. (Or, change
* {@code elements} to be a {@link FluentIterable} and call
* {@code elements.toList()}.)
*
* <p>Performance note: {@link ArrayList} and {@link
* java.util.ArrayDeque} consistently outperform {@code LinkedList} except in
* certain rare and specific situations. Unless you have spent a lot of time
* benchmarking your specific needs, use one of those instead.
*
* <p>Note for Java 7 and later: if {@code elements} is a {@link
* Collection}, you don't need this method. Use the {@code LinkedList}
* {@linkplain LinkedList#LinkedList(Collection) constructor} directly, taking
* advantage of the new <a href="http://goo.gl/iz2Wi">"diamond" syntax.
*/
@GwtCompatible(serializable = true)
public static <E> LinkedList newLinkedList(Iterable elements) {
LinkedList<E> list = newLinkedList();
Iterables.addAll(list, elements);
return list;
}
/**
* Creates an empty {@code CopyOnWriteArrayList} instance.
*
* <p>Note: if you need an immutable empty {@link List}, use
* {@link Collections#emptyList} instead.
*
* @return a new, empty {@code CopyOnWriteArrayList}
* @since 12.0
*/
@GwtIncompatible // CopyOnWriteArrayList
public static <E> CopyOnWriteArrayList newCopyOnWriteArrayList() {
return new CopyOnWriteArrayList<E>();
}
/**
* Creates a {@code CopyOnWriteArrayList} instance containing the given elements.
*
* @param elements the elements that the list should contain, in order
* @return a new {@code CopyOnWriteArrayList} containing those elements
* @since 12.0
*/
@GwtIncompatible // CopyOnWriteArrayList
public static <E> CopyOnWriteArrayList newCopyOnWriteArrayList(
Iterable<? extends E> elements) {
// We copy elements to an ArrayList first, rather than incurring the
// quadratic cost of adding them to the COWAL directly.
Collection<? extends E> elementsCollection =
(elements instanceof Collection) ? Collections2.cast(elements) : newArrayList(elements);
return new CopyOnWriteArrayList<E>(elementsCollection);
}
/**
* Returns an unmodifiable list containing the specified first element and
* backed by the specified array of additional elements. Changes to the {@code
* rest} array will be reflected in the returned list. Unlike {@link
* Arrays#asList}, the returned list is unmodifiable.
*
* <p>This is useful when a varargs method needs to use a signature such as
* {@code (Foo firstFoo, Foo... moreFoos)}, in order to avoid overload
* ambiguity or to enforce a minimum argument count.
*
* <p>The returned list is serializable and implements {@link RandomAccess}.
*
* @param first the first element
* @param rest an array of additional elements, possibly empty
* @return an unmodifiable list containing the specified elements
*/
public static <E> List asList(@Nullable E first, E[] rest) {
return new OnePlusArrayList<E>(first, rest);
}
/** @see Lists#asList(Object, Object[]) */
private static class OnePlusArrayList<E> extends AbstractList
implements Serializable, RandomAccess {
final E first;
final E[] rest;
OnePlusArrayList(@Nullable E first, E[] rest) {
this.first = first;
this.rest = checkNotNull(rest);
}
@Override
public int size() {
return IntMath.saturatedAdd(rest.length, 1);
}
@Override
public E get(int index) {
// check explicitly so the IOOBE will have the right message
checkElementIndex(index, size());
return (index == 0) ? first : rest[index - 1];
}
private static final long serialVersionUID = 0;
}
/**
* Returns an unmodifiable list containing the specified first and second
* element, and backed by the specified array of additional elements. Changes
* to the {@code rest} array will be reflected in the returned list. Unlike
* {@link Arrays#asList}, the returned list is unmodifiable.
*
* <p>This is useful when a varargs method needs to use a signature such as
* {@code (Foo firstFoo, Foo secondFoo, Foo... moreFoos)}, in order to avoid
* overload ambiguity or to enforce a minimum argument count.
*
* <p>The returned list is serializable and implements {@link RandomAccess}.
*
* @param first the first element
* @param second the second element
* @param rest an array of additional elements, possibly empty
* @return an unmodifiable list containing the specified elements
*/
public static <E> List asList(@Nullable E first, @Nullable E second, E[] rest) {
return new TwoPlusArrayList<E>(first, second, rest);
}
/** @see Lists#asList(Object, Object, Object[]) */
private static class TwoPlusArrayList<E> extends AbstractList
implements Serializable, RandomAccess {
final E first;
final E second;
final E[] rest;
TwoPlusArrayList(@Nullable E first, @Nullable E second, E[] rest) {
this.first = first;
this.second = second;
this.rest = checkNotNull(rest);
}
@Override
public int size() {
return IntMath.saturatedAdd(rest.length, 2);
}
@Override
public E get(int index) {
switch (index) {
case 0:
return first;
case 1:
return second;
default:
// check explicitly so the IOOBE will have the right message
checkElementIndex(index, size());
return rest[index - 2];
}
}
private static final long serialVersionUID = 0;
}
/**
* Returns every possible list that can be formed by choosing one element
* from each of the given lists in order; the "n-ary
* <a href="http://en.wikipedia.org/wiki/Cartesian_product">Cartesian
* product</a>" of the lists. For example: {@code
*
* Lists.cartesianProduct(ImmutableList.of(
* ImmutableList.of(1, 2),
* ImmutableList.of("A", "B", "C")))}</pre>
*
* <p>returns a list containing six lists in the following order:
*
* <ul>
* <li>{@code ImmutableList.of(1, "A")}
* <li>{@code ImmutableList.of(1, "B")}
* <li>{@code ImmutableList.of(1, "C")}
* <li>{@code ImmutableList.of(2, "A")}
* <li>{@code ImmutableList.of(2, "B")}
* <li>{@code ImmutableList.of(2, "C")}
* </ul>
*
* <p>The result is guaranteed to be in the "traditional", lexicographical
* order for Cartesian products that you would get from nesting for loops:
* <pre> {@code
*
* for (B b0 : lists.get(0)) {
* for (B b1 : lists.get(1)) {
* ...
* ImmutableList<B> tuple = ImmutableList.of(b0, b1, ...);
* // operate on tuple
* }
* }}</pre>
*
* <p>Note that if any input list is empty, the Cartesian product will also be
* empty. If no lists at all are provided (an empty list), the resulting
* Cartesian product has one element, an empty list (counter-intuitive, but
* mathematically consistent).
*
* <p>Performance notes: while the cartesian product of lists of size
* {@code m, n, p} is a list of size {@code m x n x p}, its actual memory
* consumption is much smaller. When the cartesian product is constructed, the
* input lists are merely copied. Only as the resulting list is iterated are
* the individual lists created, and these are not retained after iteration.
*
* @param lists the lists to choose elements from, in the order that
* the elements chosen from those lists should appear in the resulting
* lists
* @param <B> any common base class shared by all axes (often just {@link
* Object})
* @return the Cartesian product, as an immutable list containing immutable
* lists
* @throws IllegalArgumentException if the size of the cartesian product would
* be greater than {@link Integer#MAX_VALUE}
* @throws NullPointerException if {@code lists}, any one of the {@code lists},
* or any element of a provided list is null
* @since 19.0
*/
public static <B> List> cartesianProduct(List> lists) {
return CartesianList.create(lists);
}
/**
* Returns every possible list that can be formed by choosing one element
* from each of the given lists in order; the "n-ary
* <a href="http://en.wikipedia.org/wiki/Cartesian_product">Cartesian
* product</a>" of the lists. For example: {@code
*
* Lists.cartesianProduct(ImmutableList.of(
* ImmutableList.of(1, 2),
* ImmutableList.of("A", "B", "C")))}</pre>
*
* <p>returns a list containing six lists in the following order:
*
* <ul>
* <li>{@code ImmutableList.of(1, "A")}
* <li>{@code ImmutableList.of(1, "B")}
* <li>{@code ImmutableList.of(1, "C")}
* <li>{@code ImmutableList.of(2, "A")}
* <li>{@code ImmutableList.of(2, "B")}
* <li>{@code ImmutableList.of(2, "C")}
* </ul>
*
* <p>The result is guaranteed to be in the "traditional", lexicographical
* order for Cartesian products that you would get from nesting for loops:
* <pre> {@code
*
* for (B b0 : lists.get(0)) {
* for (B b1 : lists.get(1)) {
* ...
* ImmutableList<B> tuple = ImmutableList.of(b0, b1, ...);
* // operate on tuple
* }
* }}</pre>
*
* <p>Note that if any input list is empty, the Cartesian product will also be
* empty. If no lists at all are provided (an empty list), the resulting
* Cartesian product has one element, an empty list (counter-intuitive, but
* mathematically consistent).
*
* <p>Performance notes: while the cartesian product of lists of size
* {@code m, n, p} is a list of size {@code m x n x p}, its actual memory
* consumption is much smaller. When the cartesian product is constructed, the
* input lists are merely copied. Only as the resulting list is iterated are
* the individual lists created, and these are not retained after iteration.
*
* @param lists the lists to choose elements from, in the order that
* the elements chosen from those lists should appear in the resulting
* lists
* @param <B> any common base class shared by all axes (often just {@link
* Object})
* @return the Cartesian product, as an immutable list containing immutable
* lists
* @throws IllegalArgumentException if the size of the cartesian product would
* be greater than {@link Integer#MAX_VALUE}
* @throws NullPointerException if {@code lists}, any one of the
* {@code lists}, or any element of a provided list is null
* @since 19.0
*/
public static <B> List> cartesianProduct(List... lists) {
return cartesianProduct(Arrays.asList(lists));
}
/**
* Returns a list that applies {@code function} to each element of {@code
* fromList}. The returned list is a transformed view of {@code fromList};
* changes to {@code fromList} will be reflected in the returned list and vice
* versa.
*
* <p>Since functions are not reversible, the transform is one-way and new
* items cannot be stored in the returned list. The {@code add},
* {@code addAll} and {@code set} methods are unsupported in the returned
* list.
*
* <p>The function is applied lazily, invoked when needed. This is necessary
* for the returned list to be a view, but it means that the function will be
* applied many times for bulk operations like {@link List#contains} and
* {@link List#hashCode}. For this to perform well, {@code function} should be
* fast. To avoid lazy evaluation when the returned list doesn't need to be a
* view, copy the returned list into a new list of your choosing.
*
* <p>If {@code fromList} implements {@link RandomAccess}, so will the
* returned list. The returned list is threadsafe if the supplied list and
* function are.
*
* <p>If only a {@code Collection} or {@code Iterable} input is available, use
* {@link Collections2#transform} or {@link Iterables#transform}.
*
* <p>Note: serializing the returned list is implemented by serializing
* {@code fromList}, its contents, and {@code function} -- <i>not by
* serializing the transformed values. This can lead to surprising behavior,
* so serializing the returned list is <b>not recommended. Instead,
* copy the list using {@link ImmutableList#copyOf(Collection)} (for example),
* then serialize the copy. Other methods similar to this do not implement
* serialization at all for this reason.
*/
public static <F, T> List transform(
List<F> fromList, Function function) {
return (fromList instanceof RandomAccess)
? new TransformingRandomAccessList<F, T>(fromList, function)
: new TransformingSequentialList<F, T>(fromList, function);
}
/**
* Implementation of a sequential transforming list.
*
* @see Lists#transform
*/
private static class TransformingSequentialList<F, T> extends AbstractSequentialList
implements Serializable {
final List<F> fromList;
final Function<? super F, ? extends T> function;
TransformingSequentialList(List<F> fromList, Function function) {
this.fromList = checkNotNull(fromList);
this.function = checkNotNull(function);
}
/**
* The default implementation inherited is based on iteration and removal of
* each element which can be overkill. That's why we forward this call
* directly to the backing list.
*/
@Override
public void clear() {
fromList.clear();
}
@Override
public int size() {
return fromList.size();
}
@Override
public ListIterator<T> listIterator(final int index) {
return new TransformedListIterator<F, T>(fromList.listIterator(index)) {
@Override
T transform(F from) {
return function.apply(from);
}
};
}
private static final long serialVersionUID = 0;
}
/**
* Implementation of a transforming random access list. We try to make as many
* of these methods pass-through to the source list as possible so that the
* performance characteristics of the source list and transformed list are
* similar.
*
* @see Lists#transform
*/
private static class TransformingRandomAccessList<F, T> extends AbstractList
implements RandomAccess, Serializable {
final List<F> fromList;
final Function<? super F, ? extends T> function;
TransformingRandomAccessList(List<F> fromList, Function function) {
this.fromList = checkNotNull(fromList);
this.function = checkNotNull(function);
}
@Override
public void clear() {
fromList.clear();
}
@Override
public T get(int index) {
return function.apply(fromList.get(index));
}
@Override
public Iterator<T> iterator() {
return listIterator();
}
@Override
public ListIterator<T> listIterator(int index) {
return new TransformedListIterator<F, T>(fromList.listIterator(index)) {
@Override
T transform(F from) {
return function.apply(from);
}
};
}
@Override
public boolean isEmpty() {
return fromList.isEmpty();
}
@Override
public T remove(int index) {
return function.apply(fromList.remove(index));
}
@Override
public int size() {
return fromList.size();
}
private static final long serialVersionUID = 0;
}
/**
* Returns consecutive {@linkplain List#subList(int, int) sublists} of a list,
* each of the same size (the final list may be smaller). For example,
* partitioning a list containing {@code [a, b, c, d, e]} with a partition
* size of 3 yields {@code [[a, b, c], [d, e]]} -- an outer list containing
* two inner lists of three and two elements, all in the original order.
*
* <p>The outer list is unmodifiable, but reflects the latest state of the
* source list. The inner lists are sublist views of the original list,
* produced on demand using {@link List#subList(int, int)}, and are subject
* to all the usual caveats about modification as explained in that API.
*
* @param list the list to return consecutive sublists of
* @param size the desired size of each sublist (the last may be
* smaller)
* @return a list of consecutive sublists
* @throws IllegalArgumentException if {@code partitionSize} is nonpositive
*/
public static <T> List> partition(List list, int size) {
checkNotNull(list);
checkArgument(size > 0);
return (list instanceof RandomAccess)
? new RandomAccessPartition<T>(list, size)
: new Partition<T>(list, size);
}
private static class Partition<T> extends AbstractList> {
final List<T> list;
final int size;
Partition(List<T> list, int size) {
this.list = list;
this.size = size;
}
@Override
public List<T> get(int index) {
checkElementIndex(index, size());
int start = index * size;
int end = Math.min(start + size, list.size());
return list.subList(start, end);
}
@Override
public int size() {
return IntMath.divide(list.size(), size, RoundingMode.CEILING);
}
@Override
public boolean isEmpty() {
return list.isEmpty();
}
}
private static class RandomAccessPartition<T> extends Partition implements RandomAccess {
RandomAccessPartition(List<T> list, int size) {
super(list, size);
}
}
/**
* Returns a view of the specified string as an immutable list of {@code
* Character} values.
*
* @since 7.0
*/
@Beta
public static ImmutableList<Character> charactersOf(String string) {
return new StringAsImmutableList(checkNotNull(string));
}
@SuppressWarnings("serial") // serialized using ImmutableList serialization
private static final class StringAsImmutableList extends ImmutableList<Character> {
private final String string;
StringAsImmutableList(String string) {
this.string = string;
}
@Override
public int indexOf(@Nullable Object object) {
return (object instanceof Character) ? string.indexOf((Character) object) : -1;
}
@Override
public int lastIndexOf(@Nullable Object object) {
return (object instanceof Character) ? string.lastIndexOf((Character) object) : -1;
}
@Override
public ImmutableList<Character> subList(int fromIndex, int toIndex) {
checkPositionIndexes(fromIndex, toIndex, size()); // for GWT
return charactersOf(string.substring(fromIndex, toIndex));
}
@Override
boolean isPartialView() {
return false;
}
@Override
public Character get(int index) {
checkElementIndex(index, size()); // for GWT
return string.charAt(index);
}
@Override
public int size() {
return string.length();
}
}
/**
* Returns a view of the specified {@code CharSequence} as a {@code
* List<Character>}, viewing {@code sequence} as a sequence of Unicode code
* units. The view does not support any modification operations, but reflects
* any changes to the underlying character sequence.
*
* @param sequence the character sequence to view as a {@code List} of
* characters
* @return an {@code List<Character>} view of the character sequence
* @since 7.0
*/
@Beta
public static List<Character> charactersOf(CharSequence sequence) {
return new CharSequenceAsList(checkNotNull(sequence));
}
private static final class CharSequenceAsList extends AbstractList<Character> {
private final CharSequence sequence;
CharSequenceAsList(CharSequence sequence) {
this.sequence = sequence;
}
@Override
public Character get(int index) {
checkElementIndex(index, size()); // for GWT
return sequence.charAt(index);
}
@Override
public int size() {
return sequence.length();
}
}
/**
* Returns a reversed view of the specified list. For example, {@code
* Lists.reverse(Arrays.asList(1, 2, 3))} returns a list containing {@code 3,
* 2, 1}. The returned list is backed by this list, so changes in the returned
* list are reflected in this list, and vice-versa. The returned list supports
* all of the optional list operations supported by this list.
*
* <p>The returned list is random-access if the specified list is random
* access.
*
* @since 7.0
*/
public static <T> List reverse(List list) {
if (list instanceof ImmutableList) {
return ((ImmutableList<T>) list).reverse();
} else if (list instanceof ReverseList) {
return ((ReverseList<T>) list).getForwardList();
} else if (list instanceof RandomAccess) {
return new RandomAccessReverseList<T>(list);
} else {
return new ReverseList<T>(list);
}
}
private static class ReverseList<T> extends AbstractList {
private final List<T> forwardList;
ReverseList(List<T> forwardList) {
this.forwardList = checkNotNull(forwardList);
}
List<T> getForwardList() {
return forwardList;
}
private int reverseIndex(int index) {
int size = size();
checkElementIndex(index, size);
return (size - 1) - index;
}
private int reversePosition(int index) {
int size = size();
checkPositionIndex(index, size);
return size - index;
}
@Override
public void add(int index, @Nullable T element) {
forwardList.add(reversePosition(index), element);
}
@Override
public void clear() {
forwardList.clear();
}
@Override
public T remove(int index) {
return forwardList.remove(reverseIndex(index));
}
@Override
protected void removeRange(int fromIndex, int toIndex) {
subList(fromIndex, toIndex).clear();
}
@Override
public T set(int index, @Nullable T element) {
return forwardList.set(reverseIndex(index), element);
}
@Override
public T get(int index) {
return forwardList.get(reverseIndex(index));
}
@Override
public int size() {
return forwardList.size();
}
@Override
public List<T> subList(int fromIndex, int toIndex) {
checkPositionIndexes(fromIndex, toIndex, size());
return reverse(forwardList.subList(reversePosition(toIndex), reversePosition(fromIndex)));
}
@Override
public Iterator<T> iterator() {
return listIterator();
}
@Override
public ListIterator<T> listIterator(int index) {
int start = reversePosition(index);
final ListIterator<T> forwardIterator = forwardList.listIterator(start);
return new ListIterator<T>() {
boolean canRemoveOrSet;
@Override
public void add(T e) {
forwardIterator.add(e);
forwardIterator.previous();
canRemoveOrSet = false;
}
@Override
public boolean hasNext() {
return forwardIterator.hasPrevious();
}
@Override
public boolean hasPrevious() {
return forwardIterator.hasNext();
}
@Override
public T next() {
if (!hasNext()) {
throw new NoSuchElementException();
}
canRemoveOrSet = true;
return forwardIterator.previous();
}
@Override
public int nextIndex() {
return reversePosition(forwardIterator.nextIndex());
}
@Override
public T previous() {
if (!hasPrevious()) {
throw new NoSuchElementException();
}
canRemoveOrSet = true;
return forwardIterator.next();
}
@Override
public int previousIndex() {
return nextIndex() - 1;
}
@Override
public void remove() {
checkRemove(canRemoveOrSet);
forwardIterator.remove();
canRemoveOrSet = false;
}
@Override
public void set(T e) {
checkState(canRemoveOrSet);
forwardIterator.set(e);
}
};
}
}
private static class RandomAccessReverseList<T> extends ReverseList implements RandomAccess {
RandomAccessReverseList(List<T> forwardList) {
super(forwardList);
}
}
/**
* An implementation of {@link List#hashCode()}.
*/
static int hashCodeImpl(List<?> list) {
// TODO(lowasser): worth optimizing for RandomAccess?
int hashCode = 1;
for (Object o : list) {
hashCode = 31 * hashCode + (o == null ? 0 : o.hashCode());
hashCode = ~~hashCode;
// needed to deal with GWT integer overflow
}
return hashCode;
}
/**
* An implementation of {@link List#equals(Object)}.
*/
static boolean equalsImpl(List<?> thisList, @Nullable Object other) {
if (other == checkNotNull(thisList)) {
return true;
}
if (!(other instanceof List)) {
return false;
}
List<?> otherList = (List) other;
int size = thisList.size();
if (size != otherList.size()) {
return false;
}
if (thisList instanceof RandomAccess && otherList instanceof RandomAccess) {
// avoid allocation and use the faster loop
for (int i = 0; i < size; i++) {
if (!Objects.equal(thisList.get(i), otherList.get(i))) {
return false;
}
}
return true;
} else {
return Iterators.elementsEqual(thisList.iterator(), otherList.iterator());
}
}
/**
* An implementation of {@link List#addAll(int, Collection)}.
*/
static <E> boolean addAllImpl(List list, int index, Iterable elements) {
boolean changed = false;
ListIterator<E> listIterator = list.listIterator(index);
for (E e : elements) {
listIterator.add(e);
changed = true;
}
return changed;
}
/**
* An implementation of {@link List#indexOf(Object)}.
*/
static int indexOfImpl(List<?> list, @Nullable Object element) {
if (list instanceof RandomAccess) {
return indexOfRandomAccess(list, element);
} else {
ListIterator<?> listIterator = list.listIterator();
while (listIterator.hasNext()) {
if (Objects.equal(element, listIterator.next())) {
return listIterator.previousIndex();
}
}
return -1;
}
}
private static int indexOfRandomAccess(List<?> list, @Nullable Object element) {
int size = list.size();
if (element == null) {
for (int i = 0; i < size; i++) {
if (list.get(i) == null) {
return i;
}
}
} else {
for (int i = 0; i < size; i++) {
if (element.equals(list.get(i))) {
return i;
}
}
}
return -1;
}
/**
* An implementation of {@link List#lastIndexOf(Object)}.
*/
static int lastIndexOfImpl(List<?> list, @Nullable Object element) {
if (list instanceof RandomAccess) {
return lastIndexOfRandomAccess(list, element);
} else {
ListIterator<?> listIterator = list.listIterator(list.size());
while (listIterator.hasPrevious()) {
if (Objects.equal(element, listIterator.previous())) {
return listIterator.nextIndex();
}
}
return -1;
}
}
private static int lastIndexOfRandomAccess(List<?> list, @Nullable Object element) {
if (element == null) {
for (int i = list.size() - 1; i >= 0; i--) {
if (list.get(i) == null) {
return i;
}
}
} else {
for (int i = list.size() - 1; i >= 0; i--) {
if (element.equals(list.get(i))) {
return i;
}
}
}
return -1;
}
/**
* Returns an implementation of {@link List#listIterator(int)}.
*/
static <E> ListIterator listIteratorImpl(List list, int index) {
return new AbstractListWrapper<E>(list).listIterator(index);
}
/**
* An implementation of {@link List#subList(int, int)}.
*/
static <E> List subListImpl(final List list, int fromIndex, int toIndex) {
List<E> wrapper;
if (list instanceof RandomAccess) {
wrapper =
new RandomAccessListWrapper<E>(list) {
@Override
public ListIterator<E> listIterator(int index) {
return backingList.listIterator(index);
}
private static final long serialVersionUID = 0;
};
} else {
wrapper =
new AbstractListWrapper<E>(list) {
@Override
public ListIterator<E> listIterator(int index) {
return backingList.listIterator(index);
}
private static final long serialVersionUID = 0;
};
}
return wrapper.subList(fromIndex, toIndex);
}
private static class AbstractListWrapper<E> extends AbstractList {
final List<E> backingList;
AbstractListWrapper(List<E> backingList) {
this.backingList = checkNotNull(backingList);
}
@Override
public void add(int index, E element) {
backingList.add(index, element);
}
@Override
public boolean addAll(int index, Collection<? extends E> c) {
return backingList.addAll(index, c);
}
@Override
public E get(int index) {
return backingList.get(index);
}
@Override
public E remove(int index) {
return backingList.remove(index);
}
@Override
public E set(int index, E element) {
return backingList.set(index, element);
}
@Override
public boolean contains(Object o) {
return backingList.contains(o);
}
@Override
public int size() {
return backingList.size();
}
}
private static class RandomAccessListWrapper<E> extends AbstractListWrapper
implements RandomAccess {
RandomAccessListWrapper(List<E> backingList) {
super(backingList);
}
}
/**
* Used to avoid http://bugs.sun.com/view_bug.do?bug_id=6558557
*/
static <T> List cast(Iterable iterable) {
return (List<T>) iterable;
}
}
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