com.google.common.collect.ImmutableList Maven / Gradle / Ivy
/*
* 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.checkPositionIndexes;
import static com.google.common.collect.CollectPreconditions.checkNonnegative;
import static com.google.common.collect.ObjectArrays.checkElementsNotNull;
import static com.google.common.collect.RegularImmutableList.EMPTY;
import static java.util.Objects.requireNonNull;
import com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.J2ktIncompatible;
import com.google.common.annotations.VisibleForTesting;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import com.google.errorprone.annotations.DoNotCall;
import com.google.errorprone.annotations.InlineMe;
import java.io.InvalidObjectException;
import java.io.ObjectInputStream;
import java.io.Serializable;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.Comparator;
import java.util.Iterator;
import java.util.List;
import java.util.RandomAccess;
import java.util.Spliterator;
import java.util.function.Consumer;
import java.util.function.UnaryOperator;
import java.util.stream.Collector;
import javax.annotation.CheckForNull;
import org.checkerframework.checker.nullness.qual.Nullable;
/**
* A {@link List} whose contents will never change, with many other important properties detailed at
* {@link ImmutableCollection}.
*
* See the Guava User Guide article on immutable collections.
*
* @see ImmutableMap
* @see ImmutableSet
* @author Kevin Bourrillion
* @since 2.0
*/
@GwtCompatible(serializable = true, emulated = true)
@SuppressWarnings("serial") // we're overriding default serialization
@ElementTypesAreNonnullByDefault
public abstract class ImmutableList extends ImmutableCollection
implements List, RandomAccess {
/**
* Returns a {@code Collector} that accumulates the input elements into a new {@code
* ImmutableList}, in encounter order.
*
* @since 21.0
*/
public static Collector> toImmutableList() {
return CollectCollectors.toImmutableList();
}
/**
* Returns the empty immutable list. This list behaves and performs comparably to {@link
* Collections#emptyList}, and is preferable mainly for consistency and maintainability of your
* code.
*
* Performance note: the instance returned is a singleton.
*/
// Casting to any type is safe because the list will never hold any elements.
@SuppressWarnings("unchecked")
public static ImmutableList of() {
return (ImmutableList) EMPTY;
}
/**
* Returns an immutable list containing a single element. This list behaves and performs
* comparably to {@link Collections#singletonList}, but will not accept a null element. It is
* preferable mainly for consistency and maintainability of your code.
*
* @throws NullPointerException if {@code element} is null
*/
public static ImmutableList of(E element) {
return new SingletonImmutableList(element);
}
/**
* Returns an immutable list containing the given elements, in order.
*
* @throws NullPointerException if any element is null
*/
public static ImmutableList of(E e1, E e2) {
return construct(e1, e2);
}
/**
* Returns an immutable list containing the given elements, in order.
*
* @throws NullPointerException if any element is null
*/
public static ImmutableList of(E e1, E e2, E e3) {
return construct(e1, e2, e3);
}
/**
* Returns an immutable list containing the given elements, in order.
*
* @throws NullPointerException if any element is null
*/
public static ImmutableList of(E e1, E e2, E e3, E e4) {
return construct(e1, e2, e3, e4);
}
/**
* Returns an immutable list containing the given elements, in order.
*
* @throws NullPointerException if any element is null
*/
public static ImmutableList of(E e1, E e2, E e3, E e4, E e5) {
return construct(e1, e2, e3, e4, e5);
}
/**
* Returns an immutable list containing the given elements, in order.
*
* @throws NullPointerException if any element is null
*/
public static ImmutableList of(E e1, E e2, E e3, E e4, E e5, E e6) {
return construct(e1, e2, e3, e4, e5, e6);
}
/**
* Returns an immutable list containing the given elements, in order.
*
* @throws NullPointerException if any element is null
*/
public static ImmutableList of(E e1, E e2, E e3, E e4, E e5, E e6, E e7) {
return construct(e1, e2, e3, e4, e5, e6, e7);
}
/**
* Returns an immutable list containing the given elements, in order.
*
* @throws NullPointerException if any element is null
*/
public static ImmutableList of(E e1, E e2, E e3, E e4, E e5, E e6, E e7, E e8) {
return construct(e1, e2, e3, e4, e5, e6, e7, e8);
}
/**
* Returns an immutable list containing the given elements, in order.
*
* @throws NullPointerException if any element is null
*/
public static ImmutableList of(E e1, E e2, E e3, E e4, E e5, E e6, E e7, E e8, E e9) {
return construct(e1, e2, e3, e4, e5, e6, e7, e8, e9);
}
/**
* Returns an immutable list containing the given elements, in order.
*
* @throws NullPointerException if any element is null
*/
public static ImmutableList of(
E e1, E e2, E e3, E e4, E e5, E e6, E e7, E e8, E e9, E e10) {
return construct(e1, e2, e3, e4, e5, e6, e7, e8, e9, e10);
}
/**
* Returns an immutable list containing the given elements, in order.
*
* @throws NullPointerException if any element is null
*/
public static ImmutableList of(
E e1, E e2, E e3, E e4, E e5, E e6, E e7, E e8, E e9, E e10, E e11) {
return construct(e1, e2, e3, e4, e5, e6, e7, e8, e9, e10, e11);
}
// These go up to eleven. After that, you just get the varargs form, and
// whatever warnings might come along with it. :(
/**
* Returns an immutable list containing the given elements, in order.
*
* The array {@code others} must not be longer than {@code Integer.MAX_VALUE - 12}.
*
* @throws NullPointerException if any element is null
* @since 3.0 (source-compatible since 2.0)
*/
@SafeVarargs // For Eclipse. For internal javac we have disabled this pointless type of warning.
public static ImmutableList of(
E e1, E e2, E e3, E e4, E e5, E e6, E e7, E e8, E e9, E e10, E e11, E e12, E... others) {
checkArgument(
others.length <= Integer.MAX_VALUE - 12, "the total number of elements must fit in an int");
Object[] array = new Object[12 + others.length];
array[0] = e1;
array[1] = e2;
array[2] = e3;
array[3] = e4;
array[4] = e5;
array[5] = e6;
array[6] = e7;
array[7] = e8;
array[8] = e9;
array[9] = e10;
array[10] = e11;
array[11] = e12;
System.arraycopy(others, 0, array, 12, others.length);
return construct(array);
}
/**
* Returns an immutable list containing the given elements, in order. If {@code elements} is a
* {@link Collection}, this method behaves exactly as {@link #copyOf(Collection)}; otherwise, it
* behaves exactly as {@code copyOf(elements.iterator()}.
*
* @throws NullPointerException if {@code elements} contains a null element
*/
public static ImmutableList copyOf(Iterable elements) {
checkNotNull(elements); // TODO(kevinb): is this here only for GWT?
return (elements instanceof Collection)
? copyOf((Collection) elements)
: copyOf(elements.iterator());
}
/**
* Returns an immutable list containing the given elements, in order.
*
* Despite the method name, this method attempts to avoid actually copying the data when it is
* safe to do so. The exact circumstances under which a copy will or will not be performed are
* undocumented and subject to change.
*
*
Note that if {@code list} is a {@code List}, then {@code ImmutableList.copyOf(list)}
* returns an {@code ImmutableList} containing each of the strings in {@code list}, while
* {@code ImmutableList.of(list)} returns an {@code ImmutableList>} containing one
* element (the given list itself).
*
* This method is safe to use even when {@code elements} is a synchronized or concurrent
* collection that is currently being modified by another thread.
*
* @throws NullPointerException if {@code elements} contains a null element
*/
public static ImmutableList copyOf(Collection elements) {
if (elements instanceof ImmutableCollection) {
@SuppressWarnings("unchecked") // all supported methods are covariant
ImmutableList list = ((ImmutableCollection) elements).asList();
return list.isPartialView() ? ImmutableList.asImmutableList(list.toArray()) : list;
}
return construct(elements.toArray());
}
/**
* Returns an immutable list containing the given elements, in order.
*
* @throws NullPointerException if {@code elements} contains a null element
*/
public static ImmutableList copyOf(Iterator elements) {
// We special-case for 0 or 1 elements, but going further is madness.
if (!elements.hasNext()) {
return of();
}
E first = elements.next();
if (!elements.hasNext()) {
return of(first);
} else {
return new ImmutableList.Builder().add(first).addAll(elements).build();
}
}
/**
* Returns an immutable list containing the given elements, in order.
*
* @throws NullPointerException if {@code elements} contains a null element
* @since 3.0
*/
public static ImmutableList copyOf(E[] elements) {
switch (elements.length) {
case 0:
return of();
case 1:
return of(elements[0]);
default:
return construct(elements.clone());
}
}
/**
* Returns an immutable list containing the given elements, sorted according to their natural
* order. The sorting algorithm used is stable, so elements that compare as equal will stay in the
* order in which they appear in the input.
*
* If your data has no duplicates, or you wish to deduplicate elements, use {@code
* ImmutableSortedSet.copyOf(elements)}; if you want a {@code List} you can use its {@code
* asList()} view.
*
*
Java 8 users: If you want to convert a {@link java.util.stream.Stream} to a sorted
* {@code ImmutableList}, use {@code stream.sorted().collect(toImmutableList())}.
*
* @throws NullPointerException if any element in the input is null
* @since 21.0
*/
public static > ImmutableList sortedCopyOf(
Iterable elements) {
Comparable[] array = Iterables.toArray(elements, new Comparable[0]);
checkElementsNotNull((Object[]) array);
Arrays.sort(array);
return asImmutableList(array);
}
/**
* Returns an immutable list containing the given elements, in sorted order relative to the
* specified comparator. The sorting algorithm used is stable, so elements that compare as equal
* will stay in the order in which they appear in the input.
*
* If your data has no duplicates, or you wish to deduplicate elements, use {@code
* ImmutableSortedSet.copyOf(comparator, elements)}; if you want a {@code List} you can use its
* {@code asList()} view.
*
*
Java 8 users: If you want to convert a {@link java.util.stream.Stream} to a sorted
* {@code ImmutableList}, use {@code stream.sorted(comparator).collect(toImmutableList())}.
*
* @throws NullPointerException if any element in the input is null
* @since 21.0
*/
public static ImmutableList sortedCopyOf(
Comparator comparator, Iterable elements) {
checkNotNull(comparator);
@SuppressWarnings("unchecked") // all supported methods are covariant
E[] array = (E[]) Iterables.toArray(elements);
checkElementsNotNull(array);
Arrays.sort(array, comparator);
return asImmutableList(array);
}
/** Views the array as an immutable list. Checks for nulls; does not copy. */
private static ImmutableList construct(Object... elements) {
return asImmutableList(checkElementsNotNull(elements));
}
/**
* Views the array as an immutable list. Does not check for nulls; does not copy.
*
* The array must be internally created.
*/
static ImmutableList asImmutableList(Object[] elements) {
return asImmutableList(elements, elements.length);
}
/**
* Views the array as an immutable list. Copies if the specified range does not cover the complete
* array. Does not check for nulls.
*/
static ImmutableList asImmutableList( Object[] elements, int length) {
switch (length) {
case 0:
return of();
case 1:
/*
* requireNonNull is safe because the callers promise to put non-null objects in the first
* `length` array elements.
*/
@SuppressWarnings("unchecked") // our callers put only E instances into the array
E onlyElement = (E) requireNonNull(elements[0]);
return of(onlyElement);
default:
/*
* The suppression is safe because the callers promise to put non-null objects in the first
* `length` array elements.
*/
@SuppressWarnings("nullness")
Object[] elementsWithoutTrailingNulls =
length < elements.length ? Arrays.copyOf(elements, length) : elements;
return new RegularImmutableList(elementsWithoutTrailingNulls);
}
}
ImmutableList() {}
// This declaration is needed to make List.iterator() and
// ImmutableCollection.iterator() consistent.
@Override
public UnmodifiableIterator iterator() {
return listIterator();
}
@Override
public UnmodifiableListIterator listIterator() {
return listIterator(0);
}
@Override
public UnmodifiableListIterator listIterator(int index) {
return new AbstractIndexedListIterator(size(), index) {
@Override
protected E get(int index) {
return ImmutableList.this.get(index);
}
};
}
@Override
public void forEach(Consumer consumer) {
checkNotNull(consumer);
int n = size();
for (int i = 0; i < n; i++) {
consumer.accept(get(i));
}
}
@Override
public int indexOf(@CheckForNull Object object) {
return (object == null) ? -1 : Lists.indexOfImpl(this, object);
}
@Override
public int lastIndexOf(@CheckForNull Object object) {
return (object == null) ? -1 : Lists.lastIndexOfImpl(this, object);
}
@Override
public boolean contains(@CheckForNull Object object) {
return indexOf(object) >= 0;
}
// constrain the return type to ImmutableList
/**
* Returns an immutable list of the elements between the specified {@code fromIndex}, inclusive,
* and {@code toIndex}, exclusive. (If {@code fromIndex} and {@code toIndex} are equal, the empty
* immutable list is returned.)
*/
@Override
public ImmutableList subList(int fromIndex, int toIndex) {
checkPositionIndexes(fromIndex, toIndex, size());
int length = toIndex - fromIndex;
if (length == size()) {
return this;
} else if (length == 0) {
return of();
} else if (length == 1) {
return of(get(fromIndex));
} else {
return subListUnchecked(fromIndex, toIndex);
}
}
/**
* Called by the default implementation of {@link #subList} when {@code toIndex - fromIndex > 1},
* after index validation has already been performed.
*/
ImmutableList subListUnchecked(int fromIndex, int toIndex) {
return new SubList(fromIndex, toIndex - fromIndex);
}
class SubList extends ImmutableList {
final transient int offset;
final transient int length;
SubList(int offset, int length) {
this.offset = offset;
this.length = length;
}
@Override
public int size() {
return length;
}
@Override
public E get(int index) {
checkElementIndex(index, length);
return ImmutableList.this.get(index + offset);
}
@Override
public ImmutableList subList(int fromIndex, int toIndex) {
checkPositionIndexes(fromIndex, toIndex, length);
return ImmutableList.this.subList(fromIndex + offset, toIndex + offset);
}
@Override
boolean isPartialView() {
return true;
}
}
/**
* Guaranteed to throw an exception and leave the list unmodified.
*
* @throws UnsupportedOperationException always
* @deprecated Unsupported operation.
*/
@CanIgnoreReturnValue
@Deprecated
@Override
@DoNotCall("Always throws UnsupportedOperationException")
public final boolean addAll(int index, Collection newElements) {
throw new UnsupportedOperationException();
}
/**
* Guaranteed to throw an exception and leave the list unmodified.
*
* @throws UnsupportedOperationException always
* @deprecated Unsupported operation.
*/
@CanIgnoreReturnValue
@Deprecated
@Override
@DoNotCall("Always throws UnsupportedOperationException")
public final E set(int index, E element) {
throw new UnsupportedOperationException();
}
/**
* Guaranteed to throw an exception and leave the list unmodified.
*
* @throws UnsupportedOperationException always
* @deprecated Unsupported operation.
*/
@Deprecated
@Override
@DoNotCall("Always throws UnsupportedOperationException")
public final void add(int index, E element) {
throw new UnsupportedOperationException();
}
/**
* Guaranteed to throw an exception and leave the list unmodified.
*
* @throws UnsupportedOperationException always
* @deprecated Unsupported operation.
*/
@CanIgnoreReturnValue
@Deprecated
@Override
@DoNotCall("Always throws UnsupportedOperationException")
public final E remove(int index) {
throw new UnsupportedOperationException();
}
/**
* Guaranteed to throw an exception and leave the list unmodified.
*
* @throws UnsupportedOperationException always
* @deprecated Unsupported operation.
*/
@Deprecated
@Override
@DoNotCall("Always throws UnsupportedOperationException")
public final void replaceAll(UnaryOperator operator) {
throw new UnsupportedOperationException();
}
/**
* Guaranteed to throw an exception and leave the list unmodified.
*
* @throws UnsupportedOperationException always
* @deprecated Unsupported operation.
*/
@Deprecated
@Override
@DoNotCall("Always throws UnsupportedOperationException")
public final void sort( Comparator c) {
throw new UnsupportedOperationException();
}
/**
* Returns this list instance.
*
* @since 2.0
* @deprecated There is no reason to use this; it always returns {@code this}.
*/
@InlineMe(replacement = "this")
@Deprecated
@Override
public final ImmutableList asList() {
return this;
}
@Override
public Spliterator spliterator() {
return CollectSpliterators.indexed(size(), SPLITERATOR_CHARACTERISTICS, this::get);
}
@Override
int copyIntoArray( Object[] dst, int offset) {
// this loop is faster for RandomAccess instances, which ImmutableLists are
int size = size();
for (int i = 0; i < size; i++) {
dst[offset + i] = get(i);
}
return offset + size;
}
/**
* Returns a view of this immutable list in reverse order. For example, {@code ImmutableList.of(1,
* 2, 3).reverse()} is equivalent to {@code ImmutableList.of(3, 2, 1)}.
*
* @return a view of this immutable list in reverse order
* @since 7.0
*/
public ImmutableList reverse() {
return (size() <= 1) ? this : new ReverseImmutableList(this);
}
private static class ReverseImmutableList extends ImmutableList {
private final transient ImmutableList forwardList;
ReverseImmutableList(ImmutableList backingList) {
this.forwardList = backingList;
}
private int reverseIndex(int index) {
return (size() - 1) - index;
}
private int reversePosition(int index) {
return size() - index;
}
@Override
public ImmutableList reverse() {
return forwardList;
}
@Override
public boolean contains(@CheckForNull Object object) {
return forwardList.contains(object);
}
@Override
public int indexOf(@CheckForNull Object object) {
int index = forwardList.lastIndexOf(object);
return (index >= 0) ? reverseIndex(index) : -1;
}
@Override
public int lastIndexOf(@CheckForNull Object object) {
int index = forwardList.indexOf(object);
return (index >= 0) ? reverseIndex(index) : -1;
}
@Override
public ImmutableList subList(int fromIndex, int toIndex) {
checkPositionIndexes(fromIndex, toIndex, size());
return forwardList.subList(reversePosition(toIndex), reversePosition(fromIndex)).reverse();
}
@Override
public E get(int index) {
checkElementIndex(index, size());
return forwardList.get(reverseIndex(index));
}
@Override
public int size() {
return forwardList.size();
}
@Override
boolean isPartialView() {
return forwardList.isPartialView();
}
}
@Override
public boolean equals(@CheckForNull Object obj) {
return Lists.equalsImpl(this, obj);
}
@Override
public int hashCode() {
int hashCode = 1;
int n = size();
for (int i = 0; i < n; i++) {
hashCode = 31 * hashCode + get(i).hashCode();
hashCode = ~~hashCode;
// needed to deal with GWT integer overflow
}
return hashCode;
}
/*
* Serializes ImmutableLists as their logical contents. This ensures that
* implementation types do not leak into the serialized representation.
*/
@J2ktIncompatible // serialization
static class SerializedForm implements Serializable {
final Object[] elements;
SerializedForm(Object[] elements) {
this.elements = elements;
}
Object readResolve() {
return copyOf(elements);
}
private static final long serialVersionUID = 0;
}
@J2ktIncompatible // serialization
private void readObject(ObjectInputStream stream) throws InvalidObjectException {
throw new InvalidObjectException("Use SerializedForm");
}
@Override
@J2ktIncompatible // serialization
Object writeReplace() {
return new SerializedForm(toArray());
}
/**
* Returns a new builder. The generated builder is equivalent to the builder created by the {@link
* Builder} constructor.
*/
public static Builder builder() {
return new Builder();
}
/**
* Returns a new builder, expecting the specified number of elements to be added.
*
* If {@code expectedSize} is exactly the number of elements added to the builder before {@link
* Builder#build} is called, the builder is likely to perform better than an unsized {@link
* #builder()} would have.
*
*
It is not specified if any performance benefits apply if {@code expectedSize} is close to,
* but not exactly, the number of elements added to the builder.
*
* @since 23.1
*/
public static Builder builderWithExpectedSize(int expectedSize) {
checkNonnegative(expectedSize, "expectedSize");
return new ImmutableList.Builder(expectedSize);
}
/**
* A builder for creating immutable list instances, especially {@code public static final} lists
* ("constant lists"). Example:
*
* {@code
* public static final ImmutableList GOOGLE_COLORS
* = new ImmutableList.Builder()
* .addAll(WEBSAFE_COLORS)
* .add(new Color(0, 191, 255))
* .build();
* }
*
* Elements appear in the resulting list in the same order they were added to the builder.
*
*
Builder instances can be reused; it is safe to call {@link #build} multiple times to build
* multiple lists in series. Each new list contains all the elements of the ones created before
* it.
*
* @since 2.0
*/
public static final class Builder extends ImmutableCollection.Builder {
// The first `size` elements are non-null.
@VisibleForTesting Object[] contents;
private int size;
private boolean forceCopy;
/**
* Creates a new builder. The returned builder is equivalent to the builder generated by {@link
* ImmutableList#builder}.
*/
public Builder() {
this(DEFAULT_INITIAL_CAPACITY);
}
Builder(int capacity) {
this.contents = new Object[capacity];
this.size = 0;
}
private void getReadyToExpandTo(int minCapacity) {
if (contents.length < minCapacity) {
this.contents = Arrays.copyOf(contents, expandedCapacity(contents.length, minCapacity));
forceCopy = false;
} else if (forceCopy) {
contents = Arrays.copyOf(contents, contents.length);
forceCopy = false;
}
}
/**
* Adds {@code element} to the {@code ImmutableList}.
*
* @param element the element to add
* @return this {@code Builder} object
* @throws NullPointerException if {@code element} is null
*/
@CanIgnoreReturnValue
@Override
public Builder add(E element) {
checkNotNull(element);
getReadyToExpandTo(size + 1);
contents[size++] = element;
return this;
}
/**
* Adds each element of {@code elements} to the {@code ImmutableList}.
*
* @param elements the {@code Iterable} to add to the {@code ImmutableList}
* @return this {@code Builder} object
* @throws NullPointerException if {@code elements} is null or contains a null element
*/
@CanIgnoreReturnValue
@Override
public Builder add(E... elements) {
checkElementsNotNull(elements);
add(elements, elements.length);
return this;
}
private void add( Object[] elements, int n) {
getReadyToExpandTo(size + n);
/*
* The following call is not statically checked, since arraycopy accepts plain Object for its
* parameters. If it were statically checked, the checker would still be OK with it, since
* we're copying into a `contents` array whose type allows it to contain nulls. Still, it's
* worth noting that we promise not to put nulls into the array in the first `size` elements.
* We uphold that promise here because our callers promise that `elements` will not contain
* nulls in its first `n` elements.
*/
System.arraycopy(elements, 0, contents, size, n);
size += n;
}
/**
* Adds each element of {@code elements} to the {@code ImmutableList}.
*
* @param elements the {@code Iterable} to add to the {@code ImmutableList}
* @return this {@code Builder} object
* @throws NullPointerException if {@code elements} is null or contains a null element
*/
@CanIgnoreReturnValue
@Override
public Builder addAll(Iterable elements) {
checkNotNull(elements);
if (elements instanceof Collection) {
Collection collection = (Collection) elements;
getReadyToExpandTo(size + collection.size());
if (collection instanceof ImmutableCollection) {
ImmutableCollection immutableCollection = (ImmutableCollection) collection;
size = immutableCollection.copyIntoArray(contents, size);
return this;
}
}
super.addAll(elements);
return this;
}
/**
* Adds each element of {@code elements} to the {@code ImmutableList}.
*
* @param elements the {@code Iterator} to add to the {@code ImmutableList}
* @return this {@code Builder} object
* @throws NullPointerException if {@code elements} is null or contains a null element
*/
@CanIgnoreReturnValue
@Override
public Builder addAll(Iterator elements) {
super.addAll(elements);
return this;
}
@CanIgnoreReturnValue
Builder combine(Builder builder) {
checkNotNull(builder);
add(builder.contents, builder.size);
return this;
}
/**
* Returns a newly-created {@code ImmutableList} based on the contents of the {@code Builder}.
*/
@Override
public ImmutableList build() {
forceCopy = true;
return asImmutableList(contents, size);
}
}
}