com.google.common.primitives.ImmutableIntArray Maven / Gradle / Ivy
/*
* Copyright (C) 2017 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.primitives;
import static com.google.common.base.Preconditions.checkArgument;
import com.google.common.annotations.Beta;
import com.google.common.annotations.GwtCompatible;
import com.google.common.base.Preconditions;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import com.google.errorprone.annotations.CheckReturnValue;
import com.google.errorprone.annotations.Immutable;
import java.io.Serializable;
import java.util.AbstractList;
import java.util.Arrays;
import java.util.Collection;
import java.util.List;
import java.util.RandomAccess;
import org.checkerframework.checker.nullness.compatqual.NullableDecl;
/**
* An immutable array of {@code int} values, with an API resembling {@link List}.
*
* Advantages compared to {@code int[]}:
*
*
* - All the many well-known advantages of immutability (read Effective Java, third
* edition, Item 17).
*
- Has the value-based (not identity-based) {@link #equals}, {@link #hashCode}, and {@link
* #toString} behavior you expect
*
- Offers useful operations beyond just {@code get} and {@code length}, so you don't have to
* hunt through classes like {@link Arrays} and {@link Ints} for them.
*
- Supports a copy-free {@link #subArray} view, so methods that accept this type don't need to
* add overloads that accept start and end indexes.
*
- Access to all collection-based utilities via {@link #asList} (though at the cost of
* allocating garbage).
*
*
* Disadvantages compared to {@code int[]}:
*
*
* - Memory footprint has a fixed overhead (about 24 bytes per instance).
*
- Some construction use cases force the data to be copied (though several construction
* APIs are offered that don't).
*
- Can't be passed directly to methods that expect {@code int[]} (though the most common
* utilities do have replacements here).
*
- Dependency on {@code com.google.common} / Guava.
*
*
* Advantages compared to {@link com.google.common.collect.ImmutableList ImmutableList}{@code
* }:
*
*
* - Improved memory compactness and locality
*
- Can be queried without allocating garbage
*
*
* Disadvantages compared to {@code ImmutableList}:
*
*
* - Can't be passed directly to methods that expect {@code Iterable}, {@code Collection}, or
* {@code List} (though the most common utilities do have replacements here, and there is a
* lazy {@link #asList} view).
*
*
* @since 22.0
*/
@Beta
@GwtCompatible
@Immutable
public final class ImmutableIntArray implements Serializable {
private static final ImmutableIntArray EMPTY = new ImmutableIntArray(new int[0]);
/** Returns the empty array. */
public static ImmutableIntArray of() {
return EMPTY;
}
/** Returns an immutable array containing a single value. */
public static ImmutableIntArray of(int e0) {
return new ImmutableIntArray(new int[] {e0});
}
/** Returns an immutable array containing the given values, in order. */
public static ImmutableIntArray of(int e0, int e1) {
return new ImmutableIntArray(new int[] {e0, e1});
}
/** Returns an immutable array containing the given values, in order. */
public static ImmutableIntArray of(int e0, int e1, int e2) {
return new ImmutableIntArray(new int[] {e0, e1, e2});
}
/** Returns an immutable array containing the given values, in order. */
public static ImmutableIntArray of(int e0, int e1, int e2, int e3) {
return new ImmutableIntArray(new int[] {e0, e1, e2, e3});
}
/** Returns an immutable array containing the given values, in order. */
public static ImmutableIntArray of(int e0, int e1, int e2, int e3, int e4) {
return new ImmutableIntArray(new int[] {e0, e1, e2, e3, e4});
}
/** Returns an immutable array containing the given values, in order. */
public static ImmutableIntArray of(int e0, int e1, int e2, int e3, int e4, int e5) {
return new ImmutableIntArray(new int[] {e0, e1, e2, e3, e4, e5});
}
// TODO(kevinb): go up to 11?
/**
* Returns an immutable array containing the given values, in order.
*
* The array {@code rest} must not be longer than {@code Integer.MAX_VALUE - 1}.
*/
// Use (first, rest) so that `of(someIntArray)` won't compile (they should use copyOf), which is
// okay since we have to copy the just-created array anyway.
public static ImmutableIntArray of(int first, int... rest) {
checkArgument(
rest.length <= Integer.MAX_VALUE - 1, "the total number of elements must fit in an int");
int[] array = new int[rest.length + 1];
array[0] = first;
System.arraycopy(rest, 0, array, 1, rest.length);
return new ImmutableIntArray(array);
}
/** Returns an immutable array containing the given values, in order. */
public static ImmutableIntArray copyOf(int[] values) {
return values.length == 0 ? EMPTY : new ImmutableIntArray(Arrays.copyOf(values, values.length));
}
/** Returns an immutable array containing the given values, in order. */
public static ImmutableIntArray copyOf(Collection values) {
return values.isEmpty() ? EMPTY : new ImmutableIntArray(Ints.toArray(values));
}
/**
* Returns an immutable array containing the given values, in order.
*
* Performance note: this method delegates to {@link #copyOf(Collection)} if {@code
* values} is a {@link Collection}. Otherwise it creates a {@link #builder} and uses {@link
* Builder#addAll(Iterable)}, with all the performance implications associated with that.
*/
public static ImmutableIntArray copyOf(Iterable values) {
if (values instanceof Collection) {
return copyOf((Collection) values);
}
return builder().addAll(values).build();
}
/**
* Returns a new, empty builder for {@link ImmutableIntArray} instances, sized to hold up to
* {@code initialCapacity} values without resizing. The returned builder is not thread-safe.
*
* Performance note: When feasible, {@code initialCapacity} should be the exact number
* of values that will be added, if that knowledge is readily available. It is better to guess a
* value slightly too high than slightly too low. If the value is not exact, the {@link
* ImmutableIntArray} that is built will very likely occupy more memory than strictly necessary;
* to trim memory usage, build using {@code builder.build().trimmed()}.
*/
public static Builder builder(int initialCapacity) {
checkArgument(initialCapacity >= 0, "Invalid initialCapacity: %s", initialCapacity);
return new Builder(initialCapacity);
}
/**
* Returns a new, empty builder for {@link ImmutableIntArray} instances, with a default initial
* capacity. The returned builder is not thread-safe.
*
*
Performance note: The {@link ImmutableIntArray} that is built will very likely occupy
* more memory than necessary; to trim memory usage, build using {@code
* builder.build().trimmed()}.
*/
public static Builder builder() {
return new Builder(10);
}
/**
* A builder for {@link ImmutableIntArray} instances; obtained using {@link
* ImmutableIntArray#builder}.
*/
@CanIgnoreReturnValue
public static final class Builder {
private int[] array;
private int count = 0; // <= array.length
Builder(int initialCapacity) {
array = new int[initialCapacity];
}
/**
* Appends {@code value} to the end of the values the built {@link ImmutableIntArray} will
* contain.
*/
public Builder add(int value) {
ensureRoomFor(1);
array[count] = value;
count += 1;
return this;
}
/**
* Appends {@code values}, in order, to the end of the values the built {@link
* ImmutableIntArray} will contain.
*/
public Builder addAll(int[] values) {
ensureRoomFor(values.length);
System.arraycopy(values, 0, array, count, values.length);
count += values.length;
return this;
}
/**
* Appends {@code values}, in order, to the end of the values the built {@link
* ImmutableIntArray} will contain.
*/
public Builder addAll(Iterable values) {
if (values instanceof Collection) {
return addAll((Collection) values);
}
for (Integer value : values) {
add(value);
}
return this;
}
/**
* Appends {@code values}, in order, to the end of the values the built {@link
* ImmutableIntArray} will contain.
*/
public Builder addAll(Collection values) {
ensureRoomFor(values.size());
for (Integer value : values) {
array[count++] = value;
}
return this;
}
/**
* Appends {@code values}, in order, to the end of the values the built {@link
* ImmutableIntArray} will contain.
*/
public Builder addAll(ImmutableIntArray values) {
ensureRoomFor(values.length());
System.arraycopy(values.array, values.start, array, count, values.length());
count += values.length();
return this;
}
private void ensureRoomFor(int numberToAdd) {
int newCount = count + numberToAdd; // TODO(kevinb): check overflow now?
if (newCount > array.length) {
int[] newArray = new int[expandedCapacity(array.length, newCount)];
System.arraycopy(array, 0, newArray, 0, count);
this.array = newArray;
}
}
// Unfortunately this is pasted from ImmutableCollection.Builder.
private static int expandedCapacity(int oldCapacity, int minCapacity) {
if (minCapacity < 0) {
throw new AssertionError("cannot store more than MAX_VALUE elements");
}
// careful of overflow!
int newCapacity = oldCapacity + (oldCapacity >> 1) + 1;
if (newCapacity < minCapacity) {
newCapacity = Integer.highestOneBit(minCapacity - 1) << 1;
}
if (newCapacity < 0) {
newCapacity = Integer.MAX_VALUE; // guaranteed to be >= newCapacity
}
return newCapacity;
}
/**
* Returns a new immutable array. The builder can continue to be used after this call, to append
* more values and build again.
*
* Performance note: the returned array is backed by the same array as the builder, so
* no data is copied as part of this step, but this may occupy more memory than strictly
* necessary. To copy the data to a right-sized backing array, use {@code .build().trimmed()}.
*/
@CheckReturnValue
public ImmutableIntArray build() {
return count == 0 ? EMPTY : new ImmutableIntArray(array, 0, count);
}
}
// Instance stuff here
// The array is never mutated after storing in this field and the construction strategies ensure
// it doesn't escape this class
@SuppressWarnings("Immutable")
private final int[] array;
/*
* TODO(kevinb): evaluate the trade-offs of going bimorphic to save these two fields from most
* instances. Note that the instances that would get smaller are the right set to care about
* optimizing, because the rest have the option of calling `trimmed`.
*/
private final transient int start; // it happens that we only serialize instances where this is 0
private final int end; // exclusive
private ImmutableIntArray(int[] array) {
this(array, 0, array.length);
}
private ImmutableIntArray(int[] array, int start, int end) {
this.array = array;
this.start = start;
this.end = end;
}
/** Returns the number of values in this array. */
public int length() {
return end - start;
}
/** Returns {@code true} if there are no values in this array ({@link #length} is zero). */
public boolean isEmpty() {
return end == start;
}
/**
* Returns the {@code int} value present at the given index.
*
* @throws IndexOutOfBoundsException if {@code index} is negative, or greater than or equal to
* {@link #length}
*/
public int get(int index) {
Preconditions.checkElementIndex(index, length());
return array[start + index];
}
/**
* Returns the smallest index for which {@link #get} returns {@code target}, or {@code -1} if no
* such index exists. Equivalent to {@code asList().indexOf(target)}.
*/
public int indexOf(int target) {
for (int i = start; i < end; i++) {
if (array[i] == target) {
return i - start;
}
}
return -1;
}
/**
* Returns the largest index for which {@link #get} returns {@code target}, or {@code -1} if no
* such index exists. Equivalent to {@code asList().lastIndexOf(target)}.
*/
public int lastIndexOf(int target) {
for (int i = end - 1; i >= start; i--) {
if (array[i] == target) {
return i - start;
}
}
return -1;
}
/**
* Returns {@code true} if {@code target} is present at any index in this array. Equivalent to
* {@code asList().contains(target)}.
*/
public boolean contains(int target) {
return indexOf(target) >= 0;
}
/** Returns a new, mutable copy of this array's values, as a primitive {@code int[]}. */
public int[] toArray() {
return Arrays.copyOfRange(array, start, end);
}
/**
* Returns a new immutable array containing the values in the specified range.
*
*
Performance note: The returned array has the same full memory footprint as this one
* does (no actual copying is performed). To reduce memory usage, use {@code subArray(start,
* end).trimmed()}.
*/
public ImmutableIntArray subArray(int startIndex, int endIndex) {
Preconditions.checkPositionIndexes(startIndex, endIndex, length());
return startIndex == endIndex
? EMPTY
: new ImmutableIntArray(array, start + startIndex, start + endIndex);
}
/**
* Returns an immutable view of this array's values as a {@code List}; note that {@code
* int} values are boxed into {@link Integer} instances on demand, which can be very expensive.
* The returned list should be used once and discarded. For any usages beyond that, pass the
* returned list to {@link com.google.common.collect.ImmutableList#copyOf(Collection)
* ImmutableList.copyOf} and use that list instead.
*/
public List asList() {
/*
* Typically we cache this kind of thing, but much repeated use of this view is a performance
* anti-pattern anyway. If we cache, then everyone pays a price in memory footprint even if
* they never use this method.
*/
return new AsList(this);
}
static class AsList extends AbstractList implements RandomAccess, Serializable {
private final ImmutableIntArray parent;
private AsList(ImmutableIntArray parent) {
this.parent = parent;
}
// inherit: isEmpty, containsAll, toArray x2, {,list,spl}iterator, stream, forEach, mutations
@Override
public int size() {
return parent.length();
}
@Override
public Integer get(int index) {
return parent.get(index);
}
@Override
public boolean contains(Object target) {
return indexOf(target) >= 0;
}
@Override
public int indexOf(Object target) {
return target instanceof Integer ? parent.indexOf((Integer) target) : -1;
}
@Override
public int lastIndexOf(Object target) {
return target instanceof Integer ? parent.lastIndexOf((Integer) target) : -1;
}
@Override
public List subList(int fromIndex, int toIndex) {
return parent.subArray(fromIndex, toIndex).asList();
}
@Override
public boolean equals(@NullableDecl Object object) {
if (object instanceof AsList) {
AsList that = (AsList) object;
return this.parent.equals(that.parent);
}
// We could delegate to super now but it would still box too much
if (!(object instanceof List)) {
return false;
}
List that = (List) object;
if (this.size() != that.size()) {
return false;
}
int i = parent.start;
// Since `that` is very likely RandomAccess we could avoid allocating this iterator...
for (Object element : that) {
if (!(element instanceof Integer) || parent.array[i++] != (Integer) element) {
return false;
}
}
return true;
}
// Because we happen to use the same formula. If that changes, just don't override this.
@Override
public int hashCode() {
return parent.hashCode();
}
@Override
public String toString() {
return parent.toString();
}
}
/**
* Returns {@code true} if {@code object} is an {@code ImmutableIntArray} containing the same
* values as this one, in the same order.
*/
@Override
public boolean equals(@NullableDecl Object object) {
if (object == this) {
return true;
}
if (!(object instanceof ImmutableIntArray)) {
return false;
}
ImmutableIntArray that = (ImmutableIntArray) object;
if (this.length() != that.length()) {
return false;
}
for (int i = 0; i < length(); i++) {
if (this.get(i) != that.get(i)) {
return false;
}
}
return true;
}
/** Returns an unspecified hash code for the contents of this immutable array. */
@Override
public int hashCode() {
int hash = 1;
for (int i = start; i < end; i++) {
hash *= 31;
hash += Ints.hashCode(array[i]);
}
return hash;
}
/**
* Returns a string representation of this array in the same form as {@link
* Arrays#toString(int[])}, for example {@code "[1, 2, 3]"}.
*/
@Override
public String toString() {
if (isEmpty()) {
return "[]";
}
StringBuilder builder = new StringBuilder(length() * 5); // rough estimate is fine
builder.append('[').append(array[start]);
for (int i = start + 1; i < end; i++) {
builder.append(", ").append(array[i]);
}
builder.append(']');
return builder.toString();
}
/**
* Returns an immutable array containing the same values as {@code this} array. This is logically
* a no-op, and in some circumstances {@code this} itself is returned. However, if this instance
* is a {@link #subArray} view of a larger array, this method will copy only the appropriate range
* of values, resulting in an equivalent array with a smaller memory footprint.
*/
public ImmutableIntArray trimmed() {
return isPartialView() ? new ImmutableIntArray(toArray()) : this;
}
private boolean isPartialView() {
return start > 0 || end < array.length;
}
Object writeReplace() {
return trimmed();
}
Object readResolve() {
return isEmpty() ? EMPTY : this;
}
}