com.google.common.collect.CompactLinkedHashSet Maven / Gradle / Ivy
/*
* Copyright (C) 2012 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.checkNotNull;
import com.google.common.annotations.GwtIncompatible;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.Spliterator;
import java.util.Spliterators;
import java.util.function.Consumer;
import org.checkerframework.checker.nullness.compatqual.MonotonicNonNullDecl;
/**
* CompactLinkedHashSet is an implementation of a Set, which a predictable iteration order that
* matches the insertion order. All optional operations (adding and removing) are supported. All
* elements, including {@code null}, are permitted.
*
* {@code contains(x)}, {@code add(x)} and {@code remove(x)}, are all (expected and amortized)
* constant time operations. Expected in the hashtable sense (depends on the hash function doing a
* good job of distributing the elements to the buckets to a distribution not far from uniform), and
* amortized since some operations can trigger a hash table resize.
*
*
This implementation consumes significantly less memory than {@code java.util.LinkedHashSet} or
* even {@code java.util.HashSet}, and places considerably less load on the garbage collector. Like
* {@code java.util.LinkedHashSet}, it offers insertion-order iteration, with identical behavior.
*
*
This class should not be assumed to be universally superior to {@code
* java.util.LinkedHashSet}. Generally speaking, this class reduces object allocation and memory
* consumption at the price of moderately increased constant factors of CPU. Only use this class
* when there is a specific reason to prioritize memory over CPU.
*
* @author Louis Wasserman
*/
@GwtIncompatible // not worth using in GWT for now
class CompactLinkedHashSet extends CompactHashSet {
/**
* Creates an empty {@code CompactLinkedHashSet} instance.
*/
public static CompactLinkedHashSet create() {
return new CompactLinkedHashSet();
}
/**
* Creates a mutable {@code CompactLinkedHashSet} instance containing the elements
* of the given collection in the order returned by the collection's iterator.
*
* @param collection the elements that the set should contain
* @return a new {@code CompactLinkedHashSet} containing those elements (minus duplicates)
*/
public static CompactLinkedHashSet create(Collection collection) {
CompactLinkedHashSet set = createWithExpectedSize(collection.size());
set.addAll(collection);
return set;
}
/**
* Creates a {@code CompactLinkedHashSet} instance containing the given elements in
* unspecified order.
*
* @param elements the elements that the set should contain
* @return a new {@code CompactLinkedHashSet} containing those elements (minus duplicates)
*/
public static CompactLinkedHashSet create(E... elements) {
CompactLinkedHashSet set = createWithExpectedSize(elements.length);
Collections.addAll(set, elements);
return set;
}
/**
* Creates a {@code CompactLinkedHashSet} instance, with a high enough "initial capacity"
* that it should hold {@code expectedSize} elements without rebuilding internal
* data structures.
*
* @param expectedSize the number of elements you expect to add to the returned set
* @return a new, empty {@code CompactLinkedHashSet} with enough capacity to hold {@code
* expectedSize} elements without resizing
* @throws IllegalArgumentException if {@code expectedSize} is negative
*/
public static CompactLinkedHashSet createWithExpectedSize(int expectedSize) {
return new CompactLinkedHashSet(expectedSize);
}
private static final int ENDPOINT = -2;
// TODO(user): predecessors and successors should be collocated (reducing cache misses).
// Might also explore collocating all of [hash, next, predecessor, succesor] fields of an
// entry in a *single* long[], though that reduces the maximum size of the set by a factor of 2
/**
* Pointer to the predecessor of an entry in insertion order. ENDPOINT indicates a node is the
* first node in insertion order; all values at indices ≥ {@link #size()} are UNSET.
*/
@MonotonicNonNullDecl private transient int[] predecessor;
/**
* Pointer to the successor of an entry in insertion order. ENDPOINT indicates a node is the last
* node in insertion order; all values at indices ≥ {@link #size()} are UNSET.
*/
@MonotonicNonNullDecl private transient int[] successor;
private transient int firstEntry;
private transient int lastEntry;
CompactLinkedHashSet() {
super();
}
CompactLinkedHashSet(int expectedSize) {
super(expectedSize);
}
@Override
void init(int expectedSize, float loadFactor) {
super.init(expectedSize, loadFactor);
this.predecessor = new int[expectedSize];
this.successor = new int[expectedSize];
Arrays.fill(predecessor, UNSET);
Arrays.fill(successor, UNSET);
firstEntry = ENDPOINT;
lastEntry = ENDPOINT;
}
private void succeeds(int pred, int succ) {
if (pred == ENDPOINT) {
firstEntry = succ;
} else {
successor[pred] = succ;
}
if (succ == ENDPOINT) {
lastEntry = pred;
} else {
predecessor[succ] = pred;
}
}
@Override
void insertEntry(int entryIndex, E object, int hash) {
super.insertEntry(entryIndex, object, hash);
succeeds(lastEntry, entryIndex);
succeeds(entryIndex, ENDPOINT);
}
@Override
void moveEntry(int dstIndex) {
int srcIndex = size() - 1;
super.moveEntry(dstIndex);
succeeds(predecessor[dstIndex], successor[dstIndex]);
if (srcIndex != dstIndex) {
succeeds(predecessor[srcIndex], dstIndex);
succeeds(dstIndex, successor[srcIndex]);
}
predecessor[srcIndex] = UNSET;
successor[srcIndex] = UNSET;
}
@Override
public void clear() {
super.clear();
firstEntry = ENDPOINT;
lastEntry = ENDPOINT;
Arrays.fill(predecessor, UNSET);
Arrays.fill(successor, UNSET);
}
@Override
void resizeEntries(int newCapacity) {
super.resizeEntries(newCapacity);
int oldCapacity = predecessor.length;
predecessor = Arrays.copyOf(predecessor, newCapacity);
successor = Arrays.copyOf(successor, newCapacity);
if (oldCapacity < newCapacity) {
Arrays.fill(predecessor, oldCapacity, newCapacity, UNSET);
Arrays.fill(successor, oldCapacity, newCapacity, UNSET);
}
}
@Override
public Object[] toArray() {
return ObjectArrays.toArrayImpl(this);
}
@Override
public T[] toArray(T[] a) {
return ObjectArrays.toArrayImpl(this, a);
}
@Override
int firstEntryIndex() {
return firstEntry;
}
@Override
int adjustAfterRemove(int indexBeforeRemove, int indexRemoved) {
return (indexBeforeRemove == size()) ? indexRemoved : indexBeforeRemove;
}
@Override
int getSuccessor(int entryIndex) {
return successor[entryIndex];
}
@Override public Spliterator spliterator() {
return Spliterators.spliterator(this, Spliterator.ORDERED | Spliterator.DISTINCT);
}
@Override public void forEach(Consumer action) {
checkNotNull(action);
for (int i = firstEntry; i != ENDPOINT; i = successor[i]) {
action.accept((E) elements[i]);
}
}
}