java.lang.Object
- java.util.AbstractCollection<E>
- - java.util.AbstractSet<E>
  - - com.google.common.collect.CompactHashSet<E>

All Implemented Interfaces:

java.io.Serializable, java.lang.Iterable<E>, java.util.Collection<E>, java.util.Set<E>

Direct Known Subclasses:

CompactLinkedHashSet
```
@GwtIncompatible
class CompactHashSet<E>
extends java.util.AbstractSet<E>
implements java.io.Serializable
```
CompactHashSet is an implementation of a Set. All optional operations (adding and removing) are supported. The elements can be any objects.
contains(x), add(x) and 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.
Unlike java.util.HashSet, iteration is only proportional to the actual size(), which is optimal, and not the size of the internal hashtable, which could be much larger than size(). Furthermore, this structure only depends on a fixed number of arrays; add(x) operations do not create objects for the garbage collector to deal with, and for every element added, the garbage collector will have to traverse 1.5 references on average, in the marking phase, not 5.0 as in java.util.HashSet.
If there are no removals, then iteration order is the same as insertion order. Any removal invalidates any ordering guarantees.
This class should not be assumed to be universally superior to java.util.HashSet. 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.

Field Summary

Fields
Modifier and Type	Field	Description
`(package private) static int`	`DEFAULT_SIZE`
`(package private) java.lang.Object[]`	`elements`	The elements contained in the set, in the range of [0, size()).
`private long[]`	`entries`	Contains the logical entries, in the range of [0, size()).
`private static long`	`HASH_MASK`	Bitmask that selects the high 32 bits.
`private static float`	`LOAD_FACTOR`
`(package private) int`	`modCount`	Keeps track of modifications of this set, to make it possible to throw ConcurrentModificationException in the iterator.
`private static long`	`NEXT_MASK`	Bitmask that selects the low 32 bits.
`private int`	`size`	The number of elements contained in the set.
`private int[]`	`table`	The hashtable.
`(package private) static int`	`UNSET`

Constructor Summary

Constructors
Constructor	Description
`CompactHashSet()`	Constructs a new empty instance of `CompactHashSet`.
`CompactHashSet(int expectedSize)`	Constructs a new instance of `CompactHashSet` with the specified capacity.

Method Summary

All Methods Static Methods Instance Methods Concrete Methods
Modifier and Type	Method	Description
`boolean`	`add(E object)`
`(package private) int`	`adjustAfterRemove(int indexBeforeRemove, int indexRemoved)`	Updates the index an iterator is pointing to after a call to remove: returns the index of the entry that should be looked at after a removal on indexRemoved, with indexBeforeRemove as the index that was the next entry that would be looked at.
`(package private) void`	`allocArrays()`	Handle lazy allocation of arrays.
`void`	`clear()`
`boolean`	`contains(java.lang.Object object)`
`static <E> CompactHashSet<E>`	`create()`	Creates an empty `CompactHashSet` instance.
`static <E> CompactHashSet<E>`	`create(E... elements)`	Creates a mutable `CompactHashSet` instance containing the given elements in unspecified order.
`static <E> CompactHashSet<E>`	`create(java.util.Collection<? extends E> collection)`	Creates a mutable `CompactHashSet` instance containing the elements of the given collection in unspecified order.
`static <E> CompactHashSet<E>`	`createWithExpectedSize(int expectedSize)`	Creates a `CompactHashSet` instance, with a high enough "initial capacity" that it should hold `expectedSize` elements without growth.
`(package private) int`	`firstEntryIndex()`
`void`	`forEach(java.util.function.Consumer<? super E> action)`
`private static int`	`getHash(long entry)`
`private static int`	`getNext(long entry)`	Returns the index, or UNSET if the pointer is "null"
`(package private) int`	`getSuccessor(int entryIndex)`
`private int`	`hashTableMask()`
`(package private) void`	`init(int expectedSize)`	Pseudoconstructor for serialization support.
`(package private) void`	`insertEntry(int entryIndex, E object, int hash)`	Creates a fresh entry with the specified object at the specified position in the entry arrays.
`boolean`	`isEmpty()`
`java.util.Iterator<E>`	`iterator()`
`(package private) void`	`moveLastEntry(int dstIndex)`	Moves the last entry in the entry array into `dstIndex`, and nulls out its old position.
`(package private) boolean`	`needsAllocArrays()`	Returns whether arrays need to be allocated.
`private static long[]`	`newEntries(int size)`
`private static int[]`	`newTable(int size)`
`private void`	`readObject(java.io.ObjectInputStream stream)`
`boolean`	`remove(java.lang.Object object)`
`private boolean`	`remove(java.lang.Object object, int hash)`
`(package private) void`	`resizeEntries(int newCapacity)`	Resizes the internal entries array to the specified capacity, which may be greater or less than the current capacity.
`private void`	`resizeMeMaybe(int newSize)`	Resizes the entries storage if necessary.
`private void`	`resizeTable(int newCapacity)`
`int`	`size()`
`java.util.Spliterator<E>`	`spliterator()`
`private static long`	`swapNext(long entry, int newNext)`	Returns a new entry value by changing the "next" index of an existing entry
`java.lang.Object[]`	`toArray()`
`<T> T[]`	`toArray(T[] a)`
`void`	`trimToSize()`	Ensures that this `CompactHashSet` has the smallest representation in memory, given its current size.
`private void`	`writeObject(java.io.ObjectOutputStream stream)`

Methods inherited from class java.util.AbstractSet
equals, hashCode, removeAll

Methods inherited from class java.util.AbstractCollection
addAll, containsAll, retainAll, toString

Methods inherited from class java.lang.Object
clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Methods inherited from interface java.util.Collection
parallelStream, removeIf, stream, toArray

Methods inherited from interface java.util.Set
addAll, containsAll, retainAll

- Field Detail
  - LOAD_FACTOR
```
private static final float LOAD_FACTOR
```
    See Also:
    
    Constant Field Values
  - NEXT_MASK
```
private static final long NEXT_MASK
```
    Bitmask that selects the low 32 bits.
    
    See Also:
    
    Constant Field Values
  - HASH_MASK
```
private static final long HASH_MASK
```
    Bitmask that selects the high 32 bits.
    
    See Also:
    
    Constant Field Values
  - DEFAULT_SIZE
```
static final int DEFAULT_SIZE
```
    See Also:
    
    Constant Field Values
  - UNSET
```
static final int UNSET
```
    See Also:
    
    Constant Field Values
  - table
```
private transient int[] table
```
    The hashtable. Its values are indexes to the elements and entries arrays.
    Currently, the UNSET value means "null pointer", and any non negative value x is the actual index.
    Its size must be a power of two.
  - entries
```
private transient long[] entries
```
    Contains the logical entries, in the range of [0, size()). The high 32 bits of each long is the smeared hash of the element, whereas the low 32 bits is the "next" pointer (pointing to the next entry in the bucket chain). The pointers in [size(), entries.length) are all "null" (UNSET).
  - elements
```
transient java.lang.Object[] elements
```
    The elements contained in the set, in the range of [0, size()). The elements in [size(), elements.length) are all null.
  - modCount
```
transient int modCount
```
    Keeps track of modifications of this set, to make it possible to throw ConcurrentModificationException in the iterator. Note that we choose not to make this volatile, so we do less of a "best effort" to track such errors, for better performance.
  - size
```
private transient int size
```
    The number of elements contained in the set.
- Constructor Detail
  - CompactHashSet
```
CompactHashSet()
```
    Constructs a new empty instance of CompactHashSet.
  - CompactHashSet
```
CompactHashSet(int expectedSize)
```
    Constructs a new instance of CompactHashSet with the specified capacity.
    
    Parameters:
    
    expectedSize - the initial capacity of this CompactHashSet.
- Method Detail
  - create
```
public static <E> CompactHashSet<E> create()
```
    Creates an empty CompactHashSet instance.
  - create
```
public static <E> CompactHashSet<E> create(java.util.Collection<? extends E> collection)
```
    Creates a mutable CompactHashSet instance containing the elements of the given collection in unspecified order.
    
    Parameters:
    
    collection - the elements that the set should contain
    
    Returns:
    
    a new CompactHashSet containing those elements (minus duplicates)
  - create
```
public static <E> CompactHashSet<E> create(E... elements)
```
    Creates a mutable CompactHashSet instance containing the given elements in unspecified order.
    
    Parameters:
    
    elements - the elements that the set should contain
    
    Returns:
    
    a new CompactHashSet containing those elements (minus duplicates)
  - createWithExpectedSize
```
public static <E> CompactHashSet<E> createWithExpectedSize(int expectedSize)
```
    Creates a CompactHashSet instance, with a high enough "initial capacity" that it should hold expectedSize elements without growth.
    
    Parameters:
    
    expectedSize - the number of elements you expect to add to the returned set
    
    Returns:
    
    a new, empty CompactHashSet with enough capacity to hold expectedSize elements without resizing
    
    Throws:
    
    java.lang.IllegalArgumentException - if expectedSize is negative
  - init
```
void init(int expectedSize)
```
    Pseudoconstructor for serialization support.
  - needsAllocArrays
```
boolean needsAllocArrays()
```
    Returns whether arrays need to be allocated.
  - allocArrays
```
void allocArrays()
```
    Handle lazy allocation of arrays.
  - newTable
```
private static int[] newTable(int size)
```
  - newEntries
```
private static long[] newEntries(int size)
```
  - hashTableMask
```
private int hashTableMask()
```
  - getHash
```
private static int getHash(long entry)
```
  - getNext
```
private static int getNext(long entry)
```
    Returns the index, or UNSET if the pointer is "null"
  - swapNext
```
private static long swapNext(long entry,
                             int newNext)
```
    Returns a new entry value by changing the "next" index of an existing entry
  - add
```
public boolean add(E object)
```
    Specified by:
    
    add in interface java.util.Collection<E>
    
    Specified by:
    
    add in interface java.util.Set<E>
    
    Overrides:
    
    add in class java.util.AbstractCollection<E>
  - insertEntry
```
void insertEntry(int entryIndex,
                 E object,
                 int hash)
```
    Creates a fresh entry with the specified object at the specified position in the entry arrays.
  - resizeMeMaybe
```
private void resizeMeMaybe(int newSize)
```
    Resizes the entries storage if necessary.
  - resizeEntries
```
void resizeEntries(int newCapacity)
```
    Resizes the internal entries array to the specified capacity, which may be greater or less than the current capacity.
  - resizeTable
```
private void resizeTable(int newCapacity)
```
  - contains
```
public boolean contains(java.lang.Object object)
```
    Specified by:
    
    contains in interface java.util.Collection<E>
    
    Specified by:
    
    contains in interface java.util.Set<E>
    
    Overrides:
    
    contains in class java.util.AbstractCollection<E>
  - remove
```
public boolean remove(java.lang.Object object)
```
    Specified by:
    
    remove in interface java.util.Collection<E>
    
    Specified by:
    
    remove in interface java.util.Set<E>
    
    Overrides:
    
    remove in class java.util.AbstractCollection<E>
  - remove
```
private boolean remove(java.lang.Object object,
                       int hash)
```
  - moveLastEntry
```
void moveLastEntry(int dstIndex)
```
    Moves the last entry in the entry array into dstIndex, and nulls out its old position.
  - firstEntryIndex
```
int firstEntryIndex()
```
  - getSuccessor
```
int getSuccessor(int entryIndex)
```
  - adjustAfterRemove
```
int adjustAfterRemove(int indexBeforeRemove,
                      int indexRemoved)
```
    Updates the index an iterator is pointing to after a call to remove: returns the index of the entry that should be looked at after a removal on indexRemoved, with indexBeforeRemove as the index that *was* the next entry that would be looked at.
  - iterator
```
public java.util.Iterator<E> iterator()
```
    Specified by:
    
    iterator in interface java.util.Collection<E>
    
    Specified by:
    
    iterator in interface java.lang.Iterable<E>
    
    Specified by:
    
    iterator in interface java.util.Set<E>
    
    Specified by:
    
    iterator in class java.util.AbstractCollection<E>
  - spliterator
```
public java.util.Spliterator<E> spliterator()
```
    Specified by:
    
    spliterator in interface java.util.Collection<E>
    
    Specified by:
    
    spliterator in interface java.lang.Iterable<E>
    
    Specified by:
    
    spliterator in interface java.util.Set<E>
  - forEach
```
public void forEach(java.util.function.Consumer<? super E> action)
```
    Specified by:
    
    forEach in interface java.lang.Iterable<E>
  - size
```
public int size()
```
    Specified by:
    
    size in interface java.util.Collection<E>
    
    Specified by:
    
    size in interface java.util.Set<E>
    
    Specified by:
    
    size in class java.util.AbstractCollection<E>
  - isEmpty
```
public boolean isEmpty()
```
    Specified by:
    
    isEmpty in interface java.util.Collection<E>
    
    Specified by:
    
    isEmpty in interface java.util.Set<E>
    
    Overrides:
    
    isEmpty in class java.util.AbstractCollection<E>
  - toArray
```
public java.lang.Object[] toArray()
```
    Specified by:
    
    toArray in interface java.util.Collection<E>
    
    Specified by:
    
    toArray in interface java.util.Set<E>
    
    Overrides:
    
    toArray in class java.util.AbstractCollection<E>
  - toArray
```
public <T> T[] toArray(T[] a)
```
    Specified by:
    
    toArray in interface java.util.Collection<E>
    
    Specified by:
    
    toArray in interface java.util.Set<E>
    
    Overrides:
    
    toArray in class java.util.AbstractCollection<E>
  - trimToSize
```
public void trimToSize()
```
    Ensures that this CompactHashSet has the smallest representation in memory, given its current size.
  - clear
```
public void clear()
```
    Specified by:
    
    clear in interface java.util.Collection<E>
    
    Specified by:
    
    clear in interface java.util.Set<E>
    
    Overrides:
    
    clear in class java.util.AbstractCollection<E>
  - writeObject
```
private void writeObject(java.io.ObjectOutputStream stream)
                  throws java.io.IOException
```
    Throws:
    
    java.io.IOException
  - readObject
```
private void readObject(java.io.ObjectInputStream stream)
                 throws java.io.IOException,
                        java.lang.ClassNotFoundException
```
    Throws:
    
    java.io.IOException
    
    java.lang.ClassNotFoundException

Class CompactHashSet<E>

Field Summary

Constructor Summary

Method Summary

Methods inherited from class java.util.AbstractSet

Methods inherited from class java.util.AbstractCollection

Methods inherited from class java.lang.Object

Methods inherited from interface java.util.Collection

Methods inherited from interface java.util.Set

Field Detail

LOAD_FACTOR

NEXT_MASK

HASH_MASK

DEFAULT_SIZE

UNSET

table

entries

elements

modCount

size

Constructor Detail

CompactHashSet

CompactHashSet

Method Detail

create

create

create

createWithExpectedSize

init

needsAllocArrays

allocArrays

newTable

newEntries

hashTableMask

getHash

getNext

swapNext

add

insertEntry

resizeMeMaybe

resizeEntries

resizeTable

contains

remove

remove

moveLastEntry

firstEntryIndex

getSuccessor

adjustAfterRemove

iterator

spliterator

forEach

size

isEmpty

toArray

toArray

trimToSize

clear

writeObject

readObject