public class ObjectSet<T>
extends java.lang.Object
implements java.lang.Iterable<T>
This class performs fast contains and remove (typically O(1), worst case O(n) but that is rare in practice). Add may be slightly slower, depending on hash collisions. Hashcodes are rehashed to reduce collisions and the need to resize. Load factors greater than 0.91 greatly increase the chances to resize to the next higher POT size.
Unordered sets and maps are not designed to provide especially fast iteration. Iteration is faster with OrderedSet and OrderedMap.
This implementation uses linear probing with the backward shift algorithm for removal. Hashcodes are rehashed using Fibonacci hashing, instead of the more common power-of-two mask, to better distribute poor hashCodes (see Malte Skarupke's blog post). Linear probing continues to work even when all hashCodes collide, just more slowly.
Modifier and Type | Class and Description |
---|---|
static class |
ObjectSet.ObjectSetIterator<K> |
Modifier and Type | Field and Description |
---|---|
protected int |
mask
A bitmask used to confine hashcodes to the size of the table.
|
protected int |
shift
|
int |
size |
Constructor and Description |
---|
ObjectSet()
Creates a new set with an initial capacity of 51 and a load factor of 0.8.
|
ObjectSet(int initialCapacity)
Creates a new set with a load factor of 0.8.
|
ObjectSet(int initialCapacity,
float loadFactor)
Creates a new set with the specified initial capacity and load factor.
|
ObjectSet(ObjectSet<? extends T> set)
Creates a new set identical to the specified set.
|
Modifier and Type | Method and Description |
---|---|
boolean |
add(T key)
Returns true if the key was not already in the set.
|
void |
addAll(Array<? extends T> array) |
void |
addAll(Array<? extends T> array,
int offset,
int length) |
void |
addAll(ObjectSet<T> set) |
boolean |
addAll(T... array) |
boolean |
addAll(T[] array,
int offset,
int length) |
void |
clear()
Clears the set, leaving the backing arrays at the current capacity.
|
void |
clear(int maximumCapacity)
Clears the set and reduces the size of the backing arrays to be the specified capacity / loadFactor, if they are larger.
|
boolean |
contains(T key) |
void |
ensureCapacity(int additionalCapacity)
Increases the size of the backing array to accommodate the specified number of additional items / loadFactor.
|
boolean |
equals(java.lang.Object obj) |
T |
first() |
T |
get(T key) |
int |
hashCode() |
boolean |
isEmpty()
Returns true if the set is empty.
|
ObjectSet.ObjectSetIterator<T> |
iterator()
Returns an iterator for the keys in the set.
|
boolean |
notEmpty()
Returns true if the set has one or more items.
|
protected int |
place(T item)
Returns an index >= 0 and <=
mask for the specified item . |
boolean |
remove(T key)
Returns true if the key was removed.
|
void |
shrink(int maximumCapacity)
Reduces the size of the backing arrays to be the specified capacity / loadFactor, or less.
|
java.lang.String |
toString() |
java.lang.String |
toString(java.lang.String separator) |
static <T> ObjectSet<T> |
with(T... array) |
public int size
protected int shift
place(Object)
to bit shift the upper bits of a long
into a usable range (>= 0 and <=
mask
). The shift can be negative, which is convenient to match the number of bits in mask: if mask is a 7-bit
number, a shift of -7 shifts the upper 7 bits into the lowest 7 positions. This class sets the shift > 32 and < 64,
which if used with an int will still move the upper bits of an int to the lower bits due to Java's implicit modulus on
shifts.
mask
can also be used to mask the low bits of a number, which may be faster for some hashcodes, if
place(Object)
is overridden.
protected int mask
place(Object)
is overriden, this can be used instead of shift
to isolate usable bits of a
hash.public ObjectSet()
public ObjectSet(int initialCapacity)
initialCapacity
- If not a power of two, it is increased to the next nearest power of two.public ObjectSet(int initialCapacity, float loadFactor)
initialCapacity
- If not a power of two, it is increased to the next nearest power of two.protected int place(T item)
mask
for the specified item
.
The default implementation uses Fibonacci hashing on the item's Object.hashCode()
: the hashcode is multiplied by a
long constant (2 to the 64th, divided by the golden ratio) then the uppermost bits are shifted into the lowest positions to
obtain an index in the desired range. Multiplication by a long may be slower than int (eg on GWT) but greatly improves
rehashing, allowing even very poor hashcodes, such as those that only differ in their upper bits, to be used without high
collision rates. Fibonacci hashing has increased collision rates when all or most hashcodes are multiples of larger
Fibonacci numbers (see Malte
Skarupke's blog post).
This method can be overriden to customizing hashing. This may be useful eg in the unlikely event that most hashcodes are
Fibonacci numbers, if keys provide poor or incorrect hashcodes, or to simplify hashing if keys provide high quality
hashcodes and don't need Fibonacci hashing: return item.hashCode() & mask;
public boolean add(T key)
public boolean addAll(T... array)
public boolean addAll(T[] array, int offset, int length)
public boolean remove(T key)
public boolean notEmpty()
public boolean isEmpty()
public void shrink(int maximumCapacity)
public void clear(int maximumCapacity)
public void clear()
clear(int)
can be used to reduce the capacity.public boolean contains(T key)
public T first()
public void ensureCapacity(int additionalCapacity)
public int hashCode()
hashCode
in class java.lang.Object
public boolean equals(java.lang.Object obj)
equals
in class java.lang.Object
public java.lang.String toString()
toString
in class java.lang.Object
public java.lang.String toString(java.lang.String separator)
public ObjectSet.ObjectSetIterator<T> iterator()
If Collections.allocateIterators
is false, the same iterator instance is returned each time this method is called.
Use the ObjectSet.ObjectSetIterator
constructor for nested or multithreaded iteration.
iterator
in interface java.lang.Iterable<T>
public static <T> ObjectSet<T> with(T... array)