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com.badlogic.gdx.utils

public Class ObjectSet<T>

extends Object
implements Iterable<T>
Class Inheritance
All Implemented Interfaces
java.lang.Iterable
Known Direct Subclasses
com.badlogic.gdx.utils.OrderedSet, com.badlogic.gdx.utils.IdentitySet
Imports
java.util.Arrays, .Iterator, .NoSuchElementException, com.badlogic.gdx.math.MathUtils

An unordered set where the keys are objects. Null keys are not allowed. No allocation is done except when growing the table size.

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.

Authors
Nathan Sweet, Tommy Ettinger

Nested and Inner Type Summary

Modifier and TypeClass and Description
public static class

Field Summary

Modifier and TypeField and Description
private transient ObjectSet.ObjectSetIterator<K>
private transient ObjectSet.ObjectSetIterator<K>
pack-priv T[]
pack-priv float
protected int
mask

A bitmask used to confine hashcodes to the size of the table.

protected int
shift

Used by place(Object) to bit shift the upper bits of a long into a usable range (>= 0 and <= mask).

public int
pack-priv int

Constructor Summary

AccessConstructor and Description
public
ObjectSet()

Creates a new set with an initial capacity of 51 and a load factor of 0.8.

public
ObjectSet(int
The backing array size is initialCapacity / loadFactor, increased to the next power of two.
initialCapacity
)

Creates a new set with a load factor of 0.8.

public
ObjectSet(int
The backing array size is initialCapacity / loadFactor, increased to the next power of two.
initialCapacity
,
float loadFactor)

Creates a new set with the specified initial capacity and load factor.

public
ObjectSet(ObjectSet<? extends T> set)

Creates a new set identical to the specified set.

Method Summary

Modifier and TypeMethod and Description
public boolean
add(T key)

Returns true if the key was added to the set or false if it was already in the set.

public void
addAll(Array<? extends T> array)

public void
addAll(Array<? extends T> array, int offset, int length)

public boolean
addAll(T... array)

public boolean
addAll(T[] array, int offset, int length)

public void
addAll(ObjectSet<T> set)

private void
addResize(T key)

Skips checks for existing keys, doesn't increment size.

public 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.

public void
clear()

Clears the set, leaving the backing arrays at the current capacity.

public boolean
contains(T key)

public void
ensureCapacity(int additionalCapacity)

Increases the size of the backing array to accommodate the specified number of additional items / loadFactor.

public boolean
equals(Object obj)

Overrides java.lang.Object.equals.

Indicates whether some other object is "equal to" this one.

public T
public T
get(T key)

public int
hashCode()

Overrides java.lang.Object.hashCode.

Returns a hash code value for this object.

public boolean
isEmpty()

Returns true if the set is empty.

public ObjectSet.ObjectSetIterator<T>
iterator()

Implements java.lang.Iterable.iterator.

Returns an iterator for the keys in the set.

pack-priv int
locateKey(T key)

Returns the index of the key if already present, else -(index + 1) for the next empty index.

public 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.

public boolean
remove(T key)

Returns true if the key was removed.

private void
resize(int newSize)

public void
shrink(int maximumCapacity)

Reduces the size of the backing arrays to be the specified capacity / loadFactor, or less.

pack-priv static int
tableSize(int capacity, float loadFactor)

public String
toString()

Overrides java.lang.Object.toString.

Returns a string representation of the object.

public String
toString(String separator)

public static <T> ObjectSet<T>
with(T... array)

Inherited from java.lang.Object:
clonefinalizegetClassnotifynotifyAllwaitwaitwait

Field Detail

iterator1back to summary
private transient ObjectSet.ObjectSetIterator<K> iterator1
iterator2back to summary
private transient ObjectSet.ObjectSetIterator<K> iterator2
keyTableback to summary
pack-priv T[] keyTable
loadFactorback to summary
pack-priv float loadFactor
maskback to summary
protected int mask

A bitmask used to confine hashcodes to the size of the table. Must be all 1 bits in its low positions, ie a power of two minus 1. If place(Object) is overridden, this can be used instead of shift to isolate usable bits of a hash.

shiftback to summary
protected int shift

Used by 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.

sizeback to summary
public int size
thresholdback to summary
pack-priv int threshold

Constructor Detail

ObjectSetback to summary
public ObjectSet()

Creates a new set with an initial capacity of 51 and a load factor of 0.8.

ObjectSetback to summary
public ObjectSet(int initialCapacity)

Creates a new set with a load factor of 0.8.

Parameters
initialCapacity:int

The backing array size is initialCapacity / loadFactor, increased to the next power of two.

ObjectSetback to summary
public ObjectSet(int initialCapacity, float loadFactor)

Creates a new set with the specified initial capacity and load factor. This set will hold initialCapacity items before growing the backing table.

Parameters
initialCapacity:int

The backing array size is initialCapacity / loadFactor, increased to the next power of two.

ObjectSetback to summary
public ObjectSet(ObjectSet<? extends T> set)

Creates a new set identical to the specified set.

Method Detail

addback to summary
public boolean add(T key)

Returns true if the key was added to the set or false if it was already in the set. If this set already contains the key, the call leaves the set unchanged and returns false.

addAllback to summary
public void addAll(Array<? extends T> array)
addAllback to summary
public void addAll(Array<? extends T> array, int offset, int length)
addAllback to summary
public boolean addAll(T... array)
addAllback to summary
public boolean addAll(T[] array, int offset, int length)
addAllback to summary
public void addAll(ObjectSet<T> set)
addResizeback to summary
private void addResize(T key)

Skips checks for existing keys, doesn't increment size.

clearback to summary
public 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. The reduction is done by allocating new arrays, though for large arrays this can be faster than clearing the existing array.

clearback to summary
public void clear()

Clears the set, leaving the backing arrays at the current capacity. When the capacity is high and the population is low, iteration can be unnecessarily slow. clear(int) can be used to reduce the capacity.

containsback to summary
public boolean contains(T key)
ensureCapacityback to summary
public void ensureCapacity(int additionalCapacity)

Increases the size of the backing array to accommodate the specified number of additional items / loadFactor. Useful before adding many items to avoid multiple backing array resizes.

equalsback to summary
public boolean equals(Object obj)

Overrides java.lang.Object.equals.

Doc from java.lang.Object.equals.

Indicates whether some other object is "equal to" this one.

The equals method implements an equivalence relation on non-null object references:

  • It is reflexive: for any non-null reference value x, x.equals(x) should return true.
  • It is symmetric: for any non-null reference values x and y, x.equals(y) should return true if and only if y.equals(x) returns true.
  • It is transitive: for any non-null reference values x, y, and z, if x.equals(y) returns true and y.equals(z) returns true, then x.equals(z) should return true.
  • It is consistent: for any non-null reference values x and y, multiple invocations of x.equals(y) consistently return true or consistently return false, provided no information used in equals comparisons on the objects is modified.
  • For any non-null reference value x, x.equals(null) should return false.

An equivalence relation partitions the elements it operates on into equivalence classes; all the members of an equivalence class are equal to each other. Members of an equivalence class are substitutable for each other, at least for some purposes.

firstback to summary
public T first()
getback to summary
public T get(T key)
Annotations
@Null
hashCodeback to summary
public int hashCode()

Overrides java.lang.Object.hashCode.

Doc from java.lang.Object.hashCode.

Returns a hash code value for this object. This method is supported for the benefit of hash tables such as those provided by java.util.HashMap.

The general contract of hashCode is:

  • Whenever it is invoked on the same object more than once during an execution of a Java application, the hashCode method must consistently return the same integer, provided no information used in equals comparisons on the object is modified. This integer need not remain consistent from one execution of an application to another execution of the same application.
  • If two objects are equal according to the equals method, then calling the hashCode method on each of the two objects must produce the same integer result.
  • It is not required that if two objects are unequal according to the equals method, then calling the hashCode method on each of the two objects must produce distinct integer results. However, the programmer should be aware that producing distinct integer results for unequal objects may improve the performance of hash tables.
isEmptyback to summary
public boolean isEmpty()

Returns true if the set is empty.

iteratorback to summary
public ObjectSet.ObjectSetIterator<T> iterator()

Implements java.lang.Iterable.iterator.

Returns an iterator for the keys in the set. Remove is supported.

If Collections#allocateIterators is false, the same iterator instance is returned each time this method is called. Use the ObjectSetIterator constructor for nested or multithreaded iteration.

locateKeyback to summary
pack-priv int locateKey(T key)

Returns the index of the key if already present, else -(index + 1) for the next empty index. This can be overridden in this pacakge to compare for equality differently than Object#equals(Object).

notEmptyback to summary
public boolean notEmpty()

Returns true if the set has one or more items.

placeback to summary
protected int place(T item)

Returns an index >= 0 and <= 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 overridden 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;

removeback to summary
public boolean remove(T key)

Returns true if the key was removed.

resizeback to summary
private void resize(int newSize)
shrinkback to summary
public void shrink(int maximumCapacity)

Reduces the size of the backing arrays to be the specified capacity / loadFactor, or less. If the capacity is already less, nothing is done. If the set contains more items than the specified capacity, the next highest power of two capacity is used instead.

tableSizeback to summary
pack-priv static int tableSize(int capacity, float loadFactor)
toStringback to summary
public String toString()

Overrides java.lang.Object.toString.

Doc from java.lang.Object.toString.

Returns a string representation of the object. Satisfying this method's contract implies a non-null result must be returned.

toStringback to summary
public String toString(String separator)
withback to summary
public static <T> ObjectSet<T> with(T... array)
com.badlogic.gdx.utils back to summary

public Class ObjectSet.ObjectSetIterator<K>

extends Object
implements Iterable<K>, Iterator<K>
Class Inheritance
All Implemented Interfaces
java.util.Iterator, java.lang.Iterable
Known Direct Subclasses
com.badlogic.gdx.utils.OrderedSet.OrderedSetIterator

Field Summary

Modifier and TypeField and Description
pack-priv int
public boolean
pack-priv int
pack-priv final ObjectSet<K>
pack-priv boolean

Constructor Summary

AccessConstructor and Description
public

Method Summary

Modifier and TypeMethod and Description
private void
public boolean
hasNext()

Implements java.util.Iterator.hasNext.

Returns true if the iteration has more elements.

public ObjectSet.ObjectSetIterator<K>
iterator()

Implements java.lang.Iterable.iterator.

Returns an iterator over elements of type T.

public K
next()

Implements java.util.Iterator.next.

Returns the next element in the iteration.

public void
remove()

Overrides default java.util.Iterator.remove.

Removes from the underlying collection the last element returned by this iterator (optional operation).

public void
public Array<K>
toArray(Array<K> array)

Adds the remaining values to the array.

public Array<K>
toArray()

Returns a new array containing the remaining values.

Inherited from java.lang.Object:
cloneequalsfinalizegetClasshashCodenotifynotifyAlltoStringwaitwaitwait

Field Detail

currentIndexback to summary
pack-priv int currentIndex
hasNextback to summary
public boolean hasNext
nextIndexback to summary
pack-priv int nextIndex
setback to summary
pack-priv final ObjectSet<K> set
validback to summary
pack-priv boolean valid

Constructor Detail

ObjectSetIteratorback to summary
public ObjectSetIterator(ObjectSet<K> set)

Method Detail

findNextIndexback to summary
private void findNextIndex()
hasNextback to summary
public boolean hasNext()

Implements java.util.Iterator.hasNext.

Doc from java.util.Iterator.hasNext.

Returns true if the iteration has more elements. (In other words, returns true if next would return an element rather than throwing an exception.)

iteratorback to summary
public ObjectSet.ObjectSetIterator<K> iterator()

Implements java.lang.Iterable.iterator.

Doc from java.lang.Iterable.iterator.

Returns an iterator over elements of type T.

nextback to summary
public K next()

Implements java.util.Iterator.next.

Doc from java.util.Iterator.next.

Returns the next element in the iteration.

removeback to summary
public void remove()

Overrides default java.util.Iterator.remove.

Doc from java.util.Iterator.remove.

Removes from the underlying collection the last element returned by this iterator (optional operation). This method can be called only once per call to next.

The behavior of an iterator is unspecified if the underlying collection is modified while the iteration is in progress in any way other than by calling this method, unless an overriding class has specified a concurrent modification policy.

The behavior of an iterator is unspecified if this method is called after a call to the forEachRemaining method.

resetback to summary
public void reset()
toArrayback to summary
public Array<K> toArray(Array<K> array)

Adds the remaining values to the array.

toArrayback to summary
public Array<K> toArray()

Returns a new array containing the remaining values.