com.badlogic.gdx.utils

Class ObjectIntMap<K>

java.lang.Object

com.badlogic.gdx.utils.ObjectIntMap<K>

All Implemented Interfaces:

java.lang.Iterable<ObjectIntMap.Entry<K>>

public class ObjectIntMap<K>
extends java.lang.Object
implements java.lang.Iterable<ObjectIntMap.Entry<K>>

An unordered map where the keys are objects and the values are unboxed ints. 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.

Author:

Nathan Sweet, Tommy Ettinger

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	ObjectIntMap.Entries<K>
static class	ObjectIntMap.Entry<K>
static class	ObjectIntMap.Keys<K>
static class	ObjectIntMap.Values

Field Summary

Fields

Modifier and Type	Field and Description
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).
int	size

Constructor Summary

Constructors

Constructor and Description
ObjectIntMap() Creates a new map with an initial capacity of 51 and a load factor of 0.8.
ObjectIntMap(int initialCapacity) Creates a new map with a load factor of 0.8.
ObjectIntMap(int initialCapacity, float loadFactor) Creates a new map with the specified initial capacity and load factor.
ObjectIntMap(ObjectIntMap<? extends K> map) Creates a new map identical to the specified map.

Method Summary

Modifier and Type	Method and Description
void	clear()
void	clear(int maximumCapacity) Clears the map and reduces the size of the backing arrays to be the specified capacity / loadFactor, if they are larger.
boolean	containsKey(K key)
boolean	containsValue(int value) Returns true if the specified value is in the map.
void	ensureCapacity(int additionalCapacity) Increases the size of the backing array to accommodate the specified number of additional items / loadFactor.
ObjectIntMap.Entries<K>	entries() Returns an iterator for the entries in the map.
boolean	equals(java.lang.Object obj)
K	findKey(int value) Returns the key for the specified value, or null if it is not in the map.
int	get(K key, int defaultValue) Returns the value for the specified key, or the default value if the key is not in the map.
int	getAndIncrement(K key, int defaultValue, int increment) Returns the key's current value and increments the stored value.
int	hashCode()
boolean	isEmpty() Returns true if the map is empty.
ObjectIntMap.Entries<K>	iterator()
ObjectIntMap.Keys<K>	keys() Returns an iterator for the keys in the map.
boolean	notEmpty() Returns true if the map has one or more items.
protected int	place(K item) Returns an index >= 0 and <= mask for the specified item.
void	put(K key, int value) Doesn't return a value, unlike other maps.
void	putAll(ObjectIntMap<? extends K> map)
int	remove(K key, int defaultValue)
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)
ObjectIntMap.Values	values() Returns an iterator for the values in the map.

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Methods inherited from interface java.lang.Iterable

forEach, spliterator

Field Detail

size

public int size

shift

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.

mask

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 overriden, this can be used instead of shift to isolate usable bits of a hash.

Constructor Detail

ObjectIntMap

public ObjectIntMap()

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

ObjectIntMap

public ObjectIntMap(int initialCapacity)

Creates a new map with a load factor of 0.8.

Parameters:

initialCapacity - If not a power of two, it is increased to the next nearest power of two.

ObjectIntMap

public ObjectIntMap(int initialCapacity,
                    float loadFactor)

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

Parameters:

initialCapacity - If not a power of two, it is increased to the next nearest power of two.

ObjectIntMap

public ObjectIntMap(ObjectIntMap<? extends K> map)

Creates a new map identical to the specified map.

Method Detail

place

protected int place(K 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 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;

put

public void put(K key,
                int value)

Doesn't return a value, unlike other maps.

putAll

public void putAll(ObjectIntMap<? extends K> map)

get

public int get(K key,
               int defaultValue)

Returns the value for the specified key, or the default value if the key is not in the map.

getAndIncrement

public int getAndIncrement(K key,
                           int defaultValue,
                           int increment)

Returns the key's current value and increments the stored value. If the key is not in the map, defaultValue + increment is put into the map and defaultValue is returned.

remove

public int remove(K key,
                  int defaultValue)

notEmpty

public boolean notEmpty()

Returns true if the map has one or more items.

isEmpty

public boolean isEmpty()

Returns true if the map is empty.

shrink

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 map contains more items than the specified capacity, the next highest power of two capacity is used instead.

clear

public void clear(int maximumCapacity)

Clears the map and reduces the size of the backing arrays to be the specified capacity / loadFactor, if they are larger.

clear

public void clear()

containsValue

public boolean containsValue(int value)

Returns true if the specified value is in the map. Note this traverses the entire map and compares every value, which may be an expensive operation.

containsKey

public boolean containsKey(K key)

findKey

@Null
public K findKey(int value)

Returns the key for the specified value, or null if it is not in the map. Note this traverses the entire map and compares every value, which may be an expensive operation.

ensureCapacity

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.

hashCode

public int hashCode()

Overrides:

hashCode in class java.lang.Object

equals

public boolean equals(java.lang.Object obj)

Overrides:

equals in class java.lang.Object

toString

public java.lang.String toString(java.lang.String separator)

toString

public java.lang.String toString()

Overrides:

toString in class java.lang.Object

iterator

public ObjectIntMap.Entries<K> iterator()

Specified by:

iterator in interface java.lang.Iterable<ObjectIntMap.Entry<K>>

entries

public ObjectIntMap.Entries<K> entries()

Returns an iterator for the entries in the map. Remove is supported.

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

values

public ObjectIntMap.Values values()

Returns an iterator for the values in the map. Remove is supported.

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

keys

public ObjectIntMap.Keys<K> keys()

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

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