com.esotericsoftware.kryo.util

Class IdentityMap<K,V>

java.lang.Object

com.esotericsoftware.kryo.util.IdentityMap<K,V>

public class IdentityMap<K,V>
extends Object

An unordered map that uses identity comparison for keys. This implementation is a cuckoo hash map using 3 hashes, random walking, and a small stash for problematic keys. Null keys are not allowed. Null values are allowed. No allocation is done except when growing the table size.

This map performs very fast get, containsKey, and remove (typically O(1), worst case O(log(n))). Put may be a bit slower, depending on hash collisions. Load factors greater than 0.91 greatly increase the chances the map will have to rehash to the next higher POT size.

Author:

Nathan Sweet

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	IdentityMap.Entries<K,V>
static class	IdentityMap.Entry<K,V>
static class	IdentityMap.Keys<K>
static class	IdentityMap.Values<V>

Field Summary

Fields

Modifier and Type	Field and Description
int	size

Constructor Summary

Constructors

Constructor and Description
IdentityMap() Creates a new map with an initial capacity of 32 and a load factor of 0.8.
IdentityMap(int initialCapacity) Creates a new map with a load factor of 0.8.
IdentityMap(int initialCapacity, float loadFactor) Creates a new map with the specified initial capacity and load factor.

Method Summary

Methods

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 if they are larger.
boolean	containsKey(K key)
boolean	containsValue(Object value, boolean identity) Returns true if the specified value is in the map.
void	ensureCapacity(int additionalCapacity) Increases the size of the backing array to acommodate the specified number of additional items.
IdentityMap.Entries<K,V>	entries() Returns an iterator for the entries in the map.
K	findKey(Object value, boolean identity) Returns the key for the specified value, or null if it is not in the map.
V	get(K key)
V	get(K key, V defaultValue)
IdentityMap.Keys<K>	keys() Returns an iterator for the keys in the map.
V	put(K key, V value)
V	remove(K key)
void	shrink(int maximumCapacity) Reduces the size of the backing arrays to be the specified capacity or less.
String	toString()
IdentityMap.Values<V>	values() Returns an iterator for the values in the map.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Field Detail

size

public int size

Constructor Detail

IdentityMap

public IdentityMap()

Creates a new map with an initial capacity of 32 and a load factor of 0.8. This map will hold 25 items before growing the backing table.

IdentityMap

public IdentityMap(int initialCapacity)

Creates a new map with a load factor of 0.8. This map will hold initialCapacity * 0.8 items before growing the backing table.

IdentityMap

public IdentityMap(int initialCapacity,
           float loadFactor)

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

Method Detail

put

public V put(K key,
    V value)

get

public V get(K key)

get

public V get(K key,
    V defaultValue)

remove

public V remove(K key)

shrink

public void shrink(int maximumCapacity)

Reduces the size of the backing arrays to be the specified capacity or less. If the capacity is already less, nothing is done. If the map contains more items than the specified capacity, nothing is done.

clear

public void clear(int maximumCapacity)

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

clear

public void clear()

containsValue

public boolean containsValue(Object value,
                    boolean identity)

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.

Parameters:

identity - If true, uses == to compare the specified value with values in the map. If false, uses Object.equals(Object).

containsKey

public boolean containsKey(K key)

findKey

public K findKey(Object value,
        boolean identity)

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.

Parameters:

identity - If true, uses == to compare the specified value with values in the map. If false, uses Object.equals(Object).

ensureCapacity

public void ensureCapacity(int additionalCapacity)

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

toString

public String toString()

Overrides:

toString in class Object

entries

public IdentityMap.Entries<K,V> entries()

Returns an iterator for the entries in the map. Remove is supported. Note that the same iterator instance is returned each time this method is called. Use the IdentityMap.Entries constructor for nested or multithreaded iteration.

values

public IdentityMap.Values<V> values()

Returns an iterator for the values in the map. Remove is supported. Note that the same iterator instance is returned each time this method is called. Use the IdentityMap.Entries constructor for nested or multithreaded iteration.

keys

public IdentityMap.Keys<K> keys()

Returns an iterator for the keys in the map. Remove is supported. Note that the same iterator instance is returned each time this method is called. Use the IdentityMap.Entries constructor for nested or multithreaded iteration.