ArrayMap

public final class ArrayMap extends Object
implements Map<K, V>

ArrayMap is a generic key->value mapping data structure that is designed to be more memory efficient than a traditional HashMap. It keeps its mappings in an array data structure -- an integer array of hash codes for each item, and an Object array of the key/value pairs. This allows it to avoid having to create an extra object for every entry put in to the map, and it also tries to control the growth of the size of these arrays more aggressively (since growing them only requires copying the entries in the array, not rebuilding a hash map).

Note that this implementation is not intended to be appropriate for data structures that may contain large numbers of items. It is generally slower than a traditional HashMap, since lookups require a binary search and adds and removes require inserting and deleting entries in the array. For containers holding up to hundreds of items, the performance difference is not significant, less than 50%.

Because this container is intended to better balance memory use, unlike most other standard Java containers it will shrink its array as items are removed from it. Currently you have no control over this shrinking -- if you set a capacity and then remove an item, it may reduce the capacity to better match the current size. In the future an explicit call to set the capacity should turn off this aggressive shrinking behavior.

Public Constructor Summary

	ArrayMap() Create a new empty ArrayMap.
	ArrayMap(int capacity) Create a new ArrayMap with a given initial capacity.
	ArrayMap(ArrayMap map) Create a new ArrayMap with the mappings from the given ArrayMap.

Public Method Summary

void	clear() Make the array map empty.
boolean	containsAll(Collection<?> collection) Determine if the array map contains all of the keys in the given collection.
boolean	containsKey(Object key) Check whether a key exists in the array.
boolean	containsValue(Object value) Check whether a value exists in the array.
void	ensureCapacity(int minimumCapacity) Ensure the array map can hold at least minimumCapacity items.
Set<Entry<K, V>>	entrySet() Return a Set for iterating over and interacting with all mappings in the array map.
boolean	equals(Object object) This implementation returns false if the object is not a map, or if the maps have different sizes.
V	get(Object key) Retrieve a value from the array.
int	hashCode()
boolean	isEmpty() Return true if the array map contains no items.
K	keyAt(int index) Return the key at the given index in the array.
Set<K>	keySet() Return a Set for iterating over and interacting with all keys in the array map.
V	put(K key, V value) Add a new value to the array map.
void	putAll(ArrayMap<? extends K, ? extends V> array) Perform a put(Object, Object) of all key/value pairs in array
void	putAll(Map<? extends K, ? extends V> map) Perform a put(Object, Object) of all key/value pairs in map
V	remove(Object key) Remove an existing key from the array map.
boolean	removeAll(Collection<?> collection) Remove all keys in the array map that exist in the given collection.
V	removeAt(int index) Remove the key/value mapping at the given index.
boolean	retainAll(Collection<?> collection) Remove all keys in the array map that do not exist in the given collection.
V	setValueAt(int index, V value) Set the value at a given index in the array.
int	size() Return the number of items in this array map.
String	toString() This implementation composes a string by iterating over its mappings.
V	valueAt(int index) Return the value at the given index in the array.
Collection<V>	values() Return a Collection for iterating over and interacting with all values in the array map.

Inherited Method Summary

From class java.lang.Object

Object	clone()
boolean	equals(Object arg0)
void	finalize()
final Class<?>	getClass()
int	hashCode()
final void	notify()
final void	notifyAll()
String	toString()
final void	wait(long arg0, int arg1)
final void	wait(long arg0)
final void	wait()

From interface java.util.Map

abstract void	clear()
V	compute(K arg0, BiFunction<? super K, ? super V, ? extends V> arg1)
V	computeIfAbsent(K arg0, Function<? super K, ? extends V> arg1)
V	computeIfPresent(K arg0, BiFunction<? super K, ? super V, ? extends V> arg1)
abstract boolean	containsKey(Object arg0)
abstract boolean	containsValue(Object arg0)
abstract Set<Entry<K, V>>	entrySet()
abstract boolean	equals(Object arg0)
void	forEach(BiConsumer<? super K, ? super V> arg0)
abstract V	get(Object arg0)
V	getOrDefault(Object arg0, V arg1)
abstract int	hashCode()
abstract boolean	isEmpty()
abstract Set<K>	keySet()
V	merge(K arg0, V arg1, BiFunction<? super V, ? super V, ? extends V> arg2)
abstract V	put(K arg0, V arg1)
abstract void	putAll(Map<? extends K, ? extends V> arg0)
V	putIfAbsent(K arg0, V arg1)
boolean	remove(Object arg0, Object arg1)
abstract V	remove(Object arg0)
boolean	replace(K arg0, V arg1, V arg2)
V	replace(K arg0, V arg1)
void	replaceAll(BiFunction<? super K, ? super V, ? extends V> arg0)
abstract int	size()
abstract Collection<V>	values()

Public Constructors

public ArrayMap ()

Create a new empty ArrayMap. The default capacity of an array map is 0, and will grow once items are added to it.

public ArrayMap (int capacity)

Create a new ArrayMap with a given initial capacity.

Parameters

capacity

public ArrayMap (ArrayMap map)

Create a new ArrayMap with the mappings from the given ArrayMap.

Parameters

map

Public Methods

public void clear ()

Make the array map empty. All storage is released.

public boolean containsAll (Collection<?> collection)

Determine if the array map contains all of the keys in the given collection.

Parameters

collection	The collection whose contents are to be checked against.

Returns

• Returns true if this array map contains a key for every entry in collection, else returns false.

public boolean containsKey (Object key)

Check whether a key exists in the array.

Parameters

key	The key to search for.

Returns

• Returns true if the key exists, else false.

public boolean containsValue (Object value)

Check whether a value exists in the array. This requires a linear search through the entire array.

Parameters

value	The value to search for.

Returns

• Returns true if the value exists, else false.

public void ensureCapacity (int minimumCapacity)

Ensure the array map can hold at least minimumCapacity items.

Parameters

minimumCapacity

public Set<Entry<K, V>> entrySet ()

Return a Set for iterating over and interacting with all mappings in the array map.

Note: this is a very inefficient way to access the array contents, it requires generating a number of temporary objects.

Note:

the semantics of this Set are subtly different than that of a HashMap: most important, the Map.Entry object returned by its iterator is a single object that exists for the entire iterator, so you can not hold on to it after calling Iterator.next.

public boolean equals (Object object)

This implementation returns false if the object is not a map, or if the maps have different sizes. Otherwise, for each key in this map, values of both maps are compared. If the values for any key are not equal, the method returns false, otherwise it returns true.

Parameters

object

public V get (Object key)

Retrieve a value from the array.

Parameters

key	The key of the value to retrieve.

Returns

• Returns the value associated with the given key, or null if there is no such key.

public int hashCode ()

public boolean isEmpty ()

Return true if the array map contains no items.

public K keyAt (int index)

Return the key at the given index in the array.

Parameters

index	The desired index, must be between 0 and size()-1.

Returns

• Returns the key stored at the given index.

public Set<K> keySet ()

Return a Set for iterating over and interacting with all keys in the array map.

Note: this is a fairly inefficient way to access the array contents, it requires generating a number of temporary objects.

public V put (K key, V value)

Add a new value to the array map.

Parameters

key	The key under which to store the value. Must not be null. If this key already exists in the array, its value will be replaced.
value	The value to store for the given key.

Returns

• Returns the old value that was stored for the given key, or null if there was no such key.

public void putAll (ArrayMap<? extends K, ? extends V> array)

Perform a put(Object, Object) of all key/value pairs in array

Parameters

array	The array whose contents are to be retrieved.

public void putAll (Map<? extends K, ? extends V> map)

Perform a put(Object, Object) of all key/value pairs in map

Parameters

map	The map whose contents are to be retrieved.

public V remove (Object key)

Remove an existing key from the array map.

Parameters

key	The key of the mapping to remove.

Returns

• Returns the value that was stored under the key, or null if there was no such key.

public boolean removeAll (Collection<?> collection)

Remove all keys in the array map that exist in the given collection.

Parameters

collection	The collection whose contents are to be used to remove keys.

Returns

• Returns true if any keys were removed from the array map, else false.

public V removeAt (int index)

Remove the key/value mapping at the given index.

Parameters

index	The desired index, must be between 0 and size()-1.

Returns

• Returns the value that was stored at this index.

public boolean retainAll (Collection<?> collection)

Remove all keys in the array map that do not exist in the given collection.

Parameters

collection	The collection whose contents are to be used to determine which keys to keep.

Returns

• Returns true if any keys were removed from the array map, else false.

public V setValueAt (int index, V value)

Set the value at a given index in the array.

Parameters

index	The desired index, must be between 0 and size()-1.
value	The new value to store at this index.

Returns

• Returns the previous value at the given index.

public int size ()

Return the number of items in this array map.

public String toString ()

This implementation composes a string by iterating over its mappings. If this map contains itself as a key or a value, the string "(this Map)" will appear in its place.

public V valueAt (int index)

Return the value at the given index in the array.

Parameters

index	The desired index, must be between 0 and size()-1.

Returns

• Returns the value stored at the given index.

public Collection<V> values ()

Return a Collection for iterating over and interacting with all values in the array map.

Note: this is a fairly inefficient way to access the array contents, it requires generating a number of temporary objects.