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Added in API level 19

ArrayMap

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

java.lang.Object
   ↳ android.util.ArrayMap<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.

Summary

Public constructors

ArrayMap()

Create a new empty ArrayMap.

ArrayMap(int capacity)

Create a new ArrayMap with a given initial capacity.

ArrayMap(ArrayMap<K, V> map)

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

Public methods

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)

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

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()

Returns a hash code value for the object.

int indexOfKey(Object key)

Returns the index of a key in the set.

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()

Returns a string representation of the object.

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 methods

From class java.lang.Object
From interface java.util.Map

Public constructors

ArrayMap

Added in API level 19
ArrayMap ()

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

ArrayMap

Added in API level 19
ArrayMap (int capacity)

Create a new ArrayMap with a given initial capacity.

Parameters
capacity int

ArrayMap

Added in API level 23
ArrayMap (ArrayMap<K, V> map)

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

Parameters
map ArrayMap

Public methods

clear

Added in API level 19
void clear ()

Make the array map empty. All storage is released.

containsAll

Added in API level 19
boolean containsAll (Collection<?> collection)

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

Parameters
collection Collection: The collection whose contents are to be checked against.
Returns
boolean Returns true if this array map contains a key for every entry in collection, else returns false.

containsKey

Added in API level 19
boolean containsKey (Object key)

Check whether a key exists in the array.

Parameters
key Object: The key to search for.
Returns
boolean Returns true if the key exists, else false.

containsValue

Added in API level 19
boolean containsValue (Object value)

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

Parameters
value Object: The value to search for.
Returns
boolean Returns true if the value exists, else false.

ensureCapacity

Added in API level 19
void ensureCapacity (int minimumCapacity)

Ensure the array map can hold at least minimumCapacity items.

Parameters
minimumCapacity int

entrySet

Added in API level 19
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 and allocates additional state information associated with the container that will remain for the life of the container.

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.

Returns
Set<Entry<K, V>> a set view of the mappings contained in this map

equals

Added in API level 19
boolean equals (Object object)

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.

The equals method for class Object implements the most discriminating possible equivalence relation on objects; that is, for any non-null reference values x and y, this method returns true if and only if x and y refer to the same object (x == y has the value true).

Note that it is generally necessary to override the hashCode method whenever this method is overridden, so as to maintain the general contract for the hashCode method, which states that equal objects must have equal hash codes.

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 Object: the reference object with which to compare.
Returns
boolean true if this object is the same as the obj argument; false otherwise.

get

Added in API level 19
V get (Object key)

Retrieve a value from the array.

Parameters
key Object: The key of the value to retrieve.
Returns
V Returns the value associated with the given key, or null if there is no such key.

hashCode

Added in API level 19
int hashCode ()

Returns a hash code value for the object. This method is supported for the benefit of hash tables such as those provided by 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(Object) 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(java.lang.Object) 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.

As much as is reasonably practical, the hashCode method defined by class Object does return distinct integers for distinct objects. (This is typically implemented by converting the internal address of the object into an integer, but this implementation technique is not required by the JavaTM programming language.)

Returns
int a hash code value for this object.

indexOfKey

Added in API level 21
int indexOfKey (Object key)

Returns the index of a key in the set.

Parameters
key Object: The key to search for.
Returns
int Returns the index of the key if it exists, else a negative integer.

isEmpty

Added in API level 19
boolean isEmpty ()

Return true if the array map contains no items.

Returns
boolean true if this map contains no key-value mappings

keyAt

Added in API level 19
K keyAt (int index)

Return the key at the given index in the array.

Parameters
index int: The desired index, must be between 0 and size()-1.
Returns
K Returns the key stored at the given index.

keySet

Added in API level 19
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 and allocates additional state information associated with the container that will remain for the life of the container.

Returns
Set<K> a set view of the keys contained in this map

put

Added in API level 19
V put (K key, 
                V value)

Add a new value to the array map.

Parameters
key K: The key under which to store the value. If this key already exists in the array, its value will be replaced.
value V: The value to store for the given key.
Returns
V Returns the old value that was stored for the given key, or null if there was no such key.

putAll

Added in API level 19
void putAll (ArrayMap<? extends K, ? extends V> array)

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

Parameters
array ArrayMap: The array whose contents are to be retrieved.

putAll

Added in API level 19
void putAll (Map<? extends K, ? extends V> map)

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

Parameters
map Map: The map whose contents are to be retrieved.

remove

Added in API level 19
V remove (Object key)

Remove an existing key from the array map.

Parameters
key Object: The key of the mapping to remove.
Returns
V Returns the value that was stored under the key, or null if there was no such key.

removeAll

Added in API level 19
boolean removeAll (Collection<?> collection)

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

Parameters
collection Collection: The collection whose contents are to be used to remove keys.
Returns
boolean Returns true if any keys were removed from the array map, else false.

removeAt

Added in API level 19
V removeAt (int index)

Remove the key/value mapping at the given index.

Parameters
index int: The desired index, must be between 0 and size()-1.
Returns
V Returns the value that was stored at this index.

retainAll

Added in API level 19
boolean retainAll (Collection<?> collection)

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

Parameters
collection Collection: The collection whose contents are to be used to determine which keys to keep.
Returns
boolean Returns true if any keys were removed from the array map, else false.

setValueAt

Added in API level 19
V setValueAt (int index, 
                V value)

Set the value at a given index in the array.

Parameters
index int: The desired index, must be between 0 and size()-1.
value V: The new value to store at this index.
Returns
V Returns the previous value at the given index.

size

Added in API level 19
int size ()

Return the number of items in this array map.

Returns
int the number of key-value mappings in this map

toString

Added in API level 19
String toString ()

Returns a string representation of the object. In general, the toString method returns a string that "textually represents" this object. The result should be a concise but informative representation that is easy for a person to read. It is recommended that all subclasses override this method.

The toString method for class Object returns a string consisting of the name of the class of which the object is an instance, the at-sign character `@', and the unsigned hexadecimal representation of the hash code of the object. In other words, this method returns a string equal to the value of:

 getClass().getName() + '@' + Integer.toHexString(hashCode())
 

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.

Returns
String a string representation of the object.

valueAt

Added in API level 19
V valueAt (int index)

Return the value at the given index in the array.

Parameters
index int: The desired index, must be between 0 and size()-1.
Returns
V Returns the value stored at the given index.

values

Added in API level 19
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 and allocates additional state information associated with the container that will remain for the life of the container.

Returns
Collection<V> a collection view of the values contained in this map
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