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Summary: Ctors | Methods | Inherited Methods

# 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.

This structure is NOT thread-safe.

## 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.
`int` | `indexOfValue(Object value)` Returns an index for which `valueAt(int)` would return the specified value, or a negative number if no keys map to the specified value.
`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(java.lang.Object, java.lang.Object)` of all key/value pairs in array
`void` | `putAll(Map<? extends K, ? extends V> map)` Perform a `put(java.lang.Object, java.lang.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`
`Object` | `clone()` Creates and returns a copy of this object.
`boolean` | `equals(Object obj)` Indicates whether some other object is "equal to" this one.
`void` | `finalize()` Called by the garbage collector on an object when garbage collection determines that there are no more references to the object.
`final Class<?>` | `getClass()` Returns the runtime class of this `Object`.
`int` | `hashCode()` Returns a hash code value for the object.
`final void` | `notify()` Wakes up a single thread that is waiting on this object's monitor.
`final void` | `notifyAll()` Wakes up all threads that are waiting on this object's monitor.
`String` | `toString()` Returns a string representation of the object.
`final void` | `wait(long timeout, int nanos)` Causes the current thread to wait until another thread invokes the `notify()` method or the `notifyAll()` method for this object, or some other thread interrupts the current thread, or a certain amount of real time has elapsed.
`final void` | `wait(long timeout)` Causes the current thread to wait until either another thread invokes the `notify()` method or the `notifyAll()` method for this object, or a specified amount of time has elapsed.
`final void` | `wait()` Causes the current thread to wait until another thread invokes the `notify()` method or the `notifyAll()` method for this object.
From interface `java.util.Map`
`abstract void` | `clear()` Removes all of the mappings from this map (optional operation).
`default V` | `compute(K key, BiFunction<? super K, ? super V, ? extends V> remappingFunction)` Attempts to compute a mapping for the specified key and its current mapped value (or `null` if there is no current mapping).
`default V` | `computeIfAbsent(K key, Function<? super K, ? extends V> mappingFunction)` If the specified key is not already associated with a value (or is mapped to `null`), attempts to compute its value using the given mapping function and enters it into this map unless `null`.
`default V` | `computeIfPresent(K key, BiFunction<? super K, ? super V, ? extends V> remappingFunction)` If the value for the specified key is present and non-null, attempts to compute a new mapping given the key and its current mapped value.
`abstract boolean` | `containsKey(Object key)` Returns `true` if this map contains a mapping for the specified key.
`abstract boolean` | `containsValue(Object value)` Returns `true` if this map maps one or more keys to the specified value.
`static <K, V> Map<K, V>` | `copyOf(Map<? extends K, ? extends V> map)` Returns an unmodifiable Map containing the entries of the given Map.
`static <K, V> Entry<K, V>` | `entry(K k, V v)` Returns an immutable `Entry` containing the given key and value.
`abstract Set<Entry<K, V>>` | `entrySet()` Returns a `Set` view of the mappings contained in this map.
`abstract boolean` | `equals(Object o)` Compares the specified object with this map for equality.
`default void` | `forEach(BiConsumer<? super K, ? super V> action)` Performs the given action for each entry in this map until all entries have been processed or the action throws an exception.
`abstract V` | `get(Object key)` Returns the value to which the specified key is mapped, or `null` if this map contains no mapping for the key.
`default V` | `getOrDefault(Object key, V defaultValue)` Returns the value to which the specified key is mapped, or `defaultValue` if this map contains no mapping for the key.
`abstract int` | `hashCode()` Returns the hash code value for this map.
`abstract boolean` | `isEmpty()` Returns `true` if this map contains no key-value mappings.
`abstract Set<K>` | `keySet()` Returns a `Set` view of the keys contained in this map.
`default V` | `merge(K key, V value, BiFunction<? super V, ? super V, ? extends V> remappingFunction)` If the specified key is not already associated with a value or is associated with null, associates it with the given non-null value.
`static <K, V> Map<K, V>` | `of(K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4, K k5, V v5)` Returns an immutable map containing five mappings.
`static <K, V> Map<K, V>` | `of(K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4)` Returns an immutable map containing four mappings.
`static <K, V> Map<K, V>` | `of(K k1, V v1)` Returns an immutable map containing a single mapping.
`static <K, V> Map<K, V>` | `of(K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4, K k5, V v5, K k6, V v6, K k7, V v7, K k8, V v8)` Returns an immutable map containing eight mappings.
`static <K, V> Map<K, V>` | `of(K k1, V v1, K k2, V v2)` Returns an immutable map containing two mappings.
`static <K, V> Map<K, V>` | `of(K k1, V v1, K k2, V v2, K k3, V v3)` Returns an immutable map containing three mappings.
`static <K, V> Map<K, V>` | `of()` Returns an immutable map containing zero mappings.
`static <K, V> Map<K, V>` | `of(K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4, K k5, V v5, K k6, V v6, K k7, V v7, K k8, V v8, K k9, V v9)` Returns an immutable map containing nine mappings.
`static <K, V> Map<K, V>` | `of(K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4, K k5, V v5, K k6, V v6)` Returns an immutable map containing six mappings.
`static <K, V> Map<K, V>` | `of(K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4, K k5, V v5, K k6, V v6, K k7, V v7)` Returns an immutable map containing seven mappings.
`static <K, V> Map<K, V>` | `of(K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4, K k5, V v5, K k6, V v6, K k7, V v7, K k8, V v8, K k9, V v9, K k10, V v10)` Returns an immutable map containing ten mappings.
`static <K, V> Map<K, V>` | `ofEntries(Entry...<? extends K, ? extends V> entries)` Returns an immutable map containing keys and values extracted from the given entries.
`abstract V` | `put(K key, V value)` Associates the specified value with the specified key in this map (optional operation).
`abstract void` | `putAll(Map<? extends K, ? extends V> m)` Copies all of the mappings from the specified map to this map (optional operation).
`default V` | `putIfAbsent(K key, V value)` If the specified key is not already associated with a value (or is mapped to `null`) associates it with the given value and returns `null`, else returns the current value.
`default boolean` | `remove(Object key, Object value)` Removes the entry for the specified key only if it is currently mapped to the specified value.
`abstract V` | `remove(Object key)` Removes the mapping for a key from this map if it is present (optional operation).
`default boolean` | `replace(K key, V oldValue, V newValue)` Replaces the entry for the specified key only if currently mapped to the specified value.
`default V` | `replace(K key, V value)` Replaces the entry for the specified key only if it is currently mapped to some value.
`default void` | `replaceAll(BiFunction<? super K, ? super V, ? extends V> function)` Replaces each entry's value with the result of invoking the given function on that entry until all entries have been processed or the function throws an exception.
`abstract int` | `size()` Returns the number of key-value mappings in this map.
`abstract Collection<V>` | `values()` Returns a `Collection` view of the values contained in this map.

## Public constructors

### ArrayMap

    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.

### ArrayMap

    public ArrayMap (int capacity)

Create a new ArrayMap with a given initial capacity.

Parameters
`capacity` | `int`

### ArrayMap

    public ArrayMap (ArrayMap<K, V> map)

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

Parameters
`map` | `ArrayMap`

## Public methods

### clear

    public void clear ()

Make the array map empty. All storage is released.

### containsAll

    public 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

    public 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

    public 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

    public void ensureCapacity (int minimumCapacity)

Ensure the array map can hold at least minimumCapacity items.

Parameters
`minimumCapacity` | `int`

### entrySet

    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 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

    public 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`: This value may be `null`.

Returns
`boolean` | `true` if this object is the same as the obj argument; `false` otherwise.

### get

    public 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

    public 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 Java™ programming language.)

Returns
`int` | a hash code value for this object.

### indexOfKey

    public 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.

### indexOfValue

    public int indexOfValue (Object value)

Returns an index for which `valueAt(int)` would return the specified value, or a negative number if no keys map to the specified value. Beware that this is a linear search, unlike lookups by key, and that multiple keys can map to the same value and this will find only one of them.

Parameters
`value` | `Object`

Returns
`int` |

### isEmpty

    public boolean isEmpty ()

Return true if the array map contains no items.

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

### keyAt

    public K keyAt (int index)

Return the key at the given index in the array.

For indices outside of the range `0...size()-1`, the behavior is undefined for apps targeting `Build.VERSION_CODES.P` and earlier, and an `ArrayIndexOutOfBoundsException` is thrown for apps targeting `Build.VERSION_CODES.Q` and later.

Parameters
`index` | `int`: The desired index, must be between 0 and `size()`-1.

Returns
`K` | Returns the key stored at the given index.

### keySet

    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 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

    public 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

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

Perform a `put(java.lang.Object, java.lang.Object)` of all key/value pairs in array

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

### putAll

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

Perform a `put(java.lang.Object, java.lang.Object)` of all key/value pairs in map

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

### remove

    public 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

    public 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

    public V removeAt (int index)

Remove the key/value mapping at the given index.

For indices outside of the range `0...size()-1`, the behavior is undefined for apps targeting `Build.VERSION_CODES.P` and earlier, and an `ArrayIndexOutOfBoundsException` is thrown for apps targeting `Build.VERSION_CODES.Q` and later.

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

    public 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

    public V setValueAt (int index,
                    V value)

Set the value at a given index in the array.

For indices outside of the range `0...size()-1`, the behavior is undefined for apps targeting `Build.VERSION_CODES.P` and earlier, and an `ArrayIndexOutOfBoundsException` is thrown for apps targeting `Build.VERSION_CODES.Q` and later.

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

    public int size ()

Return the number of items in this array map.

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

### toString

    public 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

    public V valueAt (int index)

Return the value at the given index in the array.

For indices outside of the range `0...size()-1`, the behavior is undefined for apps targeting `Build.VERSION_CODES.P` and earlier, and an `ArrayIndexOutOfBoundsException` is thrown for apps targeting `Build.VERSION_CODES.Q` and later.

Parameters
`index` | `int`: The desired index, must be between 0 and `size()`-1.

Returns
`V` | Returns the value stored at the given index.

### values

    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 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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