ArraySet

Kotlin |Java

class ArraySet<E : Any!> : MutableCollection<E>, MutableSet<E>

kotlin.Any
↳	androidx.collection.ArraySet

ArraySet is a generic set data structure that is designed to be more memory efficient than a traditional java.util.HashSet. The design is very similar to ArrayMap, with all of the caveats described there. This implementation is separate from ArrayMap, however, so the Object array contains only one item for each entry in the set (instead of a pair for a mapping).

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 HashSet, 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
`<init>()` Create a new empty ArraySet.
`<init>(capacity: Int)` Create a new ArraySet with a given initial capacity.
`<init>(@Nullable set: ArraySet<E>?)` Create a new ArraySet with the mappings from the given ArraySet.
`<init>(@Nullable set: MutableCollection<E>?)` Create a new ArraySet with the mappings from the given `Collection`.

Public methods
Boolean	`add(@Nullable element: E?)` Adds the specified object to this set.
Unit	`addAll(@NonNull array: ArraySet<out E>)` Perform a `add(Object)` of all values in array
Boolean	`addAll(@NonNull elements: Collection<E>)` Perform an `add(Object)` of all values in collection
Unit	`clear()` Make the array map empty.
Boolean	`contains(@Nullable element: E?)` Check whether a value exists in the set.
Boolean	`containsAll(@NonNull elements: Collection<E>)` Determine if the array set contains all of the values in the given collection.
Unit	`ensureCapacity(minimumCapacity: Int)` Ensure the array map can hold at least minimumCapacity items.
Boolean	`equals(other: Any?)` This implementation returns false if the object is not a set, or if the sets have different sizes.
Int	`hashCode()`
Int	`indexOf(@Nullable key: Any?)` Returns the index of a value in the set.
Boolean	`isEmpty()` Return true if the array map contains no items.
MutableIterator<E>	`iterator()` Return an `java.util.Iterator` over all values in the set.
Boolean	`remove(@Nullable element: E?)` Removes the specified object from this set.
Boolean	`removeAll(@NonNull array: ArraySet<out E>)` Perform a `remove(Object)` of all values in array
Boolean	`removeAll(@NonNull elements: Collection<E>)` Remove all values in the array set that exist in the given collection.
E	`removeAt(index: Int)` Remove the key/value mapping at the given index.
Boolean	`retainAll(@NonNull elements: Collection<E>)` Remove all values in the array set that do not exist in the given collection.
Array<Any!>	`toArray()`
Array<T>	`toArray(@NonNull array: Array<T>)`
String	`toString()` This implementation composes a string by iterating over its values.
E?	`valueAt(index: Int)` Return the value at the given index in the array.

Properties
Int	`size` Return the number of items in this array map.

Public constructors

<init>

ArraySet()

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

<init>

ArraySet(capacity: Int)

Create a new ArraySet with a given initial capacity.

<init>

ArraySet(@Nullable set: ArraySet<E>?)

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

<init>

ArraySet(@Nullable set: MutableCollection<E>?)

Create a new ArraySet with the mappings from the given Collection.

Public methods

add

fun add(@Nullable element: E?): Boolean

Adds the specified object to this set. The set is not modified if it already contains the object.

Parameters
`value`	the object to add.

Return
`Boolean`	`true` if this set is modified, `false` otherwise.

Exceptions
`ClassCastException`	when the class of the object is inappropriate for this set.

addAll

fun addAll(@NonNull array: ArraySet<out E>): Unit

Perform a add(Object) of all values in array

Parameters
`array`	ArraySet<out E>: The array whose contents are to be retrieved.

addAll

fun addAll(@NonNull elements: Collection<E>): Boolean

Perform an add(Object) of all values in collection

Parameters
`collection`	The collection whose contents are to be retrieved.

clear

fun clear(): Unit

Make the array map empty. All storage is released.

contains

fun contains(@Nullable element: E?): Boolean

Check whether a value exists in the set.

Parameters
`key`	The value to search for.

Return
`Boolean`	Returns true if the value exists, else false.

containsAll

fun containsAll(@NonNull elements: Collection<E>): Boolean

Determine if the array set contains all of the values in the given collection.

Parameters
`collection`	The collection whose contents are to be checked against.

Return
`Boolean`	Returns true if this array set contains a value for every entry in collection, else returns false.

ensureCapacity

fun ensureCapacity(minimumCapacity: Int): Unit

Ensure the array map can hold at least minimumCapacity items.

equals

fun equals(other: Any?): Boolean

This implementation returns false if the object is not a set, or if the sets have different sizes. Otherwise, for each value in this set, it checks to make sure the value also exists in the other set. If any value doesn't exist, the method returns false; otherwise, it returns true.

hashCode

fun hashCode(): Int

indexOf

fun indexOf(@Nullable key: Any?): Int

Returns the index of a value in the set.

Parameters
`key`	Any?: The value to search for.

Return
`Int`	Returns the index of the value if it exists, else a negative integer.

isEmpty

fun isEmpty(): Boolean

Return true if the array map contains no items.

iterator

fun iterator(): MutableIterator<E>

Return an java.util.Iterator over all values in the set.

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.

remove

fun remove(@Nullable element: E?): Boolean

Removes the specified object from this set.

Parameters
`object`	the object to remove.

Return
`Boolean`	`true` if this set was modified, `false` otherwise.

removeAll

fun removeAll(@NonNull array: ArraySet<out E>): Boolean

Perform a remove(Object) of all values in array

Parameters
`array`	ArraySet<out E>: The array whose contents are to be removed.

removeAll

fun removeAll(@NonNull elements: Collection<E>): Boolean

Remove all values in the array set that exist in the given collection.

Parameters
`collection`	The collection whose contents are to be used to remove values.

Return
`Boolean`	Returns true if any values were removed from the array set, else false.

removeAt

fun removeAt(index: Int): E

Remove the key/value mapping at the given index.

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

Return
`E`	Returns the value that was stored at this index.

retainAll

fun retainAll(@NonNull elements: Collection<E>): Boolean

Remove all values in the array set that do not exist in the given collection.

Parameters
`collection`	The collection whose contents are to be used to determine which values to keep.

Return
`Boolean`	Returns true if any values were removed from the array set, else false.

toArray

@NonNull fun toArray(): Array<Any!>

toArray

@NonNull fun <T : Any!> toArray(@NonNull array: Array<T>): Array<T>

toString

fun toString(): String

This implementation composes a string by iterating over its values. If this set contains itself as a value, the string "(this Set)" will appear in its place.

valueAt

@Nullable fun valueAt(index: Int): E?

Return the value at the given index in the array.

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

Return
`E?`	Returns the value stored at the given index.

Properties

size

val size: Int

Return the number of items in this array map.