public final class ArraySet
extends Object implements Collection<E>, Set<E>

   ↳ androidx.collection.ArraySet<E>

ArraySet is a generic set data structure that is designed to be more memory efficient than a traditional 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.

This structure is NOT thread-safe.


Public constructors


Create a new empty ArraySet.

ArraySet(int capacity)

Create a new ArraySet with a given initial capacity.

ArraySet(ArraySet<E> set)

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

ArraySet(Collection<E> set)

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

ArraySet(E[] array)

Create a new ArraySet with items from the given array.

Public methods

boolean add(E value)

Adds the specified object to this set.

boolean addAll(Collection<? extends E> collection)

Perform an add(Object) of all values in collection

void addAll(ArraySet<? extends E> array)

Perform a add(Object) of all values in array

void clear()

Make the array map empty.

boolean contains(Object key)

Check whether a value exists in the set.

boolean containsAll(Collection<?> collection)

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

void ensureCapacity(int minimumCapacity)

Ensure the array map can hold at least minimumCapacity items.

boolean equals(Object object)

This implementation returns false if the object is not a set, or if the sets have different sizes.

int hashCode()

int indexOf(Object key)

Returns the index of a value in the set.

boolean isEmpty()

Return true if the array map contains no items.

Iterator<E> iterator()

Return an Iterator over all values in the set.

boolean remove(Object object)

Removes the specified object from this set.

boolean removeAll(Collection<?> collection)

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

boolean removeAll(ArraySet<? extends E> array)

Perform a remove(Object) of all values in array

E removeAt(int index)

Remove the key/value mapping at the given index.

boolean retainAll(Collection<?> collection)

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

int size()

Return the number of items in this array map.

<T> T[] toArray(T[] array)
Object[] toArray()
String toString()

This implementation composes a string by iterating over its values.

E valueAt(int index)

Return the value at the given index in the array.

Inherited methods