Package android.util

Class LongSparseArray<E>

  • All Implemented Interfaces:
    Cloneable
    public class LongSparseArray<E>
extends Object
implements Cloneable
    SparseArray mapping longs to Objects. Unlike a normal array of Objects, there can be gaps in the indices. It is intended to be more memory efficient than using a HashMap to map Longs to Objects, both because it avoids auto-boxing keys and its data structure doesn't rely on an extra entry object for each mapping.

    Note that this container keeps its mappings in an array data structure, using a binary search to find keys. The 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%.

    To help with performance, the container includes an optimization when removing keys: instead of compacting its array immediately, it leaves the removed entry marked as deleted. The entry can then be re-used for the same key, or compacted later in a single garbage collection step of all removed entries. This garbage collection will need to be performed at any time the array needs to be grown or the the map size or entry values are retrieved.

    It is possible to iterate over the items in this container using keyAt(int) and valueAt(int). Iterating over the keys using keyAt(int) with ascending values of the index will return the keys in ascending order, or the values corresponding to the keys in ascending order in the case of valueAt(int).

    • Constructor Summary

      Constructors 
      Constructor Description
      LongSparseArray()
      Creates a new LongSparseArray containing no mappings.
      LongSparseArray​(int initialCapacity)
      Creates a new LongSparseArray containing no mappings that will not require any additional memory allocation to store the specified number of mappings.

    • Method Summary

      All Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      void append​(long key, E value)
      Puts a key/value pair into the array, optimizing for the case where the key is greater than all existing keys in the array.
      void clear()
      Removes all key-value mappings from this LongSparseArray.
      LongSparseArray<E> clone()
      Creates and returns a copy of this Object.
      void delete​(long key)
      Removes the mapping from the specified key, if there was any.
      E get​(long key)
      Gets the Object mapped from the specified key, or null if no such mapping has been made.
      E get​(long key, E valueIfKeyNotFound)
      Gets the Object mapped from the specified key, or the specified Object if no such mapping has been made.
      int indexOfKey​(long key)
      Returns the index for which keyAt(int) would return the specified key, or a negative number if the specified key is not mapped.
      int indexOfValue​(E value)
      Returns an index for which valueAt(int) would return the specified key, or a negative number if no keys map to the specified value.
      long keyAt​(int index)
      Given an index in the range 0...size()-1, returns the key from the indexth key-value mapping that this LongSparseArray stores.
      void put​(long key, E value)
      Adds a mapping from the specified key to the specified value, replacing the previous mapping from the specified key if there was one.
      void remove​(long key)
      Alias for delete(long).
      void removeAt​(int index)
      Removes the mapping at the specified index.
      void setValueAt​(int index, E value)
      Given an index in the range 0...size()-1, sets a new value for the indexth key-value mapping that this LongSparseArray stores.
      int size()
      Returns the number of key-value mappings that this LongSparseArray currently stores.
      String toString()
      Returns a string containing a concise, human-readable description of this object.
      E valueAt​(int index)
      Given an index in the range 0...size()-1, returns the value from the indexth key-value mapping that this LongSparseArray stores.

    • Constructor Detail

      • LongSparseArray

        public LongSparseArray()
        Creates a new LongSparseArray containing no mappings.

      • LongSparseArray

        public LongSparseArray​(int initialCapacity)
        Creates a new LongSparseArray containing no mappings that will not require any additional memory allocation to store the specified number of mappings. If you supply an initial capacity of 0, the sparse array will be initialized with a light-weight representation not requiring any additional array allocations.

    • Method Detail

      • clone

        public LongSparseArray<E> clone()
        Description copied from class: Object
        Creates and returns a copy of this Object. The default implementation returns a so-called "shallow" copy: It creates a new instance of the same class and then copies the field values (including object references) from this instance to the new instance. A "deep" copy, in contrast, would also recursively clone nested objects. A subclass that needs to implement this kind of cloning should call super.clone() to create the new instance and then create deep copies of the nested, mutable objects.
        Overrides:
        clone in class Object
        Returns:
        a copy of this object.

      • get

        public E get​(long key)
        Gets the Object mapped from the specified key, or null if no such mapping has been made.

      • get

        public E get​(long key,
             E valueIfKeyNotFound)
        Gets the Object mapped from the specified key, or the specified Object if no such mapping has been made.

      • delete

        public void delete​(long key)
        Removes the mapping from the specified key, if there was any.

      • remove

        public void remove​(long key)
        Alias for delete(long).

      • removeAt

        public void removeAt​(int index)
        Removes the mapping at the specified index.

      • put

        public void put​(long key,
                E value)
        Adds a mapping from the specified key to the specified value, replacing the previous mapping from the specified key if there was one.

      • size

        public int size()
        Returns the number of key-value mappings that this LongSparseArray currently stores.

      • keyAt

        public long keyAt​(int index)
        Given an index in the range 0...size()-1, returns the key from the indexth key-value mapping that this LongSparseArray stores.

        The keys corresponding to indices in ascending order are guaranteed to be in ascending order, e.g., keyAt(0) will return the smallest key and keyAt(size()-1) will return the largest key.

      • valueAt

        public E valueAt​(int index)
        Given an index in the range 0...size()-1, returns the value from the indexth key-value mapping that this LongSparseArray stores.

        The values corresponding to indices in ascending order are guaranteed to be associated with keys in ascending order, e.g., valueAt(0) will return the value associated with the smallest key and valueAt(size()-1) will return the value associated with the largest key.

      • setValueAt

        public void setValueAt​(int index,
                       E value)
        Given an index in the range 0...size()-1, sets a new value for the indexth key-value mapping that this LongSparseArray stores.

      • indexOfKey

        public int indexOfKey​(long key)
        Returns the index for which keyAt(int) would return the specified key, or a negative number if the specified key is not mapped.

      • indexOfValue

        public int indexOfValue​(E value)
        Returns an index for which valueAt(int) would return the specified key, 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.

      • clear

        public void clear()
        Removes all key-value mappings from this LongSparseArray.

      • append

        public void append​(long key,
                   E value)
        Puts a key/value pair into the array, optimizing for the case where the key is greater than all existing keys in the array.

      • toString

        public String toString()
        Returns a string containing a concise, human-readable description of this object. Subclasses are encouraged to override this method and provide an implementation that takes into account the object's type and data. The default implementation is equivalent to the following expression: 
           getClass().getName() + '@' + Integer.toHexString(hashCode())

        See Writing a useful toString method if you intend implementing your own toString method.

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

        Overrides:
        toString in class Object
        Returns:
        a printable representation of this object.