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Android APIs
public class

SparseArray

extends Object
implements Cloneable
java.lang.Object
   ↳ android.util.SparseArray<E>

Class Overview

SparseArrays map integers 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 Integers 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) .

Summary

Public Constructors
SparseArray ()
Creates a new SparseArray containing no mappings.
SparseArray (int initialCapacity)
Creates a new SparseArray containing no mappings that will not require any additional memory allocation to store the specified number of mappings.
Public Methods
void append (int 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 SparseArray.
SparseArray <E> clone ()
Creates and returns a copy of this Object .
void delete (int key)
Removes the mapping from the specified key, if there was any.
E get (int key)
Gets the Object mapped from the specified key, or null if no such mapping has been made.
E get (int key, E valueIfKeyNotFound)
Gets the Object mapped from the specified key, or the specified Object if no such mapping has been made.
int indexOfKey (int 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.
int keyAt (int index)
Given an index in the range 0...size()-1 , returns the key from the index th key-value mapping that this SparseArray stores.
void put (int 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 (int key)
Alias for delete(int) .
void removeAt (int index)
Removes the mapping at the specified index.
void removeAtRange (int index, int size)
Remove a range of mappings as a batch.
void setValueAt (int index, E value)
Given an index in the range 0...size()-1 , sets a new value for the index th key-value mapping that this SparseArray stores.
int size ()
Returns the number of key-value mappings that this SparseArray currently stores.
String toString ()
Returns a string containing a concise, human-readable description of this object.

This implementation composes a string by iterating over its mappings.

E valueAt (int index)
Given an index in the range 0...size()-1 , returns the value from the index th key-value mapping that this SparseArray stores.
[Expand]
Inherited Methods
From class java.lang.Object

Public Constructors

public SparseArray ()

Added in API level 1

Creates a new SparseArray containing no mappings.

public SparseArray (int initialCapacity)

Added in API level 1

Creates a new SparseArray 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.

Public Methods

public void append (int key, E value)

Added in API level 1

Puts a key/value pair into the array, optimizing for the case where the key is greater than all existing keys in the array.

public void clear ()

Added in API level 1

Removes all key-value mappings from this SparseArray.

public SparseArray <E> clone ()

Added in API level 1

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.

Returns
  • a copy of this object.

public void delete (int key)

Added in API level 1

Removes the mapping from the specified key, if there was any.

public E get (int key)

Added in API level 1

Gets the Object mapped from the specified key, or null if no such mapping has been made.

public E get (int key, E valueIfKeyNotFound)

Added in API level 1

Gets the Object mapped from the specified key, or the specified Object if no such mapping has been made.

public int indexOfKey (int key)

Added in API level 1

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

public int indexOfValue (E value)

Added in API level 1

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.

Note also that unlike most collections' indexOf methods, this method compares values using == rather than equals .

public int keyAt (int index)

Added in API level 1

Given an index in the range 0...size()-1 , returns the key from the index th key-value mapping that this SparseArray 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.

public void put (int key, E value)

Added in API level 1

Adds a mapping from the specified key to the specified value, replacing the previous mapping from the specified key if there was one.

public void remove (int key)

Added in API level 1

Alias for delete(int) .

public void removeAt (int index)

Removes the mapping at the specified index.

public void removeAtRange (int index, int size)

Remove a range of mappings as a batch.

Parameters
index Index to begin at
size Number of mappings to remove

public void setValueAt (int index, E value)

Added in API level 1

Given an index in the range 0...size()-1 , sets a new value for the index th key-value mapping that this SparseArray stores.

public int size ()

Added in API level 1

Returns the number of key-value mappings that this SparseArray currently stores.

public String toString ()

Added in API level 1

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.

Returns
  • a printable representation of this object.

public E valueAt (int index)

Added in API level 1

Given an index in the range 0...size()-1 , returns the value from the index th key-value mapping that this SparseArray 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.