SparseArray

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public class SparseArray extends Object
implements Cloneable

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).

Public Constructor Summary

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 Method Summary

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()
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 indexth 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 indexth key-value mapping that this SparseArray stores.
int
size()
Returns the number of key-value mappings that this SparseArray currently stores.
String
toString()

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 indexth key-value mapping that this SparseArray stores.

Inherited Method Summary

Public Constructors

public SparseArray ()

Creates a new SparseArray containing no mappings.

public 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. 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.

Parameters
initialCapacity

Public Methods

public 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.

Parameters
key
value

public void clear ()

Removes all key-value mappings from this SparseArray.

public SparseArray<E> clone ()

public void delete (int key)

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

Parameters
key

public E get (int key)

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

Parameters
key

public 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.

Parameters
key
valueIfKeyNotFound

public 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.

Parameters
key

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.

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

Parameters
value

public int keyAt (int index)

Given an index in the range 0...size()-1, returns the key from the indexth 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.

Parameters
index

public 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.

Parameters
key
value

public void remove (int key)

Alias for delete(int).

Parameters
key

public void removeAt (int index)

Removes the mapping at the specified index.

Parameters
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)

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

Parameters
index
value

public int size ()

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

public String toString ()

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.

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 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.

Parameters
index