SparseLongArray

AI-generated Key Takeaways

• SparseLongArray maps integers to longs, allowing for gaps in the indices, and is designed for memory efficiency.

• It uses a binary search for key lookups, making it generally slower than a HashMap for large datasets but efficient for up to hundreds of items.

• It provides methods for adding, retrieving, and removing mappings, as well as iterating over keys and values in ascending key order.

• SparseLongArray is more memory-efficient than using a HashMap to map Integers to Longs due to avoiding auto-boxing and extra entry objects.

public class SparseLongArray extends Object
implements Cloneable

SparseLongArrays map integers to longs. Unlike a normal array of longs, there can be gaps in the indices. It is intended to be more memory efficient than using a HashMap to map Integers to Longs, both because it avoids auto-boxing keys and values 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%.

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

	SparseLongArray() Creates a new SparseLongArray containing no mappings.
	SparseLongArray(int initialCapacity) Creates a new SparseLongArray 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, long 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 SparseIntArray.
SparseLongArray	clone()
void	delete(int key) Removes the mapping from the specified key, if there was any.
long	get(int key) Gets the long mapped from the specified key, or 0 if no such mapping has been made.
long	get(int key, long valueIfKeyNotFound) Gets the long mapped from the specified key, or the specified value 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(long 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 SparseLongArray stores.
void	put(int key, long 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	removeAt(int index) Removes the mapping at the given index.
int	size() Returns the number of key-value mappings that this SparseIntArray currently stores.
String	toString() This implementation composes a string by iterating over its mappings.
long	valueAt(int index) Given an index in the range 0...size()-1, returns the value from the indexth key-value mapping that this SparseLongArray stores.

Inherited Method Summary

From class java.lang.Object

Object	clone()
boolean	equals(Object arg0)
void	finalize()
final Class<?>	getClass()
int	hashCode()
final void	notify()
final void	notifyAll()
String	toString()
final void	wait(long arg0, int arg1)
final void	wait(long arg0)
final void	wait()

Public Constructors

public SparseLongArray ()

Creates a new SparseLongArray containing no mappings.

public SparseLongArray (int initialCapacity)

Creates a new SparseLongArray 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, long 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 SparseIntArray.

public SparseLongArray clone ()

public void delete (int key)

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

Parameters

key

public long get (int key)

Gets the long mapped from the specified key, or 0 if no such mapping has been made.

Parameters

key

public long get (int key, long valueIfKeyNotFound)

Gets the long mapped from the specified key, or the specified value 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 (long 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.

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 SparseLongArray 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, long 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 removeAt (int index)

Removes the mapping at the given index.

Parameters

index

public int size ()

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

public String toString ()

This implementation composes a string by iterating over its mappings.

public long valueAt (int index)

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