SparseIntArray

public class SparseIntArray extends Object
implements Cloneable

SparseIntArrays map integers to integers. Unlike a normal array of integers, there can be gaps in the indices. It is intended to be more memory efficient than using a HashMap to map Integers to Integers, 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

SparseIntArray()
Creates a new SparseIntArray containing no mappings.
SparseIntArray(int initialCapacity)
Creates a new SparseIntArray 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, int 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.
SparseIntArray
clone()
void
delete(int key)
Removes the mapping from the specified key, if there was any.
int
get(int key)
Gets the int mapped from the specified key, or 0 if no such mapping has been made.
int
get(int key, int valueIfKeyNotFound)
Gets the int 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(int 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 SparseIntArray stores.
void
put(int key, int 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.

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

Inherited Method Summary

Public Constructors

public SparseIntArray ()

Creates a new SparseIntArray containing no mappings.

public SparseIntArray (int initialCapacity)

Creates a new SparseIntArray 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, int 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 SparseIntArray clone ()

public void delete (int key)

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

Parameters
key

public int get (int key)

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

Parameters
key

public int get (int key, int valueIfKeyNotFound)

Gets the int 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 (int 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 SparseIntArray 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, int 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