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SparseArray
public
class
SparseArray
extends Object
implements
Cloneable
| java.lang.Object | |
| ↳ | android.util.SparseArray<E> |
SparseArray maps integers to Objects and, unlike a normal array of Objects,
its indices can contain gaps. SparseArray is intended to be more memory-efficient
than a
HashMap, 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
HashMap because 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 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 of all removed entries. This garbage collection must be performed whenever the array needs to be grown, or when 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 returns the
keys in ascending order. In the case of valueAt(int), the
values corresponding to the keys are returned in ascending order.
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. |
boolean
|
contains(int key)
Returns true if the key exists in the array. |
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 |
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 |
int
|
indexOfValue(E value)
Returns an index for which |
int
|
keyAt(int index)
Given an index in the range |
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 |
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 |
int
|
size()
Returns the number of key-value mappings that this SparseArray currently stores. |
String
|
toString()
Returns a string representation of the object. This implementation composes a string by iterating over its mappings. |
E
|
valueAt(int index)
Given an index in the range |
Inherited methods | |
|---|---|
Public constructors
SparseArray
public SparseArray ()
Creates a new SparseArray containing no mappings.
SparseArray
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 |
int |
Public methods
append
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 |
int |
value |
E |
clear
public void clear ()
Removes all key-value mappings from this SparseArray.
clone
public SparseArray<E> clone ()
Creates and returns a copy of this object. The precise meaning
of "copy" may depend on the class of the object. The general
intent is that, for any object x, the expression:
will be true, and that the expression:x.clone() != x
will bex.clone().getClass() == x.getClass()
true, but these are not absolute requirements.
While it is typically the case that:
will bex.clone().equals(x)
true, this is not an absolute requirement.
By convention, the returned object should be obtained by calling
super.clone. If a class and all of its superclasses (except
Object) obey this convention, it will be the case that
x.clone().getClass() == x.getClass().
By convention, the object returned by this method should be independent
of this object (which is being cloned). To achieve this independence,
it may be necessary to modify one or more fields of the object returned
by super.clone before returning it. Typically, this means
copying any mutable objects that comprise the internal "deep structure"
of the object being cloned and replacing the references to these
objects with references to the copies. If a class contains only
primitive fields or references to immutable objects, then it is usually
the case that no fields in the object returned by super.clone
need to be modified.
The method clone for class Object performs a
specific cloning operation. First, if the class of this object does
not implement the interface Cloneable, then a
CloneNotSupportedException is thrown. Note that all arrays
are considered to implement the interface Cloneable and that
the return type of the clone method of an array type T[]
is T[] where T is any reference or primitive type.
Otherwise, this method creates a new instance of the class of this
object and initializes all its fields with exactly the contents of
the corresponding fields of this object, as if by assignment; the
contents of the fields are not themselves cloned. Thus, this method
performs a "shallow copy" of this object, not a "deep copy" operation.
The class Object does not itself implement the interface
Cloneable, so calling the clone method on an object
whose class is Object will result in throwing an
exception at run time.
| Returns | |
|---|---|
SparseArray<E> |
a clone of this instance. |
contains
public boolean contains (int key)
Returns true if the key exists in the array. This is equivalent to
indexOfKey(int) >= 0.
| Parameters | |
|---|---|
key |
int: Potential key in the mapping |
| Returns | |
|---|---|
boolean |
true if the key is defined in the mapping |
delete
public void delete (int key)
Removes the mapping from the specified key, if there was any.
| Parameters | |
|---|---|
key |
int |
get
public E get (int key)
Gets the Object mapped from the specified key, or null
if no such mapping has been made.
| Parameters | |
|---|---|
key |
int |
| Returns | |
|---|---|
E |
|
get
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 |
int |
valueIfKeyNotFound |
E |
| Returns | |
|---|---|
E |
|
indexOfKey
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 |
int |
| Returns | |
|---|---|
int |
|
indexOfValue
public int indexOfValue (E value)
Returns an index for which valueAt(int) would return the
specified value, 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 |
E |
| Returns | |
|---|---|
int |
|
keyAt
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.
For indices outside of the range 0...size()-1,
the behavior is undefined for apps targeting Build.VERSION_CODES.P and
earlier, and an ArrayIndexOutOfBoundsException is thrown for apps targeting
Build.VERSION_CODES.Q and later.
| Parameters | |
|---|---|
index |
int |
| Returns | |
|---|---|
int |
|
put
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 |
int |
value |
E |
removeAt
public void removeAt (int index)
Removes the mapping at the specified index.
For indices outside of the range 0...size()-1,
the behavior is undefined for apps targeting Build.VERSION_CODES.P and
earlier, and an ArrayIndexOutOfBoundsException is thrown for apps targeting
Build.VERSION_CODES.Q and later.
| Parameters | |
|---|---|
index |
int |
removeAtRange
public void removeAtRange (int index,
int size)
Remove a range of mappings as a batch.
| Parameters | |
|---|---|
index |
int: Index to begin at |
size |
int: Number of mappings to remove
For indices outside of the range |
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
SparseArray stores.
For indices outside of the range 0...size()-1, the behavior is undefined for
apps targeting Build.VERSION_CODES.P and earlier, and an
ArrayIndexOutOfBoundsException is thrown for apps targeting
Build.VERSION_CODES.Q and later.
| Parameters | |
|---|---|
index |
int |
value |
E |
size
public int size ()
Returns the number of key-value mappings that this SparseArray currently stores.
| Returns | |
|---|---|
int |
|
toString
public String toString ()
Returns a string representation of the object. In general, the
toString method returns a string that
"textually represents" this object. The result should
be a concise but informative representation that is easy for a
person to read.
It is recommended that all subclasses override this method.
The toString method for class Object
returns a string consisting of the name of the class of which the
object is an instance, the at-sign character `@', and
the unsigned hexadecimal representation of the hash code of the
object. In other words, this method returns a string equal to the
value of:
getClass().getName() + '@' + Integer.toHexString(hashCode())
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 | |
|---|---|
String |
a string representation of the object. |
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
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.
For indices outside of the range 0...size()-1,
the behavior is undefined for apps targeting Build.VERSION_CODES.P and
earlier, and an ArrayIndexOutOfBoundsException is thrown for apps targeting
Build.VERSION_CODES.Q and later.
| Parameters | |
|---|---|
index |
int |
| Returns | |
|---|---|
E |
|