public class SparseArray<E> extends Object implements Cloneable
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)
.
Constructor and Description |
---|
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.
|
Modifier and Type | Method and Description |
---|---|
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.
|
E |
removeReturnOld(int key) |
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 representation of the object.
|
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. |
public SparseArray()
public SparseArray(int initialCapacity)
public SparseArray<E> clone()
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.
public E get(int key)
null
if no such mapping has been made.public E get(int key, E valueIfKeyNotFound)
public void delete(int key)
public E removeReturnOld(int key)
public void remove(int key)
delete(int)
.public void removeAt(int index)
For indices outside of the range 0...size()-1
,
the behavior is undefined.
public void removeAtRange(int index, int size)
index
- Index to begin atsize
- Number of mappings to remove
For indices outside of the range 0...size()-1
,
the behavior is undefined.
public void put(int key, E value)
public int size()
public int keyAt(int index)
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.
For indices outside of the range 0...size()-1
,
the behavior is undefined.
public E valueAt(int index)
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.
For indices outside of the range 0...size()-1
,
the behavior is undefined.
public void setValueAt(int index, E value)
0...size()-1
, sets a new
value for the index
th key-value mapping that this
SparseArray stores.
For indices outside of the range 0...size()-1
, the behavior is undefined.
public int indexOfKey(int key)
keyAt(int)
would return the
specified key, or a negative number if the specified
key is not mapped.public int indexOfValue(E value)
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 void clear()
public void append(int key, E value)
public String toString()
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.