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SparseBooleanArray

public class SparseBooleanArray
extends Object implements Cloneable

java.lang.Object
   ↳ android.util.SparseBooleanArray


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

Summary

Public constructors

SparseBooleanArray()

Creates a new SparseBooleanArray containing no mappings.

SparseBooleanArray(int initialCapacity)

Creates a new SparseBooleanArray containing no mappings that will not require any additional memory allocation to store the specified number of mappings.

Public methods

void append(int key, boolean 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 SparseBooleanArray.

SparseBooleanArray clone()

Creates and returns a copy of this object.

void delete(int key)

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

boolean equals(Object that)

Indicates whether some other object is "equal to" this one.

boolean get(int key)

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

boolean get(int key, boolean valueIfKeyNotFound)

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

int hashCode()

Returns a hash code value for the object.

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(boolean 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 SparseBooleanArray stores.

void put(int key, boolean value)

Adds a mapping from the specified key to the specified value, replacing the previous mapping from the specified key if there was one.

int size()

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

String toString()

Returns a string representation of the object.

This implementation composes a string by iterating over its mappings.

boolean valueAt(int index)

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

Inherited methods

From class java.lang.Object

Public constructors

SparseBooleanArray

Added in API level 1
SparseBooleanArray ()

Creates a new SparseBooleanArray containing no mappings.

SparseBooleanArray

Added in API level 1
SparseBooleanArray (int initialCapacity)

Creates a new SparseBooleanArray 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

Added in API level 1
void append (int key, 
                boolean 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 boolean

clear

Added in API level 1
void clear ()

Removes all key-value mappings from this SparseBooleanArray.

clone

Added in API level 1
SparseBooleanArray 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:

 x.clone() != x
will be true, and that the expression:
 x.clone().getClass() == x.getClass()
will be true, but these are not absolute requirements. While it is typically the case that:
 x.clone().equals(x)
will be 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
SparseBooleanArray a clone of this instance.

delete

Added in API level 1
void delete (int key)

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

Parameters
key int

equals

Added in API level 1
boolean equals (Object that)

Indicates whether some other object is "equal to" this one.

The equals method implements an equivalence relation on non-null object references:

  • It is reflexive: for any non-null reference value x, x.equals(x) should return true.
  • It is symmetric: for any non-null reference values x and y, x.equals(y) should return true if and only if y.equals(x) returns true.
  • It is transitive: for any non-null reference values x, y, and z, if x.equals(y) returns true and y.equals(z) returns true, then x.equals(z) should return true.
  • It is consistent: for any non-null reference values x and y, multiple invocations of x.equals(y) consistently return true or consistently return false, provided no information used in equals comparisons on the objects is modified.
  • For any non-null reference value x, x.equals(null) should return false.

The equals method for class Object implements the most discriminating possible equivalence relation on objects; that is, for any non-null reference values x and y, this method returns true if and only if x and y refer to the same object (x == y has the value true).

Note that it is generally necessary to override the hashCode method whenever this method is overridden, so as to maintain the general contract for the hashCode method, which states that equal objects must have equal hash codes.

Parameters
that Object: the reference object with which to compare.
Returns
boolean true if this object is the same as the obj argument; false otherwise.

get

Added in API level 1
boolean get (int key)

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

Parameters
key int
Returns
boolean

get

Added in API level 1
boolean get (int key, 
                boolean valueIfKeyNotFound)

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

Parameters
key int
valueIfKeyNotFound boolean
Returns
boolean

hashCode

Added in API level 1
int hashCode ()

Returns a hash code value for the object. This method is supported for the benefit of hash tables such as those provided by HashMap.

The general contract of hashCode is:

  • Whenever it is invoked on the same object more than once during an execution of a Java application, the hashCode method must consistently return the same integer, provided no information used in equals comparisons on the object is modified. This integer need not remain consistent from one execution of an application to another execution of the same application.
  • If two objects are equal according to the equals(Object) method, then calling the hashCode method on each of the two objects must produce the same integer result.
  • It is not required that if two objects are unequal according to the equals(java.lang.Object) method, then calling the hashCode method on each of the two objects must produce distinct integer results. However, the programmer should be aware that producing distinct integer results for unequal objects may improve the performance of hash tables.

As much as is reasonably practical, the hashCode method defined by class Object does return distinct integers for distinct objects. (This is typically implemented by converting the internal address of the object into an integer, but this implementation technique is not required by the JavaTM programming language.)

Returns
int a hash code value for this object.

indexOfKey

Added in API level 1
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

Added in API level 1
int indexOfValue (boolean 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 boolean
Returns
int

keyAt

Added in API level 1
int keyAt (int index)

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

put

Added in API level 1
void put (int key, 
                boolean 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 boolean

size

Added in API level 1
int size ()

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

Returns
int

toString

Added in API level 1
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.

Returns
String a string representation of the object.

valueAt

Added in API level 1
boolean valueAt (int index)

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