What is the Clear Purpose of SparseBooleanArray?? [ I referred official android site for this ]

Question

I referred the android doc site for \"SparseBooleanArray\" class but still not getting idea of that class about what is the purpose of that class?? For what purpose we need

Answer 1

Like the javadoc says, SparseBooleanArrays map integers to booleans which basically means that it's like a map with Integer as a key and a boolean as value (Map).

However it's more efficient to use in this particular case It is intended to be more efficient than using a HashMap to map Integers to Booleans

Hope this clears out any issues you had with the description.

Answer 2

I found a very specific and wonderful use for the sparse boolean array.

You can put a true or false value to be associated with a position in a list.

For example: List item #7 was clicked, so putting 7 as the key and true as the value.

Answer 3

From what I get from the documentation it is for mapping Integer values to booleans.

That is, if you want to map, if for a certain userID a widget should be shown and some userIDs have already been deleted, you would have gaps in your mapping.

Meaning, with a normal array, you would create an array of size=maxID and add a boolean value to element at index=userID. Then when iterating over the array, you would have to iterate over maxID elements in the worst case and have to check for null if there is no boolean for that index (eg. the ID does not exist). That is really inefficient.

When using a hashmap to do that you could map the ID to the boolean, but with the added overhead of generating the hashvalue for the key (that is why it is called *hash*map), which would ultimately hurt performance firstly in CPU cycles as well as RAM usage.

So that SparseBooleanArray seems like a good middleway of dealing with such a situation.

NOTE: Even though my example is really contrieved, I hope it illustrates the situation.

Answer 4

There can be three ways to store resource id's

1 Array

Boolean array containing id's as indexes.If we have used that id set it to true else false

Though all the operations are fast but this implementation will require huge amount of space.So it can't be used

High Space Complexity

2 HashMap

Key-ID

Value-Boolean True/False

Using this we need to process each id using the hashing function which will consume memory.Also there may be some empty locations where no id will be stored and we also need to deal with crashes.So due to usage complexity and medium space complexity, it is not used.

Medium Space Complexity

3 SparseBooleanArray

It is middle way.It uses mapping and Array Implementation

Key - ID

Value - Boolean True/False

It is an ArrayList which stores id's in an increasing order.So minimum space is used as it only contains id's which are being used.For searching an id binary search is used. Though Binary Search O(logn) is slower than hashing O(1) or Array O(1),i.e. all the operations Insertion, Deletion, Searching will take more time but there is least memory wastage.So to save memory we prefer SparseBoolean Array

Least Space Complexity