使用SparseIntArray替换HashMap

一、SparseIntArray API

 

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) andvalueAt(int). Iterating over the keys usingkeyAt(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 ofvalueAt(int).

 

SparseArray是android里为<Interger,Object>这样的Hashmap而专门写的class,目的是提高效率，其核心是折半查找函数（binarySearch）

http://developer.android.com/reference/android/util/SparseIntArray.html

 

二、源码

http://www.oschina.net/code/explore/android-2.2-froyo/android/util/SparseIntArray.java