Java / Android比ArrayList快什么？

Question

What is faster than ArrayList<String> in Java ? I have a list which is of an undefined length. (sometimes 4 items, sometimes 100).

What is the FASTEST way to add and get it from any list ? arrayList.add(string) and get() are very slow.

Is there a better way for this? ( string s[] and then copyArray are the slowest?)

Answer 1

Faster for what?

"basically arraylist.add(string) and get() is very slow." - based on what evidence? And compared to what? (No need for the word 'basically' here - it's a high tech "um".) I doubt that ArrayList is the issue with your app. Profiling your code is the only way to tell whether or not you're just guessing and grasping at straws.

Even an algorithm that's O(n^2) is likely to be adequate if the data set is small.

You have to understand the Big-Oh behavior of different data structures to answer this question. Adding to the end of an ArrayList is pretty fast, unless you have to resize it. Adding in the middle may take longer.

LinkedList will be faster to add in the middle, but you'll have to iterate to get to a particular element.

Answer 2

100 items is not very many. Your bottleneck is elsewhere.

Answer 3

Both add() to end of list and get() should run in O(1). And since length is undefined, you can't use a fixed length array. You can't do any better I'm afraid.

add(int index, E element) takes linear time for worst case though if that's why you think it's slow. If that is the case, either use Hashtable (insertion takes constant time) or TreeMap (insertion takes logarithmic time).

Answer 4

Take a look the Jodd Utilities . They have some collections that implement ArrayList but on primatives (jodd/util/collection/), such as IntArrayList. So if you're creating a ArrayList of int, float, double, etc.. it will be faster and consume less memory.

Even faster than that is what they call a FastBuffer, which excels at add() and can provide a get() at O(1).

The classes have little interdependency, so it's easy to just drop in the class you need into your code.

Answer 5

You can use javolution library. http://javolution.org

http://javolution.org/target/site/apidocs/javolution/util/FastList.html

ist much faster than arraylist ;)

Answer 6

尝试使用哈希表会更快