如何实现Collection.sort？

Question

I'm using Collection.sort(Array<objectX>, Comperator<objectX>) in java/Android.

In my comperator I compare two objects using their ID.

How can I know in which method this sort is made? (quicksort, mergesort...)?

Answer 1

Technically speaking which algorithm to use is not specified (in other words it's runtime library specific).

From the documentation :

For example, the algorithm used by sort does not have to be a mergesort, but it does have to be stable .

In practice, it typically chooses one sorting technique of of several based on the length of the list etc. In the standard implementation from Sun/Oracle it chooses between insertion sort (if the length is less than 7) and merge sort otherwise.

Answer 2

You can look at the code if you want:

http://grepcode.com/file/repository.grepcode.com/java/root/jdk/openjdk/6-b14/java/util/Collections.java