DiffUtil

public class DiffUtil
extends Object

DiffUtil is a utility class that can calculate the difference between two lists and output a list of update operations that converts the first list into the second one.

It can be used to calculate updates for a RecyclerView Adapter. See ListAdapter and AsyncListDiffer which can compute diffs using DiffUtil on a background thread.

DiffUtil uses Eugene W. Myers's difference algorithm to calculate the minimal number of updates to convert one list into another. Myers's algorithm does not handle items that are moved so DiffUtil runs a second pass on the result to detect items that were moved.

If the lists are large, this operation may take significant time so you are advised to run this on a background thread, get the DiffUtil.DiffResult then apply it on the RecyclerView on the main thread.

This algorithm is optimized for space and uses O(N) space to find the minimal number of addition and removal operations between the two lists. It has O(N + D^2) expected time performance where D is the length of the edit script.

If move detection is enabled, it takes an additional O(N^2) time where N is the total number of added and removed items. If your lists are already sorted by the same constraint (e.g. a created timestamp for a list of posts), you can disable move detection to improve performance.

The actual runtime of the algorithm significantly depends on the number of changes in the list and the cost of your comparison methods. Below are some average run times for reference: (The test list is composed of random UUID Strings and the tests are run on Nexus 5X with M)

• 100 items and 10 modifications: avg: 0.39 ms, median: 0.35 ms
• 100 items and 100 modifications: 3.82 ms, median: 3.75 ms
• 100 items and 100 modifications without moves: 2.09 ms, median: 2.06 ms
• 1000 items and 50 modifications: avg: 4.67 ms, median: 4.59 ms
• 1000 items and 50 modifications without moves: avg: 3.59 ms, median: 3.50 ms
• 1000 items and 200 modifications: 27.07 ms, median: 26.92 ms
• 1000 items and 200 modifications without moves: 13.54 ms, median: 13.36 ms

Due to implementation constraints, the max size of the list can be 2^26.

Summary

Inherited methods
From class java.lang.Object Object clone() boolean equals(Object arg0) void finalize() final Class<?> getClass() int hashCode() final void notify() final void notifyAll() String toString() final void wait(long arg0, int arg1) final void wait(long arg0) final void wait()

Public methods

DiffUtil.DiffResult calculateDiff (DiffUtil.Callback cb)

DiffUtil.DiffResult calculateDiff (DiffUtil.Callback cb, 
                boolean detectMoves)