Collections vs Arrays regarding sort()

Question

Collections vs Arrays regarding sort() What is the difference between these two regarding sort() method? I know Arrays' sort() is using binary search for sort(), what about Collections'? And how to choose which to use? Thanks!

Answer 1

Well, besides operating on different stuff (Collections.sort operates on a List, and Arrays.sort operates on an array), java.util.Collections.sort() simply calls java.util.Arrays.sort() to do the heavy lifting.

Also, for what it's worth, notice that Arrays.sort runs a merge sort.

Answer 2

Collections.sort() Operates on List Whereas Arrays.sort() Operates on an Array.

Arrays.sort() uses Dual-Pivot Quicksort for Primitive Arrays and MergeSort for sorting array of Objects.

Example of Collections.sort() :

 ArrayList<Integer> arr = new ArrayList<Integer>();
 arr.add(15);
 arr.add(10);
 arr.add(5); 
 arr.add(2); 

 Collections.sort(arr);

Example of Arrays.sort() :

int[] arr = new int[4]
 arr[0]=15;
 arr[1]=10;
 arr[2]=5; 
 arr[3]=2; 

 Arrays.sort(arr);

Answer 3

I know Arrays' sort() is using binary search for sort()

No, you don't know any such thing. It doesn't do that. See the Javadoc.

The statement doesn't even make sense. You can't 'use binary search for sort'. Binary search only worked when the data is already sorted. Maybe what you read is that Arrays.binarySearch() assumes the data is sorted.

Answer 4

Use Arrays.sort() if you're dealing with an Array. Use Collections.sort() if you're dealing with something that implements the Collection interface (eg ArrayList).

Answer 5

As the other answers have said, you would use Collections.sort() when dealing with an object that implements the Collection interface and the Arrays.sort() method when dealing with an Array.

A related question is what type of data structures are better if you want to sort a set of values. If you need to use a List, then I would suggest using a LinkedList since insertions run in O(1) where something like an ArrayList would be O(n).

You could also opt for using a SortedSet if there will be no duplicates or having duplicates is unwanted. That way you don't have to bother with using an external sort method.

Answer 6

Collection.sort is used when you dealing with lists and arrays.sort is sued when dealing with arrays. But internally Collection.sort uses Arrays.sort method only. Now internally sorting is done based in Timosrt technique instead of merge sort , because stable, adaptive arrays takes O(nlogn) comparisons in Merge sort but in Timsort worst case it will take O(nlogn) and in worst case storage requies n/2 in Timsort but it is not in the case of Merge sort technique.