Java sorting a Collection in functional style [duplicate]

Question

I am learning Java and while trying to sort an ArrayList of objects I found this way of doing it.

ArrayList<String> al = new ArrayList<String>(); al.add("Friends"); al.add("Dear"); al.add("Is"); al.add("Superb"); Collections.sort(al); System.out.println("List after the use of" + " Collection.sort() :\n" + al);

This method works but since I come from a functional programming background I was wondering what are the most elegant ways to do sorting on a collection in Java in functional style (so by returning a new collection and not by modifying the original one).

Java 8 streams is what you are after: docs.oracle.com/javase/8/docs/api/java/util/stream/… — stridecolossus
– stridecolossus, Commented Dec 1, 2020 at 10:49
thanks to everyone who answered,the stream API seems to be what I'm looking for — Alessandro Messori
– Alessandro Messori, Commented Dec 1, 2020 at 10:56
Why not wrap copying the list plus sorting the copy into your own method? If the language/framework you're using doesn't quite match the language you want to use for expressing your program, create the missing parts. — Ralf Kleberhoff
– Ralf Kleberhoff, Commented Dec 1, 2020 at 12:06

Mustafa Poya · Accepted Answer · 2020-12-01 11:00:19Z

This is not like Collections.sort() where the parameter reference gets sorted. In this case you just get a sorted stream that you need to collect and assign to another variable eventually:

List result = al.stream().sorted((o1, o2) -> o1.compareTo(o2)).collect(Collectors.toList());

or :

ArrayList<String> al = new ArrayList<String>(); al.add("Friends"); al.add("Dear"); al.add("Is"); al.add("Superb"); System.out.println(al); al.sort((o1, o2) -> o1.compareTo(o2)); System.out.println(al);

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