Sorting ArrayList with Lambda in Java 8

Question

Could somebody show me a quick example how to sort an ArrayList alphabetically in Java 8 using the new lambda syntax.

Answer 1

Use list.sort(String::compareToIgnoreCase)

Using list.sort(String::compareTo) or list.sort(Comparator.naturalOrder()) will give incorrect (ie. non-alphabetical) results. It will sort any upper case letter before all lower case letters, so the array ["aAAA","Zzz", "zzz"] gets sorted to ["Zzz", "aAAA", "zzz"]

Answer 2

The syntax including a custom comparator is quite simple, and quick, for example here the ArrayList being sorted contains JSONObjects, and I will sort it based on a property called 'order':

arrayList.sort((JSONObject o1, JSONObject o2)->o1.getInt("order")-o2.getInt("order"));

I think this is a really nice and concise syntax, easy to read and less bulky than non-lambda syntax.

Answer 3

 List<Product> list = new ArrayList<>();
        List<String> list1 = new ArrayList<>();
        list.add(new Product(1));
        list.add(new Product(2));
        list.add(new Product(3));
        list.add(new Product(10));
 Collections.sort(list, Comparator.comparing((Product p) -> p.id));
        for (Product p : list) {
            System.out.println(p.id);
        }

Answer 4

For strings this would work

arrayList.sort((p1, p2) -> p1.compareTo(p2));

Answer 5

Suppose you have List of names(String) which you want to sort alphabetically.

List<String> result = names.stream().sorted(
                 Comparator.comparing(n->n.toString())).collect(Collectors.toList());

its working perfectly.

Answer 6

Are you just sorting Strings? If so, you don't need lambdas; there's no point. You just do

import static java.util.Comparator.*;

list.sort(naturalOrder());

...though if you're sorting objects with a String field, then it makes somewhat more sense:

list.sort(comparing(Foo::getString));