method reference for instance method from static method

Question

Sorry for not clearly the title, i'm still new to this and even English.

Collections.sort(aList, (s1, s2) -> Float.compare(s1.getAFloat(), s2.getAFloat()));

As above, can I use method references? if s1 and s2 are Floats and they don't use get-a-float method then things become easier:

Collections.sort(aList,Float::compare);

But with s1.getAFloat() I don't know how to use method reference or even possible to use it, thanks for answer!

• sanit: You can visit tutorials of how method reference works. java8tips.readthedocs.io/en/latest/…

Answer 1

You can use

Collections.sort(aList, Comparator.comparing(ItemType::getAFloat));

And if the retrieved type aren't sortable already, you can give an additional comparator to comparing.

Answer 2

No you can't. Look into the following code.

List<Float> aList = Arrays.asList(5.2f, 9.7f);
Collections.sort(aList, (s1, s2) -> Float.compare(s1, s2));
Collections.sort(aList, Float::compare);

If your list elements were directly of Float type then you would have used method-reference.

If elements are not of Float type then you can do like this.

List<String> aList2 = Arrays.asList("5.2f", "9.7f"); 
aList2.stream().map(Float::valueOf).sorted(Float::compare)
 .collect(Collectors.toList());