Collections.sort: cannot convert from void to List

Question

I have this list of Entities:

@Entity
@Table(name = "filters")
public class Filters {

    private String filter_settings;

    private Integer position;
}

List:

List<RiskFilters> filter_list

I have simple numbers for 'position' - 1,2,3 and etc.

How I can sort the list of 'Filters' based on the 'position' number?

I tried this:

    List<RiskFilters> sorted_filter_list = Collections.sort(filter_list, Comparator.comparingInt(RiskFilters::getPosition));

But I get Type mismatch: cannot convert from void to List

Is there some way to fix this?

`Collections.sort()` does not return a value. It actually mutates (sorts) the List passed to it. Just run that method to sort it. — KellyM, Aug 10 '19 at 21:53
@PeterPenzov Just write ` Collections.sort(filter_list, Comparator.comparingInt(RiskFilters::getPosition));` to sort the List. As long as it has been instantiated, the List will now be sorted. — KellyM, Aug 10 '19 at 21:55
@KellyM ok, but I need to create a new sorted list from the old one. — Peter Penzov, Aug 10 '19 at 21:58
@PeterPenzov Collections.sort will sort whatever is passed to it. If you need two separate lists, just create a new list from the old (`List sorted_filter_list = new ArrayList(filtered_list)`) and then sort the "new" list `Collections.sort(sorted_filter_list, Comparator.comparingInt(RiskFilters::getPosition))` — KellyM, Aug 10 '19 at 22:05
@PeterPenzov so just `Collections.copy()` the `List` and `Collections.sort()` the copy. — Christian H. Kuhn, Aug 10 '19 at 22:55
There are already many questions on sorting in Java at stackoverflow. For the interactive help experience, try the chat. — tkruse, Aug 11 '19 at 00:20

score 2 · Accepted Answer · answered Aug 11 '19 at 01:09

Thats because Collections.sort(list) sorts the list you send them. You don't need to assign it back into you're list like you would with String.

List<RiskFilters> filter_list
Collections.sort(filter_list, Comparator.comparingInt(RiskFilters::getPosition));

1 Answers1