How to sort list based on nested object property

Question

I am new to Java streams and I just want to sort the keys for my object.

So, I try something like this and it works

List<FooSelect> li= Arrays.stream(obj.getFoos().getFoo())  //Stream<Foo>
    .map(Foo::getSelect)                                   //Stream<FooSelect>
    .sorted(Comparator.comparing(FooSelect::getFoosKey))   //Stream<FooSelect>
    .collect(Collectors.toList());

This sorts it according to what I want.

But the result I get is in List<FooSelect> object, though I want it in List<Foo>.

How can I change the mapping after it is sorted?

I want to again change the response in

//Stream<Foo> after it is sorted.

I want something like

List<Foo> li = same result of code above;

Class : FooSelect
just has some String fields
string FooKey
string FooTKey

and getters and setters for that (one of them is getFoosKey by which I am sorting)

Class: Foo
private FooSelect select
private FooInsert insert

Foo(select, insert)

public FooSelect getSelect() {
return select; }

Same way setter.

@Aomine How can i do that ? I tried, but it gives me error only. Can you please just describe that line ? — s shah
– s shah, Commented Oct 3, 2019 at 16:08
show how Foo and FooSelect look like i.e. their definitions then it would make it easier for people to answer your post — Ousmane D.
– Ousmane D., Commented Oct 3, 2019 at 16:09
List<Foo> li = same result of code above; => List<FooSelect>, can you show us, how is that possible? — Naman
– Naman, Commented Oct 3, 2019 at 16:13

Ryuzaki L · Accepted Answer · 2019-10-03 16:27:20Z

1

You can use lambda expression in Comparator.comparing instead of method reference

List<Foo> res = foos.stream()             
                    .sorted(Comparator.comparing(fo->fo.getSelect().getFooKey()))
                    .collect(Collectors.toList());

For just sorting you don't even need stream

foos.sort(Comparator.comparing(fo->fo.getSelect().getFooKey()));

edited Oct 3, 2019 at 16:27

answered Oct 3, 2019 at 16:15

Ryuzaki L

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Comments

Naman · Accepted Answer · 2019-10-03 16:23:04Z

1

Remove the map. The map changes the object in the stream. Update the sorted statement as

.sorted(Comparator.comparing(f -> f.getSelect().getFoosKey()))

edited Oct 3, 2019 at 16:23

Naman

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answered Oct 3, 2019 at 16:14

mavriksc

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