Java8 lambda: sort a stream in reverse order?

Question

I have this list that I want to order in reserve order, but I didn't find any .reversed() function in autocomplete assist

 myMenus(user)
                .stream()
                .filter(mps ->  mps.get1PercentageChange() > 0 &&
                                mps.get2PercentageChange() > 0 &&
                                mps.get3PercentageChange() > 0 &
                                mps.get4PercentageChange() > 0)
                .sorted(comparing(mps -> mps.getDailyPercentageChange()))
                .collect(toList());

I have also tried:

myMenus(user)
        .stream()
        .filter(mps ->  mps.get1PercentageChange() > 0 &&
                        mps.get2PercentageChange() > 0 &&
                        mps.get3PercentageChange() > 0 &
                        mps.get4PercentageChange() > 0)
        .sorted(comparing(mps -> mps.getDailyPercentageChange()).reversed())
        .collect(toList());

but then I have the compilation error:

Cannot infer type argument(s) for <T, U> comparing(Function<? super T,? 
     extends U>)

How about just using comparing(mps -> -mps.getDailyPercentageChange())? — Holger
– Holger, Commented Jun 1, 2018 at 14:43

Ousmane D. · Accepted Answer · 2018-06-01 15:26:21Z

8

It's a type inference issue. You'll need to help the compiler out.

few things you could try:

.sorted(comparing(T::getDailyPercentageChange).reversed())

or

.sorted(comparing((T mps) -> mps.getDailyPercentageChange()).reversed())

Where T is the type of elements being compared.

edited Jun 1, 2018 at 15:26

answered Jun 1, 2018 at 15:21

Ousmane D.

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Comments

Jean-Baptiste Yunès · Accepted Answer · 2018-06-01 14:45:27Z

5

Comparators have a reversed method to get the reverse ordering, so :

.sorted(comparing(mps -> mps.getDailyPercentageChange()).reversed())

should work.

answered Jun 1, 2018 at 14:45

Jean-Baptiste Yunès

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2 Comments

jub0bs Over a year ago

How about using a method reference instead: .sorted(comparing(Mps::getDailyPercentageChange).reversed()) (where Mps is the type of mps)? That would be a bit more readable.

senjin.hajrulahovic Over a year ago

Depending on the class name length, a lambda can sometimes be conciser. I also presume that Mps is not the actual class name but an acronym.

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