Using Comparator.nullsFirst not working with reverse()

Question

I am trying to sort Car by three values: first by type, then within the "type" bucket I want to sort those by price (lowest to highest), then if there are any that have the same price, I want to sort by age (newest to oldest).

However, some Cars have a null price. In these cases, I want all the null values to be at the end of the list.

I am trying to use Comparator.nullsFirst and Comparator.nullsLast, but neither of these are doing anything. I end up getting all the nulls first (regardless of which one I use), then the items sorted on price. I am wondering if it is because I have .reverse() which is negating the nullsFirst/Last?

Here is what I am trying:

cars.stream().sorted(Comparator.comparingInt((Car car) -> car.getCarMetadata().getCarType().getPriority())
     .thenComparing((Car car -> car.getCarMetadata().getPrice(), Comparator.nullsLast(Double::compareTo)).reversed()
     .thenComparing((Car car) -> car.getAge).reversed()).collect(Collectors.toList());

Any ideas on this?

N.A · Accepted Answer · 2023-09-26 06:01:50Z

1

Just figured it out.. Moving the reversed() inside the comparison ended up working, like so:

cars.stream().sorted(Comparator.comparingInt((Car car) -> car.getCarMetadata().getCarType().getPriority())
     .thenComparing((Car car -> car.getCarMetadata().getPrice(), Comparator.nullsLast(Double::compareTo)).reversed()
     .thenComparing((Car car) -> car.getAge).reversed()).collect(Collectors.toList());

I'm not sure I totally understand why this fixed it though.

answered Sep 26, 2023 at 6:01

N.A

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1 Comment

Sören Over a year ago

I don't see the difference between the two code pieces.

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