Sort list of objects based on a value found in another list of object

Question

There are 2 lists of objects A and B. So List<A> and List<B>. A and B have a common Sting field id which connects them. B also has a numeric field value. We want to sort list A based on the value present in list B.

What's the best way to do it using Java APIs, perhaps like Comparator?

shmosel · Accepted Answer · 2021-06-30 05:23:40Z

5

I would create a map ranking id by value for efficient lookup:

Map<String, Integer> rank = listB.stream()
        .collect(Collectors.toMap(b -> b.id, b -> b.value));

Then you can construct a comparator based on your map and use it to sort the A list:

listA.sort(Comparator.comparing(a -> rank.get(a.id));

answered Jun 30, 2021 at 5:23

shmosel

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