Java 17 - Inconsistent Behavior in Stream API When Collecting to Map with Custom Key Comparator
I tried several approaches but none seem to work... I'm encountering inconsistent behavior when trying to collect elements into a `Map` using Java 17's Stream API, specifically when applying a custom comparator for the keys. The goal is to group a list of objects by a specific property, but I'm ending up with unexpected results. Here's the code snippet I'm working with: ```java import java.util.List; import java.util.Map; import java.util.stream.Collectors; class Person { String name; int age; Person(String name, int age) { this.name = name; this.age = age; } } public class StreamExample { public static void main(String[] args) { List<Person> people = List.of( new Person("Alice", 30), new Person("Bob", 25), new Person("Alice", 28) ); Map<String, Person> groupedByName = people.stream() .collect(Collectors.toMap( p -> p.name, p -> p, (existing, replacement) -> existing.age < replacement.age ? existing : replacement, TreeMap::new // Using TreeMap to apply natural ordering )); groupedByName.forEach((name, person) -> System.out.println(name + ": " + person.age) ); } } ``` In this code, I'm trying to collect `Person` objects by their `name`, preferring the one with the smaller age in case of duplicates. However, when I run this, the output is not what I expect—I'm seeing duplicates for names instead of a single entry. Specifically, the printed output looks like this: ``` Alice: 30 Bob: 25 Alice: 28 ``` I expected to only see one entry for 'Alice' with the age of 28 being preferred, but it seems to be retaining both entries. I've tried using different strategies for merging, but these haven't resolved the issue. I suspect this might be related to the behavior of the `TreeMap` with respect to the ordering of keys when duplicates exist. Is there a specific way to handle this or is there something I'm missing in my implementation? Any insights would be appreciated! This is part of a larger application I'm building. I'm working on a REST API that needs to handle this. Any advice would be much appreciated.