Java: What is the difference between Stream.distinct() and Stream.filter()?

distinct() — removes duplicate elements. filter() — removes elements by condition. Think of distinct() as a deduplication filter, while filter() as a selective sieve.

distinct():

• Uses equals() and hashCode() for comparison.
• Stateful — remembers seen elements.
• Maintains encounter order.

1List<Integer> result = List.of(1,2,2,3,3,3).stream()
2    .distinct()
3    .toList();
4// [1, 2, 3]

filter():

• Uses a Predicate.
• Stateless — no memory of previous elements.
• Custom condition.

1List<Integer> result = List.of(1,2,3,4,5).stream()
2    .filter(x -> x % 2 == 0)
3    .toList();
4// [2, 4]

Key difference:

• distinct() — remove duplicates, stateful.
• filter() — remove by condition, stateless.