Convert to Set

Question

Convert to Set

Accepted Answer

Collectors.toSet() is a collector that gathers stream elements into a Set, automatically discarding duplicates in the process.

Key Points:
• collect(Collectors.toSet()) uses the elements' equals()/hashCode() to deduplicate, just like any Set implementation.
• The specific Set implementation returned isn't guaranteed - typically a HashSet, so iteration order isn't preserved.
• For an ordered, deduplicated result, use Collectors.toCollection(LinkedHashSet::new) instead.
• This is a simpler alternative to distinct().collect(toList()) when you specifically need Set semantics rather than a list.
• Since Sets don't allow duplicates, converting a list with repeated values directly shrinks the resulting collection size.

Example:
Given the list [1, 2, 2, 3, 3, 3], collecting into a Set produces {1, 2, 3}, with duplicates removed and no guaranteed ordering.

Code Example:
```
Set uniqueNumbers = numbers.stream()
        .collect(Collectors.toSet());
```

Interview Tip:
A concise interview answer is:

"Collecting a stream with Collectors.toSet() gathers the elements into a Set, which removes duplicates based on equals()/hashCode() as a side effect of Set semantics. If I need a predictable iteration order too, I use Collectors.toCollection(LinkedHashSet::new) instead."