Java: What is the difference between Stream.min() and Stream.max()?

min() — returns Optional with the minimum element. max() — returns Optional with the maximum element. They are logical opposites using the same Comparator-based selection mechanism.

min():

• Returns Optional<T>.
• Uses natural ordering or a custom Comparator.
• Empty stream returns Optional.empty().

1Optional<Integer> min = numbers.stream()
2    .min(Integer::compareTo);
3Optional<Integer> min = numbers.stream()
4    .min(Comparator.naturalOrder());

max():

• Returns Optional<T>.
• Uses natural ordering or a custom Comparator.
• Empty stream returns Optional.empty().

1Optional<Integer> max = numbers.stream()
2    .max(Integer::compareTo);
3Optional<Integer> max = numbers.stream()
4    .max(Comparator.naturalOrder());

Both:

• Terminal operations.
• Return Optional to handle empty streams.
• Can use Comparator for custom ordering.

1// Find longest string
2Optional<String> longest = words.stream()
3    .max(Comparator.comparing(String::length));
4
5// Find oldest person
6Optional<Person> oldest = people.stream()
7    .min(Comparator.comparing(Person::getAge));

Performance considerations:

• Both are O(n) — must examine every element.
• For parallel streams, each thread finds its local min/max, then they are compared.
• For primitive streams, use IntStream.min() which returns OptionalInt — no boxing.
• If you need both min and max, a single pass with IntSummaryStatistics is more efficient.

1// Single pass for both min and max
2IntSummaryStatistics stats = numbers.stream()
3    .mapToInt(Integer::intValue)
4    .summaryStatistics();
5int min = stats.getMin();
6int max = stats.getMax();

Key difference:

• min() — value-based, returns smallest.
• max() — value-based, returns largest.