Stream API

import java.util.*;
import java.util.stream.*;

List<Integer> numbers = List.of(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);

// Filter even numbers and sum squares
int sumOfSquares = numbers.stream()
    .filter(n -> n % 2 == 0)
    .mapToInt(n -> n * n)
    .sum();

// Grouping
Map<Boolean, List<Integer>> partitioned = numbers.stream()
    .collect(Collectors.partitioningBy(n -> n % 2 == 0));

// String join
String joined = numbers.stream()
    .map(String::valueOf)
    .collect(Collectors.joining(", ", "[", "]"));