Try It Yourself - SyntaxStudy Editor

HTML / CSS / JS

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

public class StreamReduceDemo {
    public static void main(String[] args) {
        List<Integer> numbers = List.of(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);

// reduce: sum
        int sum = numbers.stream()
            .reduce(0, Integer::sum);
        System.out.println("Sum: " + sum);

// reduce: product
        long product = numbers.stream()
            .reduce(1, (a, b) -> a * b);
        System.out.println("Product: " + product);

// IntStream — no boxing
        IntSummaryStatistics stats = numbers.stream()
            .mapToInt(Integer::intValue)
            .summaryStatistics();
        System.out.printf("Count=%d, Sum=%d, Min=%d, Max=%d, Avg=%.1f%n",
            stats.getCount(), stats.getSum(),
            stats.getMin(),   stats.getMax(), stats.getAverage());

// partitioningBy
        Map<Boolean, List<Integer>> evenOdd = numbers.stream()
            .collect(Collectors.partitioningBy(n -> n % 2 == 0));
        System.out.println("Even: " + evenOdd.get(true));
        System.out.println("Odd:  " + evenOdd.get(false));

// IntStream.range
        int sumTo100 = IntStream.rangeClosed(1, 100).sum();
        System.out.println("Sum 1..100 = " + sumTo100);

// flatMap: flatten nested lists
        List<List<Integer>> nested = List.of(List.of(1,2), List.of(3,4), List.of(5));
        List<Integer> flat = nested.stream()
            .flatMap(Collection::stream)
            .collect(Collectors.toList());
        System.out.println("Flattened: " + flat);
    }
}