12. Solution: Parallel Streams

Solution: Parallel Streams

Main.java

import java.time.LocalDate;
import java.time.Year;
import java.time.ZoneId;
import java.util.Comparator;
import java.util.List;
import java.util.Map;
import java.util.concurrent.Callable;
import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.Future;
import java.util.stream.Collectors;

public final class SummarizeClients {
  public static void main(String[] args) throws Exception {

    List<UdacisearchClient> clients = ClientStore.getClients();
    int numClients = clients.size();

    ForkJoinPool pool = new ForkJoinPool();

    Future<Integer> totalQuarterlySpend =
        pool.submit(() ->
            clients
                .parallelStream()
                .mapToInt(UdacisearchClient::getQuarterlyBudget)
                .sum());

    Future<Double> averageBudget =
        pool.submit(() ->
            clients
                .parallelStream()
                .mapToDouble(UdacisearchClient::getQuarterlyBudget)
                .average()
                .orElse(0));

    Future<Long> nextExpiration =
        pool.submit(() ->
            clients
                .parallelStream()
                .min(Comparator.comparing(UdacisearchClient::getContractEnd))
                .map(UdacisearchClient::getId)
                .orElse(-1L));

    Future<List<ZoneId>> representedZoneIds =
        pool.submit(() ->
            clients
                .parallelStream()
                .flatMap(c -> c.getTimeZones().stream())
                .distinct()  // Or use Collectors.toSet()
                .collect(Collectors.toList()));

    Future<Map<Year, Long>> contractsPerYear =
        pool.submit(() ->
            clients
                .parallelStream()
                .collect(
                    Collectors.groupingByConcurrent(
                        SummarizeClients::getContractYear, Collectors.counting())));

    pool.shutdown();

    System.out.println("Num clients: " + numClients);
    System.out.println("Total quarterly spend: " + totalQuarterlySpend.get());
    System.out.println("Average budget: " + averageBudget.get());
    System.out.println("ID of next expiring contract: " + nextExpiration.get());
    System.out.println("Client time zones: " + representedZoneIds.get());
    System.out.println("Contracts per year: " + contractsPerYear.get());
  }

  private static Year getContractYear(UdacisearchClient client) {
    LocalDate contractDate =
        LocalDate.ofInstant(client.getContractStart(), client.getTimeZones().get(0));
    return Year.of(contractDate.getYear());
  }
}