imports.java

import java.util.stream.*;
import static java.util.Map.*;
import static java.util.stream.Collectors.*;
import java.util.*;

import static java.util.stream.Collectors.groupingBy;

class Payment
{
    private final int value;

    public Payment(final int value)
    {
        this.value = value;
    }

    public int getValue()
    {
        return value;
    }

    @Override
    public String toString()
    {
        return "Payment{" +
            "value=" + value +
            '}';
    }
}

class Setting
{
    static Optional<Setting> lookupSettingByName(final String name)
    {
        return Optional.ofNullable(System.getProperty(name))
                       .map(Setting::new);
    }

    private final String value;

    Setting(final String value)
    {
        this.value = value;
    }

    public String getValue()
    {
        return value;
    }

    public String toString()
    {
        return "[value="+value+"]";
    }
}

class Booking
{
    static Optional<Booking> lookupBooking(final String reference)
    {
        return reference.startsWith("LCY")
             ? Optional.of(new Booking(reference))
             : Optional.empty();
    }

    private final String reference;

    Booking(final String reference)
    {
        this.reference = reference;
    }

    public String getReference()
    {
        return reference;
    }

    public String toString()
    {
        return "Booking{"+reference+"}";
    }
}

class Ui
{
    static void displayCheckIn(final Booking booking)
    {
        System.out.println("Checking in ... " + booking);
    }

    static void displayMissingBookingPage()
    {
        System.out.println("Missing Booking");
    }
}

class Client
{
    private final String address;

    Client(String address)
    {
        this.address = address;
    }

    public String toString()
    {
        return "Client{address="+address+"}";
    }
}

public class Expense {
    private final long amount;
    private final int year;
    private final List<Tag> tags;

    public Expense(long amount, int year, List<Tag> tags) {
        this.amount = amount;
        this.year = year;
        this.tags = tags;
    }

    public long getAmount() {
        return amount;
    }

    public int getYear() {
        return year;
    }

    public List<Tag> getTags() {
        return tags;
    }

    @Override
    public String toString() {
        return "Expense{" +
                "amount=" + amount +
                ", year=" + year +
                ", tags=" + tags +
                '}';
    }
}

public enum Tag {
    FOOD, ENTERTAINMENT, TRAVEL, UTILITY
}

Optional<Client> findClient(final String clientId)
{
    return "aClient".equals(clientId)
         ? Optional.of(new Client("London"))
         : Optional.empty();
}

Optional<Client> lookupCompanyDetails(final String clientId)
{
    return "anotherCompany".equals(clientId)
         ? Optional.of(new Client("Cambridge"))
         : Optional.empty();
}

List<String> SETTING_NAMES = List.of("userHome", "user.home");

List<Payment> paymentsByValue =
	Stream.of(900, 700, 500, 300, 100, 0).map(Payment::new).collect(toList());

String bookingReference = "LCY to ANR"

List<String> toc = new ArrayList<>(List.of(
    "  Introduction",
    "  Collection Factory Methods",
    "    motivation",
    "    of()",
    "    ofEntries()",
    "  Streams",
    "    ofNullable (properties)",
    "    takeWhile/dropWhile (paymentsByValue)",
    "    iterate (termination)",
    "  Collectors",
    "    filtering",
    "    flatMapping",
    "  Optional",
    "    stream (Setting)",
    "    ifPresentOrElse (Flight Bookings)",
    "    or (Client addresses)",
    "  Conclusions"));

int tocIndex = 0;

void printToc()
{
    toc.forEach(System.out::println);
}

void next()
{
    String current = toc.get(tocIndex);
    current = "✓" + current.substring(1);
    toc.set(tocIndex, current);
    tocIndex++;
    printToc();
}

String takeWhile = "paymentsByValue.stream().filter(transaction -> transaction.getValue() >= 500).collect(toList());";

String iterate = "Stream.iterate(1, n -> n+ 1).filter(n -> n < 5).forEach(System.out::println)";

String optionalStream = "Setting.lookupSettingByName";

String optionalPresentOrElse = "Booking.lookupBooking(), Ui.displayCheckIn(booking.get()), Ui.displayMissingBookingPage()"

String optionalOr = "findClient, lookupCompany"

List<Expense> purchases = List.of(
            new Expense(500, 2016, List.of(Tag.FOOD, Tag.ENTERTAINMENT)),
            new Expense(1_500, 2016, List.of(Tag.UTILITY)),
            new Expense(700, 2015, List.of(Tag.TRAVEL, Tag.ENTERTAINMENT)));