functional_java/src/main/java/streams/FlatMapDemo.java at main · 66-24/functional_java · GitHub

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package streams;

import java.util.List;

import java.util.stream.Stream;

public class FlatMapDemo {

public static void main(String[] args) {

Customer sheridan = new Customer("Sheridan");

Customer ivanova = new Customer("Ivanova");

Customer garibaldi = new Customer("Garibaldi");

sheridan.addOrder(new Order(1))

.addOrder(new Order(2))

.addOrder(new Order(3));

ivanova.addOrder(new Order(4))

.addOrder(new Order(5));

List<Customer> customers = List.of(sheridan, ivanova, garibaldi);

// map for 1-1 customer to name --> Stream<String>

customers.stream()

.map(Customer::getName) // function<Customer,String>

.forEach(System.out::println);

// map 1-many customer to orders --> Stream<List<Order>>

customers.stream()

.map(Customer::getOrders) // function<Customer,List<Order>>

.forEach(System.out::println);

// map 1-many customer to orders.stream() --> Stream<Stream<Order>>

customers.stream()

.map(customer -> customer.getOrders().stream()) // function<Customer,Stream<Order>>

.forEach(System.out::println);

// stream() on an empty collection is already an empty Stream

customers.stream()

.flatMap(customer -> customer.getOrders().stream()) // function<Customer,Stream<Order>>

.forEach(System.out::println);

// flatMap 1-many customer to orders.stream() --> Stream<Order>

// Note: extra detail included just for illustration;

// stream() on an empty collection already returns an empty stream

customers.stream()

.flatMap(customer ->

customer.getOrders().isEmpty() ? Stream.empty() :

customer.getOrders().stream())

.forEach(System.out::println);

}

functional_java/src/main/java/streams/FlatMapDemo.java at main · 66-24/functional_java · GitHub

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