rnaufal

Collection<Car> allPeopleCars = people
                .stream()
                .map(Person::getCars)
                .flatMap(Optional::stream)
                .flatMap(Collection::stream)
                .collect(Collectors.toList());

rnaufal

Collection<Car> allPeopleCars = people
                .stream()
                .map(Person::getCars)
                .flatMap(mayHaveCars -> mayHaveCars.map(Collection::stream).orElseGet(Stream::empty))
                .collect(Collectors.toList());

rnaufal

Collection<Car> allPeopleCars = people
                .stream()
                .map(Person::getCars)
                .flatMap(mayHaveCars -> mayHaveCars.map(Collection::stream).orElse(Stream.empty()))
                .collect(Collectors.toList());

rnaufal

Collection<Car> allPeopleCars = people
                .stream()
                .map(Person::getCars)
                .flatMap(mayHaveCars -> mayHaveCars.isPresent() ? mayHaveCars.get().stream() : Stream.empty())
                .collect(Collectors.toList());

rnaufal

Collection<Car> markCars = people
                .stream()
                .filter(person -> "Mark".equals(person.getName()))
                .findFirst()
                .map(Person::getCars)
                .filter(Optional::isPresent)
                .map(Optional::get)
                .orElse(Collections.emptyList());

rnaufal

Person mark = new Person("Mark");
 
List<Person> people = ...

rnaufal

public class Person {

    private String name;

    .
    .
    .

    public Optional<Collection<Car>> getCars() {
        return Optional.ofNullable(cars);

rnaufal

data class Employee(val name: String, val department: String)
 
val mark = Employee("Mark", "Accounting")
val john = Employee("John", "Management")
val smith = Employee("Smith", "Administrative")
val paul = Employee("Paul", "Accounting")
 
val employees = listOf(mark, john, smith, paul)
 
val employeesByDepartment = employees.groupBy { it.department }

rnaufal

public class Employee {
 
    private final String name;
 
    private final String department;
 
    public Employee(final String name, final String department) {
        this.name = name;
        this.department = department;
    }

rnaufal

package com.beust.coding.challenge.slidingwindowmap;

import java.util.HashMap;
import java.util.Map;
import java.util.Set;

/**
 * 
 * @author rnaufal
 *