Beyond Lambdas - the Aftermath

Beyond Lambdas, the aftermath @DanielSawano @DanielDeogun Spotify 2016

About Us… Daniel Deogun Daniel Sawano Omegapoint Stockholm - Gothenburg - Malmoe - Umea - New York

[insert code here]

Optionals 1 7
final Oracle oracle = new Oracle(); 8
9 String _() { 10
final Advise advise = currentAdvise(); 11
12
if (advise != null ) { 13
return advise.cheap(); 14 } 15
else { 16
return oracle.advise().expensive(); 17 } 18 }

Optionals 1 25
final Oracle oracle = new Oracle(); 26
27 String _() { 28
final Advise advise = currentAdvise(); 29
30
return Optional.ofNullable(advise) 31 .map(Advise::cheap) 32 .orElse(oracle.advise().expensive()); 33 }

Optionals 1 25
final Oracle oracle = new Oracle(); 26
27 String _() { 28
final Advise advise = currentAdvise(); 29
30
return Optional.ofNullable(advise) 31 .map(Advise::cheap) 32 .orElseGet( () -> oracle.advise().expensive()); 33 }

Optionals 2 26 String _( final Optional<String> optOfSomeValue) { 27
28
return optOfSomeValue.map(v -> calculate(v)) 29 .filter(someCriteria()) 30 .map(v -> transform(v)) 31 .orElseGet(() -> completelyDifferentCalculation()); 32
33 }

Optionals 2 26 String _( final Optional<String> optOfSomeValue) { 27
28
if (optOfSomeValue.isPresent()) { 29
final String calculatedValue = calculate(optOfSomeValue.get()); 30
if (someCriteria().test(calculatedValue)) { 31
return transform(calculatedValue); 32 } 33 } 34
35
return completelyDifferentCalculation(); 36
37 }

Optionals 2 26 String _() { 27
return value() 28 .flatMap(v -> firstCalculation(v)) 29 .orElseGet(() -> completelyDifferentCalculation()); 30 } 31
32 Optional<String> value() { 33
return Optional.of(someValue()); 34 } 35
36 Optional<String> firstCalculation( final String v) { 37
return Optional.of(calculate(v)) 38 .filter(someCriteria()) 39 .map(value -> transform(value)); 40 }

Optionals 3 27 <T> void _( final Optional<T> argument) { 28 argument.map(a -> doSomething(a)); 29 }

Optionals 3 25 <T> void _( final T argument) { 26
if (argument != null ) { 27 doSomething(argument); 28 } 29 }

Optionals 3 26 <T> void _( final T argument) { 27 doSomething(notNull(argument)); 28 }

Streams 1 30 @Test 31
public void _() { 32
33
final Stream<String> stream = elements().stream() 34 .sorted(); 35
36
final String result = stream.collect(joining( "," )); 37
38 assertEquals( "A,B,C" , result); 39
40 } 41
42
static List<String> elements() { 43
return asList( "C" , "B" , null , "A" ); 44 }

Streams 1 31 @Test 32
public void _() { 33
34
final Stream<String> stream = elements().stream() 35 .filter(Objects::nonNull) 36 .sorted(); 37
38
final String result = stream.collect(joining( "," )); 39
40 assertEquals( "A,B,C" , result); 41
42 } 43
44
static List<String> elements() { 45
return asList( "C" , "B" , null , "A" ); 46 }

Streams 2 27 @Test 28
public void _() { 29
30
final long idToFind = 6 ; 31
final Predicate<Item> idFilter = item -> item.id().equals(idToFind); 32
33 service().itemsMatching(idFilter) 34 .findFirst() 35 .ifPresent(Support::doSomething); 36
37 }

Streams 2 28 @Test 29
public void _() { 30
31
final long idToFind = 6 ; 32
final Predicate<Item> idFilter = item -> item.id().equals(idToFind); 33
34 service().itemsMatching(idFilter) 35 .reduce(toOneItem()) 36 .ifPresent(Support::doSomething); 37
38 } 39
40 BinaryOperator<Item> toOneItem() { 41
return (item, item2) -> { 42
throw new IllegalStateException( "Found more than one item with the same id" ); 43 }; 44 }

Streams 3 29
private final UserService userService = new UserService(); 30
private final OrderService orderService = new OrderService(); 31
32 @Test 33
public void _() { 34 givenALoggedInUser(userService); 35
36 itemsToBuy().stream() 37 .map(item -> new Order(item.id(), currentUser().id())) 38 .forEach(orderService::sendOrder); 39
40 System.out.println(format( "Sent %d orders" , orderService.sentOrders())); 41 } 42
43 User currentUser() { 44
final User user = userService.currentUser(); 45 validState(user != null , "No current user found" ); 46
return user; 47 }

Streams 3 29
private final UserService userService = new UserService(); 30
private final OrderService orderService = new OrderService(); 31
32 @Test 33
public void _() { 34 givenALoggedInUser(userService); 35
36
final User user = currentUser(); 37 itemsToBuy().parallelStream() 38 .map(item -> new Order(item.id(), user.id())) 39 .forEach(orderService::sendOrder); 40
41 System.out.println(format( "Sent %d orders" , orderService.sentOrders())); 42 } 43
44 User currentUser() { 45
final User user = userService.currentUser(); 46 validState(user != null , "No current user found" ); 47
return user; 48 }

LAmbdas 1 28
static Integer numberOfFreeApples( final User user, 29
final Function<User, Integer> foodRatio) { 30
return 2

• foodRatio.apply(user); 31 } 32

33 @Test 34
public void _() { 35

36
final Function<User, Integer> foodRatioForVisitors = u -> u.age() > 12 ? 2 : 1 ; 37

38
final int numberOfFreeApples = numberOfFreeApples(someUser(), foodRatioForVisitors); 39

40 System.out.println(format( "Number of free apples: %d" , numberOfFreeApples)); 41

42 }

LAmbdas 1 29 @Test 30
public void _() { 31
32
final Function<User, Integer> foodRatioForVisitors = u -> u.age() > 12 ? 2 : 1 ; 33
final Function<User, Integer> age = User::age; 34
35
final int numberOfFreeApples_1 = numberOfFreeApples(someUser(), foodRatioForVisitors); 36
final int numberOfFreeApples_2 = numberOfFreeApples(someUser(), age); // This is a bug!

37
38 System.out.println(format( "Number of free apples (1): %d" , numberOfFreeApples_1)); 39 System.out.println(format( "Number of free apples (2): %d" , numberOfFreeApples_2)); 40
41 }

LAmbdas 1 28 @FunctionalInterface 29
interface FoodRatioStrategy { 30
31 Integer ratioFor(User user); 32 } 33
34
static Integer numberOfFreeApples( final User user, 35
final FoodRatioStrategy ratioStrategy) { 36
return 2

• ratioStrategy.ratioFor(user); 37 } 38

39 @Test 40

public void _() { 41

42
final FoodRatioStrategy foodRatioForVisitors = user -> user.age() > 12 ? 2 : 1 ; 43
final Function<User, Integer> age = User::age; 44

45
final Integer numberOfFreeApples_1 = numberOfFreeApples(someUser(), foodRatioForVisitors); 46
//final Integer numberOfFreeApples_2 = numberOfFreeApples(someUser(), age);

47

48 System.out.println(format( "Number of free apples (1): %d" , numberOfFreeApples_1)); 49 }

LAmbdas 2 25 @Test 26
public void should_build_tesla() { 27
28 assertEquals( 1000 , new TeslaFactory().createTesla().engine().horsepower()); 29
30 } 31
32 @Test 33
public void should_build_volvo() { 34
35 assertEquals( 250 , new VolvoFactory().createVolvo().engine().horsepower()); 36
37 }

LAmbdas 3 29 @Test 30
public void _() { 31
32
final List<Integer> values = asList( 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 ); 33
34 allEvenNumbers(values); 35
36 System.out.println( "Hello" ); 37
38 } 39
40
static List<Integer> allEvenNumbers( final List<Integer> values) { 41
return values.stream() 42 .filter(Support::isEven) 43 .collect(toList()); 44 }

LAmbdas 3 31 @Test 32
public void _() { 33
34
final List<Integer> values = asList( 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 ); 35
36
final Supplier<List<Integer>> integers = () -> allEvenNumbers(values); 37
38 System.out.println(integers.get()); 39
40 } 41
42
static List<Integer> allEvenNumbers( final List<Integer> values) { 43
return values.stream() 44 .filter(Support::isEven) 45 .collect(toList()); 46 }

LAmbdas 4 24
private final String pattern; 25
26
public _14( final String pattern) { 27
this .pattern = pattern; 28 } 29
30
public List<String> allMatchingElements( final List<String> elements) { 31
return elements.stream() 32 .filter(e -> e.contains(pattern)) 33 .collect(toList()); 34 }

LAmbdas 4 25
private final String pattern; 26
27
public _14( final String pattern) { 28
this .pattern = pattern; 29 } 30
31
public List<String> allMatchingElements( final List<String> elements) { 32
return elements.stream() 33 .filter(matches(pattern)) 34 .collect(toList()); 35 } 36
37
private Predicate<String> matches( final String pattern) { 38
return e -> e.contains(pattern); 39 }

Q & A [Questions]

Code examples can be found here: https://github.com/sawano/beyond-lambdas-the-aftermath

Thank you! @DanielSawano @DanielDeogun