Beyond Lambdas - the Aftermath

A presentation at GeeCon Kraków 2016 in May 2016 in Kraków, Poland by Daniel Sawano

About us… Daniel Sawano, Daniel Deogun Kraków, 11-13 May 201 6 Daniel Deogun Daniel Sawano Stockholm - Gothenburg - Malmoe - Umea - New York

[inert code here] Daniel Sawano, Daniel Deogun Kraków, 11-13 May 201 6

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 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 }

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 Daniel Sawano, Daniel Deogun Kraków, 11-13 May 201 6 [Questions]

Code examples can be found here: https://github.com/sawano/beyond-lambdas-the-aftermath Daniel Sawano, Daniel Deogun Kraków, 11-13 May 201 6

Thank you! @DanielSawano @DanielDeogun Daniel Sawano, Daniel Deogun Kraków, 11-13 May 201 6

Daniel Sawano
@sawano

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As Java developers we are used to having rich ecosystems of libraries and tools that make our lives easier. As of the release of Java 8, we finally got our hands on building blocks like lambdas, optionals, and streams. All sorts of tools that help us write more concise code. But now, when the honeymoon is over, are there any downsides to Java 8 or is it a silver bullet? Are there any new anti-patterns emerging? Or subtle bugs caused by the new style of programming? Have there been any lessons learned? Are there any best practices?

If you are interested in learning about the challenges encountered when moving over to a functional style of Java programming, what code constructs to avoid, and best practices to use, well then this session is for you.

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https://github.com/sawano/beyond-lambdas-the-aftermath

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