1. Favoring Composition
- The Groovy Way
Naresha K
@naresha_k
https://blog.nareshak.com/
APACHECON @HOME
Spt, 29th – Oct. 1st 2020

2. About me
Developer, Architect &
Tech Excellence Coach
Founder & Organiser
Bangalore Groovy User
Group
2

3. Object-Oriented
Maturity Model!
3

4. 2 No inheritance. Mostly
Procedural code
1 Inheritance Everywhere
0
No inheritance. Mostly
Procedural code
Evolution of OO Programmer 4

5. INHERITANCE
5

6. 6

7. 2 No inheritance. Mostly
Procedural code
1 Inheritance Everywhere
0
No inheritance. Mostly
Procedural code
Evolution of OO Programmer 7

8. Liskov Substitution
Principle
8

9. 2 Favour composition
1 Inheritance Everywhere
0
No inheritance. Mostly
Procedural code
Evolution of OO Programmer 9

10. Favour
Composition to Inheritance
10

11. The difference between
theory and practice is
in theory
somewhat smaller
than in practice
11

12. Inheritance is
Easy
12

13. List<String> phoneNumbers = new ArrayList<>()
phoneNumbers += ['19876512345', '19876512346',
‘919876512347', '49876512348']
println phoneNumbers
13

14. List<String> phoneNumbers = new ArrayList<>()
phoneNumbers += ['19876512345', '19876512346',
‘919876512347', '49876512348']
println phoneNumbers
println phoneNumbers.collect { "+" + it }
14

15. List<String> phoneNumbers = new ArrayList<>()
phoneNumbers += ['19876512345', '19876512346',
‘919876512347', '49876512348']
println phoneNumbers
println phoneNumbers.collect { "+" + it }
println phoneNumbers.find { it == '919876512347' }
15

16. List<String> phoneNumbers = new ArrayList<>()
phoneNumbers += ['19876512345', '19876512346',
‘919876512347', '49876512348']
println phoneNumbers
println phoneNumbers.collect { "+" + it }
println phoneNumbers.find { it == '919876512347' }
println phoneNumbers.usPhoneNumbers();
Method usPhoneNumbers() not
available in ArrayList
16

17. class PhoneNumbers extends ArrayList<String> {
List<String> usPhoneNumbers() {
iterator().findAll { number -> number.startsWith("1") }
}
}
17

18. PhoneNumbers phoneNumbers = new PhoneNumbers()
phoneNumbers += ['19876512345', '19876512346', '919876512347',
'49876512348']
println phoneNumbers
println phoneNumbers.collect { "+" + it }
println phoneNumbers.find { it == '919876512347' }
println phoneNumbers.usPhoneNumbers();
18

19. @ToString(includePackage = false, includes = "data")
class PhoneNumbers {
List<String> data = []
String find(Closure closure) {
data.find { closure }
}
public <T> List<T> collect(Closure<T> closure) {
data.collect(closure)
}
List<String> usPhoneNumbers() {
data.findAll { number -> number.startsWith("1") }
}
PhoneNumbers plus(List list) {
new PhoneNumbers(data: data + list)
}
}
19

20. @ToString(includePackage = false, includes = "data")
class PhoneNumbers {
List<String> data = []
String find(Closure closure) {
data.find { closure }
}
public <T> List<T> collect(Closure<T> closure) {
data.collect(closure)
}
List<String> usPhoneNumbers() {
data.findAll { number -> number.startsWith("1") }
}
PhoneNumbers plus(List list) {
new PhoneNumbers(data: data + list)
}
}
class PhoneNumbers extends ArrayList<String> {
List<String> usPhoneNumbers() {
iterator().findAll { number -> number.startsWith("1") }
}
}
20

21. @ToString(includePackage = false, includes = "data")
class PhoneNumbers {
@Delegate
List<String> data = []
List<String> usPhoneNumbers() {
data.findAll { number -> number.startsWith("1") }
}
}
21

22. @ToString(includePackage = false, includes = "data")
class PhoneNumbers {
@Delegate
List<String> data = []
List<String> usPhoneNumbers() {
data.findAll { number -> number.startsWith("1") }
}
}
PhoneNumbers phoneNumbers
phoneNumbers = ['19876512345', '19876512346', '919876512347',
'49876512348'] as PhoneNumbers
println phoneNumbers
println phoneNumbers.collect { "+" + it }
println phoneNumbers.find { it == '919876512347' }
println phoneNumbers.usPhoneNumbers();
22

23. 23

24. Bird sunny = new Bird()
sunny.fly()
24

25. Bird sunny = new Bird()
sunny.fly()
ButterFly aButterFly = new ButterFly()
aButterFly.fly()
25

26. Bird sunny = new Bird()
sunny.fly()
ButterFly aButterFly = new ButterFly()
aButterFly.fly()
interface Flyable {
void fly()
}
26

27. Bird sunny = new Bird()
sunny.fly()
ButterFly aButterFly = new ButterFly()
aButterFly.fly()
interface Flyable {
void fly()
}
List<Flyable> fliers = [sunny, aButterFly]
fliers.each { flier -> flier.fly() }
27

28. class Bird implements Flyable {
@Override
void fly() {
println "Flying..."
}
}
class ButterFly implements Flyable {
@Override
void fly() {
println "Flying..."
}
}
28

29. class Bird implements Flyable {
@Override
void fly() {
println "Flying..."
}
}
class ButterFly implements Flyable {
@Override
void fly() {
println "Flying..."
}
}
Potential violation of
DRY
principle
29

30. 30

31. class DefaultFlyable implements Flyable {
@Override
void fly() {
println "Flying..."
}
}
class Bird implements Flyable {
private Flyable defaultFlyable = new DefaultFlyable()
@Override
void fly() {
defaultFlyable.fly()
}
}
31

32. class DefaultFlyable implements Flyable {
@Override
void fly() {
println "Flying..."
}
}
class Bird implements Flyable {
@Delegate
private Flyable defaultFlyable = new DefaultFlyable()
}
interface Flyable {
void fly()
}
32

33. trait Flyable {
void fly() {
println "Flying..."
}
}
class Bird implements Flyable {}
class ButterFly implements Flyable {}
33

34. public interface Flyable {
public abstract void fly()
}
public static class Flyable$Trait$Helper {
public static void fly(Flyable $self) {
$self.println('Flying...')
}
}
public class Bird implements Flyable {
public void fly() {
Flyable$Trait$Helper.fly(this)
}
}
trait Flyable
34

35. interface Flyable {
void fly()
}
trait FlyableTrait implements Flyable {
@Override
void fly() {
println "Flying..."
}
}
35

36. class Actor implements Singer, Dancer {}
Actor actor = new Actor()
actor.sing()
actor.dance()
trait Singer {
void sing() {
println "Singing"
}
}
trait Dancer {
void dance() {
println "Dancing"
}
}
Composing multiple behaviours
36

37. trait BusinessObject {
UUID uuid = UUID.randomUUID()
}
class Product implements BusinessObject {
}
Product product = new Product()
println product.uuid
Composing state
37

38. public interface BusinessObject {
public abstract java.util.UUID getUuid()
public abstract void setUuid(java.util.UUID value)
}
public static interface BusinessObject$Trait$FieldHelper {}
public abstract static class BusinessObject$Trait$Helper {
public static java.util.UUID getUuid(BusinessObject $self) {
(( $self ) as
BusinessObject$Trait$FieldHelper).BusinessObject__uuid$get()
}
public static void setUuid(BusinessObject $self, java.util.UUID
value) {
(( $self ) as
BusinessObject$Trait$FieldHelper).BusinessObject__uuid$set(value)
}
}
38

39. public class Product implements BusinessObject,
BusinessObject$Trait$FieldHelper {
private java.util.UUID BusinessObject__uuid
}
39

40. class Person {
}
Person person = new Person()
person.fly()
Composing at Runtime
40

41. class Person {
}
Person person = new Person()
Flyable passanger = boardPlane(person)
passanger.fly()
Flyable boardPlane(Person person) {
person.withTraits FlyableTrait
}
41

42. trait JavaProgrammer {
def codeObjectOriented() {
println 'Coding OOP'
}
}
trait GroovyProgrammer extends JavaProgrammer {
def codeFunctional() {
println 'Coding FP'
}
}
class Developer implements GroovyProgrammer {}
Developer raj = new Developer()
raj.codeFunctional()
raj.codeObjectOriented()
Trait extending another Trait
42

43. trait Reader {
def read() { println 'Reading'}
}
trait Evaluator {
def eval() { println 'Evaluating'}
}
trait Printer {
def print() { println 'Printing'}
}
trait Repl implements Reader, Evaluator, Printer {
}
class GroovyRepl implements Repl{}
Repl groovyRepl = new GroovyRepl()
groovyRepl.read()
groovyRepl.eval()
groovyRepl.print()
Trait extending multiple Traits
43

44. interface MyInterface {
default void doSomething() {
println "Doing"
}
}
// is equivalent to
trait MyInterface {
void doSomething() {
println "Doing"
}
}
default methods in Groovy Interfaces
44

45. Function Composition
45

46. List<String> firstNamesOfDevs(List<Developer> devs, Closure
devSelector) {
List<Developer> selectedDevs = devSelector(devs)
selectedDevs.collect { it.name }
}
Closure groovyDevSelector = …
Closure javaDevSelector = …
Closure javaAndGroovyDevSelector = ?
println firstNamesOfDevs(developers, javaAndGroovyDevSelector)
46

47. List<String> firstNamesOfDevs(List<Developer> devs, Closure
devSelector) {
List<Developer> selectedDevs = devSelector(devs)
selectedDevs.collect { it.name }
}
Closure groovyDevSelector = …
Closure javaDevSelector = …
Closure javaAndGroovyDevSelector =
groovyDevSelector << javaDevSelector
println firstNamesOfDevs(developers, javaAndGroovyDevSelector)
47

48. Happy Composing
Thank You
APACHECON @HOME
Spt, 29th – Oct. 1st 2020