Slides from GR8 Conf EU 2019 talk - "Groovy Refactoring Patterns". In this talk, I share the refactoring patterns I observed during Groovy development.

1. Groovy
Refactoring Patterns
Naresha K
@naresha_k
https://blog.nareshak.com/

2. About me
Developer, Coach, Consultant
Founder & Organiser
Bangalore Groovy User Group

3. Refactoring

4. noun: a change made to the internal structure
of software to make it easier to understand
and cheaper to modify without changing its
observable behaviour
verb: to restructure software by applying
a series of refactorings without changing
its observable behaviour.
Refactoring
https://refactoring.com/

5. Red Green
Refactor
TDD

6. Address Common Code Smells

7. A code smell is a surface indication that
usually corresponds to a deeper problem in
the system. The term was first coined by Kent
Beck while helping me with
my Refactoring book.
~ Martin Fowler
https://martinfowler.com/bliki/CodeSmell.html

8. { Code Smells }
Long Methods
Duplicated Code Large Class
Long Param List
Primitive Obsession
Data Class
Inappropriate Intimacy

9. int calculateM1(int value1, int value2, int value3) {
int maxValue
if (value1 > value2 && value1 > value3) {
maxValue = value1
} else if (value2 > value3) {
maxValue = value2
} else {
maxValue = value3
}
maxValue + 1
}
int calculateM2(int value1, int value2, int value3) {
int maxValue
if (value1 > value2 && value1 > value3) {
maxValue = value1
} else if (value2 > value3) {
maxValue = value2
} else {
maxValue = value3
}
maxValue * 2
}

10. int calculateM1(int value1, int value2, int value3) {
int maxValue
if (value1 > value2 && value1 > value3) {
maxValue = value1
} else if (value2 > value3) {
maxValue = value2
} else {
maxValue = value3
}
maxValue + 1
}
int calculateM2(int value1, int value2, int value3) {
int maxValue
if (value1 > value2 && value1 > value3) {
maxValue = value1
} else if (value2 > value3) {
maxValue = value2
} else {
maxValue = value3
}
maxValue * 2
}
Duplicate Code
Reinventing the wheel

11. int calculateM1(int value1, int value2, int value3) {
Math.max(value1, Math.max(value2, value3)) + 1
}
int calculateM2(int value1, int value2, int value3) {
Math.max(value1, Math.max(value2, value3)) * 2
}

13. int calculateM1(int value1, int value2, int value3) {
int maxValue
if (value1 > value2 && value1 > value3) {
maxValue = value1
} else if (value2 > value3) {
maxValue = value2
} else {
maxValue = value3
}
maxValue + 1
}
int calculateM2(int value1, int value2, int value3) {
int maxValue
if (value1 > value2 && value1 > value3) {
maxValue = value1
} else if (value2 > value3) {
maxValue = value2
} else {
maxValue = value3
}
maxValue * 2
}

14. int calculateM1(int value1, int value2, int value3) {
int maxValue
if (value1 > value2 && value1 > value3) {
maxValue = value1
} else if (value2 > value3) {
maxValue = value2
} else {
maxValue = value3
}
maxValue + 1
}
int calculateM1(int value1, int value2, int value3) {
int maxValue = max(value1, value2, value3)
maxValue + 1
}
private int max(int value1, int value2, int value3) {
int maxValue
if (value1 > value2 && value1 > value3) {
maxValue = value1
} else if (value2 > value3) {
maxValue = value2
} else {
maxValue = value3
}
maxValue
}
Extract
Method

15. int calculateM1(int value1, int value2, int value3) {
int maxValue = max(value1, value2, value3)
maxValue + 1
}
private int max(int value1, int value2, int value3) {
int maxValue
if (value1 > value2 && value1 > value3) {
maxValue = value1
} else if (value2 > value3) {
maxValue = value2
} else {
maxValue = value3
}
maxValue
}
int calculateM2(int value1, int value2, int value3) {
int maxValue
if (value1 > value2 && value1 > value3) {
maxValue = value1
} else if (value2 > value3) {
maxValue = value2
} else {
maxValue = value3
}
maxValue * 2
}

16. int calculateM1(int value1, int value2, int value3) {
int maxValue = max(value1, value2, value3)
maxValue + 1
}
private int max(int value1, int value2, int value3) {
int maxValue
if (value1 > value2 && value1 > value3) {
maxValue = value1
} else if (value2 > value3) {
maxValue = value2
} else {
maxValue = value3
}
maxValue
}
int calculateM2(int value1, int value2, int value3) {
int maxValue = max(value1, value2, value3)
maxValue * 2
}

17. private int max(int value1, int value2, int value3) {
int maxValue
if (value1 > value2 && value1 > value3) {
maxValue = value1
} else if (value2 > value3) {
maxValue = value2
} else {
maxValue = value3
}
maxValue
}
private int max(int value1, int value2, int value3) {
Math.max(value1, Math.max(value2, value3))
}

18. private int max(int value1, int value2, int value3) {
Math.max(value1, Math.max(value2, value3))
}
int calculateM1(int value1, int value2, int value3) {
int maxValue = max(value1, value2, value3)
maxValue + 1
}
int calculateM2(int value1, int value2, int value3) {
int maxValue = max(value1, value2, value3)
maxValue * 2
}

19. private int max(int value1, int value2, int value3) {
Math.max(value1, Math.max(value2, value3))
}
int calculateM1(int value1, int value2, int value3) {
int maxValue = Math.max(value1, Math.max(value2, value3))
maxValue + 1
}
int calculateM2(int value1, int value2, int value3) {
int maxValue = Math.max(value1, Math.max(value2, value3))
maxValue * 2
}
Inline Method

20. int calculateM1(int value1, int value2, int value3) {
int maxValue = Math.max(value1, Math.max(value2, value3))
maxValue + 1
}
int calculateM2(int value1, int value2, int value3) {
int maxValue = Math.max(value1, Math.max(value2, value3))
maxValue * 2
}
int calculateM1(int value1, int value2, int value3) {
Math.max(value1, Math.max(value2, value3)) + 1
}
int calculateM2(int value1, int value2, int value3) {
Math.max(value1, Math.max(value2, value3)) * 2
}
Inline
Variable

21. Importance of small steps
in refactoring

23. List<Integer> numbers = [1, 2, 3, 4, 5]
for(number in numbers) {
println number
}

24. External Iterator
To
Internal Iterator

25. List<Integer> numbers = [1, 2, 3, 4, 5]
for(number in numbers) {
println number
}
List<Integer> numbers = [1, 2, 3, 4, 5]
numbers.forEach { println it }
List<Integer> numbers = [1, 2, 3, 4, 5]
numbers.forEach(System.out.&println)

27. Refactoring to
Idiomatic Groovy

28. def numbers = [1, 2, 3, 4, 5]
for(number in numbers) {
println number
}
def numbers = [1, 2, 3, 4, 5]
numbers.each { println it }

29. def evenNumbers = []
numbers.each { number ->
if (number % 2 == 0) {
evenNumbers << number
}
}
def evenNumbers = numbers
.findAll { it % 2 == 0}

30. def sum = 0
numbers.each {
sum += it
}
def sum = numbers.inject(0,
{ result, number -> result + number }
)

31. List<Integer> numbers = [1, 2, 3, 4, 5]
def result = [:]
numbers.forEach { number ->
result[number] = number * number
}
List<Integer> numbers = [1, 2, 3, 4, 5]
def result = numbers.collectEntries {
[it, it * it]
}

33. List<Integer> numbers = [1, 2, 3, 4, 5]
def evenNumbers = numbers.findAll { it % 2 == 0}

34. Extract Closure

35. List<Integer> numbers = [1, 2, 3, 4, 5]
def evenNumbers = numbers.findAll { it % 2 == 0}
List<Integer> numbers = [1, 2, 3, 4, 5]
def evenNumbers = numbers.findAll({ it % 2 == 0 })
List<Integer> numbers = [1, 2, 3, 4, 5]
def isEven = { it % 2 == 0 }
def evenNumbers = numbers.findAll(isEven)

36. Inline Closure

37. List<Integer> numbers = [1, 2, 3, 4, 5]
def isEven = { it % 2 == 0 }
def evenNumbers = numbers.findAll(isEven)
List<Integer> numbers = [1, 2, 3, 4, 5]
def evenNumbers = numbers.findAll { it % 2 == 0}

39. def numbers = [1, 2, 3, 4, 5]
def sumOfSuqaresOfEvenNumbers = 0
numbers.forEach { number ->
if(number % 2 == 0 ){
sumOfSuqaresOfEvenNumbers += number * number
}
}

40. To Functional Style

41. def numbers = [1, 2, 3, 4, 5]
def sumOfSuqaresOfEvenNumbers = 0
numbers.forEach { number ->
if(number % 2 == 0 ){
sumOfSuqaresOfEvenNumbers += number * number
}
}
def sumOfSuqaresOfEvenNumbers = numbers
.findAll { it % 2 == 0 }
.collect { it * it }
.sum()

43. def numbers = [1, 2, 3, 4, 5]
def sumOfSuqaresOfEvenNumbers = 0
numbers.forEach { number ->
if(number % 2 == 0 ){
sumOfSuqaresOfEvenNumbers += number * number
}
}
def square = { it * it }
def sumOfSuqaresOfEvenNumbers = 0
numbers.forEach { number ->
if(number % 2 == 0 ){
sumOfSuqaresOfEvenNumbers += square(number)
}
}

44. def square = { it * it }
def sumOfSuqaresOfEvenNumbers = 0
numbers.forEach { number ->
if(number % 2 == 0 ){
sumOfSuqaresOfEvenNumbers += square(number)
}
}
def sumOfSuqaresOfEvenNumbers = 0
def evenNumbers = numbers.findAll { it % 2 == 0}
evenNumbers.forEach { number ->
sumOfSuqaresOfEvenNumbers += square(number)
}

45. def sumOfSuqaresOfEvenNumbers = 0
def evenNumbers = numbers.findAll { it % 2 == 0}
evenNumbers.forEach { number ->
sumOfSuqaresOfEvenNumbers += square(number)
}
def sumOfSuqaresOfEvenNumbers = 0
def evenNumbers = numbers.findAll { it % 2 == 0}
def squaresOfEvenNumbers = evenNumbers.collect(square)
squaresOfEvenNumbers.forEach { number ->
sumOfSuqaresOfEvenNumbers += number
}

46. def square = { it * it }
def evenNumbers = numbers.findAll { it % 2 == 0 }
def squaresOfEvenNumbers = evenNumbers
.collect ( square )
def sumOfSuqaresOfEvenNumbers = squaresOfEvenNumbers.sum()
def sumOfSuqaresOfEvenNumbers = 0
def evenNumbers = numbers.findAll { it % 2 == 0}
def squaresOfEvenNumbers = evenNumbers.collect(square)
squaresOfEvenNumbers.forEach { number ->
sumOfSuqaresOfEvenNumbers += number
}

47. def square = { it * it }
def evenNumbers = numbers.findAll { it % 2 == 0 }
def squaresOfEvenNumbers = evenNumbers
.collect ( square )
def sumOfSuqaresOfEvenNumbers = squaresOfEvenNumbers.sum()
def sumOfSuqaresOfEvenNumbers = numbers
.findAll { it % 2 == 0 }
.collect (square)
.sum()
Inline

49. class Multiplier {
private final int times
Multiplier(int times) {
this.times = times
}
int multiply(int number) {
times * number
}
}
Multiplier doubler = new Multiplier(2)
Multiplier triple = new Multiplier(3)
println doubler.multiply(10)
println triple.multiply(10)

50. def multiply = { int times, int number ->
times * number
}
def doubler = multiply.curry(2)
def triple = multiply.curry(3)
println doubler(10)
println triple(10)

52. def numbers = [1, 2, 3, 4, 5, 6]
println numbers
.findAll { it % 2 == 0 }
.find { it > 2 }

53. To Streams API

54. def numbers = [1, 2, 3, 4, 5, 6]
println numbers
.findAll { it % 2 == 0 }
.find { it > 2 }
def numbers = [1, 2, 3, 4, 5, 6]
println numbers
.stream()
.filter { it % 2 == 0 }
.filter { it > 2 }
.findFirst()
.orElse(null)

56. interface CanSwim {
def swim()
}
class Fish implements CanSwim {
def swim() {
println "Fish Swimming"
}
}
class Person implements CanSwim {
def swim() {
println "Person Swimming"
}
}

57. To Dynamic Groovy

58. interface CanSwim {
def swim()
}
class Fish implements CanSwim {
def swim() {
println "Fish Swimming"
}
}
class Person implements CanSwim {
def swim() {
println "Person Swimming"
}
}
CanSwim swimmer = new Person() //new Fish()
swimmer.swim()

59. interface CanSwim {
def swim()
}
class Fish implements CanSwim {
def swim() {
println "Fish Swimming"
}
}
class Person implements CanSwim {
def swim() {
println "Person Swimming"
}
}
def swimmer = new Person() //new Fish()
swimmer.swim()

61. class Employee {
def employeeId
def firstName
def lastName
def dateOfBirth
def toSummaryString() {
"$employeeId -> $firstname"
}
}

62. class Employee {
def employeeId
def firstName
def lastName
def dateOfBirth
def toSummaryString() {
"$employeeId -> $firstname"
}
}

63. To Static Groovy

64. class Employee {
def employeeId
def firstName
def lastName
def dateOfBirth
def toSummaryString() {
"$employeeId -> $firstname"
}
}
Exception in thread "main" groovy.lang.MissingPropertyException:
No such property: firstname for class

65. @TypeChecked
class Employee {
def employeeId
def firstName
def lastName
def dateOfBirth
def toSummaryString() {
"$employeeId -> $firstname"
}
}
Error:(17, 30) Groovyc: [Static type checking] -
The variable [firstname] is undeclared.

66. @TypeChecked
class Employee {
def employeeId
def firstName
def lastName
def dateOfBirth
def toSummaryString() {
"$employeeId -> $firstname"
}
}
@TypeChecked
class Employee {
String employeeId
String firstName
String lastName
LocalDateTime dateOfBirth
def toSummaryString() {
"$employeeId -> $firstname"
}
}

67. TypeChecked
Vs
CompileStatic

68. class Greeter {
String message
def greet() {
message
}
}
@TypeChecked
def runTypeChecked(Greeter greeter) {
println greeter.greet()
}
@CompileStatic
def runCompileStatic(Greeter greeter) {
println greeter.greet()
}

69. def greeter = new Greeter(message: 'Good Morning')
greeter.metaClass.greet = { "Hello, ${delegate.message}" }
runTypeChecked(greeter)
runCompileStatic(greeter)
Hello, Good Morning
Good Morning

70. @Transactional
class MyService {
@Transactional(propagation = Propagation.REQUIRES_NEW)
def m1() {}
def m2(){
m1()
}
}

71. Introduce Meta-programming

72. @Transactional
class MyService implements ApplicationContextAware {
ApplicationContext context
@Transactional(propagation = Propagation.REQUIRES_NEW)
def m1() {}
def m2() {
MyService service = context.getBean('myService')
service.m1()
}
@Override
void setApplicationContext(ApplicationContext applicationContext)
throws BeansException {
context = applicationContext
}
}

73. def grailsApplication
def init = { servletContext ->
injectSelfProxy()
}
private def injectSelfProxy(){
for (sc in grailsApplication.serviceClasses) {
String propertyName = sc.propertyName
sc.clazz.metaClass.getMyProxy = { ->
grailsApplication.mainContext
.getBean(propertyName)
}
}
}

74. @Transactional
class MyService {
ApplicationContext context
@Transactional(propagation = Propagation.REQUIRES_NEW)
def m1() {}
def m2() {
myProxy.m1()
}
}

75. Introduce Traits

76. class Product {
UUID uuid = UUID.randomUUID()
//other fields
}
class Order {
UUID uuid = UUID.randomUUID()
//other fields
}

77. class Product {
UUID uuid = UUID.randomUUID()
//other fields
}
class Order {
UUID uuid = UUID.randomUUID()
//other fields
}
trait BusinessObject {
}

78. class Product implements BusinessObject {
//other fields
}
class Order implements BusinessObject {
//other fields
}
trait BusinessObject {
UUID uuid = UUID.randomUUID()
}

80. class Technologies extends ArrayList {
def filterGr8() {
this.findAll { it.startsWith('Gr')}
}
}
Technologies list =
[‘Groovy', 'Grails', 'Gradle', 'Java'] as Technologies
println list
println list.filterGr8()

81. Replace Inheritance
with Delegation

82. class Technologies {
@Delegate
private List list
Technologies(List list) {
this.list = list
}
def filterGr8() {
list.findAll { it.startsWith('Gr') }
}
}

83. Thank You