1.
Effective Java
With Groovy -
How Language
Influences Adoption of
Good Practices
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

3.
3
Java Language
JVM
Platform/ Real Machine Platform/ Real Machine Platform/ Real Machine

4.
4
Java Language
Platform/ Real Machine Platform/ Real Machine Platform/ Real Machine
Groovy
JVM

5.
5
Most people talk about Java the language,
and this may sound odd coming from me,
but I could hardly care less. At the core of
the Java ecosystem is the JVM.
- James Gosling,
Creator of the Java Programming Language(2011, TheServerSide)

6.
6

7.
initial idea was to make a little
dynamic language which compiles
directly to Java classes and provides
all the nice (alleged) productivity
benefits
- James Strachan
http://radio-weblogs.com/0112098/2003/08/29.html

8.
Know your guides
Context/ the Problem
What does “Effective Java” say?
The traps
Groovier Solution
Lessons Learned
Tool Wisdom
9

9.
float price = 0.1f;
float total = 0;
for(int i=0; i<10; i++){
total += price;
}
System.out.println("Total: " + total);
Total: 1.0000001

10.
double price = 0.1;
double total = 0;
for(int i=0; i<10; i++){
total += price;
}
System.out.println("Total: " + total);
Total: 0.9999999999999999

11.
#48: Avoid float and double if exact
answers are required

12.
BigDecimal price = new BigDecimal(0.1);
BigDecimal total = new BigDecimal(0);
for(int i=0; i<10; i++){
total = total.add(price);
}
System.out.println("Total: " + total);
Total: 1.0000000000000000555111512312578270211815834045410156250

13.
BigDecimal price = new BigDecimal(0.1);
BigDecimal total = new BigDecimal(0);
for(int i=0; i<10; i++){
total = total.add(price);
}
System.out.println("Total: " + total);
Total: 1.0000000000000000555111512312578270211815834045410156250

14.
def price = 0.1
def total = 0
for(int i=0; i<10; i++){
total += price
}
println "Total: " + total
Total: 1.0

15.
def price = 0.1
def total = 0
for(int i=0; i<10; i++){
total += price
}
println "Total: " + total
println price.class
println total.class
Total: 1.0
class java.math.BigDecimal
class java.math.BigDecimal

16.
Select appropriate default
Principle of Least Astonishment

17.
class Product {
String sku
String description
BigDecimal price
}

18.
Product book1 = new Product(
sku: 'P101',
description: 'Effective Java’,
price: 40.0)
Product book2 = new Product(
sku: 'P101',
description: 'Effective Java’,
price: 40.0)
println book1 == book2
false

19.
Product book1 = new Product(
sku: 'P101',
description: 'Effective Java’,
price: 40.0)
Product book2 = new Product(
sku: 'P101',
description: 'Effective Java’,
price: 40.0)
def stock = [:]
stock[book1] = 100
println stock[book2]
null

20.
#8: Obey the general contract when
overriding equals
#9: Always override hashCode when
you override equals

21.
class Product {
String sku
String description
BigDecimal price
}
class Product {
String sku
String description
BigDecimal price
LocalDate dateOfManufacture
} class Product {
String sku
String description
BigDecimal price
LocalDate dateOfManufacture
LocalDate dateOfExpiry
}

22.
@EqualsAndHashCode
class Product {
String sku
String description
BigDecimal price
}

23.
Product book1 = new Product(
sku: 'P101',
description: 'Effective Java’,
price: 40.0)
Product book2 = new Product(
sku: 'P101',
description: 'Effective Java’,
price: 40.0)
println book1 == book2
true

24.
Product book1 = new Product(
sku: 'P101',
description: 'Effective Java’,
price: 40.0)
Product book2 = new Product(
sku: 'P101',
description: 'Effective Java’,
price: 40.0)
def stock = [:]
stock[book1] = 100
println stock[book2]
100

25.
@EqualsAndHashCode(includes = 'id')
class Product {
Long id
String sku
String description
BigDecimal price
static constraints = {
sku unique: true
}
}

26.
@EqualsAndHashCode(includes = 'id')
class Product {
Long id
String sku
String description
BigDecimal price
static constraints = {
sku unique: true
}
}

27.
@EqualsAndHashCode(includes = ‘sku')
class Product {
Long id
String sku
String description
BigDecimal price
static constraints = {
sku unique: true
}
}

28.
AST Transformation
Single point of representation
of any knowledge

29.
#46: Prefer for-each loops to
traditional for loops

30.
def numbers = [10, 20, 30, 40]
def sum = 0
for(int number in numbers){
sum += number
}
println "Sum: " + sum

31.
numbers.each { number ->
println number
}
println numbers.collect { number ->
number * 2
}
println numbers.inject(0,
{ result, number -> result + number }
)
10
20
30
40
[20, 40, 60, 80]
100

32.
Closures
Favor Internal iterators to
external iterators
Minimise the moving parts

33.
Billion Dollor Effort

34.
Billion Dollor Effort
null check

35.
40
List<Speaker> getSpeakers(String conference) {
return null;
}
List<Speaker> speakers = getSpeakers(“ApacheCon@Home 2020“);
if (speakers != null) {
//...
}

36.
#43: Return empty arrays or
collections, not nulls

37.
println getSpeakers(‘ApacheCon@Home 2020')
.collect { it.firstName }
println getSpeakers(‘ApacheCon@Home 2020’)
.findAll { it.firstName.length() > 5 }

38.
println getSpeakers(‘ApacheCon@Home 2020')
.collect { it.firstName } // []
println getSpeakers(‘ApacheCon@Home 2020’)
.findAll { it.firstName.length() > 5 } // []

39.
NullObject Pattern
No boilerplate code - $$$
Life is too short for null checks!

40.
https://www.flickr.com/photos/38080114@N07/8594601982/

41.
#15: Minimize Mutability

42.
Rules to make a class immutable
1. Don’t provide any mutators
2. Ensure that the class can’t be extended
3. Make all fields final
4. Make all fields private
5. Ensure exclusive access to any mutable
components

43.
class ImmutableClass{
private final def field1
private final def field2
//...
private final def field10
public ImmutableClass(f1, f2,… f10){
//initialization
}
}

44.
import groovy.transform.Immutable
@Immutable
class Rectangle{
int length
int breadth
}
def r = new Rectangle(length: 10, breadth: 5)
println r // Rectangle(10, 5)

45.
public Rectangle(java.util.HashMap args) {
if ( args .length == null) {
} else {
this .length = (( args .length) as int)
}
if ( args .breadth == null) {
} else {
this .breadth = (( args .breadth) as int)
}
}

46.
AST Transformation
Readability Matters
Syntactic Sugar

47.
#15: Favour composition over
inheritance

48.
def ph = ['919812312345', '4512341234', ‘19252199916']
as PhoneNumbers
println ph.find { it == '19252199916'}
println ph.findAll { it.endsWith('4') }

49.
def ph = ['919812312345', '4512341234', ‘19252199916']
as PhoneNumbers
println ph.find { it == '19252199916'}
println ph.findAll { it.endsWith('4') }
println ph.indianNumbers()

50.
class PhoneNumbers extends ArrayList {
}

51.
class PhoneNumbers {
private @Delegate List phoneNumbers
PhoneNumbers(numbers) {
phoneNumbers = numbers
}
def indianNumbers() {
phoneNumbers.findAll { it.startsWith('91') }
}
}

52.
Favoring Composition
- The Groovy Way
APACHECON @HOME
Spt, 29th – Oct. 1st 2020

53.
AST Transformation
Simplify

54.
#3: Enforce the singleton property
with a private constructor
or an enum type

55.
class Manager {
private static final Manager manager =
new Manager()
private Manager() { super() }
static Manager getInstance() { manager }
}
def m1 = Manager.getInstance()
def m2 = Manager.getInstance()
println m1 == m2
true

56.
class Manager {
private static final Manager manager =
new Manager()
private Manager() { super() }
static Manager getInstance() { manager }
}
def m1 = Manager.getInstance()
def m2 = Manager.getInstance()
println m1 == m2
true
def m3 = new Manager()
println m3 Manager@b968a76

57.
@Singleton
class Manager {}
def m1 = Manager.getInstance()
def m2 = Manager.getInstance()
println m1 == m2
def m3 = new Manager()
println m3
true
Caught: java.lang.RuntimeException: Can't instantiate singleton Manager.
Use Manager.instance

58.
private static Manager manager
static Manager getInstance() {
if(!manager){ manager = new Manager() }
manager
}

59.
private static Manager manager
static synchronized Manager getInstance() {
if(!manager){ manager = new Manager() }
manager
}

60.
private static volatile Manager manager
static synchronized Manager getInstance() {
if(!manager){ manager = new Manager() }
manager
}

61.
@Singleton(lazy=true)
class Manager {}
public static Manager getInstance() {
if (instance != null) {
return instance
} else {
synchronized (Manager) {
if (instance != null) {
return instance
} else {
return instance = new Manager()
}
}
}
}

62.
AST Transformation
YAGNI
Premature optimisation is the root
of all evil

63.
Take Away
Some of the ‘Effective Java’ already built into
the language
AST Transformations reduce the effort to
implement few more
Effective Java implementations may not always
be effective Groovy implementations (Traps)

64.
Take Away
Programming languages can reduce the
friction to implement good practices

65.
Take Away
The power of AST transformations is
available to the developers

66.
https://blog.nareshak.com/effective-java-with-groovy/

67.
Thank You
APACHECON @HOME
Spt, 29th – Oct. 1st 2020