This document discusses the ThreeTen library, which provides a replacement for the Java date and time API. It notes issues with the existing Calendar and Date classes, such as mutability and difficulty testing. ThreeTen addresses these by providing immutable classes like LocalDate and LocalTime, avoiding nulls, and making testing easier. The document outlines ThreeTen's API, how to convert between it and Date, and how to integrate it with Kotlin using operator overloading and extensions. It emphasizes conventions like using plus and minus for addition/subtraction of temporal amounts.

1. JSR310

2. JSR310

3. ThreeTen : a better
calendar library
GDG devFest 2017

4. Colorgy

5. Outline
1. What’s wrong with Calendar and Date?
2. Introduce ThreeTen
3. Convert between ThreeTen and Date
4. Unit test with ThreeTen
5. Integrate with kotlin

6. What’s wrong with
Calendar and Date?

7. Begin of this Month?
private Date beginOfThisMonth(){
Calendar calendar = Calendar.getInstance();
calendar.set(Calendar.DAY_OF_MONTH, 1);
calendar.set(Calendar.HOUR_OF_DAY, 0);
calendar.set(Calendar.MINUTE, 0);
calendar.set(Calendar.SECOND, 0);
calendar.set(Calendar.MILLISECOND, 0);
return calendar.getTime();
}

8. Other use cases
Boolean isSameday(Date date1, Date date2)
Date firstDayOfWeek()
Date getBeginOfDay(int year, int month, int day)
int dayDiff(Date date1, Date date2)

9. Other Date use cases
Boolean isSameday(Date date1, Date date2)
Date firstDayOfWeek()
Date getBeginOfDay(int year, int month, int day)
int dayDiff(Date date1, Date date2)
int dayDiff(Calendar date1, Calendar date2) ?????

10. Unit test is hard
1. Date() has Singleton component and Calendar.getInstance() is
Singleton
2. Need to adjust timezone
3. DateFormat cannot be mocked

11. Introduce ThreeTen

12. What is ThreeTen?

13. What is ThreeTen?
● JSR310 : A Date and Time api in Java8
● ThreeTen : integrate JSR310 into OpenJDK

14. Why not JodaTime?
JodaTime has design flaw :
http://www.infoq.com/cn/news/2010/05/jsr-310

15. Why ThreeTen?
1. Immutable
2. Avoid null
3. OpenJDK
4. Easy to use, easy to test

16. Gradle 3.0 setting
dependencies {
implementation "com.jakewharton.threetenabp:threetenabp:1.0.5"
testImplementation "org.threeten:threetenbp:1.3.3"
}
android.unitTestVariants.all { variant ->
variant.getCompileConfiguration().exclude group:
'com.jakewharton.threetenabp', module: 'threetenabp'
variant.getRuntimeConfiguration().exclude group:
'com.jakewharton.threetenabp', module: 'threetenabp'
}

17. ThreeTen Api

18. LocalDate
LocalDate today = LocalDate.now();
LocalDate tomorrow = today.plusDays(1);
LocalDate myBirthDay = LocalDate.of(1988, 4, 23);
boolean todayIsMyBirthday = today.equals(myBirthDay);

19. LocalDate
LocalDate today = LocalDate.now();
LocalDate tomorrow = today.plusDays(1);
LocalDate myBirthDay = LocalDate.of(1988, 4, 23);
boolean todayIsMyBirthday = today.equals(myBirthDay);
Immutable

20. LocalTime
LocalTime offWork = LocalTime.of(18 , 30);
LocalTime goToWork = LocalTime.of(9, 0);
LocalTime lunchTime = LocalTime.of(12, 10, 30);

21. Let’s look Date again
Date now = new Date();
Date today = new Date();
Now ?? Today??

22. Let’s look Date again
Date now = new Date();
Date today = new Date();
The Date is not a Date!! It is a instant!!

23. Period
Period training = Period.ofDays(40);
Period sprints = Period.ofWeeks(2);
LocalDate retireDay = LocalDate.of(2018, 6, 6);
Period logoutArmy = Period.between(LocalDate.now(), retireDay);

25. More Examples
Temporal = Temporal + TemporalAmount
Tomorrow = Today + 1 day
LocalDate tomorrow = LocalDate.now().plus(Period.ofDays(1))

26. More Examples
TemporalAmount = TemporalAmount + TemporalAmount
4 days = 3days + 1days
Period fourDays = Period.ofDays(3).plus(Period.ofDays(1))

27. More Examples
Boolean = Temporal < Temporal
true = 8:00 < 12:00
boolean shouldBeTure = LocalTime.of(8, 0).compareTo(LocalTime.of(12, 0)) <
0

28. Convert between String and LocalDate
LocalDate today = LocalDate.now();
String format = today.format(DateTimeFormatter.ISO_OFFSET_DATE);
LocalDate christmas = LocalDate.parse("2017-12-25");
LocalDate christmas2 = LocalDate.parse("2017-12-25",
DateTimeFormatter.ISO_DATE);

29. Convert between String and LocalDate
LocalDate today = LocalDate.now();
String format = today.format(DateTimeFormatter.ISO_OFFSET_DATE);
LocalDate christmas = LocalDate.parse("2017-12-25");
LocalDate christmas2 = LocalDate.parse("2017-12-25",
DateTimeFormatter.ISO_DATE);
No more “yyyyMMdd - hh:mm” m?? M??

30. And Others...
● LocalDateTime
● Duration
● Instant
● TemporalAdjuster
● Month
● DayOfWeek

31. Convert Between
ThreeTen and Date

32. https://gist.github.com/hungyanbin/5b9fdfd
c62b1c7f1b8f4bfcd7958b69f

33. Unit test with ThreeTen

34. Test with date-related code
//should climb mountain at Wednesday
boolean shouldClimbMountain()

35. Test with date-related code
//** this test only passed at Wednesday
void testShouldClimbMountain(){
...
}

36. Test with date-related code
//** this test only passed at Wednesday
@Ignore
void testShouldClimbMountain(){
...
}

37. Test with date-related code
//** this test only passed at Wednesday
/*Unit test sucks
void testShouldClimbMountain(){
...
}*/

38. Solution: Set System Time
private var clock = Clock.systemDefaultZone()
@VisibleForTesting
@JvmStatic
fun setSystemClock(clock: Clock){
this.clock = clock
}
@JvmStatic
fun getNow(): LocalDateTime = LocalDateTime.now(clock)

39. Integrate with kotlin

40. Operator overloading and Conventions
class Point(val x: Int, val y: Int){
}

41. Operator overloading and Conventions
class Point(val x: Int, val y: Int){
}
fun AddPoints(){
val p1 = Point(10, 15)
val p2 = Point(5, -5)
val p3 = p1 + p2
print(p3)
//Point(5, 10)
}

42. Operator overloading and Conventions
class Point(val x: Int, val y: Int){
operator fun plus(other: Point): Point{
return Point(x + other.x, y + other.y)
}
}
fun AddPoints(){
val p1 = Point(10, 15)
val p2 = Point(5, -5)
val p3 = p1 + p2
print(p3)
//Point(5, 10)
}

43. Operator overloading and Conventions
class Point(val x: Int, val y: Int){
operator fun plus(other: Point): Point{
return Point(x + other.x, y + other.y)
}
}
fun AddPoints(){
val p1 = Point(10, 15)
val p2 = Point(5, -5)
val p3 = p1 + p2
print(p3)
//Point(5, 10)
}

44. Operator overloading and Conventions(java)
public class Point {
int x;
int y;
public Point(int x, int y) {
this.x = x;
this.y = y;
}
public Point plus(Point other){
return new Point(x + other.x, y + other.y);
}
}

45. Operator overloading and Conventions(java)
public class Point {
int x;
int y;
public Point(int x, int y) {
this.x = x;
this.y = y;
}
public Point plus(Point other){
return new Point(x + other.x, y + other.y);
}
}

46. ThreeTen Api conventions
1. Plus
2. Minus
3. Range
4. compareTo
5. contains

47. Plus, Minus
public final class LocalDate extends ChronoLocalDate implements Temporal{
...
Public LocalDate plus(TemporalAmount var1);
Public LocalDate minus(TemporalAmount var1);
...
}

48. Plus(+), Minus(-)
val today = LocalDate.now()
val tomorrow = today + Period.ofDays(1)
val lastWeek = today - Period.ofWeeks(1)

49. Kotlin Method Extensions
fun Int.Days(): Period = Period.ofDays(this)
fun Int.Weeks(): Period = Period.ofWeeks(this)

50. Method Extensions
fun Int.Days(): Period = Period.ofDays(this)
fun Int.Weeks(): Period = Period.ofWeeks(this)
val now = LocalDateTime.now()
val tomorrow = now + 1.Days()
val lastWeek = now - 1.Weeks()

51. CompareTo (<, >, =, >=, <=)
fun isFutureTime(dateTime: LocalDateTime): Boolean {
val now = LocalDateTime.now()
return dateTime > now
}

52. CompareTo (<, >, =, >=, <=)
fun isFutureTime(dateTime: LocalDateTime): Boolean {
val now = LocalDateTime.now()
return dateTime > now
}

53. range(...), contains(in)
fun isInThirtyDays(localDate: LocalDate): Boolean{
val now = LocalDate.now()
val nextThirtyDay = now + 30.Days()
val range = now..nextThirtyDay
return localDate in range
}

54. range(...), contains(in)
fun isInThirtyDays(localDate: LocalDate): Boolean{
val now = LocalDate.now()
val nextThirtyDay = now + 30.Days()
val range = now..nextThirtyDay
return localDate in range
}

55. range(...), contains(in)
fun isInThirtyDays(localDate: LocalDate): Boolean{
val now = LocalDate.now()
val nextThirtyDay = now + 30.Days()
val range = now..nextThirtyDay
return localDate in range
}

56. After this talk...
1. How to design a good Api ?
2. When you design a class, have you choosen it’s class name
carefully?
3. Can you list bad smell of Calendar?
4. What makes test hard ? How to write it easily ?

57. Q & A