[HD Pg 351, Sec. 12.3.6 - chaining-method-calls]

[OCAJO1]

You should change the second line to ld = ld.plusMonths(2).plusDays(10); if you want to see 2018-02-10 in the output.

Should be

2018-03-11.

Also,

LocalDate ld = LocalDate.of(2018, 1, 1);
ld = ld.withYear(2010).plusDays(10).atTime(10, 20).plusMonths(2);

The above example of what doesn't work, has two tricks in it. One, atTime() returns LocalDateTime and two, LocalDateTime does not have atTime() method.

Do the date and time questions on the exam get this tricky? Thanks

[admin]

1. Correct.
2. Yes, you may see this on the exam.

[Username987654]

Thus, LocalDate.of(2018, 1, 31) produces a new LocalDate instance and chaining another of method to this LocalDate instance is actually the same as invoking LocalDate.of(2019, 1, 31) independently.

should be

Thus, LocalDate.of(2018, 1, 31) produces a new LocalDate instance and chaining another of method to this LocalDate instance is actually the same as invoking LocalDate.of(2019, 1, 1) independently.

?

[admin]

Correct. Should be fixed.

thank you for your feedback!

[Username987654]

The boook shows the following code and quote:

Code: Select all

LocalDate ld = LocalDate.of(2018, 1, 1);
ld.plusHours(10); // will not compile

Creating a date/time object using an existing date/time object

For example, adding hours to a LocalDate or adding months to a LocalTime, will throw a DateTimeException at runtime.

Typo? Or can both of these be true at the same time? If so, what's the best way to remember what happens in each case?

[admin]

This seems fine because it is explaining the general pattern of these methods i.e. creating a new object using an existing one but it also notes the limitations of these methods.

LocalDate has only the date component (no time), so, if you try to add time components to it (i.e. hours, mins, or secs) to LocalDate, it will throw an exception.
Similarly, LocalTime has only the time component (no date), so, if you try to add date components to it (i.e. days, months, year) to LocalTime, it will throw an exception.

Only LocalDateTime has both the date and the time components, so, you can add date as well as time components to a LocalDateTime object.

[Username987654]

It's just that from reading (alone), it seems like a possible typo, or maybe a point that could potentially be made more clear, that would allow me to answer a potential exam question correctly since "adding hours to a LocalDate" results sometimes in a compile error, and other times as a DateTImeException?

[Username987654]

(Maybe I could use some sleep.)

[admin]

OK, I see your point.

LocalDate does not have methods to add time components that is why there is a compilation error if you try to call addHours on a LocalDate reference. (Same with LocalTime, which does not have methods to add the date components).

However, all of them (i.e. LocalDate, LocalTime, and LocalDateTIme) have plus/minus(TemporalAmount ) methods. If you use these method, the compiler cannot check what are you trying to add/subtract. So, the compilation succeeds but an exception will be thrown at run time when you do something like:
LocalDate ld = LocalDate.now();
ld.plus(Duration.ofHours(1)); //no compilation error but exception at run time. java.time.temporal.UnsupportedTemporalTypeException: Unsupported unit: Seconds

[Username987654]

Perfect! Thanks!