1Z0-819 Core APIs & Data Manipulation 2

Question 1

What does `String.format("%05d", 42)` produce?

Accepted Answer

00042

Answer

The `%05d` format specifier pads the integer with leading zeros to a width of 5.

Question 2

Which method returns an `OptionalInt` containing the sum of an `IntStream`?

Accepted Answer

reduce(Integer::sum)

Answer

`IntStream.reduce(Integer::sum)` returns an `OptionalInt` because the stream might be empty; `sum()` returns a plain `int`.

Question 3

What is the result of `"hello".substring(2, 4)`?

Accepted Answer

ll

Answer

`substring(beginIndex, endIndex)` extracts characters from index 2 (inclusive) to 4 (exclusive), yielding "ll".

Question 4

Which `LocalDate` method adds a specified number of months and adjusts the day if the result month is shorter?

Accepted Answer

plusMonths()

Answer

`plusMonths()` adds months and normalizes the day-of-month if the target month has fewer days.

Question 5

Which interface does `HashMap` NOT implement?

Accepted Answer

SortedMap

Answer

`HashMap` implements `Map`, `Cloneable`, and `Serializable`, but NOT `SortedMap` — that is implemented by `TreeMap`.

(1Z0-819) Oracle Java SE 11 Developer Practice Test