1Z0-811 Core Java API 3

Question 1

What does `Collections.unmodifiableList(list)` guarantee?

Accepted Answer

Mutations through the wrapper throw UnsupportedOperationException

Answer

The unmodifiable wrapper throws UnsupportedOperationException on mutating calls, but mutations to the backing list are still visible through the wrapper.

Question 2

What is printed by `System.out.println(Integer.toBinaryString(-1))`?

Accepted Answer

"11111111111111111111111111111111"

Answer

`Integer.toBinaryString(-1)` returns the unsigned 32-bit binary representation of -1, which is 32 ones.

Question 3

Which `Map` method returns the value associated with a key, or a default if the key is absent?

Accepted Answer

getOrDefault()

Answer

`Map.getOrDefault(key, defaultValue)` returns the mapped value or the specified default without modifying the map.

Question 4

What is the result of `String.format("%05d", 42)`?

Accepted Answer

"00042"

Answer

The format specifier `%05d` pads the integer with leading zeros to a width of 5, producing "00042".

Question 5

Which statement about `ArrayList` vs `LinkedList` is accurate?

Accepted Answer

ArrayList has O(1) random get by index

Answer

ArrayList backed by an array supports O(1) index-based access, while LinkedList requires O(n) traversal to reach an element.

(1Z0-811) Oracle Java SE11 Programmer Practice Test

(1Z0-811) Oracle Java SE11 Programmer Practice Test

1Z0-811 Core Java API 3