Groovy and Grails Groovy Language Fundamentals & Metaprogramming

Question 1

In Groovy, what does the `?.` operator do?

Accepted Answer

Safely navigates null references, returning null instead of throwing NullPointerException

Answer

The `?.` (safe navigation) operator returns null if the object on its left is null, preventing NullPointerException.

Question 2

Which of the following correctly defines a Groovy closure that accepts two parameters and returns their sum?

Accepted Answer

def sum = { a, b -> a + b }

Answer

Groovy closures are defined with curly braces, parameters listed before `->`, and the body after.

Question 3

What is the implicit variable name for the single parameter of a Groovy closure when no parameter is declared?

Accepted Answer

it

Answer

When a Groovy closure has one parameter and no explicit declaration, Groovy automatically creates a variable named `it`.

Question 4

In Groovy, what is the result of `[1, 2, 3].collect { it * 2 }`?

Accepted Answer

[2, 4, 6]

Answer

`collect` transforms each element by applying the closure, so multiplying each by 2 yields [2, 4, 6].

Question 5

Which Groovy GDK method filters a list and returns only elements that match a condition?

Accepted Answer

findAll

Answer

`findAll` iterates over a collection and returns a new list of elements for which the closure returns true.

Groovy and Grails Practice Test