1Z0-819 Functional Interfaces 5

Question 1

A lambda body attempts to modify a local variable declared in the enclosing method. What happens?

Accepted Answer

A compilation error occurs because local variables captured by lambdas must be effectively final

Answer

Local variables captured by a lambda must be final or effectively final; reassigning them causes a compile-time error.

Question 2

What does the keyword `this` refer to inside a lambda expression?

Accepted Answer

The enclosing class instance

Answer

Unlike anonymous classes, lambdas do not introduce a new scope; `this` refers to the enclosing class instance.

Question 3

Which statement is true about checked exceptions inside a lambda that implements `Runnable`?

Accepted Answer

Checked exceptions must be caught or wrapped inside the lambda body

Answer

Runnable.run() does not declare any checked exceptions, so a lambda implementing it must catch any checked exceptions internally.

Question 4

Which of the following is a valid `@FunctionalInterface`?

Accepted Answer

An interface with one abstract method that does not override any Object method

Answer

A functional interface must be an interface with exactly one abstract method that is not a re-declaration of an Object method.

Question 5

What is the result of compiling an interface annotated with `@FunctionalInterface` that declares two abstract methods?

Accepted Answer

A compilation error is produced

Answer

@FunctionalInterface causes the compiler to enforce the single-abstract-method constraint, producing an error if violated.

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