Create and use Lambda expressions.
1. The correct answer is C.
Option A is invalid since the parameter list doesn't have parenthesis.
Option B is invalid since an empty return statement is invalid.
Option C is valid. The body doesn't need to use the return keyword if it only has one statement.
Option D is invalid since the body has two statements and they must be enclosed in curly brackets.
2. The correct answer is D.
Option A is invalid because a is already used as the variable identifier.
Option B is invalid because the lambda expression must return an int value.
Option C is invalid because you can't pass a constant value in the parameter list of the lambda expression.
Option D is valid because it takes a String argument and returns an int value.
3. The correct answers are A and C.
Lambda expressions can be used in:
4. The correct answer is B.
Option A is invalid because the interface is not functional (it doesn't have an abstract method).
Option B is correct because the interface method doesn't take an argument and the type of the lambda expression can be cast to a java.lang.Number object.
Option C is invalid because a double can't be cast to an int.
Option D is invalid because the lambda expression's signature doesn't match the signature of the functional interface method m(Integer[]).
5. The correct answer is C.
A lambda expression can access the default methods of its functional interface (aMethod() in this case), since default methods are inherited. But it cannot be accessed from main() because it's a static method and has no this reference.
6. The only correct answer is A.
A return keyword is not always required (or optional) in a lambda expression. It depends on the signature of the functional interface method.
Curly brackets are required whenever the return keyword is used in a lambda expression. Both can be omitted if the lambda expression's body is just one statement:
() -> 2 * 3; // Valid
() -> { return 2 * 3; }; // Valid
() -> return 2 * 3; // Not Valid!
7. The correct answer is D.
For a lambda expression, this resolves to the enclosing class where the lambda is written.
8. The correct answer is C.
Lambda expressions can access instance and static variables, but in this case, the parameter of the lambda expression shadows the instance variable i, so the value of 6 is used.