Chapter ELEVEN
Method References

Answers

1. The correct answer is B.

Runnable r = Question_11_1::print;

It's equivalent to:

Runnable r = () -> Question_11_1.print();

And equivalent to:

Runnable r = new Runnable() {
     public void run() {
         Question_11_1.print();
     }
}

The print() method returns another Runnable instance, but as this is not saved or executed, nothing is done.

2. The correct answer is A.

Consumer c = Question_11_2::print;

It's equivalent to:

Consumer c = (Question_11_2 q) -> q.print();

And equivalent to:

Consumer c = new Consumer() {
     public void accept(Question_11_2 q) {
         q.print();
     }
}

That when executed, it just prints "Hi".

3. The correct answers are A and C.
Option A is true. You can have a method reference of a constructor.
Option B is false. Method references only replace one-method lambda expressions.
Option C is true. When using method references, you don't have to specify the arguments the method receives.
Option D is false. The :: operator is just used in method references.

4. The correct answer is D.
Option A and B are not valid method references.
Option C would be right if the method drive(int) were static, but because it's an instance method, option D is the right one.

5. The correct answer is B.

Runnable r = Question_11_5::new;

It's equivalent to:

Runnable r = () -> new Question_11_5();

And equivalent to:

Runnable r = new Runnable() {
     public void run() {
         new Question_11_5();
     }
}

However, r.run() is never executed, so nothing is printed.

6. The correct answer is D.
Compilation fails because

BiFunction<String, String, Test> f = Test::new;

It's equivalent to:

BiFunction<String, String, Test> f =
         (String s1, String s2) -> new Test(s1, s2);

And class Test only has constructors that take zero and one arguments.

7. The correct answers are A and D.
Option A is correct because the private constructor can be used inside the main method.
Option B is wrong because with an UnaryOperator, a parameter of type Question_11_7 is expected.
Option C is wrong because with a Consumer a parameter of type Question_11_7 is expected, and nothing is returned.
Option D is correct because a Supplier returns an instance of Question_11_7 by calling the static method create().