Chapter 8 Lambdas and Functional Interfaces

Question 1

What is the result of the following class?
1: import java.util.function.*;
2:
3: public class Panda {
4: int age;
5: public static void main(String[] args) {
6: Panda p1 = new Panda();
7: p1.age = 1;
8: check(p1, p -> p.age < 5);
9: }
10: private static void check(Panda panda,
11: Predicate<Panda> pred) {
12: String result =
13: pred.test(panda) ? "match" : "not match";
14: System.out.print(result);
15: } }
1.
A. match
B. not match
C. Compiler error on line 8
D. Compiler error on lines 10 and 11
E. Compiler error on lines 12 and 13
F. A runtime exception is thrown.</Panda>

Question 2

What is the result of the following code?
1: interface Climb {
2: boolean isTooHigh(int height, int limit);
3: }
4:
5: public class Climber {
6: public static void main(String[] args) {
7: check((h, m) -> h.append(m).isEmpty(), 5);
8: }
9: private static void check(Climb climb, int height) {
10: if (climb.isTooHigh(height, 10))
11: System.out.println(“too high”);
12: else
13: System.out.println(“ok”);
14: }
15: }
2.
A. ok
B. too high
C. Compiler error on line 7
D. Compiler error on line 10
E. Compiler error on a different line
F. A runtime exception is thrown.

Question 3

3. Which statements about functional interfaces are true? (Choose all that apply.)
   A. A functional interface can contain default and private methods.
   B. A functional interface can be defined as a class or an interface.
   C. Abstract methods with signatures that are contained in public methods
   of java.lang.Object do not count toward the abstract method count
   for a functional interface.
   D. A functional interface cannot contain static or private static
   methods.
   E. A functional interface must be marked with the
   @FunctionalInterface annotation.

Question 4

Which lambda can replace the MySecret class to return the same value? (Choose all that
apply.)
interface Secret {
String magic(double d);
}
class MySecret implements Secret {
public String magic(double d) {
return “Poof”;
} }
4.
A. (e) -> “Poof”
B. (e) -> {“Poof”}
C. (e) -> { String e = “”; “Poof” }
D. (e) -> { String e = “”; return “Poof”; }
E. (e) -> { String e = “”; return “Poof” }
F. (e) -> { String f = “”; return “Poof”; }

Question 5

5. Which of the following functional interfaces contain an abstract method that returns a
   primitive value? (Choose all that apply.)
   A. BooleanSupplier
   B. CharSupplier
   C. DoubleSupplier
   D. FloatSupplier
   E. IntSupplier
   F. StringSupplier

Question 6

6. Which of the following lambda expressions can be passed to a function of
   Predicate<String> type? (Choose all that apply.)
   A. s -> s.isEmpty()
   B. s --> s.isEmpty()
   C. (String s) -> s.isEmpty()
   D. (String s) --> s.isEmpty()
   E. (StringBuilder s) -> s.isEmpty()
   F. (StringBuilder s) --> s.isEmpty()</String>

Question 7

Which of these statements is true about the following code?
public void method() {
x((var x) -> {}, (var x, var y) -> false);
}
public void x(Consumer<String> x, BinaryOperator<Boolean> y) {}
7.
A. The code does not compile because of one of the variables named x.
B. The code does not compile because of one of the variables named y.
C. The code does not compile for another reason.
D. The code compiles, and the x in each lambda refers to the same type.
E. The code compiles, and the x in each lambda refers to a different type.</Boolean></String>

Question 8

Which of the following is equivalent to this code? (Choose all that apply.)
UnaryOperator<Integer> u = x -> x * x;
8.
A. BiFunction<Integer> f = x -> x*x;
B. BiFunction<Integer, Integer> f = x -> x*x;
C. BinaryOperator<Integer, Integer> f = x -> x*x;
D. Function<Integer> f = x -> x*x;
E. Function<Integer, Integer> f = x -> x*x;
F. None of the above</Integer></Integer></Integer>

Question 9

9. Which statements are true? (Choose all that apply.)
   A. The Consumer interface is good for printing out an existing value.
   B. The Supplier interface is good for printing out an existing value.
   C. The IntegerSupplier interface returns an int.
   D. The Predicate interface returns an int.
   E. The Function interface has a method named test().
   F. The Predicate interface has a method named test().

Question 10

Which of the following can be inserted without causing a compilation error? (Choose all that
apply.)
public void remove(List<Character> chars) {
char end = 'z';
Predicate<Character> predicate = c -> {
char start = 'a'; return start <= c && c <= end; };
// INSERT LINE HERE
}
10.
A. char start = 'a';
B. char c = 'x';
C. chars = null;
D. end = '1';
E. None of the above</Character></Character>

Question 11

How many times istrue printed out by this code?
import java.util.function.Predicate;
public class Fantasy {
public static void scary(String animal) {
var dino = s -> “dino”.equals(animal);
var dragon = s -> “dragon”.equals(animal);
var combined = dino.or(dragon);
System.out.println(combined.test(animal));
}
public static void main(String[] args) {
scary(“dino”);
scary(“dragon”);
scary(“unicorn”);
}
}
11.
A. One
B. Two
C. Three
D. The code does not compile.
E. A runtime exception is thrown.

Question 12

What does the following code output?
Function<Integer, Integer> s = a -> a + 4;
Function<Integer, Integer> t = a -> a * 3;
Function<Integer, Integer> c = s.compose(t);
System.out.print(c.apply(1));
12.
A. 7
B. 15
C. The code does not compile because of the data types in the lambda
expressions.
D. The code does not compile because of thecompose() call.
E. The code does not compile for another reason.

Question 13

Which is true of the following code?
int length = 3;
for (int i = 0; i<3; i++) {
if (i%2 == 0) {
Supplier<Integer> supplier = () -> length; // A
System.out.println(supplier.get()); // B
} else {
int j = i;
Supplier<Integer> supplier = () -> j; // C
System.out.println(supplier.get()); // D
}
}
13.
A. The first compiler error is on lineA.
B. The first compiler error is on lineB.
C. The first compiler error is on lineC.
D. The first compiler error is on lineD.
E. The code compiles successfully.</Integer></Integer>

Question 14

14. Which of the following are valid lambda expressions? (Choose all that apply.)
    A. (Wolf w, var c) -> 39
    B. (final Camel c) -> {}
    C. (a,b,c) -> {int b = 3; return 2;}
    D. (x,y) -> new RuntimeException()
    E. (var y) -> return 0;
    F. () -> {float r}
    G. (Cat a, b) -> {}

Question 15

Which lambda expression, when entered into the blank line in the following code, causes the
program to printhahaha? (Choose all that apply.)
import java.util.function.Predicate;
public class Hyena {
private int age = 1;
public static void main(String[] args) {
var p = new Hyena();
double height = 10;
int age = 1;
testLaugh(p, _________________________);
age = 2;
}
static void testLaugh(Hyena panda, Predicate<Hyena> joke) {
var r = joke.test(panda) ? "hahaha" : "silence";
System.out.print(r);
}
}
15.
A. var -> p.age <= 10
B. shenzi -> age==1
C. p -> true
D. age==1
E. shenzi -> age==2
F. h -> h.age < 5
G. None of the above, as the code does not compile</Hyena>

Question 16

Which of the following can be inserted without causing a compilation error? (Choose all that
apply.)
public void remove(List<Character> chars) {
char end = 'z';
// INSERT LINE HERE
Predicate<Character> predicate = c -> {
char start = 'a'; return start <= c && c <= end; };
}
16.
A. char start = 'a';
B. char c = 'x';
C. chars = null;
D. end = '1';
E. None of the above</Character></Character>

Question 17

What is the result of running the following class?
1: import java.util.function.*;
2:
3: public class Panda {
4: int age;
5: public static void main(String[] args) {
6: Panda p1 = new Panda();
7: p1.age = 1;
8: check(p1, p -> {p.age < 5});
9: }
10: private static void check(Panda panda,
11: Predicate<Panda> pred) {
12: String result = pred.test(panda)
13: ? "match" : "not match";
14: System.out.print(result);
15: } }
17.
A. match
B. not match
C. Compiler error on line 8
D. Compiler error on line 10
E. Compiler error on line 12
F. A runtime exception is thrown.</Panda>

Question 18

Which functional interfaces complete the following code? For line 7, assumem andn are
instances of functional interfaces that exist and have the same type asy. (Choose three.)
6: _________ x = String::new;
7: _________ y = m.andThen(n);
8: _________ z = a -> a + a;
18.
A. BinaryConsumer<String, String>
B. BiConsumer<String, String>
C. BinaryFunction<String, String>
D. BiFunction<String, String>
E. Predicate<String>
F. Supplier<String>
G. UnaryOperator<String>
H. UnaryOperator<String, String></String></String></String>

Question 19

Which of the following compiles and prints out the entire set? (Choose all that apply.)
Set<?> set = Set.of(“lion”, “tiger”, “bear”);
var s = Set.copyOf(set);
Consumer<object> consumer = ____________________;
s.forEach(consumer);
19.
A. () -> System.out.println(s)
B. s -> System.out.println(s)
C. (s) -> System.out.println(s)
D. System.out.println(s)
E. System::out::println
F. System.out::println</object>

Question 20

Which lambdas can replace thenew Sloth() call in themain() method and produce the
same output at runtime? (Choose all that apply.)
import java.util.List;
interface Yawn {
String yawn(double d, List<Integer> time);
}
class Sloth implements Yawn {
public String yawn(double zzz, List<Integer> time) {
return "Sleep: " + zzz;
} }
public class Vet {
public static String takeNap(Yawn y) {
return y.yawn(10, null);
}
public static void main(String… unused) {
System.out.print(takeNap(new Sloth()));
} }
20.
A. (z,f) -> { String x = ""; return "Sleep: " + x }
B. (t,s) -> { String t = ""; return "Sleep: " + t; }
C. (w,q) -> {"Sleep: " + w}
D. (e,u) -> { String g = ""; "Sleep: " + e }
E. (a,b) -> "Sleep: " + (double)(b==null ? a : a)
F. (r,k) -> { String g = ""; return "Sleep:"; }
G. None of the above, as the program does not compile</Integer></Integer>

Question 21

Which of the following are valid functional interfaces? (Choose all that apply.)
public interface Transport {
public int go();
public boolean equals(Object o);
}
public abstract class Car {
public abstract Object swim(double speed, int duration);
}
public interface Locomotive extends Train {
public int getSpeed();
}
public interface Train extends Transport {}
abstract interface Spaceship extends Transport {
default int blastOff();
}
public interface Boat {
int hashCode();
int hashCode(String input);
}
21.
A. Boat
B. Car
C. Locomotive
D. Spaceship
E. Transport
F. Train
G. None of these is a valid functional interface.