Chapter 11

Question 1

A class design requires that a particular member variable must be accessible by any subclasses of this class, but otherwise not by classes which are not members of the same package. What should be done to achieve this?

Answer 1

The variable should be marked protected.

Question 2

Invoking _________ returns the first element in an ArrayList x.

Answer 2

x.get(0)

Question 3

Invoking _________ returns the number of the elements in an ArrayList x.

Answer 3

x.size()

Question 4

Assume Cylinder is a subtype of Circle. Analyze the following code:
Cylinder cy = new Cylinder(1, 1);
Circle c = cy;

Answer 4

The code is fine.

Question 5

What modifier should you use on the members of a class so that they are not accessible to another class in a different package, but are accessible to any subclasses in any package?

Answer 5

protected

Question 6

Which of the following are Java keywords?

Answer 6

instanceof

Question 7

What is the output of running class C?
class A {
     public A() {
          System.out.println(
               "The default constructor of A is invoked");
     }
}
class B extends A {
     public B() {
          System.out.println(
               "The default constructor of B is invoked");
     }
}
public class C {
     public static void main(String[] args) {
          B b = new B();
     }
}

Answer 7

“The default constructor of A is invoked” followded by “The default constructor of B is invoked”

Question 8

Given the following code:
class C1 {}
class C2 extends C1 { }
class C3 extends C2 { }
class C4 extends C1 {}
C1 c1 = new C1();
C2 c2 = new C2();
C3 c3 = new C3();
C4 c4 = new C4();
Which of the following expressions evaluates to false?

Answer 8

c4 instanceof C2

Question 9

Inheritance means ______________.

Answer 9

that a class can extend another class

Question 10

Polymorphism means ______________.

Answer 10

that a variable of supertype can refer to a subtype object

Question 11

Invoking _________ removes all elements in an ArrayList x.

Answer 11

x.clear()

Question 12

What modifier should you use on a class so that a class in the same package can access it but a class (including a subclass) in a different package cannot access it?

Answer 12

Use the default modifier.

Question 13

Suppose an ArrayList list contains {“red”, “green”, “red”, “green”}. What is the list after the following code?
list.remove(“red”);

Answer 13

{“green”, “red”, “green”}

Question 14

What is the output of the following code:
public class Test {
     public static void main(String[] args) {
          Object o1 = new Object();
          Object o2 = new Object();
          System.out.print((o1 == o2) + " " + (o1.equals(o2)));
     }
}

Answer 14

false false

Question 15

Given two reference variables t1 and t2, if t1 == t2 is true, t1.equals(t2) must be ___________.

Answer 15

True

Question 16

What is the output of the following code:
public class Test {
     public static void main(String[] args) {
          String s1 = new String("Java");
          String s2 = new String("Java");
          System.out.print((s1 == s2) + " " + (s1.equals(s2)));
     }
}

Answer 16

false true

Question 17

Which of the following is incorrect?

Answer 17

A constructor may be static.

Question 18

Encapsulation means ______________.

Answer 18

that data fields should be declared private

Question 19

You can create an ArrayList using _________.

Answer 19

new ArrayList<>()