Computer Science Fundamentals II Tuesday, October 8, 2019
Quiz 2
CS1027A University of Western Ontario
1 Object-Oriented Programming
Consider the following code fragment:
1 public class Foo {
2 private int x;
3 public Foo(int x) {
4 this.x = x;
5 }
6 public static void main(String[] args) {
7 int x;
8 for (int i = 0; i < 10; i++) {
9 x = i;
10 }
11 Foo foo = new Foo(5);
12 }
13 }
1. What is the scope of the variable defined on line 2?
(a) Class (b) Constructor (c) Main (d) For loop
2. What is the scope of the variable defined on line 3?
(a) Class (b) Constructor (c) Main (d) For loop
3. What is the scope of the variable defined on line 8?
(a) Class (b) Constructor (c) Main (d) For loop
4. What is the scope of the variable ’x’ used on line 9?
(a) Class (b) Constructor (c) Main (d) For loop
5. In the constructor call on line 11, is ’5’ a formal parameter or actual parameter?
(a) Formal parameter (b) Actual parameter
1
2 Memory
Consider the following code fragment:
1 public class Foo {
2 public static void bar(int x) {
3 x = 3;
4 }
5 public static void barr(int[] arr) {
6 arr[0] = 3;
7 }
8 public static void main(String[] args) {
9 int x = 5;
10 bar(x);
11 System.out.println(x);
12 int[] arr = new int[1];
13 arr[0] = 5;
14 barr(arr);
15 System.out.println(arr[0]);
16 }
17 }
6. What is output by the println statement on line 11?
(a) 5 (b) 3
7. What is output by the println statement on line 15?
(a) 5 (b) 3
8. The value stored in the variable defined on line 9 (x) is:
(a) A memory location (b) A value
9. The value stored in the variable defined on line 12 (arr) is:
(a) A memory location (b) A value
10. A reference variable is a variable that holds a primitive value.
(a) True (b) False
2
3 Inheritance
Figure 1: Example of a class hierarchy.
11. Given the hierarchy shown in Figure 1, Shape is a subclass of 2DShape.
(a) True (b) False
12. Given the hierarchy shown in Figure 1, Rectangle is a superclass of Square.
(a) True (b) False
Consider the following two Java classes:
1 public class A {
2 public A() { }
3 public void m() { System.out.println("Class A"); }
4 }
5 public class B extends A {
6 public B() { }
7 public void m() { System.out.println("Class B"); }
8 }
Consider now the following code fragment:
1 A var1 = new B();
2 var1.m();
13. What does this code fragment print when it is executed?
(a) ”Class A” (b) ”Class B” (c) There is a compilation error (d) There is a runtime ex-
ception
3
Consider now the following code fragment:
1 B var2 = new A();
2 var2.m();
14. Which line has a compilation error in the above code fragment?
(a) Line 1 (b) Line 2 (c) Both of the above (d) None of the above
Consider now the following code fragment:
1 public class TestBankAccounts {
2 public static void main(String[] args) {
3 BankAccount bacc = new BankAccount(100);
4 bacc = new SavingsAccount(100);
5 bacc = new CheckingAccount(100);
6 double x = Math.random();
7 if (x < 0.5)
8 bacc = new SavingsAccount(500);
9 else
10 bacc = new CheckingAccount(500);
11 System.out.println(bacc.toString());
12 }
13 }
15. Lines 3-5 are an example of:
(a) Abstraction (b) Dynamic binding (c) Casting (d) Polymorphism (e) None of the above
16. Lines 6-11 are an example of:
(a) Abstraction (b) Dynamic binding (c) Casting (d) Polymorphism (e) None of the above
17. Which class’s toString() method is called on line 11?
(a) BankAccount (b) CheckingAccount (c) SavingsAccount (d) I don’t know
18. The super keword:
(a) Refers to a subclass (b) Refers to a sibling (c) Refers to the superclass
(d) Throws an Exception
19. The extends keword:
(a) Is used in a classes constructor (b) Modifies the visibility of an instance variable
(c) Appears in the line declaring the class name
20. Polymorphism can be achieved using interfaces instead of inheritance.
(a) True (b) False
4
4 Stacks
stack 0 1 2 3 4
s
A B C
top
Figure 2: Example of a stack.
21. Given the stack shown in Figure 2, how many elements are in the stack?
(a) 0 (b) 1 (c) 2 (d) 3 (e) 4
22. Given the stack shown in Figure 2, what kind of variable do you think stack is?
(a) Array (b) Linked List (c) Graph (d) Tree
23. Given the stack shown in Figure 2, what would s.pop() return?
(a) 0 (b) 2 (c) 3 (d) A (e) B (f ) C
24. Given the stack shown in Figure 2, what would be the value of top after calling s.pop()
2 times?
(a) 0 (b) 1 (c) 2 (d) 3 (e) 4
25. Given the stack shown in Figure 2, and given how we implemented the array stack in
lecture, what should return/happen after we call s.pop() 4 times?
(a) 0 (b) -1 (c) A (d) NullPointerException (e) EmptyCollectionException
26. Given the stack shown in Figure 2, and given how we implemented the array stack in
lecture, what should return/happen after we push 3 more letters to the stack?
(a) NullPointerException (b) ArrayIndexOutOfBoundsException (c) false
(d) expandCapacity() is called
