Deck 10: Inheritance and Polymorphism

Question 1

In Java, stream classes are implemented using the inheritance mechanism.

Answer 1

True

Question 2

If a class is declared final, then no other class can be derived from this class.

Answer 2

True

Question 3

The superclass inherits all its properties from the subclass.

Answer 3

False

Question 4

The class Object is directly or indirectly the superclass of every class in Java.

Question 5

A polymorphic reference variable can refer to either an object of its own class or an object of the subclasses inherited from its class.

Question 6

In Java, polymorphism is implemented using late binding.

Question 7

A subclass cannot directly access public members of a superclass.

Question 8

You must always use the reserved word super to use a method from the superclass in the subclass.

Question 9

In dynamic binding, the method that gets executed is determined at compile time, not at execution time.

Question 10

A subclass inherits all its data members from the superclass; it has none of its own.

Question 11

To override a public method of a superclass in a subclass, the corresponding method in the subclass must have the same name but a different number of parameters.

Question 12

In multiple inheritance, the subclass is derived from more than one superclass.

Question 13

A subclass can directly access protected members of a superclass.

Question 14

Suppose that the class Mystery is derived from the class Secret. The following statements are legal in Java. Secret secRef; Mystery mysRef = new Mystery(); secRef = mysRef;

Question 15

Redefining a method of a superclass is also known as overloading a method.

Question 16

A subclass can override public methods of a superclass.

Question 17

In Java, you can automatically make a reference variable of a subclass type point to an object of its superclass.

Question 18

Inheritance implies an "is-a" relationship.

Question 19

The private members of a superclass can be accessed by a subclass.

Question 20

Java uses late binding for methods that are private but not for methods that are marked final.

Question 21

An interface is a class that contains only abstract methods and/or named constants.

Question 22

Interfaces are defined using the reserved word interface and the reserved word class.

Question 23

In the scenario described in the accompanying figure, what will the first statement do?

A) The cost method in Honda will be called.
B) The cost method in Car will be called.
C) Nothing will be called since the code will not compile as a result of multiple definitions of speed.
D) Overloading will be used to determine which cost method to use.

Question 24

If class Dog has a subclass Retriever, which of the following is true?

A) Because of single inheritance, Dog can have no other subclasses.
B) Because of single inheritance, Retriever can extend no other class except Dog.
C) The relationship between these classes implies that Dog "is-a" Retriever.
D) The relationship between these classes implies that Retriever "has-a" Dog.

Question 25

Based on the diagram in the accompanying figure, which of the following members will Box NOT have direct access to?

A) getHeight()
C) length
B) setDimension()
D) print()

Question 26

To determine whether a reference variable that points to an object is of a particular class type, Java provides the operator instanceof.

Question 27

Consider the following class definitions. public class BClass {private int x; public void set(int a) { x = a; } public void print(){ }} public class DClass extends BClass {private int y; public void set(int a, int b) {//Postcondition: x = a; y = b;} public void print(){ }} Which of the following is the correct definition of the method set of the class DClass? (i) public void set(int a, int b) {super.set(a); y = b;} (ii) public void set(int a, int b) {x = a; y = b;}

A) Only (i)
B) Only (ii)
C) Both (i) and (ii)
D) None of these

Question 28

Composition is a "has-a" relationship.

Question 29

Inheritance is an example of what type of relationship?

A) is-a
C) was-a
B) has-a
D) had-a

Question 30

What is the correct syntax for defining a new class Parakeet based on the superclass Bird?

A) class Parakeet isa Bird{ }
B) class Bird defines Parakeet{ }
C) class Bird hasa Parakeet{ }
D) class Parakeet extends Bird{ }

Question 31

Consider the following class definitions. public class BClass {private int x; private double y; public void print() { }} public class DClass extends BClass {private int a; private int b; public void print() { }} Suppose that you have the following statement. DClass dObject = new DClass(); How many instance variables does dObject have?

A) zero
C) three
B) two
D) four

Question 32

What type of inheritance does Java support?

A) single inheritance
C) multiple inheritance
B) double inheritance
D) Java does not support inheritance.

Question 33

Suppose there are three classes named Shape, Circle, and Square. What is the most likely relationship between them?

A) Square is a superclass, and Shape and Circle are subclasses of Square.
B) Shape is a superclass, and Circle and Square are subclasses of Shape.
C) Shape, Circle, and Square are all sibling classes.
D) These three classes cannot be related.

Question 34

Which of the following statements about the reference super is true?

A) It must be used every time a method from the superclass is called.
B) It must be the last statement of the subclass constructor.
C) It must be the first statement of the subclass constructor.
D) It can only be used once in a program.

Question 35

Based on the diagram in the accompanying figure, the method area in the class Box ____ the method area in the class Rectangle.

A) overloads
C) overstates
B) overrides
D) deletes

Question 36

Consider the following class definitions. public class BClass {private int x; public void set(int a) {x = a;} public void print() {System.out.print(x);}} public class DClass extends BClass {private int y; public void set(int a, int b) {//Postcondition: x = a; y = b;} public void print(){ }} Which of the following correctly redefines the method print of DClass? (i) public void print() {System.out.print(x + " " + y);} (ii) public void print() {super.print(); System.out.print(" " + y);}

A) Only (i)
B) Only (ii)
C) Both (i) and (ii)
D) None of these

Question 37

A subclass can directly access ____.

A) public members of a superclass
C) all members of a superclass
B) private members of a superclass
D) none of the members of a superclass

Question 38

Based on the diagram in the accompanying figure, the method setDimension in the class Box ____ the method setDimension in the class Rectangle.

A) overloads
C) overstates
B) overrides
D) deletes

Question 39

Any new class you create from an existing class is called a(n) ____.

A) base class
C) derived class
B) superclass
D) extended class

Question 40

An abstract method is a method that has only the heading with no body.

Question 41

An abstract class ____.

A) does not have any subclasses
C) cannot be instantiated
B) is a superclass with many subclasses
D) is the base class of all other classes

Question 42

Composition is also called ____.

A) inheritance
C) overloading
B) aggregation
D) overriding

Question 43

The classes Reader and Writer are derived from the class ____.

A) Streams
C) Outputs
B) Inputs
D) Object

Question 44

An abstract method ____.

A) is any method in the abstract class
B) cannot be inherited
C) has no body
D) is found in a subclass and overrides methods in a superclass using the reserved word abstract

Question 45

An abstract class can contain ____.

A) only abstract methods
C) abstract and non-abstract methods
B) only non-abstract methods
D) nothing

Question 46

Which operator is used to determine if an object is of a particular class type?

A) The operator new
C) The instanceof operator
B) The dot (.) operator
D) The + operator

Question 47

If a class implements an interface, it must ____.

A) provide definitions for each of the methods of the interface
B) override all constants from the interface
C) rename all the methods in the interface
D) override all variables from the interface

Question 48

Suppose that the class Mystery is derived from the class Secret. Consider the following statements. Secret mySecret = new Secret(); Secret secRef; Mystery myMystery = new Mystery(); Mystery mysRef; secRef = myMystery; Which of the following statements is legal in Java? (i) mysRef = (Mystery) mySecret; (ii) mysRef = (Mystery) secRef;

A) Only (i)
C) Both (i) and (ii)
B) Only (ii)
D) None of these

Question 49

Suppose that the class Mystery is derived from the class Secret. Consider the following statements. Secret secRef = new Secret(); Mystery mysRef = new Mystery(); Which of the following statements is legal in Java? (i) secRef = mysRef; (ii) mysRef = secRef;

A) Only (i)
C) Both (i) and (ii)
B) Only (ii)
D) None of these

Question 50

The method toString() is a public member of the class ____.

A) Object
C) Writer
B) String
D) Output