Question 1

Which of the following statements about abstract superclasses is true?

Accepted Answer

Abstract superclasses can contain data, including instance variables with assigned values, and can also contain concrete (implemented) methods alongside abstract methods. They do not need to declare all methods or data members as abstract.

Question 2

The UML distinguishes an interface from other classes by placing the word "interface" in above the interface name.

Accepted Answer

UML uses guillemets (« ») to distinguish an interface from other classes by placing the word "interface" above the interface name.

Question 3

In Java SE 7 and earlier,an interface may contain:

Accepted Answer

In Java SE 7 and earlier, interfaces can contain only public static final data (constants) and public abstract methods.

Question 4

Which of the following is false?

Accepted Answer

It is not always okay to call any of a class's methods from its constructors. If the method being called is an abstract method that needs implementation in the subclass, or if it is an overridable method that may call a method or access a variable that has not been initialized in the subclass, it may lead to errors or unexpected behavior. The other options are true.

Question 5

Declaring a method final means:

Accepted Answer

Declaring a method final means that it cannot be overridden by any subclasses, ensuring that its functionality remains consistent throughout the inheritance hierarchy. This is useful when you want to ensure that a method is not accidentally changed or modified by a subclass, and can be particularly important for methods that are critical for an object's behavior or state.

Question 6

Consider classes A,B and C,where A is an abstract superclass,B is a concrete class that inherits from A and C is a concrete class that inherits from B.Class A declares abstract method originalMethod,implemented in class B.Which of the following statements is true of class C?

Accepted Answer

None of the statements A, B, or C are true. In Java, once an abstract method is implemented in a concrete subclass, it is not implicitly final and can be overridden in further subclasses. There is no requirement for further subclasses to override it unless the method is abstract again, and calling it without overriding will simply use the implementation from the nearest superclass.

Question 7

A(n) class cannot be instantiated.

Accepted Answer

An abstract class cannot be instantiated because it is designed to be extended by other classes, which will provide implementations for its abstract methods. Abstract classes are used when you want to define a blueprint for a class hierarchy but don't want instances of the base class to be created directly.

Question 8

If the superclass contains only abstract method declarations,the superclass is used for ________.

Accepted Answer

If the superclass contains only abstract method declarations, it is essentially an interface and is used for interface inheritance. Implementation inheritance requires the superclass to provide actual implementation of methods.

Question 9

Which of the following could be used to declare abstract method method1 in abstract class Class1 (method1 returns an int and takes no arguments)?

Accepted Answer

Option A is not correct as it doesn't declare the method as abstract. 
Option B is syntactically incorrect as you cannot have both the modifier "abstract" and the method body present. 
Option C correctly declares the method as abstract. 
Option D is not a valid syntax for declaring an abstract method.

Question 10

For which of the following would polymorphism not provide a clean solution?

Accepted Answer

Polymorphism is useful when there are multiple types or classes that need to be treated through a common interface, especially when behavior varies. In option C, the computation of a fixed 5% interest does not require different behaviors or types, making polymorphism unnecessary.

Question 11

Polymorphism enables you to:

Accepted Answer

Polymorphism allows you to program in the general by creating code that can work with objects of multiple classes. This is because polymorphism enables objects to be treated as if they are of a parent type, allowing for flexibility and scalability in your code.

Question 12

Assigning a subclass reference to a superclass variable is safe ________.

Accepted Answer

Assigning a subclass reference to a superclass variable is safe because the subclass object is an object of its superclass. This is known as polymorphism, and it allows for flexibility in programming and easier maintenance of code.

Question 13

When a superclass variable refers to a subclass object and a method is called on that object,the proper implementation is determined at execution time.What is the process of determining the correct method to call?

Accepted Answer

This process is called late binding or dynamic binding. It occurs when the decision to call a specific implementation of a method is delayed until the program is executed, based on the actual type of the object that the method is called on.

Question 14

All of the following methods are implicitly final except:

Accepted Answer

A method in an abstract class is not implicitly final because it can be overridden by subclasses.

Question 15

Classes and methods are declared final for all but the following reasons:

Accepted Answer

Final methods are not inherently static. Declaring a method or class as final primarily prevents it from being overridden or inherited, respectively. It does not imply that the method is static. Static methods belong to the class rather than any instance of the class and can be called without creating an instance of the class.

Question 16

Interfaces can have methods.

Accepted Answer

Interfaces can have any number of methods.

Question 17

Polymorphism allows for specifics to be dealt with during:

Accepted Answer

Polymorphism is a feature that allows an object to take on many forms. This means that during execution, a specific method or behavior can be applied based on the type of object being used. Therefore, polymorphism deals with specifics during execution.

Question 18

Which statement best describes the relationship between superclass and subclass types?

Accepted Answer

A subclass reference can be assigned to a superclass variable because a subclass is a type of superclass. However, a superclass reference cannot be assigned to a subclass variable because a superclass does not necessarily have all the methods and properties of a subclass.

Question 19

It is a UML convention to denote the name of an abstract class in ________.

Accepted Answer

It is a UML convention to denote the name of an abstract class in italics.

Question 20

Non-abstract classes are called ________.

Accepted Answer

Non-abstract classes are also called concrete classes because they provide a complete implementation of all the methods defined in their class declaration. This means that they can be instantiated and used to create objects.

Quiz 10: Object-Oriented Programming: Polymorphism