Creating Subclasses: A Comprehensive Guide for Object-Oriented Programming

Question 1

In Java, which keyword is used to create a subclass?

Accepted Answer

extends

Answer

implements

Answer

overrides

Answer

abstracts

Question 2

What is the primary purpose of creating a subclass?

Accepted Answer

To reuse and extend existing functionality

Answer

To create a completely new data type

Answer

To store objects of the same type

Answer

To define abstract methods

Question 3

What is the relationship between a subclass and its superclass?

Accepted Answer

The subclass inherits all the public and protected methods and fields of the superclass

Answer

The subclass can access only the private methods of the superclass

Answer

The superclass inherits all the methods and fields of the subclass

Answer

The subclass and the superclass are completely independent

Question 4

Can a subclass have multiple superclasses in Java?

Accepted Answer

No, Java does not support multiple inheritance

Answer

Yes, through multiple inheritance

Answer

Yes, but only if the superclasses are interfaces

Answer

Yes, but only if the superclasses are abstract classes

Question 5

Which of the following is an example of method overriding?

Accepted Answer

Declaring a method with the same name and signature in the subclass

Answer

Declaring a method with the same name but different signature in the subclass

Answer

Calling a method from the superclass in the subclass

Answer

Overloading a method in the subclass

Question 6

What is the purpose of the 'super' keyword in a subclass?

Accepted Answer

To call the constructor of the superclass

Answer

To access the private members of the superclass

Answer

To override a method in the superclass

Answer

To create an instance of the superclass

Question 7

Which access modifier should be used for methods that should be accessible only within the subclass and its subclasses?

Accepted Answer

protected

Answer

public

Answer

private

Answer

default

Question 8

What is a key advantage of using subclasses in object-oriented programming?

Accepted Answer

Increases code reusability by inheriting shared functionality.

Answer

Complicates code maintenance and makes it more error-prone.

Answer

Eliminates the need for polymorphism and encapsulation.

Answer

Compromises encapsulation by revealing internal data.

Question 9

In Java, which keyword is used to create a subclass?

Accepted Answer

extends

Answer

inherits

Answer

subclasses

Answer

creates

Question 10

What is the primary purpose of creating subclasses in object-oriented programming?

Accepted Answer

To extend the functionality of existing classes

Answer

To create new classes from scratch

Answer

To modify the behavior of parent classes

Answer

To improve code readability

Question 11

Which of the following is a potential advantage of subclassing?

Accepted Answer

Code reusability

Answer

Increased code complexity

Answer

Difficulty in maintaining the codebase

Answer

Reduced flexibility

Question 12

What access specifier is commonly used for methods and fields inherited from a parent class in Java?

Accepted Answer

protected

Answer

public

Answer

private

Answer

default

Question 13

Which of the following would NOT be a valid Java subclass of the 'Animal' class?

Accepted Answer

Vehicle

Answer

Dog

Answer

Cat

Answer

Fish

Question 14

What is the name of the special constructor that is automatically invoked when a subclass is created?

Accepted Answer

super constructor

Answer

default constructor

Answer

parameterized constructor

Answer

subclass constructor

Question 15

What is the key difference between a subclass and an interface?

Accepted Answer

Subclasses inherit implementation details, while interfaces only specify contracts.

Answer

Interfaces inherit implementation details, while subclasses only specify contracts.

Answer

Subclasses and interfaces both inherit implementation details.

Answer

Subclasses and interfaces both specify contracts.

Question 16

In Java, which keyword is used to create a subclass?

Accepted Answer

extends

Answer

implements

Answer

inherits

Answer

subclasses

Question 17

What is the primary purpose of creating a subclass?

Accepted Answer

To reuse existing code and add specialized functionality

Answer

To create a completely new class

Answer

To modify the behavior of an existing class

Answer

To create a class that can be used in multiple programs

Question 18

Which of the following is NOT a potential benefit of using inheritance?

Accepted Answer

Increased code complexity

Answer

Code reusability

Answer

Faster development

Answer

Reduced maintenance costs

Question 19

What is the relationship between a subclass and its superclass?

Accepted Answer

The subclass inherits all public and protected members of the superclass

Answer

The subclass inherits all private members of the superclass

Answer

The subclass is completely independent of the superclass

Answer

The subclass cannot access any members of the superclass

Question 20

Which of these actions demonstrates polymorphism using subclasses?

Accepted Answer

Overriding a method in a subclass to provide unique behavior.

Answer

Adding new instance variables to a subclass.

Answer

Inheriting properties and methods from a parent class without changes.

Question 21

In object-oriented programming, what is the main benefit of creating subclasses?

Accepted Answer

Increased code reuse and faster development

Answer

Reduced code complexity and easier maintenance

Answer

Improved performance and simpler debugging

Question 22

Which keyword in Java is used to create a subclass?

Accepted Answer

extends

Answer

inherits

Answer

implements

Answer

subclasses

Question 23

What is the main purpose of creating a subclass?

Accepted Answer

To create a new class with specialized functionality that extends an existing class.

Answer

To create a new object that inherits the properties of an existing class.

Answer

To replace the functionality of an existing class.

Question 24

Which of the following is a disadvantage of using subclasses?

Accepted Answer

Increased code complexity

Answer

Code reusability

Answer

Extensibility

Answer

Improved maintainability

Question 25

Consider the code:

`public class Animal { ... } 
public class Dog extends Animal { ... }`
 What does this code indicate?

Accepted Answer

Dog is a subclass of Animal.

Answer

Dog and Animal are unrelated.

Answer

Animal is a subclass of Dog.

Answer

The code is invalid.

Question 26

Which access modifier should method have in a superclass to allow inheritance by subclasses?

Accepted Answer

protected

Answer

private

Answer

default

Answer

public

Question 27

What is the distinction between the 'super' and 'this' keywords in subclass methods?

Accepted Answer

'super' refers to the parent class, while 'this' refers to the current class.

Answer

'this' refers to the parent class, while 'super' refers to the current class.

Answer

'super' and 'this' both refer to the current class.

Question 28

Which practice is considered good when designing subclasses?

Accepted Answer

Keep subclasses focused and cohesive to a specific purpose.

Answer

Subclass every class, even when unnecessary.

Answer

Create subclasses frequently to avoid code duplication.

Question 29

What is the term for a method in a subclass that has the same name as a method in its parent class?

Accepted Answer

Method overriding

Answer

Method shadowing

Answer

Method hiding

Answer

Method overloading

Question 30

Consider the code:

`public class Animal { public void eat() { ... } } 
public class Dog extends Animal { @Override public void eat() { ... } }`
 What is the function of the '@Override' annotation in the Dog class's 'eat()' method?

Accepted Answer

To indicate that the method overrides the 'eat()' method in the Animal class.

Answer

To prevent the Dog class from inheriting the 'eat()' method from the Animal class.

Answer

To make the 'eat()' method in the Dog class private.

Question 31

Which of the following is NOT a potential limitation of inheritance?

Accepted Answer

Inheritance increases flexibility.

Answer

Inheritance introduces potential complexity and fragility.

Answer

Inheritance can lead to diamond problems.

Answer

Inheritance can hinder changing subclass behavior without affecting other subclasses.

Question 32

In Java, which keyword is used to create a subclass that inherits from a superclass?

Accepted Answer

extends

Answer

inherits

Answer

subclasses

Question 33

What is the primary purpose of overriding methods in subclasses?

Accepted Answer

To provide specialized implementations of inherited methods that suit the specific needs of the subclass.

Answer

To prevent access to inherited methods.

Answer

To create new methods with the same name as inherited ones.

Question 34

When overriding inherited methods in a subclass, which access modifier should be used to ensure accessibility is maintained or broadened?

Accepted Answer

Same or broader

Answer

Private

Answer

Protected only

Answer

Narrower

Question 35

When a subclass constructor invokes its superclass constructor, which keyword is used?

Accepted Answer

super

Answer

this

Answer

self

Question 36

Which of the following is NOT a potential benefit of using subclasses?

Accepted Answer

Complete avoidance of code duplication

Answer

Enhanced code organization

Answer

Improved code reusability

Question 37

Consider the following code snippet:

class Vehicle {
        public void move() {
            System.out.println("Vehicle is moving");
        }
    }

Which of the following subclass declarations would correctly override the move() method?

Accepted Answer

@Override
public class Car extends Vehicle {
    @Override
    public void move() {
        System.out.println("Car is moving");
    }
}

Answer

class Car extends Vehicle {
    protected void move() {
        System.out.println("Car is moving");
    }
}

Answer

class Car extends Vehicle {
    public void move() {
        System.out.println("Vehicle is moving");
    }
}

Question 38

Consider the following code snippet:

class Animal {
        private String name;
    }

class Dog extends Animal {
        public Dog(String name) { 
            this.name = name; 
        }
    }

What is the purpose of the constructor in the Dog class?

Accepted Answer

To initialize the name attribute inherited from the Animal class.

Answer

To create a new object of type Dog.

Answer

To invoke the constructor of the Animal class.

Question 39

Which of the following statements best describes the relationship between a subclass and its superclass?

Accepted Answer

An "is-a" relationship

Answer

A "depends-on" relationship

Answer

A "has-a" relationship

Answer

A "uses-a" relationship

Question 40

In object-oriented programming, which keyword is used to create a subclass, indicating that it inherits properties and methods from a parent class?

Accepted Answer

extends

Answer

implements

Answer

inherits

Answer

super

Question 41

The primary reason for creating a subclass is to:

Accepted Answer

Extend the functionality of an existing class by adding new methods or attributes.

Answer

Define a new data structure separate from the original class.

Answer

Replace an existing class with a different implementation.

Answer

Create a completely new, unrelated class.

Question 42

In object-oriented programming, what is the fundamental purpose of creating a subclass?

Accepted Answer

To specialize and extend the behavior of an existing class.

Answer

To create a separate copy of an existing class.

Answer

To replace an existing class with a more efficient version.

Answer

To define a completely new class with no relation to existing classes.

Question 43

In Java, which keyword is used to explicitly declare that a class is a subclass of another class?

Accepted Answer

extends

Answer

implements

Answer

superclass

Answer

inherits

Question 44

In Java, which keyword signifies that a class is derived from another class, inheriting its characteristics?

Accepted Answer

extends

Answer

derive

Answer

subclass

Answer

inherit

Question 45

What is the main advantage of using subclasses in object-oriented programming?

Accepted Answer

Code reusability and specialization, allowing for efficient code organization and tailored functionality.

Answer

Faster program execution, while subclassing can sometimes introduce slight overhead.

Answer

Reduced memory usage, although this is not a primary benefit of subclassing.

Answer

Increased code complexity, leading to potential confusion and maintenance challenges.

Question 46

If 'Animal' is a superclass and 'Dog' is its subclass, what is true about a 'Dog' object?

Accepted Answer

A 'Dog' object inherits and can access all members (methods and attributes) of the 'Animal' class.

Answer

A 'Dog' object can only access methods, not variables, of the 'Animal' class.

Answer

A 'Dog' object cannot access any members of the 'Animal' class.

Question 47

Suppose 'Shape' is a superclass with a method 'calculateArea()'. How can a subclass 'Rectangle' override this method to provide its own area calculation?

Accepted Answer

By defining a method named 'calculateArea()' with the same parameters (signature) within the 'Rectangle' class.

Answer

By calling the superclass method directly within the 'Rectangle' class, which wouldn't override the behavior.

Answer

By using a different method name in the 'Rectangle' class, which wouldn't override the inherited method.

Question 48

What is the primary purpose of the 'super' keyword when used within a subclass?

Accepted Answer

To access members (methods and attributes) of the superclass.

Answer

To make a method abstract, abstract methods are declared with the 'abstract' keyword.

Answer

To define a new constructor within the subclass, constructors are specific to the class itself.

Answer

To create an instance of the subclass, instances are created using the 'new' keyword.

Question 49

Which of the following is NOT a valid way to create a subclass in object-oriented programming?

Accepted Answer

Using the 'new' keyword directly with the subclass name, as this creates an instance, not a new subclass.

Answer

Instantiating an object of the subclass using its constructor, which is a valid way to create an object from the subclass.

Answer

Declaring a class with the 'extends' keyword, which is the standard way to create a subclass.

Question 50

What is the relationship between a superclass and its subclass?

Accepted Answer

Inheritance: the subclass inherits properties and methods from the superclass.

Answer

Aggregation: the subclass contains an instance of the superclass.

Answer

Composition: the subclass is entirely composed of the superclass.

Question 51

You have a superclass 'Vehicle' and a subclass 'Car'. Which of the following could be a valid method in the 'Car' subclass that's NOT present in the 'Vehicle' superclass?

Accepted Answer

honkHorn()

Answer

startEngine()

Answer

applyBrakes()

Answer

accelerate()

Question 52

Given a superclass 'Shape' with an abstract method 'calculateArea()', what must a subclass 'Circle' do?

Accepted Answer

Provide an implementation for the 'calculateArea()' method.

Answer

Declare the 'calculateArea()' method as abstract in the 'Circle' subclass.

Answer

Call the 'calculateArea()' method from the 'Shape' superclass.