Java 9.1.2 Quiz: Defining Subclasses with Superclasses

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Questions and Answers

What is the primary relationship between a subclass and its superclass?

has-a relationship

is-a relationship (correct)

part-of relationship

uses-a relationship

What does a subclass inherit from its superclass?

only public methods

accessible data fields and methods (correct)

all data fields and methods, regardless of access

only private data fields

What can a subclass do in addition to inheriting from its superclass?

only change the access modifier of existing methods

only add new data fields

add new data fields and methods (correct)

only override methods

What is a new feature present in the Circle class that is not present in the GeometricObject class?

radius data field Signup and view all the answers

Which of the following classes is a subclass of the GeometricObject class?

Circle Signup and view all the answers

What is the symbol used to denote the inheritance relationship between two classes?

A triangular arrow Signup and view all the answers

What is the purpose of the keyword extends in the Circle class?

To inherit methods from the GeometricObject class Signup and view all the answers

Why can't we access the data fields color and filled directly in the constructor of the Circle class?

Because they are private Signup and view all the answers

How can we access the private data fields color and filled in the GeometricObject class?

Through the getter and setter methods Signup and view all the answers

What is the result of attempting to use the data fields color and filled directly in the constructor of the Circle class?

It will not compile due to access restrictions Signup and view all the answers

What is the relationship between the Circle class and the GeometricObject class?

Circle is a subclass of GeometricObject Signup and view all the answers

What happens when the Circle class extends the GeometricObject class?

The Circle class gains the methods of the GeometricObject class Signup and view all the answers

What is the keyword used to define a subclass in Java?

extends Signup and view all the answers

What is the relationship between the Tree and Person classes in terms of inheritance?

Tree class inherits Person class Signup and view all the answers

Do subclasses inherit constructors from their superclasses?

No, they do not inherit constructors Signup and view all the answers

How can a superclass's constructor be invoked from a subclass?

Using the keyword 'super' Signup and view all the answers

What is the syntax to call a superclass's constructor with arguments?

super(arguments) Signup and view all the answers

What is the rule for using the 'super' keyword in a subclass constructor?

It must be the first statement in the constructor Signup and view all the answers

What is the first constructor that gets invoked when a new Faculty object is created?

Person's no-arg constructor Signup and view all the answers

What is the output of the statement new Faculty()?

(1) Person's no-arg constructor is invoked (2) Invoke Employee’s overloaded constructor (3) Employee's no-arg constructor is invoked (4) Faculty's no-arg constructor is invoked Signup and view all the answers

What is the purpose of the statement this("(2) Invoke Employee’s overloaded constructor") in the Employee's no-arg constructor?

To invoke the overloaded constructor of Employee Signup and view all the answers

What is the relationship between the classes Faculty, Employee, and Person?

Faculty is a subclass of Employee, and Employee is a subclass of Person Signup and view all the answers

What is the order of constructor invocation when a new Faculty object is created?

Person, Employee, Faculty Signup and view all the answers

Why is the no-arg constructor of Employee invoked when a new Faculty object is created?

Because Faculty is a subclass of Employee Signup and view all the answers

What is the main purpose of overriding a method in a subclass?

To provide a new implementation of the method that is different from the superclass Signup and view all the answers

Why can a private method not be overridden in a subclass?

Because it is not accessible outside its own class Signup and view all the answers

What happens when a static method is redefined in a subclass?

The method in the superclass is hidden Signup and view all the answers

What is the difference between method overloading and overriding?

Overloading is used for multiple methods with the same name, while overriding is used for a new implementation of a method Signup and view all the answers

Why can a subclass inherit a static method from its superclass?

Because a static method is accessible outside its own class Signup and view all the answers

What is the purpose of the toString() method in the Circle class?

To return a string representation of the circle Signup and view all the answers

Study Notes

Constructors and Inheritance

The Faculty class extends the Employee class, which in turn extends the Person class.
When a new Faculty object is created, the constructors of Faculty, Employee, and Person are called in that order.
The Employee class has an overloaded constructor that takes a string argument, and a no-arg constructor.
The Person class has a no-arg constructor.

Superclasses and Subclasses

A subclass inherits accessible data fields and methods from its superclass.
A subclass may also add new data fields and methods.
The extends keyword is used to denote the inheritance relationship between two classes.
A subclass and its superclass must have an "is-a" relationship.
Private data fields in a superclass are not accessible outside the class, but can be accessed/mutated through public accessors/mutators if defined in the superclass.

Using the `super` Keyword

A subclass does not inherit constructors from its superclass.
A subclass can invoke its superclass's constructors using the super keyword.
The syntax to call a superclass's constructor is super() or super(parameters).
The super keyword must be the first statement in the constructor.

Overriding vs. Overloading

Overloading means defining multiple methods with the same name but different signatures.
Overriding means providing a new implementation for a method in the subclass.
An instance method can be overridden only if it is accessible.
A private method cannot be overridden because it is not accessible outside its own class.
A static method can be inherited, but it cannot be overridden. If a static method defined in the superclass is redefined in a subclass, the method defined in the superclass is hidden.

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Description

This quiz covers the concept of superclasses and subclasses in Java programming, including inheritance relationships, accessible data fields and methods, and the is-a relationship. Learn how a subclass inherits from its superclass and adds new data fields and methods.

Java Programming: Superclasses and Subclasses