CoreJava-9 - OOP - Abstraction
Abstraction
Abstraction
is a fundamental concept in object-oriented programming (OOP), including the
Java programming language. It refers to the process of simplifying complex
reality by modelling classes, objects, or systems with well-defined and
simplified interfaces. In other words, abstraction allows you to hide the
unnecessary details of an object or system's internal workings while exposing
only the essential features.
In Java,
abstraction is achieved using abstract classes and interfaces. An abstract
class is a class that cannot be instantiated on its own and may contain
abstract methods (methods without a body) that must be implemented by its
subclasses. An interface is a collection of abstract methods that a class can
implement, allowing multiple inheritance of behaviour.
Benefits
of Abstraction:
- Encapsulation: Abstraction
promotes encapsulation, which means the internal implementation details
are hidden from the outside world, reducing complexity and improving
security.
- Code Reusability: Abstract
classes and interfaces allow for code reusability by defining common
methods that can be shared among multiple classes.
- Modularity: Abstraction
encourages modular design by breaking down complex systems into manageable
and distinct parts.
Real-Life
Example:
Let's consider a real-life scenario of a banking system. We'll create an
abstraction for bank accounts using Java's abstract classes and interfaces.
// Abstract class representing a Bank
Account
abstract class BankAccount {
private String accountNumber;
private double balance;
public BankAccount(String accountNumber) {
this.accountNumber = accountNumber;
this.balance = 0.0;
}
public String getAccountNumber() {
return accountNumber;
}
public double getBalance() {
return balance;
}
// Abstract method for withdrawing funds
public abstract void withdraw(double amount);
// Abstract method for depositing funds
public abstract void deposit(double amount);
}
// Concrete class representing a Savings
Account
class SavingsAccount extends BankAccount
{
private double interestRate;
public SavingsAccount(String accountNumber, double interestRate) {
super(accountNumber);
this.interestRate = interestRate;
}
@Override
public void withdraw(double amount) {
if (amount <= getBalance()) {
// Perform withdrawal
// Deduct amount from balance
} else {
System.out.println("Insufficient balance.");
}
}
@Override
public void deposit(double amount) {
// Perform deposit
// Add amount to balance
}
// Additional methods specific to SavingsAccount
public double calculateInterest() {
return getBalance() * interestRate;
}
}
// Interface representing a Loan Account
interface LoanAccount {
void applyForLoan(double amount);
void makeLoanPayment(double amount);
}
// Concrete class representing a
Personal Loan Account
class PersonalLoanAccount extends
BankAccount implements LoanAccount {
private double loanAmount;
public PersonalLoanAccount(String accountNumber, double loanAmount) {
super(accountNumber);
this.loanAmount = loanAmount;
}
@Override
public void withdraw(double amount) {
System.out.println("Cannot withdraw from a loan account.");
}
@Override
public void deposit(double amount) {
System.out.println("Cannot deposit into a loan account.");
}
@Override
public void applyForLoan(double amount) {
if (amount <= loanAmount) {
// Process loan application
// Deduct loan amount from
available loan balance
} else {
System.out.println("Loan amount
exceeds available balance.");
}
}
@Override
public void makeLoanPayment(double amount) {
// Process loan payment
// Reduce loan amount by the payment made
}
}
public class Main {
public static void main(String[] args) {
SavingsAccount savingsAccount = new SavingsAccount("SA12345",
0.05);
PersonalLoanAccount loanAccount = new
PersonalLoanAccount("PLA98765", 10000.0);
// Usage of methods defined by abstraction
savingsAccount.deposit(2000);
savingsAccount.withdraw(500);
double interest = savingsAccount.calculateInterest();
System.out.println("Interest earned: $" + interest);
loanAccount.applyForLoan(5000);
loanAccount.makeLoanPayment(1000);
}
}
In this
example, BankAccount is an abstract class that defines common attributes
and methods for bank accounts. SavingsAccount and PersonalLoanAccount
are concrete classes that extend the BankAccount class and implement
specific behaviors. The LoanAccount interface provides a contract for
loan-related operations.
Through
abstraction, the implementation details of each account type are hidden, and
the usage of accounts is simplified through well-defined methods and
interfaces. This allows for code reusability and modularity while maintaining
the necessary separation of concerns.
1. What
is abstraction in Java, and why is it important in object-oriented programming?
Answer: Abstraction in Java refers to the process of simplifying complex reality
by modelling classes, objects, or systems with well-defined and simplified
interfaces. It involves hiding the unnecessary details and exposing only the
essential features. In Java, abstraction is achieved through abstract classes
and interfaces.
Abstraction
is crucial in object-oriented programming because it promotes modularity,
encapsulation, and code reusability. It allows developers to focus on essential
functionalities without worrying about implementation details. By defining
abstract classes and interfaces, developers can create a clear separation of
concerns, making code maintenance and scalability easier.
Question 2: What is the difference between an
abstract class and an interface in Java?
Answer: Both abstract classes and interfaces are used for achieving
abstraction, but they have differences:
·
An
abstract class can have both abstract and concrete methods, while an interface
can only have abstract methods except for default and static methods with Java
8.
·
An
abstract class can have instance variables with any access modifier, while
interface variables are implicitly public, static, and final.
·
A
class can extend only one abstract class, but it can implement multiple
interfaces.
·
An
abstract class provides a partial implementation, allowing code reuse, while an
interface defines a contract that implementing classes must adhere to.
·
An
abstract class can have constructors, while an interface cannot.
Question 3: How do you achieve multiple inheritance
in Java using interfaces?
Answer: Java doesn't support multiple inheritance through classes (i.e., a class
can't extend multiple classes). However, multiple inheritance can be achieved
using interfaces. A class can implement multiple interfaces, inheriting the
method signatures from all the implemented interfaces. This allows a class to
inherit behaviors from multiple sources.
For
example:
interface A {
void methodA();
}
interface B {
void methodB();
}
class MyClass implements A, B {
@Override
public void methodA() {
// Implement methodA
}
@Override
public void methodB() {
// Implement methodB
}
}
Question 4: When would you use an abstract class
over an interface, and vice versa?
Answer: The choice between using an abstract
class and an interface depends on the scenario:
·
Use
an abstract class when you want to provide a common base with some default
implementations for subclasses. This is useful when you want to share code
among closely related classes and enforce a certain structure.
·
Use
an interface when you want to define a contract that multiple unrelated classes
can adhere to. Interfaces are suitable for achieving multiple inheritance and
are ideal when you want to ensure a specific set of methods are implemented
across different classes.
Question 5: Can you provide an example of using
abstraction to model a real-world scenario?
Answer: Sure! Let's consider a real-world
scenario of different types of vehicles.
interface Vehicle {
void start();
void stop();
}
class Car implements Vehicle {
@Override
public void start() {
// Start car engine
}
@Override
public void stop() {
// Stop car engine
}
}
class Bicycle implements Vehicle {
@Override
public void start() {
// Start pedaling
}
@Override
public void stop() {
// Stop pedaling
}
}
public class Main {
public static void main(String[] args) {
Vehicle car = new Car();
Vehicle bicycle = new Bicycle();
car.start();
car.stop();
bicycle.start();
bicycle.stop();
}
}
In this
example, the Vehicle interface defines the common methods start() and stop().
The Car and Bicycle classes implement the Vehicle interface, providing their
own implementations for starting and stopping. This abstraction allows you to
treat different types of vehicles uniformly, focusing on their common behaviours
rather than implementation details.
Question
6: Can an abstract class have a constructor? If so, how can you invoke it in a
subclass?
Answer: Yes, an abstract class can have a
constructor. Constructors in abstract classes are used to initialize common
properties of the subclass. When a subclass is instantiated, its constructor
can invoke the constructor of the abstract class using the super() keyword.
abstract class AbstractClass {
int value;
AbstractClass(int value) {
this.value = value;
}
abstract void displayValue();
}
class ConcreteClass extends
AbstractClass {
ConcreteClass(int value) {
super(value);
}
@Override
void displayValue() {
System.out.println("Value: " + value);
}
}
Question
7: Can you create an instance of an abstract class in Java? Why or why not?
Answer: No, you cannot create an instance of
an abstract class in Java. Abstract classes are incomplete and are meant to be
subclassed. They may contain abstract methods without implementations that must
be overridden by concrete subclasses. Since abstract classes have undefined behaviour
for these abstract methods, it's not possible to create instances of them
directly.
Question
8: How does abstraction promote code reusability in Java?
Answer: Abstraction promotes code reusability
by allowing you to define common behaviors and methods in abstract classes or
interfaces. Subclasses or classes implementing interfaces can then inherit and
reuse these common methods without having to redefine them. This approach
reduces duplication of code, promotes a modular design, and simplifies
maintenance.
Question
9: Can an interface extend another interface? If yes, how does it affect the
implementing class?
Answer: Yes, an interface can extend another
interface using the extends keyword. When an interface extends another
interface, the extending interface inherits the abstract methods of the parent
interface. Any class implementing the child interface is required to provide
implementations for all the abstract methods from both interfaces.
interface Parent {
void methodA();
}
interface Child extends Parent {
void methodB();
}
class ImplementingClass implements Child
{
@Override
public void methodA() {
// Implementation for methodA
}
@Override
public void methodB() {
// Implementation for methodB
}
}
Question
10: Explain the concept of the "is-a" relationship in abstraction and
how it's used in Java.
Answer: The "is-a" relationship is
a fundamental concept in object-oriented programming where one class is
considered a subtype of another class. It signifies inheritance or subclassing.
In Java, this relationship is used to establish the connection between an
abstract class (parent class) and its concrete subclasses. The concrete
subclasses "are-a" type of the abstract class.
For example,
in the code below, SavingsAccount "is-a" type of BankAccount:
abstract class BankAccount {
// Common methods and attributes
}
class SavingsAccount extends BankAccount
{
// Specific methods and attributes for savings accounts
}
The
"is-a" relationship forms the basis of polymorphism and allows
instances of subclasses to be treated as instances of their parent class,
facilitating code flexibility and modularity.
Question
11: How can you achieve abstraction without using abstract classes or
interfaces in Java?
Answer: While abstract classes and interfaces are the primary mechanisms for
achieving abstraction in Java, you can also achieve a certain level of
abstraction using regular classes and methods. By designing classes with
well-defined responsibilities and providing public methods that encapsulate the
internal implementation details, you can hide complexities and expose only
necessary functionalities.
class Calculator {
public double add(double num1, double num2) {
return num1 + num2;
}
public double subtract(double num1, double num2) {
return num1 - num2;
}
}
public class Main {
public static void main(String[] args) {
Calculator calculator = new Calculator();
double result = calculator.add(10.5, 5.3);
System.out.println("Result: " + result);
}
}
In this
example, the Calculator class abstracts the addition and subtraction
operations, providing a simplified interface to the user.
Question
12: How does abstraction contribute to the concept of polymorphism in Java?
Answer:
Abstraction and
polymorphism are closely related concepts in object-oriented programming.
Abstraction allows you to define common interfaces and behaviours, while
polymorphism allows instances of different classes to be treated as instances
of a common superclass or interface. By using abstraction through abstract
classes and interfaces, you define a contract that subclasses or implementing
classes must adhere to. This contract ensures that different implementations
can be used interchangeably, promoting polymorphism. Whenever we write the code
that operates on the abstract type (e.g., using interfaces or abstract classes
as references), we can switch between various concrete implementations without
affecting the behaviour of our code.
Question
13: How can you prevent the instantiation of an abstract class in Java?
Answer:
You can prevent the
instantiation of an abstract class in Java by declaring the class as abstract
using the abstract keyword. Abstract classes cannot be directly instantiated;
they serve as a blueprint for concrete subclasses to extend.
abstract class AbstractClass {
// Abstract methods and/or concrete methods
}
class ConcreteClass extends
AbstractClass {
// Implementations of abstract and concrete methods
}
public class Main {
public static void main(String[] args) {
// Cannot instantiate an abstract class directly
// AbstractClass instance = new AbstractClass(); // This will result in
a compilation error
AbstractClass instance = new ConcreteClass(); // Valid
}
}
In this
example, you cannot create an instance of AbstractClass, but you can
create an instance of ConcreteClass that extends it.
Question
14: Can an abstract class have both abstract and non-abstract (concrete)
methods?
Answer: Yes, an abstract class can have both
abstract and non-abstract methods. An abstract method is a method without a
body that must be overridden by concrete subclasses. A non-abstract method in
an abstract class has a defined implementation and can be used as-is or
optionally overridden by subclasses.
abstract class MyAbstractClass {
abstract void abstractMethod(); // Abstract method without
implementation
void nonAbstractMethod() {
// Concrete implementation
}
}
In this example, abstractMethod() is an
abstract method, while nonAbstractMethod() is a non-abstract (concrete)
method.
Question
15: How does abstraction relate to the concept of encapsulation in Java?
Answer:
Abstraction and
encapsulation are two key principles of object-oriented programming, and they
are closely related.
·
Abstraction: Abstraction focuses on hiding
unnecessary details and exposing only essential features. It involves defining
abstract classes, interfaces, and methods to create a clear separation between
the external interface of a class and its internal implementation.
·
Encapsulation: Encapsulation is the practice of
bundling the data (attributes) and methods (functions) that operate on the data
into a single unit, known as a class. It involves using access modifiers to
restrict the access to certain components, promoting information hiding and preventing
direct manipulation of data from outside the class.
In Java,
abstraction and encapsulation work together to achieve well-designed, modular,
and maintainable code. Abstraction hides the complex implementation details,
while encapsulation ensures that the internal state of an object can only be
accessed and modified through controlled methods, enhancing data integrity and
security.
Question
16: explain the difference between a class and an Interface?
Class: A class is a fundamental building
block in object-oriented programming (OOP). It serves as a blueprint for
creating objects, which are instances of that class. A class defines the
structure and behavior of objects by specifying attributes (fields) and
methods. Here are the key characteristics of a class:
- Instance Creation: You can create multiple
instances (objects) of a class using the new keyword. Objects
encapsulate data (attributes) and methods that operate on that data.
- Constructor: A class can have a constructor
that initializes the object's state when it's created.
- Fields (Attributes): A class can have fields
(instance variables) to store data that's specific to each object of the
class.
- Methods: A class can have methods
(functions) that define its behavior. Methods can access and manipulate
the object's attributes.
- Inheritance: Classes can inherit attributes
and methods from a parent class, allowing for code reuse and hierarchical
relationships.
- Access Modifiers: Fields and methods within a
class can have access modifiers (public, private, protected, default) to
control their visibility.
Interface:
An interface
is a reference type in Java, similar to a class that defines a contract for
classes that implement it. It specifies a set of abstract methods that must be
implemented by any class that claims to conform to the interface. Here are the
key characteristics of an interface:
- Abstract Methods: An interface only contains
abstract methods (methods without a body) that define what actions a class
implementing the interface must support.
- Multiple Inheritance: A class can implement multiple
interfaces. This allows a class to inherit behavior from multiple sources,
facilitating a form of multiple inheritance.
- No Constructor or Fields: Interfaces cannot have
constructors or fields (instance variables). They define behavior but do
not provide implementation details.
- Full Abstraction: Interfaces represent full
abstraction, as they define a contract without providing any
implementation. Classes implementing an interface must provide the
implementation.
- Default Methods (Java 8+): Interfaces can have default
methods, which provide a default implementation for a method. Classes
implementing the interface can use or override these methods.
- Access Modifiers: All methods in an interface are
implicitly public and abstract (before Java 8) or public and default (with
default methods).
In summary,
a class is a blueprint for creating objects with fields and methods, while an
interface defines a contract for classes to implement specific behaviour.
Classes can implement multiple interfaces but can extend only one class.
Interfaces are useful for achieving multiple inheritance, enforcing contracts,
and creating loosely coupled systems.
Question
17: explain the difference between Encapsulation and Abstraction?
Encapsulation:
Encapsulation
is a principle that involves bundling the data (attributes) and methods
(functions) that operate on the data into a single unit, known as a class. The
key idea behind encapsulation is to restrict direct access to the internal
state of an object and provide controlled access through methods. This helps in
achieving data hiding, protecting data integrity, and allowing changes to be
made to the internal implementation without affecting the external code that
uses the class.
Key
Characteristics of Encapsulation:
- Access Modifiers: Access modifiers like private,
protected, and public are used to control the visibility of
fields and methods within a class. This restricts external access and
allows the class to define controlled points of interaction with the data.
- Data Hiding: By making fields private and
providing getter and setter methods, encapsulation hides the internal
details of the object's state from external code. This prevents
unauthorized modification of data and ensures data consistency.
- Information Hiding: Encapsulation encapsulates both
data and the implementation details of methods. This way, the internal
workings of the class can be changed without affecting code that uses the
class.
Abstraction:
Abstraction
is a process of simplifying complex reality by modelling classes, objects, or
systems with well-defined and simplified interfaces. It involves hiding the
unnecessary details and exposing only the essential features. Abstraction
allows you to create models that focus on the core functionalities and ignore
the implementation specifics.
Key
Characteristics of Abstraction:
- Abstract Classes: Abstract classes define a
common base for a group of related classes. They can include both abstract
(unimplemented) methods and concrete (implemented) methods.
- Interfaces: Interfaces define contracts for
classes to implement a specific set of methods. They provide a way to
achieve multiple inheritance and ensure that classes adhere to certain
behaviors.
- Method Signatures: In both abstract classes and
interfaces, methods can be declared without providing implementations,
leaving the implementation details to the subclasses or classes
implementing the interface.
Question
18: Difference between Encapsulation and Abstraction:
- Focus:
- Encapsulation focuses on
controlling access to data and methods within a class to ensure data
integrity and encapsulate implementation details.
- Abstraction focuses on defining
a simplified, well-defined interface that hides complex implementation
details and presents only the essential features.
- Purpose:
- Encapsulation aims to protect
and manage the state of objects and promote information hiding.
- Abstraction aims to simplify
the complexity of a system by modelling only the relevant aspects and
ignoring unnecessary details.
- Level of Detail:
- Encapsulation is concerned with
both data and methods and how they interact within a class.
- Abstraction is concerned with
providing a high-level view of the system's behaviour and
functionalities.
In summary,
encapsulation is about controlling access and protecting data, while
abstraction is about simplifying complexity and defining clear interfaces for
interaction.
Question
18: What is the need of introducing default and static methods with examples in
interfaces in Java 8?
In Java 8,
default methods and static methods were introduced in interfaces to provide
additional flexibility and utility to the language. Let's understand the need
for these features with examples:
Default
Methods:
Need: Before Java 8, once an interface was
published, you couldn't change it without breaking the classes that implemented
it. This posed a problem when you wanted to add new methods to an existing
interface, as it would require modifying all the implementing classes. Default
methods were introduced to solve this issue by allowing interfaces to provide a
default implementation for methods.
Example: Consider an interface Shape
that represents various shapes. Later, you want to add a method to calculate
the perimeter of shapes. Without default methods, you would need to update all
implementing classes. With default methods, you can provide a default
implementation in the interface itself, and implementing classes can choose to
override it if needed.
interface Shape {
double calculateArea();
default double calculatePerimeter() {
return 0.0; // Default implementation
}
}
class Circle implements Shape {
double radius;
public Circle(double radius) {
this.radius = radius;
}
@Override
public double calculateArea() {
return Math.PI * radius * radius;
}
@Override
public double calculatePerimeter() {
return 2 * Math.PI * radius;
}
}
class Square implements Shape {
double side;
public Square(double side) {
this.side = side;
}
@Override
public double calculateArea() {
return side * side;
}
}
In this
example, calculatePerimeter() is a default method in the Shape interface. The Circle
class overrides it, while the Square class doesn't, using the default
implementation.
Static Methods:
Need: Prior to Java 8, interfaces could
only declare abstract methods, which meant you couldn't include static methods
that belong to the interface itself. Static methods in interfaces are
introduced to provide utility methods that are related to the interface, even
though they don't depend on the specific implementation.
Example: Consider an interface Math
Operations that defines static methods for common mathematical operations like
square and cube. These methods are logically related to the interface, and they
can be made available to all classes implementing the interface without any
implementation burden.
interface MathOperations {
static int square(int num) {
return num * num;
}
static int cube(int num) {
return num * num * num;
}
}
class NumberProcessor implements
MathOperations {
public void process(int num) {
int squared = square(num);
int cubed = cube(num);
// Rest of the processing
}
}
In this
example, the MathOperations interface defines static methods square() and cube().
The NumberProcessor class can directly use these methods without implementing
them.
In summary,
default methods and static methods in interfaces were introduced in Java 8 to
address the limitations of modifying existing interfaces and to provide utility
methods that are logically related to the interface. They enhance the
flexibility and extensibility of interfaces without breaking existing code.
Question
18: What is the need of introducing interfaces when we have Classes?
The introduction
of interfaces in Java was motivated by the need to address certain limitations
and achieve specific design goals that classes alone couldn't fulfill. While
both classes and interfaces have their distinct roles, interfaces provide
several benefits that complement the capabilities of classes. Let's explore the
reasons for introducing interfaces when we already have classes:
·
Multiple Inheritance: One of the primary reasons for introducing interfaces
is to allow multiple inheritance of behavior. Unlike classes, which can only
extend a single class, a class can implement multiple interfaces. This enables
a class to inherit and implement multiple sets of behaviors, promoting code
reusability and flexibility. This is particularly useful when a class needs to
inherit behaviors from unrelated sources.
·
Loose Coupling:
Interfaces promote loose coupling between different components of a system. By
programming to interfaces rather than concrete classes, you create a separation
between the contract (interface) and the implementation. This allows for easier
maintenance and modification of code without affecting other parts of the
system.
·
Contract and Abstraction: Interfaces define a contract that implementing
classes must adhere to. This contract ensures that classes provide specific
methods and behaviors. This level of abstraction helps in designing systems
where components can interact based on well-defined interfaces without needing
to know the specific implementation details.
·
API Design and Standardization: Interfaces are commonly used to define APIs
(Application Programming Interfaces). By using interfaces to define a set of
methods that should be supported, you ensure a standardized way for different
parts of a system to communicate. This allows multiple teams to work
independently as long as they adhere to the specified interface.
·
Testing and Mocking: Interfaces are valuable for testing and mocking. When you program
against interfaces, you can easily replace actual implementations with mock
implementations for unit testing. This helps isolate and test individual
components of a system.
·
Extending Existing Classes: Interfaces allow you to add functionality to existing
classes without changing their hierarchy. You can create new interfaces and
implement them in existing classes to introduce new behaviors without affecting
the original class structure.
·
Future Compatibility: Interfaces allow you to add new methods to existing
interfaces without breaking classes that implement them. This is achieved
through default methods, which provide default implementations for new methods.
This prevents the need to modify all implementing classes when extending
interfaces.
In summary,
while classes provide a blueprint for objects and encapsulate data and
behavior, interfaces serve as contracts that define specific behaviors that
classes must implement. The introduction of interfaces complements classes by
allowing for multiple inheritance, promoting loose coupling, defining
standardized interactions, facilitating testing, and enabling future
compatibility. Both classes and interfaces play essential roles in creating
flexible, maintainable, and extensible software systems.
Example:
Messaging Application
Imagine you
are developing a messaging application that supports multiple messaging
services, such as SMS, Email, and Social Media Messaging (e.g., Facebook Messenger).
Each messaging service has different functionalities and behaviors, but they
all share some common actions like sending messages and receiving messages.
Using
Classes:
If you were
to design this application using only classes, you might have a class hierarchy
like this:
class MessageService {
void sendMessage(String recipient, String message) {
// Implementation for sending messages
}
void receiveMessage(String sender, String message) {
// Implementation for receiving messages
}
}
class SMSService extends MessageService
{
// Specific implementation for SMS messaging
}
class EmailService extends
MessageService {
// Specific implementation for Email messaging
}
class SocialMediaService extends
MessageService {
// Specific implementation for Social Media messaging
}
However,
using this approach, you'll face a few challenges:
·
Rigidity: If
you want to add a new messaging service in the future, you'd have to modify the
existing class hierarchy, potentially affecting the functionality of other
services.
·
Code Reuse:
Some methods like sendMessage and receiveMessage are common to all services,
but there's no standardized way to ensure they are implemented consistently
across all classes.
Using Interfaces: Now let's see how interfaces can address these
challenges:
interface MessageService {
void sendMessage(String recipient, String message);
void receiveMessage(String sender, String message);
}
class SMSService implements
MessageService {
@Override
public void sendMessage(String recipient, String message) {
// Implementation for sending SMS
}
@Override
public void receiveMessage(String sender, String message) {
// Implementation for receiving SMS
}
}
class EmailService implements
MessageService {
@Override
public void sendMessage(String recipient, String message) {
// Implementation for sending Email
}
@Override
public void receiveMessage(String sender, String message) {
// Implementation for receiving Email
}
}
class SocialMediaService implements
MessageService {
@Override
public void sendMessage(String recipient, String message) {
// Implementation for sending Social Media message
}
@Override
public void receiveMessage(String sender, String message) {
// Implementation for receiving Social Media message
}
}
With
interfaces, you gain the following benefits:
·
Flexibility:
You can easily add new messaging services by implementing the Message Service
interface, without modifying existing code.
·
Code Reuse: Interfaces
provide a standardized contract for implementing the common methods, ensuring
consistent behavior across different messaging services.
·
Loose Coupling:
Clients of the messaging services can interact with them based on the Message
Service interface, promoting loose coupling and allowing for easier integration
and testing.
·
Future Compatibility: If you need to introduce new methods in the Message Service
interface, you can do so using default methods without breaking existing
implementations.
In this example,
interfaces help achieve modularity, code reusability, flexibility, and future
compatibility, making the messaging application more maintainable and
extensible.
Question
19: With java 8, is it a must to define all the methods of an interface in the
class that implements it?
No, with the
introduction of default methods in Java 8, it is not necessary to define all
the methods of an interface in the class that implements it. Java 8 introduced
default methods to allow you to provide default implementations for methods in
an interface. This enables you to add new methods to an existing interface
without breaking the classes that implement it.
Here's a
breakdown of the scenarios related to interface methods and their
implementations in classes:
- Abstract Methods: These
are the methods declared in the interface without any implementation. When
a class implements an interface, it must provide concrete implementations
for all the abstract methods in the interface.
- Default Methods: These
are methods declared in the interface with a default implementation. A
class that implements the interface can choose to use the default
implementation provided by the interface or override it with its own
implementation.
- Static Methods: These
are methods declared in the interface with the static keyword. They belong
to the interface itself and do not need to be implemented in the
implementing class. They can be directly called using the interface name.
In summary,
if an interface includes only abstract methods, the implementing class must
provide concrete implementations for all those methods. However, if the
interface includes default methods, the implementing class can choose to
override them or use the default implementations. Static methods in an
interface do not require implementation in the implementing class, as they are
not associated with instance-level behavior.
Assignments:
Coding
Question 1: Abstract Class Inheritance Description: Create an abstract class Shape with
methods to calculate area and perimeter. Implement subclasses Circle and
Rectangle that inherit from Shape.
Algorithm:
- Define an abstract class Shape
with abstract methods calculateArea() and calculatePerimeter().
- Define subclasses Circle
and Rectangle that extend Shape.
- Implement the abstract methods
in each subclass.
Coding
Question 2: Interface Implementation Description: Create an interface Drawable with a
method draw(). Implement classes Circle and Square that
implement Drawable.
Algorithm:
- Define an interface Drawable
with an abstract method draw().
- Implement classes Circle
and Square that implement the Drawable interface.
- Provide concrete implementations
of the draw() method in each class.
Continue in
the same pattern with the following questions:
Coding
Question 3: Bank Account Abstraction Description: Create an abstract class BankAccount with
methods for deposit, withdrawal, and balance inquiry. Implement subclasses SavingsAccount
and CheckingAccount.
Coding
Question 4: Vehicle Abstraction Description: Create an interface Vehicle with methods
for starting and stopping. Implement classes Car and Motorcycle
that implement the Vehicle interface.
Coding
Question 5: Employee Abstraction Description: Create an abstract class Employee with
methods for calculating salary. Implement subclasses FullTimeEmployee
and PartTimeEmployee.
Coding
Question 6: Online Shopping Cart Description: Implement an online shopping cart system using
abstraction, with classes for Product, Cart, and User.
Coding
Question 7: Geometric Shapes Description: Implement a program that stores and manages a
collection of different geometric shapes using abstraction.
Coding
Question 8: School Management System Description: Create an abstraction for a school management
system with classes for Person, Student, Teacher, and Course.
Coding
Question 9: Library Management System Description: Implement a library management system using
abstraction, with classes for Library, Book, and Member.
Coding
Question 10: Banking Transactions Description: Implement a program that simulates banking
transactions using abstraction, with classes for Bank, Account,
and Transaction.
For each of
these coding questions, you'll need to design appropriate classes, methods, and
relationships to achieve the desired abstraction and functionality.
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