Abstract Vs Interface in Java

In Java, both abstract classes and interfaces serve as mechanisms for achieving abstraction and defining contracts for classes to implement.

However, they have distinct differences in terms of their features and usage:

Abstract Classes:

An abstract class is a class that cannot be instantiated on its own and is typically used as a base class for other classes to inherit from.
Abstract classes can contain both abstract methods (methods without a body) and concrete methods (methods with a body).
Abstract classes can have constructors, fields, and instance variables.
Subclasses of an abstract class must provide implementations for all the abstract methods, unless the subclass is also declared abstract.
Abstract classes are useful when we want to define common behaviour and characteristics for a group of related classes and provide a default implementation for some methods.

Example:

abstract class Animal {
    abstract void sound(); // Abstract method
    void displayNickName(String nickName) {
        System.out.println("Displaying Nick Name: "+ nickName);
    }
}

Interfaces:

Example:

interface Animal {
    void sound(); // Method signature
}

An interface is a reference type similar to a class but can only contain method signatures (abstract methods) and constant declarations.
Interfaces cannot have constructors, fields, or instance variables (prior to Java 8).
Classes can implement multiple interfaces but can only extend one class.
Interfaces support multiple inheritance of type, allowing a class to inherit behaviours from multiple interfaces.
Starting from Java 8, interfaces can have default methods (methods with a default implementation) and static methods.
Interfaces are useful for defining contracts that classes must adhere to, promoting loose coupling and code flexibility.
Interfaces enable polymorphism, allowing objects of different classes to be treated interchangeably if they implement the same interface.

When to Use:

Use abstract classes when we want to provide a common base implementation for a group of related classes, and when we want to define default behaviour for some methods.
Use interfaces when we want to define a contract for classes to implement, especially when multiple inheritance of type is required, or when we want to ensure loose coupling between components.

Note:

abstract classes and interfaces are both important tools for achieving abstraction and defining contracts in Java, but they have different features and are used in different scenarios based on the requirements of your application.

<-- Interface

Abstract Vs Interface in Java

In Java, both abstract classes and interfaces serve as mechanisms for achieving abstraction and defining contracts for classes to implement.

However, they have distinct differences in terms of their features and usage:

Abstract Classes:

An abstract class is a class that cannot be instantiated on its own and is typically used as a base class for other classes to inherit from.
Abstract classes can contain both abstract methods (methods without a body) and concrete methods (methods with a body).
Abstract classes can have constructors, fields, and instance variables.
Subclasses of an abstract class must provide implementations for all the abstract methods, unless the subclass is also declared abstract.
Abstract classes are useful when we want to define common behaviour and characteristics for a group of related classes and provide a default implementation for some methods.

Example:

abstract class Animal {
    abstract void sound(); // Abstract method
    void displayNickName(String nickName) {
        System.out.println("Displaying Nick Name: "+ nickName);
    }
}

Interfaces:

Example:

interface Animal {
    void sound(); // Method signature
}

An interface is a reference type similar to a class but can only contain method signatures (abstract methods) and constant declarations.
Interfaces cannot have constructors, fields, or instance variables (prior to Java 8).
Classes can implement multiple interfaces but can only extend one class.
Interfaces support multiple inheritance of type, allowing a class to inherit behaviours from multiple interfaces.
Starting from Java 8, interfaces can have default methods (methods with a default implementation) and static methods.
Interfaces are useful for defining contracts that classes must adhere to, promoting loose coupling and code flexibility.
Interfaces enable polymorphism, allowing objects of different classes to be treated interchangeably if they implement the same interface.

When to Use:

Use abstract classes when we want to provide a common base implementation for a group of related classes, and when we want to define default behaviour for some methods.
Use interfaces when we want to define a contract for classes to implement, especially when multiple inheritance of type is required, or when we want to ensure loose coupling between components.

Note:

<-- Interface