Difference between abstract class and interface

An Interface in Java programming language is defined as an abstract type used to specify the behavior of a class.

Marker interface in java

An interface in Java is a blueprint of a behavior. A Java interface contains static constants and abstract methods.

• The interface in Java is a mechanism to achieve abstraction.
• By default, variables in an interface are public, static, and final.
• It is used to achieve abstraction and multiple inheritances in Java.
  Interface with parameters java

• It is also used to achieve loose coupling.
• In other words, interfaces primarily define methods that other classes must implement.
• An interface in Java defines a set of behaviors that a class can implement, usually representing an IS-A relationship, but not always in every scenario.

Example:

Note: In Java, the abstract keyword applies only to classes and methods, indicating that they cannot be instantiated directly and must be implemented.

When we decide on a type of entity by its behaviour and not via attribute we should define it as an interface.

Syntax

interface {
// declare