Explain the difference between a class and an interface in Java. When would you use each?

In Java, classes and interfaces are key elements of object-oriented programming, but they have different purposes and characteristics. Here's an in-depth explanation of the difference between a class and an interface in Java, along with the scenarios when you would use each:

1. Class:

* Definition: A class in Java is a blueprint that defines the properties (attributes) and behaviors (methods) that objects of that class will possess. It represents a specific entity or concept.
* Characteristics:
+ A class can have instance variables, constructors, methods, static members, and can define its own behavior.
+ Objects are created by instantiating a class using the `new` keyword.
+ A class can be extended by other classes to inherit its properties and behaviors using inheritance.
* Usage:
+ Use a class when you want to model real-world entities, encapsulate related data and behavior into a single unit, and create instances (objects) of that class.
+ Classes are used to define the structure and behavior of objects, allowing you to create multiple instances with different data values but the same behavior.
+ Use classes to create reusable components, implement abstraction, encapsulation, and inheritance, and build complex systems with object-oriented design principles.
2. Interface:

* Definition: An interface in Java is a reference type that defines a contract or a set of method signatures that implementing classes must adhere to. It represents a behavior or capability that a class can have.
* Characteristics:
+ An interface only declares method signatures, constants, and default methods (from Java 8 onwards), without providing any implementation details.
+ It cannot be instantiated directly and acts as a contract for classes that implement it.
+ A class can implement multiple interfaces, allowing for multiple inheritance of type.
* Usage:
+ Use an interface when you want to establish a contract or a common set of methods that multiple unrelated classes should implement.
+ Interfaces provide a way to achieve abstraction and define behavior without specifying the implementation details.
+ They are used to achieve loose coupling and promote code reusability by allowing different classes to implement the same interface, enabling polymorphism and substitutability.
+ Use interfaces when you want to define a common behavior that can be shared across different classes, allowing for flexibility and extensibility in your codebase.

In summary, classes in Java represent specific entities or concepts and provide a blueprint for creating objects with their own properties and behaviors. Interfaces, on the other hand, define contracts for classes to adhere to, specifying a set of methods that must be implemented. Classes are used when you need to create objects, define their behavior, and implement inheritance, while interfaces are used when you want to establish a common contract, achieve loose coupling, and promote code reusability through polymorphism and multiple inheritance of type.