Interface in Java

 Interface in java

Definiton :

Interface is a collection of abstract methods and constants (i.e. static and final fields). It is used to achieve complete abstraction.

• Interface in non- primitive datatype in java.
• An interface is a reference type in Java that defines a contract for classes .
• An interface in Java is a blueprint for a class.
• Interfaces are widely used in Java for defining contracts, ensuring code reusability, and enabling loose coupling between components in object-oriented programming.
• Use the interface keyword to declare an interface.

   - Syntax: 

interface InterfaceName 

{ 

// interface body 

}

• All variables declared in an interface are public, static, and final.
• All methods are implicitly public and abstract (no method body) in the interface.
• Interfaces can also have static methods that can be called using the interface name.
•  An interface does not contain any implementation for its methods; it only declares their signatures.
• Classes can implement an interface using the `implements` keyword.
• A class implementing an interface must provide concrete implementations for all the methods declared in the interface, as well as in any parent interfaces that the interface extends.

   - Syntax: 

class ClassName implements InterfaceName 

{ 

// class body 

}

Multiple Inheritance via Interfaces:

•  Java supports multiple inheritance through interfaces since a class can implement multiple interfaces.
• A class can implement multiple interfaces but extend only one class (single inheritance rule).
• Interfaces can extend other interfaces, forming an interface hierarchy.
• A class implementing a derived interface must provide implementations for all methods in both interfaces.

1.class extends class

2.class implements interface

3.interface extends interface

4. Single Class can extend another class & implement more than one interface

5.Single interface can extends more than one interface

Interface vs. Abstract Class: 

Unlike abstract classes, interfaces cannot have constructors and cannot be directly instantiated. However, a class can implement multiple interfaces, while it can extend only one abstract class.

Differenece between class & interface 

 An interface is declared like a class but the only difference is that it contains only final variables and method declarations. It is a fully abstract class.