Interface in the Java programming language is an abstract type that is used to specify a behavior that classes must implement. They are similar to protocols. Interfaces are declared using the interface keyword, and may only contain method signature and constant declarations.

All methods of an Interface do not contain implementation (method bodies) as of all versions below Java 8. Starting with Java 8, default and static methods may have implementation in the interface definition. Then, in Java 9, private and private static methods were added. At present, a Java interface can have up to six different types.

Interfaces cannot be instantiated, but rather are implemented. A class that implements an interface must implement all of the non-default methods described in the interface, or be an abstract class. Object references in Java may be specified to be of an interface type; in each case, they must either be null, or be bound to an object that implements the interface.

One benefit of using interfaces is that they simulate multiple inheritance. All classes in Java must have exactly one base class, the only exception being java.lang.Object (the root class of the Java type system); multiple inheritance of classes is not allow. However, it may inherit multiple interfaces and a class may implement multiple interfaces.

What is interface use?

It is use to achieve total abstraction. Since java does not support multiple inheritance in case of class, but by using interface it can achieve multiple inheritance . It is also use to achieve loose coupling. Interfaces are use to implement abstraction.

What is difference between class and interface?

A class can instantiated i.e, we can create objects of a class. This cannot instantiate i.e, we cannot create objects. Classes does not support multiple inheritance. It supports multiple inheritance.

What are the advantages of interface?

  • Space efficiency.
  • Compiler optimization.
  • Efficient multiple inheritance.
  • Object creation efficiency.
  • Forces a clean separation of interface and implementation.
  • Not type intrusive.
  • Objects can implement the same interface in different ways.
  • Avoidance of heap allocations.

Why do we need interface and abstract class?

An abstract class allows you to create functionality that subclasses can implement or override. This only allows you to define functionality, not implement it. And whereas a class can extend only one abstract class, it can take advantage of multiple interfaces.

What are the 2 benefits of using interface for a service in your code?

  1. Code readability: It constitutes a declaration about intentions.
  2. Code semantics: By providing interfaces and implementing them you’re actively separating concepts in a similar way HTML and CSS does.

What is the need of abstraction?

Abstraction allows us to create a general idea of what the problem is and how to solve it. The process instructs us to remove all specific detail, and any patterns that will not help us solve our problem. This helps us form our idea of the problem.

How do you do abstraction?

A method defined abstract must always be redefine in the subclass, thus making overriding compulsory OR either make the subclass itself abstract. Any class that contains one or more abstract methods must also be declared with an abstract keyword. There can be no object of an abstract class.

Can an abstract class implement an interface?

Java Abstract class can implement interfaces without even providing the implementation of this methods. Java Abstract class is use to provide common method implementation to all the subclasses or to provide default implementation.

What is pure virtual function?

A pure virtual function or pure virtual method is a virtual function that is require to implemented by a derived class if the derived class is not abstract. Pure virtual methods typically have a declaration (signature) and no definition (implementation).