Java – Interface with Syntax and Example2 min read

An Interface in Java is the same as a class, like any other class, an interface can have methods and Variables. But unlike a class, the method in it is an abstract method (only method signature, contain no body), and also by default, the declared variables in an interface are public, static & final.

Uses of Interfaces:

  • It is used to achieve abstraction.
  • As we have learned that Java does not support multiple inheritance but through the interface, we can achieve multiple inheritance.
  • It is also used to achieve loose coupling.

Note: Abstraction cannot be used to create objects. Hence it cannot contain a constructor.

Declaring an Interface in Java:

The keyword ‘interface‘ is used to declare an interface. Syntax of Interface in Java:

Example of interface:


Implementation of Interface in Java:

To implement an interface in a class, we use the keyword ‘implements’ The following example shows the use of implements. In the example below, the class Puppy implements the interface Dog.

Output of Interfaces in Java:

Dog Barks
Dog eat Bones


Multiple Interfaces and inheritance in Java:

We know class in java allows only a single extends but with the use of interfaces, we can implement more than one parent interface.

Java Interface

In the diagram above,

  • The class extends a class
  • The interface extends an interface
  • class implements interface

Example of Multiple Interface in Java:

Output:

Displaying first method
Displaying second method


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