What is an interface

What is an interface?

Interface looks like class but it is not a class. An interface can have methods and variables just like the class but the methods declared in interface are by default abstract (only method signature, no body). Also, the variables declared in an interface are public, static & final by default.

What is the use of interfaces?

As mentioned above they are used for abstraction. Since methods in interfaces do not have body, they have to be implemented by the class before you can access them. The class that implements interface must implement all the methods of that interface. Also, java programming language does not support multiple inheritance, using interfaces we can achieve this as a class can implement more than one interfaces, however it cannot extend more than one classes.

Benefits of having interfaces:

Following are the advantages of using interfaces:

Without bothering about the implementation part, we can achieve the security of implementation

In java,  multiple inheritance is not allowed, However by using interfaces you can achieve the same . A class can extend only one class but can implement any number of interfaces. It saves you from Deadly Diamond of Death(DDD) problem.

Syntax

interface MyInterface

{

   public void method1();

   public void method2();

}

Note:

 All the methods are public abstract by default

These methods are not having body

Interface Implementation

This is how a class implements an interface. It has to provide the body of all the methods that are declared in interface.
Note: class implements interface but an interface extends another interface.

Example

package com.opps;

public interface Customer {

            public void saveCustomer();

            public void displayCustomer();

            public void editCustomer();

            public void deleteCustomer();

            }

package com.opps;

public class CustomerImpl implements Customer{

            public void saveCustomer() {           

                        System.out.println("Save the Customer Details");

            }

            public void displayCustomer() {

                        System.out.println("Display the Customer Details");

            }

            public void editCustomer() {

                        System.out.println("Edit the Customer Details");

            }

            public void deleteCustomer() {         

                        System.out.println("Delete the Customer Details");

            }

}

package com.opps;

public class CustomerTest {

            public static void main(String[] args)

            {

Customer customer=new CustomerImpl();

customer.saveCustomer();

customer.displayCustomer();

customer.editCustomer();

customer.deleteCustomer();

}

}

output:

Save the Customer Details
Display the Customer Details
Edit the Customer Details
Delete the Customer Details