interface keyword
An interface is a keyword in java, it is
used to declare interface in java. Like a class, interface can have methods and
variables, but the methods declared in interface must be abstract. It is used
to achieve abstraction and multiple inheritance in java. Methods in an
interface are implicitly public.
Writing interface similar to writing a
class. But class describes the attributes and behaviours of an object. And an
interface contains behaviours that a class implements.
Syntax to declare interface:
interface <interface-name>{
//abstract methods
}
Example:
interface Add{
public int add( );
}
How to implement interface
A class uses implement keyword to
implement an interface. If class does not define all the methods of interface
then the class must be declared as abstract.
Now we will explain how to implement an
interface via this following example.
Example
File:
Sum.java
interface Add{
public int add( int a, int b);
}
class Complete implements
Add{
public int add(int a, int b){
return a+b;
}
}
public class Sum{
public static void main(String [
]q){
Complete obj=new Complete();
int c=obj.add(5,12);
System.out.println("Sum of two numbers is "+c);
}
}
Output:
Sum of two numbers is 17
Code
explanation:
In this program First we created one
interface named as Add and then after we implement this interface by Complete
class and this Complete class define the method that is declared inside
interface. Now we create third class named as Sum and this class contains main
method. Inside this main method we create object of Complete class and via this
object we access the method and get the value of addition of two numbers. After
getting the addition of two numbers we print that value using System.out.println(
).
Note:
Since java 8, interface can have
default and static methods.
