Interface in OOPS

 What is interface ?
Ans:an interface is a class with all its functions as abstract .

interface A{
    public void method();
}
class One{
    public void method(){
        System.out.println("Class One method");
    }
}
class Two extends One implements A{
    public void method(){
        System.out.println("Class Two method");
    }
}

In this example u can see first class is not completed and second class (two) is completed just bcse we are mention implements 

Why to use interface?
Ans: Interface ka use tab krte hai jab koi page me hame mandatory feature rkhna hai bina uske complete na ho to us case me interface ka use kiya jata hai.