What is use of Interface

• Interfaces are better suited to situations in which your applications require many possibly unrelated object types to provide certain functionality.

• Interfaces are more flexible than base classes because you can define a single implementation that can implement multiple interfaces.

• Interfaces are better in situations in which you do not have to inherit implementation from a base class.

• Interfaces are useful when you cannot use class inheritance. For example, structures cannot inherit from classes, but they can implement interfaces.

Sure. Here's a simple implementation of that. First define your interface with the Sum, Difference, Multiply and Divide methods like:

public interface ICalulator
{
        T Sum(T a, T b);
        T Difference(T a, T b);
        T Multiply(T a, T b);
        T Divide(T a, T b);
}

the "T" there is the type that the iterface will be using to do the operations for example int, decimal or whatever.

Now you can then create a concrete class than implement the interface:

public class Int32Calculator : ICalulator
{
        public Int32 Sum(Int32 a, Int32 b) {
            return a + b;
        }

        public Int32 Difference(Int32 a, Int32 b) {
            return a - b;
        }

        public Int32 Multiply(Int32 a, Int32 b) {
            return a * b;
        }

        public Int32 Divide(Int32 a, Int32 b) {
            return a / b;
        }

}

and use it like this:

Int32Calculator calcu = new Int32Calculator();
int sum = calcu.Sum(5, 8);
int sub = calcu.Difference(5,5);
int mul = calcu.Multiply(2,3);
int div = calcu.Divide(10,2);
 

• Interface helps to obtain full abstraction in Java.
• Interface helps to do loose coupling in Java application.
• Interface helps to obtain multiple inheritances in Java.