C# | How to use Interface References

// C# program to illustrate the 
// concept of Interface References
using System;

// interface declaration
public interface Race {
    
    // declaration of abstract methods of
    // interface that will be implemented 
    // by the class which inherits the interface
    void Speed(int s);
    void Distance(int d);
}

// class implementing interface
public class Person1 : Race {
    
    int sp1, di1;
    
    // abstract method of 
    // Race interface
    public void Speed(int p1s) {
        
        sp1 = p1s;
        Console.WriteLine("Speed Method implemented by Person1");
        
    }
    
    // abstract method of 
    // Race interface
    public void Distance(int p1d) {
        
        di1 = p1d;
        Console.WriteLine("Distance Method implemented by Person1");
        
    }
    
    // method of class Person1
    public void display1() {
        
        Console.WriteLine("The Speed of 1st person is: "+sp1);
        Console.WriteLine("The distance covered by 1st person is: "+di1);
        
    }
    
}

// class implementing interface
public class Person2 : Race {
    
    int sp2, di2;
    
    // abstract method of 
    // Race interface
    public void Speed(int p2s) {
        
        sp2 = p2s;
        Console.WriteLine("Speed Method implemented by Person2");
        
    }
    
    // abstract method of 
    // Race interface
    public void Distance(int p2d) {
        
        di2 = p2d;
        Console.WriteLine("Distance Method implemented by Person2");
        
    }
    
    // method of class Person2
    public void display2() {
        
        Console.WriteLine("The Speed of 2nd person is: "+sp2);
        Console.WriteLine("The distance covered by 2nd person is: "+di2);
        
    }
    
}

// Driver Class
public class GFG {
    
    // Main method
    public static void Main(String []args) {
        
        // creating an instance of Person1 class
        Person1 obj1 = new Person1();
        
        // creating an instance of Person2 class
        Person2 obj2 = new Person2();
        
        // creating an Reference 
        // of interface Race
        Race r;
        
        // ----- For Person1 Class ----------
        
        // assigning Person1 object 'obj1'
        // to interface Reference 'r'
        r = obj1;
        
        // Now you can access the abstract method
        // of Race interface which are implemented
        // by class Person1
        r.Speed(10);
        r.Distance(50);

        // if you will try to call display1() 
        // method using 'r' it will give error
        //r.display1();
        
        // calling the display1() 
        // method of Person1 Class
        obj1.display1();
        
        // ----- For Person2 Class ----------
        
        // assigning Person2 object 'obj2'
        // to interface Reference 'r'
        r = obj2;
        
        // Now you can access the abstract method
        // of Race interface which are implemented
        // by class Person2
        r.Speed(15);
        r.Distance(45);

        // if you will try to call display2() 
        // method using 'r' it will give error
        //r.display2();
        
        // calling the display1() 
        // method of Person1 Class
        obj2.display2();
        
    }
    
}

// C# program to illustrate the 
// concept of Interface References
using System;

// interface declaration
interface Vehicle {

    // all are the abstract methods.
    void changeGear(int a);
    void speedUp(int a);
    void applyBrakes(int a);
    void printStates();
}

// class implements interface
class Bicycle : Vehicle {

    int speed;
    int gear;

    // to change gear
    public void changeGear(int newGear)
    {

        gear = newGear;
    }

    // to increase speed
    public void speedUp(int increment)
    {

        speed = speed + increment;
    }

    // to decrease speed
    public void applyBrakes(int decrement)
    {

        speed = speed - decrement;
    }

    public void printStates()
    {
        Console.WriteLine("speed: " + speed + " gear: " + gear);
    }
}

// Driver Class
class GFG {

    // Main Method
    public static void Main(String[] args)
    {

        // creating an instance of Bicycle
        Bicycle bicycle = new Bicycle();

        // Creating interface references
        Vehicle obj;

        // assigning Bicycle object 'bicycle'
        // to interface Reference 'obj'
        obj = bicycle;

        // calling the abstract methods 
        // implemented by class Bicycle
        obj.changeGear(4);
        obj.speedUp(5);
        obj.applyBrakes(2);

        Console.WriteLine("Bicycle Present State:");

        // calling the method of class Bicycle 
        obj.printStates();
    }
}