Java vs. C#

Inheritance

Java
 
A class can have one super class, but may 
implement many interfaces.
class Sub extends Super implements InterA, 
                InterB, ...


//class A's super class is Object.
//class A is a subclass of Object class implicitly
class A 
{
    public void F() { 
        System.out.println("A.F"); 
    }
}

class B extends A 
{
    public void G() { 
        System.out.println("B.G"); 
    }
}
class Test 
{
    public static void main(String[] args) {
        B b = new B();
        b.F();            // Inherited from A
        b.G();            // Introduced in B

        A a = b;        // Treat a B as an A
        a.F();
    }
}    


class A 
{
    public void F() { 
        System.out.println("A.F"); 
    }
}
class B extends A 
{
    public void F() { 
        super.F();
        System.out.println("B.F"); 
    }
}
class Test 
{
    public static void main(String[] args) {
        B b = new B();
        b.F();
        A a = b; 
        a.F();
    }
}    


abstract class A 
{
    public abstract void F();
}
class B extends A 
{
    public void F() { 
        System.out.println("B.F"); 
    }
}
class Test 
{
    public static void main(String[] args) {
        B b = new B();
        b.F();
        A a = b;
        a.F();
    }
}


//A popular example
public class DrawingObject
{
    public void Draw()
    {
        System.out.println("I'm just a generic drawing object.");
    }
}
public class Line extends DrawingObject
{
    public void Draw()
    {
        System.out.println("I'm a Line.");
    }
}

public class Circle extends DrawingObject
{
    public void Draw()
    {
        System.out.println("I'm a Circle.");
    }
}

public class Square extends DrawingObject
{
    public void Draw()
    {
        System.out.println("I'm a Square.");
    }
}
public class DrawDemo
{
    public static void main(String[] args)
    {
        DrawingObject[] dObj = new DrawingObject[4];

        dObj[0] = new Line();
        dObj[1] = new Circle();
        dObj[2] = new Square();
        dObj[3] = new DrawingObject();

        for(int i= 0; i < dObj.length; i++)
        {
            dObj[i].Draw();
        }

        
    }
}


Output:
    I'm a Line.
    I'm a Circle.
    I'm a Square.
    I'm just a generic drawing object

C#
 
A class can have one super class, but may 
implement many interfaces.
class Sub: Super, InterA, 
                InterB, ...


//class A's base class is object
//class A is a subclass of object class implicitly
class A
{
    public void F() { 
        Console.WriteLine("A.F"); 
    }
}

class B: A
{
    public void G() { 
        Console.WriteLine("B.G"); 
    }
}
class Test
{
    static void Main() {
        B b = new B();
        b.F();            // Inherited from A
        b.G();            // Introduced in B

        A a = b;        // Treat a B as an A
        a.F();
    }
}    


class A
{
    public virtual void F() { 
        Console.WriteLine("A.F"); 
    }
}
class B: A
{
    public override void F() { 
        base.F();
        Console.WriteLine("B.F"); 
    }
}
class Test
{
    static void Main() {
        B b = new B();
        b.F();
        A a = b; 
        a.F();
    }
}    


abstract class A
{
    public abstract void F();
}
class B: A
{
    public override void F() { 
        Console.WriteLine("B.F"); 
    }
}
class Test
{
    static void Main() {
        B b = new B();
        b.F();
        A a = b;
        a.F();
    }
}


//A popular example
public class DrawingObject
{
    public virtual void Draw()
    {
        Console.WriteLine("I'm just a generic drawing object.");
    }
}

public class Line : DrawingObject
{
    public override void Draw()
    {
        Console.WriteLine("I'm a Line.");
    }
}

public class Circle : DrawingObject
{
    public override void Draw()
    {
        Console.WriteLine("I'm a Circle.");
    }
}

public class Square : DrawingObject
{
    public override void Draw()
    {
        Console.WriteLine("I'm a Square.");
    }
}

public class DrawDemo
{
    public static int Main(string[] args)
    {
        DrawingObject[] dObj = new DrawingObject[4];

        dObj[0] = new Line();
        dObj[1] = new Circle();
        dObj[2] = new Square();
        dObj[3] = new DrawingObject();

        foreach (DrawingObject drawObj in dObj)
        {
            drawObj.Draw();
        }

        return 0;
    }
}
Output:
    I'm a Line.
    I'm a Circle.
    I'm a Square.
    I'm just a generic drawing object