Java vs. C#

Override

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

the output:
   B.F
   B.F
   B.G
   B.G


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

the output:
    B.F
    B.F
    D.F
    D.F


override modifier
You cannot override to be more private
class A
{
    public void F() {}
}
class B extends A
{
    public void F() {}//cannot be private
}
class C extends B
{
    public void F() {}
}
You can hide B.F by controlling runtime type

C#
 
using System;
class A
{
    public void F() { 
        Console.WriteLine("A.F"); 
    }
    public virtual void G() { 
        Console.WriteLine("A.G"); 
    }
}
class B: A
{
    new public void F() { 
        Console.WriteLine("B.F"); 
    }
    public override void G() { 
        Console.WriteLine("B.G"); 
    }
}
class Test
{
    static void Main() {
        B b = new B();
        A a = b;
        a.F();
        b.F();
        a.G();
        b.G();
    }
}
the output:
   A.F
   B.F
   B.G
   B.G


using System;
class A
{
    public virtual void F() { 
        Console.WriteLine("A.F"); 
    }
}
class B: A
{
    public override void F() { 
        Console.WriteLine("B.F"); 
    }
}
class C: B
{
    new public virtual void F() { 
        Console.WriteLine("C.F"); 
    }
}
class D: C
{
    public override void F() { 
        Console.WriteLine("D.F"); 
    }
}
class Test
{
    static void Main() {
        D d = new D();
        A a = d;
        B b = d;
        C c = d;
        a.F();
        b.F();
        c.F();
        d.F();
    }
}
the output:
    B.F
    B.F
    D.F
    D.F


override modifier
class A
{
    public virtual void F() {}
}
class B: A
{
    new private void F() {} // Hides A.F within B
}
class C: B
{
    public override void F() {} // Ok, overrides A.F
}