Java vs. C#

Polymorphism

Java
 
By default, all methods are virtual.

class B {
    public void foo () {}
}

class D extends B {
    public void foo () {}
}


to hide a superclass method
declare it private or final
class B {
    private void foo () {}
}

class D extends B {
    public void foo () {}
}

C#
 
The virtual keyword must be used so that the method 
will be called by the base class.
class B {
    public virtual void foo () {}
}

class D : B {
    public override void foo () {}
}


using new to override a non virtual method.

class B {
    public void foo () {}//hide from D
}

class D : B {
    public new void foo () {}
}