Jump To C#
By Vyas Bharghava

When I started learning C# half the time I was trying to find Java equivalents so that I can learn effectively, leveraging my existing Java skills. At times I was so frustrated by my knowledge or lack there of.  I'm penning this piece in the hope that my experience might help Java programmers to learn Java's new cousin (or villain according to some view points!). I'll only deal with those functionalities which are present in Java but are modified / changed completely in C#. You don't have to worry about another article detailing Delegates & Events. :)

1. final vs. sealed 

final Keyword is used in three contexts in Java.
1. A final class is not available for inheritance
2. A final method cannot be overridden
3. A final instance variable is a constant

People will tell you that there's a equivalent new 'sealed' keyword.  Take it with a grain of salt. For there are pitfalls.

1. A sealed class cannot be inherited from.
2. A sealed method cannot be overridden
(pitfall: This functionality is only available in Beta 2)
3. Two news keywords are provided for the third Java functionality.

const int a = 5; // Compile time
readonly Singleton s = new Singleton(); // Runtime

In Java,

1. Private members of an outer class are accessible from the inner class.
2. There's a concept of enclosing instance
3. Static inner classes were actually akin to top level classes

In C#,

1. Inner classes are called Nested Types
2. Private members of outer class are accessible from the nested class but 
     the enclosing instance must be passed to the nested class.
3. In fact, C#'s Nested classes are akin to Static inner classes of Java
   (but even then you have to access members of the outer classes thru either an instance
   or class name in case of a static member)

In Java, you accessed parent class members in the child class by using super.method(); format. 

In C#, just replace the super with base, i.e.
base.method(), and viola! It works.

But (it's a big but), you also invoked super class' constructors using the
notation super() as the first line in the constructor:

Constructor() {
    super();
}

You can't do this in C#! :

Constructor() {
    base();
}

I know you are incredulous.  There no way to call a super class' constructor?
Hold your horses.  Of course, you can.  Let's examine this writing a custom exception.

using System;

class SomeUserDefinedError: Exception
{
 // THIS IS HOW YOU CALL SUPER CLASS' CONSTRUCTOR
 public SomeUserDefinedError(string Message): base(Message)  
  {
  }
}

public class ThrowException {

 public static void Main(string [] args) {
  throw new SomeUserDefinedError("Great! I'm throwing errors");
 }

}