Coding Standards for easy maintenance

1. Software Should Have Testable Goals

2. Close Customer Involvement Is Key

3. Software Development Is A Learning Process

4. Do The Important Stuff First

5. Communicating Is The Principal Activity

6. Prevention Is (Usually) Cheaper Than Cure

7. Software That Can't Be Put To Use Has No Value

8. Interfaces Are For Communicating

9. Automate The Donkey Work

10. Grow Complex Software Using The Simplest Parts

11. To Learn, We Must Be Open To Change

Difference between List Of and Collection Of

List<T> inherits from Collection<T>. So they have a lot of the same functionality. List just extends it by adding members and methods to make things easier, like ForEach, TrimExcess, and ConvertAll. Collection<T> is used as the base class for all generic collections in the 2.0 Framework. You would almost always use List. The only time you would use Collection is to make your own class and use Collection as the base.

Constructors and Destructor in Dot Net

Constructor:

1. The Constructor is the first method that is run when an instance of a type is created. In visual basic a constructor is always Sub new ().

2. Constructor are use to initialize class and structure data before use. Constructor never returns a value and can be overridden to provide custom initialization functionality.

3. The constructor provides a way to set default values for data or perform other necessary functions before the object available for use.

Destructor:

Destructors are called just before an object is destroyed and can be used to run clean-up code. You can’t control when a destructor is called.
Points to remember:
1. Destructors are invoked automatically, and cannot be invoked explicitly.
2. Destructors cannot be overloaded. Thus, a class can have, at most, one destructor.
3. Destructors are not inherited. Thus, a class has no destructors other than the one, which may
    be declared in it.
4. Destructors cannot be used with structs. They are only used with classes.

Destructor and finalize
Generally in C++ the destructor is called when objects gets destroyed. And one can explicitly call the destructors in C++. And also the objects are destroyed in reverse order that they are created in. So in C++ you have control over the destructors.
In C# you can never call them, the reason is one cannot destroy an object. So who has the control over the destructor (in C#)? it's the .Net frameworks Garbage Collector (GC). GC destroys the objects only when necessary. Some situations of necessity are memory is exhausted or user explicitly calls System.GC.Collect() method.
Points to remember:
1. Destructors are invoked automatically, and cannot be invoked explicitly.
2. Destructors cannot be overloaded. Thus, a class can have, at most, one destructor.
3. Destructors are not inherited. Thus, a class has no destructors other than the one, which may be declared in it.
4. Destructors cannot be used with structs. They are only used with classes.
5. An instance becomes eligible for destruction when it is no longer possible for any code to use the instance.
6. Execution of the destructor for the instance may occur at any time after the instance becomes eligible for destruction.
7. When an instance is destructed, the destructors in its inheritance chain are called, in order, from most derived to least derived.
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/cpguide/html/cpconfinalizemethodscdestructors.asp


What is the difference between Finalize and Dispose (Garbage collection)
Class instances often encapsulate control over resources that are not managed by the runtime, such as window handles (HWND), database connections, and so on. Therefore, you should provide both an explicit and an implicit way to free those resources. Provide implicit control by implementing the protected Finalize Method on an object (destructor syntax in C# and the Managed Extensions for C++). The garbage collector calls this method at some point after there are no longer any valid references to the object.
In some cases, you might want to provide programmers using an object with the ability to explicitly release these external resources before the garbage collector frees the object. If an external resource is scarce or expensive, better performance can be achieved if the programmer explicitly releases resources when they are no longer being used. To provide explicit control, implement the Dispose method provided by the IDisposable Interface. The consumer of the object should call this method when it is done using the object. Dispose can be called even if other references to the object are alive.
Note that even when you provide explicit control by way of Dispose, you should provide implicit cleanup using the Finalize method. Finalize provides a backup to prevent resources from permanently leaking if the programmer fails to call Dispose.

Difference between type constructor and instance constructor? What is static constructor, when it will be fired? And what is its use?
(Class constructor method is also known as type constructor or type initializer)
Instance constructor is executed when a new instance of type is created and the class constructor is executed after the type is loaded and before any one of the type members is accessed. (It will get executed only 1st time, when we call any static methods/fields in the same class.) Class constructors are used for static field initialization. Only one class constructor per type is permitted, and it cannot use the vararg (variable argument) calling convention.
A static constructor is used to initialize a class. It is called automatically to initialize the class before the first instance is created or any static members are referenced.

What is Abstract Class, Interfaces and Multiple inheritence in Dot Net

Static Class: 

• A Class which cannot be instantiated is called static class.
• You can use the class but cannot create object of it 
• like: You can use inbuilt classes  System.Math , System.IO etc.

Abstract Class:

• Abstract classes are classes which cannot be instantiated
• Abstract classes are classes which can contain both Signature as well as the implementation.
• When You derive the abstract class you may or may not write the implementation depending upon the base class.

Interfaces:
Interfaces are used for Multiple inheritance
Interface contains only the Signatures.
The derived class has to write the implementation if using the interface.

Multiple Inheritance :

• In .Net practically Multiple inheritance is not possible .
• But we need to Find out some way by which we can use multiple inheritance as its a very crucial function of OOPS.
• So we created Interfaces for that.
• We cannot inherit multiple classes but we can do multiple inheritance by using Interfaces or by inheriting multiple interfaces.
• In Interfaces we have to define only the signatures .

Can we call a base class method without creating instance?

• Its possible If its a static method.
• Its possible by inheriting from that class also.
• Its possible from derived classes using base keyword
  

Feature	Interface	Abstract class
Multiple inheritance	A class may implement several interfaces.	A class may extend only one abstract class.
Default implementation	An interface cannot provide any code at all, much less default code.	An abstract class can provide complete code, default code, and/or just stubs that have to be overridden.
Constants	Static final constants only, can use them without qualification in classes that implement the interface. On the other paw, these unqualified names pollute the namespace. You can use them and it is not obvious where they are coming from since the qualification is optional.	Both instance and static constants are possible. Both static and instance intialiser code are also possible to compute the constants.
Third party convenience	An interface implementation may be added to any existing third party class.	A third party class must be rewritten to extend only from the abstract class.
is-a vs -able or can-do	Interfaces are often used to describe the peripheral abilities of a class, not its central identity, e.g. an Automobile class might implement the Recyclable interface, which could apply to many otherwise totally unrelated objects.	An abstract class defines the core identity of its descendants. If you defined a Dog abstract class then Damamation descendants are Dogs, they are not merely dogable. Implemented interfaces enumerate the general things a class can do, not the things a class is.
Plug-in	You can write a new replacement module for an interface that contains not one stick of code in common with the existing implementations. When you implement the interface, you start from scratch without any default implementation. You have to obtain your tools from other classes; nothing comes with the interface other than a few constants. This gives you freedom to implement a radically different internal design.	You must use the abstract class as-is for the code base, with all its attendant baggage, good or bad. The abstract class author has imposed structure on you. Depending on the cleverness of the author of the abstract class, this may be good or bad. Another issue that's important is what I call "heterogeneous vs. homogeneous." If implementors/subclasses are homogeneous, tend towards an abstract base class. If they are heterogeneous, use an interface. (Now all I have to do is come up with a good definition of hetero/homogeneous in this context.) If the various objects are all of-a-kind, and share a common state and behavior, then tend towards a common base class. If all they share is a set of method signatures, then tend towards an interface.
Homogeneity	If all the various implementations share is the method signatures, then an interface works best.	If the various implementations are all of a kind and share a common status and behavior, usually an abstract class works best.
Maintenance	If your client code talks only in terms of an interface, you can easily change the concrete implementation behind it, using a factory method.	Just like an interface, if your client code talks only in terms of an abstract class, you can easily change the concrete implementation behind it, using a factory method.
Speed	Slow, requires extra indirection to find the corresponding method in the actual class. Modern JVMs are discovering ways to reduce this speed penalty.	Fast
Terseness	The constant declarations in an interface are all presumed public static final, so you may leave that part out. You can't call any methods to compute the initial values of your constants. You need not declare individual methods of an interface abstract. They are all presumed so.	You can put shared code into an abstract class, where you cannot into an interface. If interfaces want to share code, you will have to write other bubblegum to arrange that. You may use methods to compute the initial values of your constants and variables, both instance and static. You must declare all the individual methods of an abstract class abstract.
Adding functionality	If you add a new method to an interface, you must track down all implementations of that interface in the universe and provide them with a concrete implementation of that method.	If you add a new method to an abstract class, you have the option of providing a default implementation of it. Then all existing code will continue to work without change.

Different Types if  access-specifiers available in c#

• Private
• Protected
• Public
• Internal
• Protected Internal

Explain about Protected and protected internal, “internal” access-specifier?
protected - Access is limited to the containing class or types derived from the containing class.
internal - Access is limited to the current assembly.
protected internal - Access is limited to the current assembly or types derived from the containing class.

Diffrence Between Value Type and Refrence type

Most programming languages provide built-in data types, such as integers and floating-point numbers, that are copied when they are passed as arguments (that is, they are passed by value).
In the .NET Framework, these are called value types. The runtime supports two kinds of value types:

Built-in value types
The .NET Framework defines built-in value types, such as System.Int32 and System.Boolean, which correspond and are identical to primitive data types used by programming languages.
User-defined value types
Your language will provide ways to define your own value types, which derive from System.ValueType. If you want to define a type representing a value that is small, such as a complex number (using two floating-point numbers), you might choose to define it as a value type because you can pass the value type efficiently by value. If the type you are defining would be more efficiently passed by reference, you should define it as a class instead.

Variables of reference types, referred to as objects, store references to the actual data.
Following are the Reference types:

1. class
2. interface
3. delegate

Following are the built-in reference types:

1. object
2. string

OOPS CONCEPTS

Encapsulation: A simple definition of encapsulation is - combining the data (information) and the methods (functions) that can manipulate that data into one capsule (class/object). Depending on how you write program encapsulation, it guarantees that the encapsulated data is not accessed by any other function/method/program outside the encapsulated object. For example,

class MyCapsule

{

private:

int myInt;

char myChar;

public:

MyIntFunc() { myInt = 10; }

MyCharFunc() { myChar = 'A'};

};

In this case, no other program/function/method can access myInt other than MyIntFunc. Same is true for myChar and MyCharFunc.

Abstraction: A simple definition of abstraction is to hide actual implementation of an object from the external world that would use the object. For example, a program that is drawing circles and squares using those objects need not know how those objects are implemented. It is enough for the program to know what the behavior of these objects is, and how to use these objects (rather than how these objects are implemented internally).

So, drawing a parallel between abstraction and encapsulation, when you encapsulate data and methods that operate on data into one object, the external program that uses this object need not know the internal workings of the object to use the object. Thus making the object abstract data type to the external program. Classic examples of abstract data type in C (yes) are int, char, float, double etc. Classes are OOPL variations and extensions of the traditional abstract data types.

------------------------------                      

OOP with VB

OOP Basics

Visual Basic was Object-Based, Visual Basic .NET is Object-Oriented, which means that it's a true Object-Oriented Programming Language. Visual Basic .NET supports all the key OOP features like Polymorphism, Inheritance, Abstraction and Encapsulation. It's worth having a brief overview of OOP before starting OOP with VB.

Why Object Oriented approach?

A major factor in the invention of Object-Oriented approach is to remove some of the flaws encountered with the procedural approach. In OOP, data is treated as a critical element and does not allow it to flow freely. It bounds data closely to the functions that operate on it and protects it from accidental modification from outside functions. OOP allows decomposition of a problem into a number of entities called objects and then builds data and functions around these objects. A major advantage of OOP is code reusability.

Some important features of Object Oriented programming are as follows:

●     Emphasis on data rather than procedure

●     Programs are divided into Objects

●     Data is hidden and cannot be accessed by external functions

●     Objects can communicate with each other through functions

●     New data and functions can be easily added whenever necessary

●     Follows bottom-up approach

Concepts of OOP:

●     Objects

●     Classes

●     Data Abstraction and Encapsulation

●     Inheritance

●     Polymorphism

Briefly on Concepts:

Objects

Objects are the basic run-time entities in an object-oriented system. Programming problem is analyzed in terms of objects and nature of communication between them. When a program is executed, objects interact with each other by sending messages. Different objects can also interact with each other without knowing the details of their data or code.

Classes

A class is a collection of objects of similar type. Once a class is defined, any number of objects can be created which belong to that class.

Data Abstraction and Encapsulation

Abstraction refers to the act of representing essential features without including the background details or explanations. Classes use the concept of abstraction and are defined as a list of abstract attributes.

Storing data and functions in a single unit (class) is encapsulation. Data cannot be accessible to the outside world and only those functions which are stored in the class can access it.

Inheritance

Inheritance is the process by which objects can acquire the properties of objects of other class. In OOP, inheritance provides reusability, like, adding additional features to an existing class without modifying it. This is achieved by deriving a new class from the existing one. The new class will have combined features of both the classes.

Polymorphism

Polymorphism means the ability to take more than one form. An operation may exhibit different behaviors in different instances. The behavior depends on the data types used in the operation. Polymorphism is extensively used in implementing Inheritance.

Advantages of OOP

Object-Oriented Programming has the following advantages over conventional approaches:

●     OOP provides a clear modular structure for programs which makes it good for defining abstract datatypes where implementation details are hidden and the unit has a clearly defined interface.

●     OOP makes it easy to maintain and modify existing code as new objects can be created with small differences to existing ones.

●     OOP provides a good framework for code libraries where supplied software components can be easily adapted and modified by the programmer. This is particularly useful for developing graphical user interfaces.