Object Oriented Programming

1. What is object-oriented programming (OOP)?
OOP is a technique to develop logical modules, such as classes that contain properties, methods, fields, and events. An object is created in the program to represent a class. Therefore, an object encapsulates all the features, such as data and behavior that are associated to a class. OOP allows developers to develop modular programs and assemble them as software. Objects are used to access data and behaviors of different software modules, such as classes, namespaces, and sharable assemblies. .NET Framework supports only OOP languages, such as Visual Basic .NET, Visual C#, and Visual C++.

2. What is a class?
A class describes all the attributes of objects, as well as the methods that implement the behavior of member objects. It is a comprehensive data type, which represents a blue print of objects. It is a template of object.

A class can be defined as the primary building block of OOP. It also serves as a template that describes the properties, state, and behaviors common to a particular group of objects.

A class contains data and behavior of an entity. For example, the aircraft class can contain data, such as model number, category, and color and behavior, such as duration of flight, speed, and number of passengers. A class inherits the data members and behaviors of other classes by extending from them.

3. What is an object?
They are instance of classes. It is a basic unit of a system. An object is an entity that has attributes, behavior, and identity. Attributes and behavior of an object are defined by the class definition.

4. What is the relationship between a class and an object?
A class acts as a blue-print that defines the properties, states, and behaviors that are common to a number of objects. An object is an instance of the cass. For example, you have a class called Vehicle and Car is the object of that class. You can create any number of objects for the class named Vehicle, such as Van, Truck, and Auto.

The new operator is used to create an object of a class. When an object of a class is instantiated, the system allocates memory for every data member that is present in the class.

5. Explain the basic features of OOPs.
The following are the four basic features of OOP:
• Abstraction - Refers to the process of exposing only the relevant and essential data to the users without showing unnecessary information.
• Polymorphism - Allows you to use an entity in multiple forms.
• Encapsulation - Prevents the data from unwanted access by binding of code and data in a single unit called object.
• Inheritance - Promotes the reusability of code and eliminates the use of redundant code. It is the property through which a child class obtains all the features defined in its parent class. When a class inherits the common properties of another class, the class inheriting the properties is called a derived class and the class that allows inheritance of its common properties is called a base class.

6. What is the difference between arrays and collection?
Array:
1. You need to specify the size of an array at the time of its declaration. It cannot be resized dynamically.
2. The members of an array should be of the same data type.

Collection:
1. The size of a collection can be adjusted dynamically, as per the user's requirement. It does not have fixed size.
2. Collection can have elements of different types.

7. What are collections and generics?
A collection can be defined as a group of related items that can be referred to as a single unit. TheSystem.Collections namespace provides you with many classes and interfaces. Some of them are -ArrayList, List, Stack, ICollection, IEnumerable, and IDictionary. Generics provide the type-safety to your class at the compile time. While creating a data structure, you never need to specify the data type at the time of declaration. The System.Collections.Generic namespace contains all the generic collections.

8. How can you prevent your class to be inherited further?
You can prevent a class from being inherited further by defining it with the sealed keyword.

9. What is the index value of the first element in an array?
In an array, the index value of the first element is 0 (zero).


10. Can you specify the accessibility modifier for methods inside the interface?
All the methods inside an interface are always public, by default. You cannot specify any other access modifier for them.

11. Is it possible for a class to inherit the constructor of its base class?
No, a class cannot inherit the constructor of its base class.

12. How is method overriding different from method overloading?
Overriding involves the creation of two or more methods with the same name and same signature in different classes (one of them should be parent class and other should be child).

Overloading is a concept of using a method at different places with same name and different signatures within the same class.

13. What is the difference between a class and a structure?
Class:
1. A class is a reference type.
2. The members of a class are private by default.
3. While instantiating a class, CLR allocates memory for its instance in heap.
4. Classes support inheritance.
5. Variables of a class can be assigned as null.
6. Class can contain constructor/destructor.

Structure:
1. A structure is a value type.
2. The members of a structure are public by default
3. In structure, memory is allocated on stack.
4. Structures do not support inheritance.
5. Structure members cannot have null values.
6. Structure does not require constructor/destructor and members can be initialiazed automatically.

14. What are similarities between a class and a structure.
Structures and classes are the two most important data structures that are used by programmers to build modular programs by using OOP languages, such as Visual Basic .NET, and Visual C#. The following are some of the similarities between a class and a structure:
• Access specifiers, such as public, private, and protected, are identically used in structures and classes to restrict the access of their data and methods outside their body.
• Both can have constructors, methods, properties, fields, constants, enumerations, events, and event handlers.
• Both structures and classes can implement interfaces to use multiple-inheritance in code.
• Both structures and classes can have constructors with parameter.
• Both structures and classes can have delegates and events.

15. What is a multicast delegate?
Each delegate object holds reference to a single method. However, it is possible for a delegate object to hold references of and invoke multiple methods. Such delegate objects are called multicast delegates or combinable delegates.

16. Can you declare an overridden method to be static if the original method is not static?
No. Two virtual methods must have the same signature.

17. Why is the virtual keyword used in code?
The virtual keyword is used while defining a class to specify that the methods and the properties of that class can be overridden in derived classes.

18. Can you allow a class to be inherited, but prevent a method from being overridden in C#?
Yes. Just declare the class public and make the method sealed.

19. Define enumeration?
Enumeration is defined as a value type that consists of a set of named values. These values are constants and are called enumerators. An enumeration type is declared using the enum keyword. Each enumerator in an enumeration is associated with an underlying type that is set, by default, on the enumerator. The following is an example that creates an enumeration to store different varieties of fruits:

enum Fruits {Mango, Apple, orange, Guava};

In the preceding example, an enumeration Fruits is created, where number 0 is associated with Mango, number 1 with Apple, number 2 with Orange, and number 3 with Guava. You can access the enumerators of an enumeration by these values.

20. In which namespace, all .NET collection classes are contained?
The System.Collections namespace contains all the collection classes.

21. Is it a good practice to handle exceptions in code?
Yes, you must handle exceptions in code so that you can deal with any unexpected situations that occur when a program is running. For example, dividing a number by zero or passing a string value to a variable that holds an integer value would result in an exception.

22. Explain the concept of constructor?
Constructor is a special method of a class, which is called automatically when the instance of a class is created. It is created with the same name as the class and initializes all class members, whenever you access the class. The main features of a constructor are as follows:
• Constructors do not have any return type
• Constructors are always public
• It is not mandatory to declare a constructor; it is invoked automatically by .NET Framework.

23. Can you inherit private members of a class?
No, you cannot inherit private members of a class because private members are accessible only to that class and not outside that class.

24. Does .NET support multiple inheritance?
.NET does not support multiple inheritance directly because in .NET, a class cannot inherit from more than one class. .NET supports multiple inheritance through interfaces.

25. How has exception handling changed in .NET Framework 4.0?
In .NET 4.0, a new namespace, System.Runtime.ExceptionServices, has been introduced which contains the following classes for handling exceptions in a better and advanced manner:
• HandleProcessCorruptedStateExceptionsAttribute Class - Enables managed code to handle the corrupted state exceptions that occur in an operating system. These exceptions cannot be caught by specifying the try...catch block. To handle such exceptions, you can apply this attribute to the method that is assigned to handle these exceptions.
• FirstChanceExceptionEventArgs Class - Generates an event whenever a managed exception first occurs in your code, before the common language runtime begins searching for event handlers.

26. What is a delegate?
A delegate is similar to a class that is used for storing the reference to a method and invoking that method at runtime, as required. A delegate can hold the reference of only those methods whose signatures are same as that of the delegate. Some of the examples of delegates are type-safe functions, pointers, or callbacks.

27. What is the syntax to inherit from a class in C#?
When a class is derived from another class, then the members of the base class become the members of the derived class. The access modifier used while accessing members of the base class specifies the access status of the base class members inside the derived class.

The syntax to inherit a class from another class in C# is as follows:
class MyNewClass : MyBaseclass

28. State the features of an interface.
An interface is a template that contains only the signature of methods. The signature of a method consists of the numbers of parameters, the type of parameter (value, reference, or output), and the order of parameters. An interface has no implementation on its own because it contains only the definition of methods without any method body. An interface is defined using the interface keyword. Moreover, you cannot instantiate an interface. The various features of an interface are as follows:
• An interface is used to implement multiple inheritance in code. This feature of an interface is quite different from that of abstract classes because a class cannot derive the features of more than one class but can easily implement multiple interfaces.
• It defines a specific set of methods and their arguments.
• Variables in interface must be declared as public, static, and final while methods must be publicand abstract.
• A class implementing an interface must implement all of its methods.
• An interface can derive from more than one interface.

29. Can you use the 'throws' clause to raise an exception?
No, the throws clause cannot be used to raise an exception. The throw statement signals the occurrence of an exception during the execution of a program. When the program encounters a throw statement, the method terminates and returns the error to the calling method.

30. Define an array.
An array is defined as a homogeneous collection of elements, stored at contiguous memory locations, which can be referred by the same variable name. All the elements of an array variable can be accessed by index values. An Index value specifies the position of a particular element in an array variable.

31. What are methods?
Methods are the building blocks of a class, in which they are linked together to share and process data to produce the result. In other words, a method is a block of code that contains a series of statements and represents the behavior of a class. While declaring a method you need to specify the access specifier, the return value, the name of the method, and the method parameters. All these combined together is called the signature of the method.

32. What is a namespace?
Namespace is considered as a container that contains functionally related group of classes and other types.

33. Do events have return type
No, events do not have return type.

34. What is the function of the Try-Catch-Finally block?
The try block encloses those statements that can cause exception and the catch block handles the exception, if it occurs. Catch block contains the statements that have to be executed, when an exception occurs. Thefinally block always executes, irrespective of the fact whether or not an exception has occurred. The finallyblock is generally used to perform the cleanup process. If any exception occurs in the try block, the program control directly transfers to its corresponding catch block and later to the finally block. If no exception occurs inside the try block, then the program control transfers directly to the finally block.
35. How can you prevent a class from overriding in C# and Visual Basic?
You can prevent a class from overriding in C# by using the sealed keyword; whereas, the NotInheritablekeyword is used to prevent a class from overriding in Visual Basic.

36. What are abstract classes? What are the distinct characteristics of an abstract class?
An abstract class is a class that cannot be instantiated and is always used as a base class.
The following are the characteristics of an abstract class:
• You cannot instantiate an abstract class directly. This implies that you cannot create an object of the abstract class; it must be inherited.
• You can have abstract as well as non-abstract members in an abstract class.
• You must declare at least one abstract method in the abstract class.
• An abstract class is always public.
• An abstract class is declared using the abstract keyword.

The basic purpose of an abstract class is to provide a common definition of the base class that multiple derived classes can share.

37. Give a brief description of properties in C# and the advantages that are obtained by using them in programs.
In C#, a property is a way to expose an internal data element of a class in a simple and intuitive manner. In other words, it is a simple extension of data fields. You can create a property by defining an externally available name and then writing the set and get property accessors. The get property accessor is used to return the property value. The set property accessor is used to assign a new value to the property.

38. Explain different types of inheritance.
Inheritance in OOP is of four types:
• Single inheritance - Contains one base class and one derived class
• Hierarchical inheritance - Contains one base class and multiple derived classes of the same base class
• Multilevel inheritance - Contains a class derived from a derived class
• Multiple inheritance - Contains several base classes and a derived class
All .NET languages supports single, hierarchical, and multilevel inheritance. They do not support multiple inheritance because in these languages, a derived class cannot have more than one base class. However, you can implement multiple inheritance in.NET through interfaces.

39. You have defined a destructor in a class that you have developed by using the C# programming language, but the destructor never executed. Why did the destructor not execute?
The runtime environment automatically invokes the destructor of a class to release the resources that are occupied by variables and methods of an object. However, in C#, programmers cannot control the timing for invoking destructors, as Garbage Collector is only responsible for releasing the resources used by an object. Garbage Collector automatically gets information about unreferenced objects from .NET's runtime environment and then invokes the Finalize() method.

Although, it is not preferable to force Garbage Collector to perform garbage collection and retrieve all inaccessible memory, programmers can use the Collect() method of the Garbage Collector class to forcefully execute Garbage Collector.

40. What is a hashtable?
Hashtable is a data structure that implements the IDictionary interface. It is used to store multiple items and each of these items is associated with a unique string key. Each item can be accessed using the key associated with it. In short, hashtable is an object holding the key-value pairs.

41. Can users define their own exceptions in code?
Yes, customized exceptions can be defined in code by deriving from the System.Exception class.

42. Is it possible to execute two catch blocks?
You are allowed to include more than one catch block in your program; however, it is not possible to execute them in one go. Whenever, an exception occurs in your program, the correct catch block is executed and the control goes to the finally block.

43. What do you mean by data encapsulation?
Data encapsulation is a concept of binding data and code in single unit called object and hiding all the implementation details of a class from the user. It prevents unauthorized access of data and restricts the user to use the necessary data only.

44. What is the difference between procedural and object-oriented programming?
Procedural programming is based upon the modular approach in which the larger programs are broken into procedures. Each procedure is a set of instructions that are executed one after another. On the other hand, OOP is based upon objects. An object consists of various elements, such as methods and variables.

Access modifiers are not used in procedural programming, which implies that the entire data can be accessed freely anywhere in the program. In OOP, you can specify the scope of a particular data by using access modifiers - public, private, internal, protected, and protected internal.

45. Explain the concept of destructor?
A destructor is a special method for a class and is invoked automatically when an object is finally destroyed. The name of the destructor is also same as that of the class but is followed by a prefix tilde (~).

A destructor is used to free the dynamic allocated memory and release the resources. You can, however, implement a custom method that allows you to control object destruction by calling the destructor.

The main features of a destructor are as follows:
• Destructors do not have any return type
• Similar to constructors, destructors are also always public
• Destructors cannot be overloaded.

46. Can you declare a private class in a namespace?
The classes in a namespace are internal, by default. However, you can explicitly declare them as public only and not as private, protected, or protected internal. The nested classes can be declared as private,protected, or protected internal.

47. A structure in C# can implement one or more interfaces. Is it true or false?
Yes, it is true. Like classes, in C#, structures can implement one or more interfaces.

48. What is a static constructor?
Static constructors are introduced with C# to initialize the static data of a class. CLR calls the static constructor before the first instance is created.

The static constructor has the following features:
• No access specifier is required to define it.
• You cannot pass parameters in static constructor.
• A class can have only one static constructor.
• It can access only static members of the class.
• It is invoked only once, when the program execution begins.

49. What are the different ways a method can be overloaded?
The different ways to overload a method are given as follows:
• By changing the number of parameters used
• By changing the order of parameters
• By using different data types for the parameters

50. Differentiate between an abstract class and an interface.
Abstract Class:
1. A class can extend only one abstract class
2. The members of abstract class can be private as well as protected.
3. Abstract classes should have subclasses
4. Any class can extend an abstract class.
5. Methods in abstract class can be abstract as well as concrete.
6. There can be a constructor for abstract class.
7. The class extending the abstract class may or may not implement any of its method.
8. An abstract class can implement methods.

Interface
1. A class can implement several interfaces
2. An interface can only have public members.
3. Interfaces must have implementations by classes
4. Only an interface can extend another interface.
5. All methods in an interface should be abstract
6. Interface does not have constructor.
7. All methods of interface need to be implemented by a class implementing that interface.
8. Interfaces cannot contain body of any of its method.

51. What are queues and stacks?
Stacks refer to a list in which all items are accessed and processed on the Last-In-First-Out (LIFO) basis. In a stack, elements are inserted (push operation) and deleted (pop operation) from the same end called top.

Queues refer to a list in which insertion and deletion of an item is done on the First-In-First-Out (FIFO) basis. The items in a queue are inserted from the one end, called the rear end, and are deleted from the other end, called the front end of the queue.

52. Define an event.
Whenever an action takes place in a class, that class provides a notification to other classes or objects that are assigned to perform particular tasks. These notifications are called events. For example, when a button is clicked, the class generates an event called Click. An event can be declared with the help of the event keyword.

53. What are structures?
Structure is a heterogeneous collection of elements referenced by the same name. A structure is declared using the struct keyword. The following is an example that creates a structure to store an employee's information:
struct emp
{
fixed int empID[15];
fixed char name[30];
fixed char addr[50];
fixed char dept[15];
fixed char desig[15];
}
The preceding example defines a structure emp and the members of this structure specify the information of an employee.

54. When do you really need to create an abstract class?
We define abstract classes when we define a template that needs to be followed by all the derived classes.

.NET Framework

1. What is .NET Framework?
.NET Framework is a complete environment that allows developers to develop, run, and deploy the following applications:
• Console applications
• Windows Forms applications
• Windows Presentation Foundation (WPF) applications
• Web applications (ASP.NET applications)
• Web services
• Windows services
• Service-oriented applications using Windows Communication Foundation (WCF)
• Workflow-enabled applications using Windows Workflow Foundation (WF)

.NET Framework also enables a developer to create sharable components to be used in distributed computing architecture. NET Framework supports the object-oriented programming model for multiple languages, such as Visual Basic, Visual C#, and Visual C++. .NET Framework supports multiple programming languages in a manner that allows language interoperability. This implies that each language can use the code written in some other language.

2. What are the main components of .NET Framework?
.NET Framework provides enormous advantages to software developers in comparison to the advantages provided by other platforms. Microsoft has united various modern as well as existing technologies of software development in .NET Framework. These technologies are used by developers to develop highly efficient applications for modern as well as future business needs. The following are the key components of .NET Framework:
• .NET Framework Class Library
• Common Language Runtime
• Dynamic Language Runtimes (DLR)
• Application Domains
• Runtime Host
• Common Type System
• Metadata and Self-Describing Components
• Cross-Language Interoperability
• .NET Framework Security
• Profiling
• Side-by-Side Execution

3. List the new features added in .NET Framework 4.0.
The following are the new features of .NET Framework 4.0:
• Improved Application Compatibility and Deployment Support
• Dynamic Language Runtime
• Managed Extensibility Framework
• Parallel Programming framework
• Improved Security Model
• Networking Improvements
• Improved Core ASP.NET Services
• Improvements in WPF 4
• Improved Entity Framework (EF)
• Integration between WCF and WF

4. What is an IL?
Intermediate Language is also known as MSIL (Microsoft Intermediate Language) or CIL (Common Intermediate Language). All .NET source code is compiled to IL. IL is then converted to machine code at the point where the software is installed, or at run-time by a Just-In-Time (JIT) compiler.

5. What is Manifest?
Assembly metadata is stored in Manifest. Manifest contains all the metadata needed to do the following things
• Version of assembly.
• Security identity.
• Scope of the assembly.
• Resolve references to resources and classes.

The assembly manifest can be stored in a PE file either (an .exe or) .dll with Microsoft
intermediate language (MSIL code with Microsoft intermediate language (MSIL) code or in a
stand-alone PE file, that contains only assembly manifest information.

6. What are code contracts?
Code contracts help you to express the code assumptions and statements stating the behavior of your code in a language-neutral way. The contracts are included in the form of pre-conditions, post-conditions and object-invariants. The contracts help you to improve-testing by enabling run-time checking, static contract verification, and documentation generation.

The System.Diagnostics.Contracts namespace contains static classes that are used to express contracts in your code.

7. Name the classes that are introduced in the System.Numerics namespace.
The following two new classes are introduced in the System.Numerics namespace:
• BigInteger - Refers to a non-primitive integral type, which is used to hold a value of any size. It has no lower and upper limit, making it possible for you to perform arithmetic calculations with very large numbers, even with the numbers which cannot hold by double or long.
• Complex - Represents complex numbers and enables different arithmetic operations with complex numbers. A number represented in the form a + bi, where a is the real part, and b is the imaginary part, is a complex number.

8. What is managed extensibility framework?
Managed extensibility framework (MEF) is a new library that is introduced as a part of .NET 4.0 and Silverlight 4. It helps in extending your application by providing greater reuse of applications and components. MEF provides a way for host application to consume external extensions without any configuration requirement.

9. Explain memory-mapped files.
Memory-mapped files (MMFs) allow you map the content of a file to the logical address of an application. These files enable the multiple processes running on the same machine to share data with each Other. TheMemoryMappedFile.CreateFromFile() method is used to obtain a MemoryMappedFile object that represents a persisted memory-mapped file from a file on disk.

These files are included in the System.IO.MemoryMappedFiles namespace. This namespace contains four classes and three enumerations to help you access and secure your file mappings.

10. What is Common Type System (CTS)?
CTS is the component of CLR through which .NET Framework provides support for multiple languages because it contains a type system that is common across all the languages. Two CTS-compliant languages do not require type conversion when calling the code written in one language from within the code written in another language. CTS provide a base set of data types for all the languages supported by.NET Framework. This means that the size of integer and long variables is same across all .NET-compliant programming languages. However, each language uses aliases for the base data types provided by CTS. For example, CTS uses the data type system. int32 to represent a 4 byte integer value; however, Visual Basic uses the alias integer for the same; whereas, C# uses the alias int. This is done for the sake of clarity and simplicity.

11. Give a brief introduction on side-by-side execution. Can two applications, one using private assembly and the other using the shared assembly be stated as side-by-side executables?
Side-by-side execution enables you to run multiple versions of an application or component and CLR on the same computer at the same time. As versioning is applicable only to shared assemblies and not to private assemblies, two applications, one using a private assembly and other using a shared assembly, cannot be stated as side-by-side executables.

12. Which method do you use to enforce garbage collection in .NET?
The System.GC.Collect() method.

13. State the differences between the Dispose() and Finalize().
CLR uses the Dispose and Finalize methods to perform garbage collection of run-time objects of .NET applications.

The Finalize method is called automatically by the runtime. CLR has a garbage collector (GC), which periodically checks for objects in heap that are no longer referenced by any object or program. It calls the Finalize method to free the memory used by such objects. The Dispose method is called by the programmer.Dispose is another method to release the memory used by an object. The Dispose method needs to be explicitly called in code to dereference an object from the heap. The Dispose method can be invoked only by the classes that implement the IDisposable interface.

14. What is code access security (CAS)?
Code access security (CAS) is part of the .NET security model that prevents unauthorized access of resources and operations, and restricts the code to perform particular tasks.

15. Differentiate between managed and unmanaged code?
Managed code is the code that is executed directly by the CLR instead of the operating system. The code compiler first compiles the managed code to intermediate language (IL) code, also called as MSIL code. This code doesn't depend on machine configurations and can be executed on different machines.

Unmanaged code is the code that is executed directly by the operating system outside the CLR environment. It is directly compiled to native machine code which depends on the machine configuration.
In the managed code, since the execution of the code is governed by CLR, the runtime provides different services, such as garbage collection, type checking, exception handling, and security support. These services help provide uniformity in platform and language-independent behavior of managed code applications. In the unmanaged code, the allocation of memory, type safety, and security is required to be taken care of by the developer. If the unmanaged code is not properly handled, it may result in memory leak. Examples of unmanaged code are ActiveX components and Win32 APIs that execute beyond the scope of native CLR.

16. What are tuples?
Tuple is a fixed-size collection that can have elements of either same or different data types. Similar to arrays, a user must have to specify the size of a tuple at the time of declaration. Tuples are allowed to hold up from 1 to 8 elements and if there are more than 8 elements, then the 8th element can be defined as another tuple. Tuples can be specified as parameter or return type of a method.

17. How can you turn-on and turn-off CAS?
YOU can use the Code Access Security Tool (Caspol.exe) to turn security on and off.

To turn off security, type the following command at the command prompt:
caspol -security off

To turn on security, type the following command at the command prompt:
caspol -security on

In the .NET Framework 4.0, for using Caspol.exe, you first need to set the element totrue.

18. What is garbage collection? Explain the difference between garbage collections in .NET 4.0 and earlier versions.
Garbage collection prevents memory leaks during execution of programs. Garbage collector is a low-priority process that manages the allocation and deallocation of memory for your application. It checks for the unreferenced variables and objects. If GC finds any object that is no longer used by the application, it frees up the memory from that object.

GC has changed a bit with the introduction of .NET 4.0. In .NET 4.0, the GC.Collect() method contains the following overloaded methods:
GC.Collect(int)
GC.Collect(int, GCCollectionMode)

Another new feature introduced in .NET is to notify you when the GC.Collect() method is invoked and completed successfully by using different methods. The .NET 4.0 supports a new background garbage collection that replaces the concurrent garbage collection used in earlier versions. This concurrent GC allocates memory while running and uses current segment (which is 16 MB on a workstation) for that. After that, all threads are suspended. In case of background GC, a separate ephemeral GC - gen0 and gen1 can be started, while the full GC - gen0, 1, and 2 - is already running.

19. How does CAS works?
There are two key concepts of CAS security policy- code groups and permissions. A code group contains assemblies in it in a manner that each .NET assembly is related to a particular code group and some permissions are granted to each code group. For example, using the default security policy, a control downloaded from a Web site belongs to the Zone, Internet code group, which adheres to the permissions defined by the named permission set. (Normally, the named permission set represents a very restrictive range of permissions.)

Assembly execution involves the following steps:
1. Evidences are gathered about assembly.
2. Depending on the gathered evidences, the assembly is assigned to a code group.
3. Security rights are allocated to the assembly, depending on the code group.
4. Assembly runs as per the rights assigned to it.

20. What is Difference between NameSpace and Assembly?
Following are the differences between namespace and assembly:
• Assembly is physical grouping of logical units, Namespace, logically groups classes.
• Namespace can span multiple assembly.

21. Mention the execution process for managed code.
A piece of managed code is executed as follows:
• Choosing a language compiler
• Compiling the code to MSIL
• Compiling MSIL to native code
• Executing the code.

22. Is there a way to suppress the finalize process inside the garbage collector forcibly in .NET?
Use the GC.SuppressFinalize() method to suppress the finalize process inside the garbage collector forcibly in .NET.

23. How can you instantiate a tuple?
The following are two ways to instantiate a tuple:
• Using the new operator. For example,
Tuple t = new Tuple ("Hellow", 2);
• Using the Create factory method available in the Tuple class. For example,
Tuple t = Tuple.Create (2, 4, 5);

24. Which is the root namespace for fundamental types in .NET Framework?
System.Object is the root namespace for fundamental types in .NET Framework.

25. What are the improvements made in CAS in .NET 4.0?
The CAS mechanism in .NET is used to control and configure the ability of managed code. Earlier, as this policy was applicable for only native applications, the security guarantee was limited. Therefore, developers used to look for alternating solutions, such as operating system-level solutions. This problem was solved in .NET Framework 4 by turning off the machine-wide security. The shared and hosted Web applications can now run more securely. The security policy in .NET Framework 4 has been simplified using the transparency model. This model allows you to run the Web applications without concerning about the CAS policies.

As a result of security policy changes in .NET Framework 4.0, you may encounter compilation warnings and runtime exceptions, if your try to use the obsolete CAS policy types and members either implicitly or explicitly. However, you can avoid the warnings and errors by using the configuration element in the runtime settings schema to opt into the obsolete CAS policy behavior.

26. What is Microsoft Intermediate Language (MSIL)?
The .NET Framework is shipped with compilers of all .NET programming languages to develop programs. There are separate compilers for the Visual Basic, C#, and Visual C++ programming languages in .NET Framework. Each .NET compiler produces an intermediate code after compiling the source code. The intermediate code is common for all languages and is understandable only to .NET environment. This intermediate code is known as MSIL.

27. What is lazy initialization?
Lazy initialization is a process by which an object is not initialized until it is first called in your code. The .NET 4.0 introduces a new wrapper class, System.Lazy, for executing the lazy initialization in your application. Lazy initialization helps you to reduce the wastage of resources and memory requirements to improve performance. It also supports thread-safety.

28. How many types of generations are there in a garbage collector?
Memory management in the CLR is divided into three generations that are build up by grouping memory segments. Generations enhance the garbage collection performance. The following are the three types of generations found in a garbage collector:
• Generation 0 - When an object is initialized, it is said to be in generation 0.
• Generation 1 - The objects that are under garbage collection process are considered to be in generation 1.
• Generation 2 - Whenever new objects are created and added to the memory, they are added to generation 0 and the old objects in generation 1 are considered to be in generation 2.

29. Explain covariance and contra-variance in .NET Framework 4.0. Give an example for each.
In .NET 4.0, the CLR supports covariance and contravariance of types in generic interfaces and delegates. Covariance enables you to cast a generic type to its base types, that is, you can assign a instance of typeIEnumerable to a variable of type IEnumerable where, T1 derives from T2. For example,
IEnumerable str1= new List ();
IEnumerable