Dot Net Framework FAQ - Part Seven

What is Value type and refernce type in .Net?.
Value Type : A variable of a value type always contains a value of that type. The assignment to a variable of a value type creates a copy of the assigned value, while the assignment to a variable of a reference type creates a copy of the reference but not of the referenced object.
The value types consist of two main categories:

• Stuct Type
• Enumeration Type
  

Reference Type :Variables of reference types, referred to as objects, store references to the actual data. This section introduces the following keywords used to declare reference types:

• Class
• Interface
• Delegate
  

This section also introduces the following built-in reference types:

• object
• string
  

What is the difference between structures and enumeration?.
Unlike classes, structs are value types and do not require heap allocation. A variable of a struct type directly contains the data of the struct, whereas a variable of a class type contains a reference to the data. They are derived from System.ValueType class.
Enum->An enum type is a distinct type that declares a set of named constants.They are strongly typed constants. They are unique types that allow to declare symbolic names to integral values. Enums are value types, which means they contain their own value, can't inherit or be inherited from and assignment copies the value of one enum to another.

public enum Grade
{
A,
B,
C
}

What is namespaces?.
Namespace is a logical naming scheme for group related types.Some class types that logically belong together they can be put into a common namespace. They prevent namespace collisions and they provide scoping. They are imported as "using" in C# or "Imports" in Visual Basic. It seems as if these directives specify a particular assembly, but they don't. A namespace can span multiple assemblies, and an assembly can define multiple namespaces. When the compiler needs the definition for a class type, it tracks through each of the different imported namespaces to the type name and searches each referenced assembly until it is found.
Namespaces can be nested. This is very similar to packages in Java as far as scoping is concerned.

How do you create shared assemblies?.
Just look through the definition of Assemblies..

• An Assembly is a logical unit of code
• Assembly physically exist as DLLs or EXEs
• One assembly can contain one or more files
• The constituent files can include any file types like image files, text files etc. along with DLLs or EXEs
• When you compile your source code by default the exe/dll generated is actually an assembly
• Unless your code is bundled as assembly it can not be used in any other application
• When you talk about version of a component you are actually talking about version of the assembly to which the component belongs.
• Every assembly file contains information about itself. This information is called as Assembly Manifest.
  

Following steps are involved in creating shared assemblies :

• Create your DLL/EXE source code
• Generate unique assembly name using SN utility
• Sign your DLL/EXE with the private key by modifying AssemblyInfo file
• Compile your DLL/EXE
• Place the resultant DLL/EXE in global assembly cache using AL utility
  

What is global assembly cache?
Each computer where the common language runtime is installed has a machine-wide code cache called the global assembly cache. The global assembly cache stores assemblies specifically designated to be shared by several applications on the computer.
There are several ways to deploy an assembly into the global assembly cache:

• Use an installer designed to work with the global assembly cache. This is the preferred option for installing assemblies into the global assembly cache.
• Use a developer tool called the Global Assembly Cache tool (Gacutil.exe), provided by the .NET Framework SDK.
• Use Windows Explorer to drag assemblies into the cache.
  

What is MSIL?.
When compiling to managed code, the compiler translates your source code into Microsoft intermediate language (MSIL), which is a CPU-independent set of instructions that can be efficiently converted to native code. MSIL includes instructions for loading, storing, initializing, and calling methods on objects, as well as instructions for arithmetic and logical operations, control flow, direct memory access, exception handling, and other operations. Before code can be run, MSIL must be converted to CPU-specific code, usually by a just-in-time (JIT) compiler. Because the common language runtime supplies one or more JIT compilers for each computer architecture it supports, the same set of MSIL can be JIT-compiled and run on any supported architecture.
When a compiler produces MSIL, it also produces metadata. Metadata describes the types in your code, including the definition of each type, the signatures of each type's members, the members that your code references, and other data that the runtime uses at execution time. The MSIL and metadata are contained in a portable executable (PE) file that is based on and extends the published Microsoft PE and common object file format (COFF) used historically for executable content. This file format, which accommodates MSIL or native code as well as metadata, enables the operating system to recognize common language runtime images. The presence of metadata in the file along with the MSIL enables your code to describe itself, which means that there is no need for type libraries or Interface Definition Language (IDL). The runtime locates and extracts the metadata from the file as needed during execution.

What is Jit compilers?.How many are available in CLR?
Just-In-Time compiler- it converts the language that you write in .Net into machine language that a computer can understand. there are tqo types of JITs one is memory optimized & other is performace optimized.

What is tracing?Where it used.Explain few methods available?
Tracing refers to collecting information about the application while it is running. You use tracing information to troubleshoot an application.
Tracing allows us to observe and correct programming errors. Tracing enables you to record information in various log files about the errors that might occur at run time. You can analyze these log files to find the cause of the errors.
In .NET we have objects called Trace Listeners. A listener is an object that receives the trace output and outputs it somewhere; that somewhere could be a window in your development environment, a file on your hard drive, a Windows Event log, a SQL Server or Oracle database, or any other customized data store.
The System.Diagnostics namespace provides the interfaces, classes, enumerations and structures that are used for tracing The System.Diagnostics namespace provides two classes named Trace and Debug that are used for writing errors and application execution information in logs.
All Trace Listeners have the following functions. Functionality of these functions is same except that the target media for the tracing output is determined by the Trace Listener.
Method Name
Result Fail Outputs the specified text with the Call Stack.
Write Outputs the specified text.
WriteLine Outputs the specified text and a carriage return.
Flush Flushes the output buffer to the target media.
Close Closes the output stream in order to not receive the tracing/debugging output.

How to set the debug mode?
Debug Mode for ASP.NET applications - To set ASP.NET appplication in debugging mode, edit the application's web.config and assign the "debug" attribute in
<> section to "true" as show below:
<>
<>
< defaultlanguage="vb" debug="true">
....
...
..
< / configuration >
This case-sensitive attribute 'debug tells ASP.NET to generate symbols for dynamically generated files and enables the
debugger to attach to the ASP.NET application. ASP.NET will detect this change automatically, without the need to restart the server. Debug Mode for ASP.NET Webservices - Debugging an XML Web service created with ASP.NET is similar to the debugging an ASP.NET Web application.

What is the property available to check if the page posted or not?
The Page_Load event handler in the page checks for IsPostBack property value, to ascertain whether the page is posted. The Page.IsPostBack gets a value indicating whether the page is being loaded in response to the client postback, or it is for the first time. The value of Page.IsPostBack is True, if the page is being loaded in response to the client postback; while its value is False, when the page is loaded for the first time. The Page.IsPostBack property facilitates execution of certain routine in Page_Load, only once (for e.g. in Page load, we need to set default value in controls, when page is loaded for the first time. On post back, we check for true value for IsPostback value and then invoke server-side code to
update data).

Which are the abstract classes available under system.xml namespace?
The System.XML namespace provides XML related processing ability in .NET framework. XmlReader and XMLWriter are the two abstract classes at the core of .NET Framework XML classes:

1. XmlReader provides a fast, forward-only, read-only cursor for processing an XML document stream.
2. XmlWriter provides an interface for producing XML document streams that conform to the W3C's XML standards.
   

Both XmlReader and XmlWriter are abstract base classes, which define the functionality that all derived classes must support.

Is it possible to use multipe inheritance in .net?
Multiple Inheritance is an ability to inherit from more than one base class i.e. ability of a class to have more than one superclass, by inheriting from different sources and thus combine separately-defined behaviors in a single class. There are two types of multiple inheritance: multiple type/interface inheritance and multiple implementation inheritance. C# & VB.NET supports only multiple type/interface inheritance, i.e.
you can derive an class/interface from multiple interfaces. There is no support for multiple implementation inheritance in .NET. That means a class can only derived from one class.

What are the derived classes from xmlReader and xmlWriter?
Both XmlReader and XmlWriter are abstract base classes, which define the functionality that all derived classes must support.
There are three concrete implementations of XmlReader:

1. XmlTextReader
2. XmlNodeReader
3. XmlValidatingReader
   

There are two concrete implementations of XmlWriter:

1. XmlTextWriter
2. XmlNodeWriter
   

XmlTextReader and XmlTextWriter support reading data to/from text-based stream, while XmlNodeReader and XmlNodeWriter are designed for working with in-memory DOM tree structure. The custom readers and writers can also be developed to extend the built-in functionality of XmlReader and XmlWriter.

What is managed and unmanaged code?
The .NET framework provides several core run-time services to the programs that run within it - for example exception handling and security. For these services to work, the code must provide a minimum level of information to the runtime. i.e., code executing under the control of the CLR is called managed code. For example, any code written in C# or Visual Basic .NET is managed code.
Code that runs outside the CLR is referred to as "unmanaged code." COM components, ActiveX components, and Win32 API functions are examples of unmanaged code.