What is garbage collection? Explain the difference between garbage collections in .NET 4.0 and earlier versions

ASP.NET – Interview Questions

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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)


2. What are the main 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


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?


5. What is Manifest?


Version of assembly.

Security identity.

Scope of the assembly.

Resolve references to resources and classes.



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. The MemoryMappedFile.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().


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. 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, 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.

18. 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.

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