Answers for scott hanselman .net interview questions

By Akhil Raj | Published Sunday, November 10, 2013

This is just for knowledge sharing . When I search answers of Scott Hanselman's Interview Questions, got more blogs and articles but most of them not have full answers. So i just search and put a common post to see all the answers..Anyway I am really thankful to the original answers..

I searched and added some answers with Reply to Scott Henselman's Interview Questions from stack overflow or some other blogs. See Original Post from here. I think it may helpfull to you...

What Great .NET Developers Ought To Know

Everyone who writes code

Describe the difference between a Thread and a Process?

Thread is minimum unit for processor to execute. Collections of threads make process. By dividing process into threads, processor achieves multi tasking (by running threads concurrently not parallel). Threads can share memory but processes can’t share memory. Threads can communicate with each other of same process without any middle layer but process can’t they required inter process communication kind of thingy.

What is a Windows Service and how does its lifecycle differ from a "standard" EXE?

Windows service is windows based background process which has no user interface like any other service (aka daemon in UNIX based environment). Windows service needs to be installed before executing unlike EXE. Windows service used to perform such tasks which doesn’t required user interaction but system status based events like performing tasks at specific intervals or at different state of system like alarm user when disk is about to get full to clean up. Windows service is controlled by Service control manager (SCM) and it started automatically even user didn’t login to his/her windows account (as SCM already has account credentials so SCM knows if system start which service needs to start and by which account), where as EXE is controlled by OS and runs only when user get login using windows account.

What is the maximum amount of memory any single process on Windows can address? Is this different than the maximum virtual memory for the system? How would this affect a system design?

Single process on windows can address different amount of memory as it depends upon systems (32bit/64bit processor) and OS as well. Yes process memory consumption size can be different from maximum virtual memory size. If software/process code is written by keeping 64 bit processor (as 64 bit processor support more than double memory) then it won’t be able to run that process on 32 bit system.

What is the difference between an EXE and a DLL?

Exe is executable and independent program/process to run which has its own reserved memory space whereas DLL (Dynamic Link Library) is neither executable and not even independent, it used by other DLL/program.

What is strong-typing versus weak-typing? Which is preferred? Why?

Strong typing means a person who has great typing skills and that chat do too much chatting :D just joking. Strong typing means when code compiles, type rules enforced strictly according to their data assigned to them whereas weak typing is quite opposite of this definition. JavaScript/C/C++ is weak typing but .net based languages are strongly typed. Strong typing is preferred by means of less run time errors risk and efficient during execution of program but not during compile time.

Corillian's product is a "Component Container." Name at least 3 component containers that ship now with the Windows Server Family.

System.Web.UI.Page,
System.Windows.Forms.Form
System.ComponentModel.Container

Components are any version controlled reusable code elements and component container manages these either visually or not. For example the form is nothing more that visual component container of IComponnet based controls that are rendered and the life cycle of which is managed. Important to note that not all component containers are visual in nature.

What is a PID? How is it useful when troubleshooting a system?

PID is Process ID which is unique to identify any process within a system. Whilst troubleshooting we can kill process through its PID.

How many processes can listen on a single TCP/IP port?

I think single process can only hold handler of any port at a time means can listen on single port. Once I got error when I ran my web application as another application (skype) was using that port. It make sense as well, ports are like doors if two people talk on specific door and third one comes up then no privacy :-D (divorce ratio would be dramatically raised)

What is the GAC? What problem does it solve?
GAC stands for Global Access Cache where shareable/public assemblies (DLL) stored to be used by multiple programs. It gives a shared platform for programs to use single assembly and can store same assembly (of same name) with different versions and can help to solve DLL HELL.

Mid-Level .NET Developer

· Describe the difference between Interface-oriented, Object-oriented and Aspect-oriented programming.

Aspect-oriented programming looks at how many components or pieces of a system might need to interact. The intersections of these pieces are what are important in AOP. "Crosscutting" is a slice across several units, all of which interact during some operation. The article Discussing aspects of AOP in Communications of the ACM, Volume 44, Number 10 (2001) shows an example of a drawing editor with point and line elements. If the drawing is moved, both point and line elements need to update. A crosscut hits these elements for this event. Other examples might include logging or exception handling which hit several different layers in a system. (Viji Sarathy, Aspect Orienting .NET Components ) Sarathy's article shows using attributes to "dynamically alter the manner in which the code executes", thereby causing events to be fired during runtime when a particular method, field or property is accessed. Interface-oriented programming is a contract-based approach. Nether side of the interface cares how the other does its work, only that the two sides can communicate via an agreed-upon contract. WSDL-based web services are the prime example of this. Object-Oriented programming is based on abstraction, encapsulation (data hiding), polymorphism and inheritance. Classes implement these concepts to build objects controlling or implementing a system. Abstraction allows loose coupling between components by providing a layer between objects so that one object isn't concerned with how the other implements its business rules. (Interfaces, layers) Great stuff when you want to isolate parts of the system so they can be swapped out without killing the rest of the sytsem. Encapsulation allows abstraction to work by hiding details of a class's implementation from calling classes. (Public vs. private fields) Inheritance enables base (parent) classes to have common functionality defined in it and passed down to child classes. A Shape class might have a field for color which is inherited by child classes of Square or Circle type. Polymorphism enables implementation of same-named public fields, allowing different classes to perform different actions on the same call - rendering a Square or Circle object differently in a graphic program, even though they might both be subclassed from a base Shape class. (Overriding)

· Describe what an Interface is and how it’s different from a Class.

· An interface is strictly a Contract without implementation means interface can only declare properties or methods. Class can have implementation of its methods, can have different level of access identifiers whereas interface’s properties or methods can have only public access identifier and can implement class and multiple interfaces.

· What is Reflection?

· Reflection is mechanism to load dynamically assembly at runtime and using assembly Meta data can access its namespace, class and their properties, methods and even events.

· What is the difference between XML Web Services using ASMX and .NET Remoting using SOAP?

· Remoting assumes the other end is .NET. This is because .NET remoting using SOAP uses the SoapFormatter to serialize data. SoapFormatter embeds the type information required to deserialize the object into the message itself. This requires that the client and the server must have access to this assembly. Remoting believes in the .NET Type System. Remoting believes in sharing types and assemblies. Remoting can support DCOM style Client Activated Objects which are stateful. The use of CAOs though have to be carefully thought about because CAOs cannot be load balanced. ASMX model does not assume that the other end is .NET. ASMX uses XmlSerializer to serialize data. Xmlserailizer believes that the XML Type System, that is the XSD is superior and works on serializing data conforming to a schema. In other words XML Web Services believe in sharing schema and contracts over types and assemblies. This makes the Web Services interoperable. ASMX services are usually stateless. Ref

· Are the type system represented by XmlSchema and the CLS isomorphic?

· No, there is some impedence mismtach. That's the reason you ned IXmlSerializable to help the XmlSerializer. XSD is not a type system in the traditional sense. Ref

· Conceptually, what is the difference between early-binding and late-binding?

· Early binding means compiler get information of type calling/path execution during compilation of code and in late binding compiler doesn’t get that information but this information determined at runtime/execution time.

· Is using Assembly.Load a static reference or dynamic reference?

· Its dynamic load (Reflection)

· When would using Assembly.LoadFrom or Assembly.LoadFile be appropriate?

· Difference is only about binding. LoadFrom is flexible and if it doesn’t get assembly where it was pointing then it can be redirect to another path on the other hand LoadFile points/depends upon strictly to reference/path of the assembly defined, don’t redirect in case of failure.

· What is an Asssembly Qualified Name? Is it a filename? How is it different?

· Assembly qualified name contains assembly name, version, token key whereas filename is simple file name physically on file system. Assembly names store as Meta data as is very important by means of defining scope.

· Is this valid? Assembly.Load("foo.dll")

· Ofcouse NOT :D as its file name not Assembly qualified name which is required.

· How is a strongly-named assembly different from one that isn’t strongly-named?

· Strongly named assembly have strong names due to public token key so can be stored in GAC (shared environment) and can be referred by multiple programs whereas non-strongly name can’t be stored in GAC.

· Can DateTimes be null?

· Before .net 2.0 it was not possible as datetime/integer… are struct/value types which can’t be null but due to nullable types now its possible.

· What is the JIT? What is NGEN? What are limitations and benefits of each?

· I remember, once I was being interviewed at very big name (company), interviewer asked me about .net IL compilation… I start telling and talked about JIT as well after listening me he said hmmm JIT exist in Java technologies not .net technologies, I said no I read about it and it does but he kept negating me so I got quite and said Ok. Anyhow JIT stands for Just in time compiler it compiles code into native code to execute by processor in three different techniques. It compiles code just before code required to be run which makes execution little slow (depends) so to avoid that we use NGEN which converts IL into native code like JIT but during deployment. It comes with large image which also includes that codes compiled version which is not being calling frequently.

· How does the generational garbage collector in the .NET CLR manage object lifetime? What is non-deterministic finalization?

· Object life time divides into three different generations, 1 short term and 2 long terms so manage accordingly. Non deterministic finalization means GC calls finalize method of object not right after object goes out of scope rather when GC got idle time to prioritize it.

· What is the difference between Finalize() and Dispose()?

· Finalize called by GC and Dispose called by programmer to free up resources.

· How is the using() pattern useful? What is IDisposable? How does it support deterministic finalization?

· Using statement is quite handy and makes code quite efficient as right after end of using statement object created/declared in that statement disposed automatically means dispose method get called in deterministic way to free up memory. IDisposible is interface which classes implements to dispose unmanaged resources in deterministic manner.

· What does this useful command line do? tasklist /m "mscor*"

· It will list down all the processes that have loaded modules which start from mscor… hosting by the .net environment.

· What is the difference between in-proc and out-of-proc?

· As name implies in proc means loading in the same process memory domain of invoker/host, it is fast technique but less reliable than out proc in case of any fault/exception occurs. Out proc is opposite to in proc definition and as loading out of the host process so is not depending and could be safe in host process failure for some reason.

· What technology enables out-of-proc communication in .NET?

· .net remoting through marshalling

· When you’re running a component within ASP.NET, what process is it running within on Windows XP? Windows 2000? Windows 2003?

· Aspnet_wp.exe in case of winxp and win2k but w3pw.exe in case of win2k3.

Senior Developers/Architects

· What’s wrong with a line like this? DateTime.Parse(myString);

· There is nothing wrong necessarily but could be wrong means no error no exception but some logical error like unexpected result could be produce due to lack of locale/culture info.

· What are PDBs? Where must they be located for debugging to work?

· PDB stands for Program database store debugging symbols and meta information for debugging. Normally they are located at bin or debug folder.

· What is cyclomatic complexity and why is it important?

Cyclomatic complexity is a computer science metric (measurement) developed by Thomas McCabe used to generally measure the complexity of a program. It directly measures the number of linearly independent paths through a program’s source code.
The concept, although not the method, is somewhat similiar to that of general text complexity measured by the Flesch-Kincaid Readability Test.
Cyclomatic complexity is computed using a graph that describes the control flow of the program. The nodes of the graph correspond to the commands of a program. A directed edge connects two nodes, if the second command might be executed immediately after the first command. By definition,
CC = E - N + P
where
CC = cyclomatic complexity
E = the number of edges of the graph
N = the number of nodes of the graph
P = the number of connected components.

[1]

· Write a standard lock() plus “double check” to create a critical section around a variable access.

· Object objLock; bool isLocked = true; if (isLocked) {lock(objLock){if (isLocked) {//bingooooo}}}}

· What is FullTrust? Do GAC’ed assemblies have FullTrust?

· FullTrust means newly happily marriage :D and in .net it means Assembly have full access of system resources (which is quite dangerous and in shared hosting domain only medium trust level is allowed). YES GACed assemblies have fulltrust.

· What benefit does your code receive if you decorate it with attributes demanding specific Security permissions?

· It let user know what your code/program required to do so and either it’s allowed to do operation or not so it becomes user friendly by means of security permissions.

· What does this do? gacutil /l | find /i "Corillian"

· List all assemblies in the GAC that has a case insenstive world "Corillian" in it...

· What does this do? sn -t foo.dll

· SN stands for strong name and used to generate strong names of assemblies but not sure about –t param here but my searching told me its for Token Key.

· What ports must be open for DCOM over a firewall? What is the purpose of Port 135?

· DCOM is distributed COM technology which used to remote procedure call and it used port 135 by default. 135 is port of Remote procedure call Service and as DCOM is OO based RPC mechanism so no wonder about it ;) by the way good question can kill any 1J

· Contrast OOP and SOA. What are tenets of each?

· OOP tenets are Polymorphism, inheritance, abstraction…. And SOA tenets would be (not much sure) as it based on services so discovering/access, interoperatibility, security, distributeable

· How does the XmlSerializer work? What ACL permissions does a process using it require?

· XmlSerializer used read/write interfaces to deserialize/serialize respectively xml based data so it’s understood that it uses reflection.

· Why is catch(Exception) almost always a bad idea?

· Catch(exception) is always a time consuming and somehow it means programmer knows/expecting there would/can be some exception so better approach is to use checks as much as programmer can rather catch exception but ofcourse its unavoidable.

· What is the difference between Debug.Write and Trace.Write? When should each be used?

· As names implies .write means printing something and debug would be used whilst debugging and Trace is useable at release mode and according to my knowledge during release mode if debug statement is used it would be ignored gracefully so chill.

· What is the difference between a Debug and Release build? Is there a significant speed difference? Why or why not?

· Debug build contains debug symbols in (pdb) files and debugging related meta information which release build doesn’t that’s why more compact and efficient.

· Does JITting occur per-assembly or per-method? How does this affect the working set?

· JITing occue per method as NGEN make image of whole assembly at once. JITing degrade efficiency if method is very highly coupled means dependent upon other methods (call/invoke other methods which were not JIT)

· Contrast the use of an abstract base class against an interface?

· Aaaaah typical interview question but thanks there is something typical scott asked :D. abstract class can have implementation of methods at different access levels whereas interface can have only declarations of methods and must be public, abstract class is inheritable. I think interesting and bit difficult contract would be between PURE abstract class and interface. Sounds good?

· What is the difference between a.Equals(b) and a == b?

· Equals checks type as well as it compares on heap to objects whereas == doesn’t, it just check value on stack.

· In the context of a comparison, what is object identity versus object equivalence?

· Identity means two references on stack point to same address of heap whereas object equivalence means objects has same value.

· How would one do a deep copy in .NET?

· Normally I hate typical interview questions as this but in this (scott) case I am more than happy to hear. Anyhow Implement ICloneable simple.

· What is boxing?

· To convert value type into reference type is called boxing.

· Is string a value type or a reference type?

· It’s not even again typical interview question but also for heaven sake scott it’s not suppose to be known by some senior/architect level of .net guru. Anyhow string is reference type due to its any length of size.

· What is the significance of the "PropertySpecified" pattern used by the XmlSerializer? What problem does it attempt to solve?

The XMLSerializer enables how to control how objects are encoded into XML. Serializes and deserializes objects into and from XML documents. In .NET 1.x ithe PropertySpecified pattern tried to solve the problem that numeric values such as int and float could not be null, so it had no other way to indicate that the attribute/element existed in the XML file or not. Since .NET 2.0 one can use Nullable<T> and for example int? instead

· Why are out parameters a bad idea in .NET? Are they?

· Ofcourse they are not encouraging as out keyword is somehow violating the rule of returning single value which keep function easy to readable and debuggable as we know only there is single point to return value and somehow caller can send any vulnerable value which always should be validate. Anyhow there are many solutions like using array (if return values are of same type or ENUM if feasible or Collection or Class with multiple properties…)

· Can attributes be placed on specific parameters to a method? Why is this useful?

· Yes I have seen that being using in case of .net remoting but didn’t use/need much sooo.

C# Component Developers

· Juxtapose the use of override with new. What is shadowing?

· Overriding means giving implementation of virtual/abstract/overrideable method in derived class and if we use new it means it can’t be access through by any other class ref/object. Shadowing is somehow opposite to overriding as it lets redefine method implementation with signature as well.

· Explain the use of virtual, sealed, override, and abstract.

· Through Virtual keyword, we enforce programmer of derive class to override this function. Sealed make sure that class won’t be able to inherit (you may say Such mother who can’t birth a baby :D) and through abstract class, we are able to define methods as abstract to make them must overrideable by child classes and don’t let anyone to instantiate it.

· Explain the importance and use of each component of this string: Foo.Bar, Version=2.0.205.0, Culture=neutral, PublicKeyToken=593777ae2d274679d :)

· Foo.Bar Assembly name, Version defines its version in following pattern (Major, Miner, Build) to track version number of that assembly, Culture specifies culture for locale settings and publickeytoken makes it unique so could be kept and accessed in shared environment.

· Explain the differences between public, protected, private and internal.

· Public is shareable so anyone can access no matter out of the class/assembly/assembly. Through Protected you can only access within class or from child classes and through internal you can access within the assembly only.

· What benefit do you get from using a Primary Interop Assembly (PIA)?

PIAs provide unique type identity. The PIA distinguishes the official type definitions from counterfeit definitions provided by other interop assemblies. Having a single type identity ensures type compatibility between applications that share the types defined in the PIA. Because the PIA is signed by its publisher and labeled with the PrimaryInteropAssembly attribute, it can be differentiated from other interop assemblies that define the same types

· By what mechanism does NUnit know what methods to test?

· Using attributes

· What is the difference between: catch(Exception e){throw e;} and catch(Exception e){throw;}

· Throw also return stack trace which throw e doesn’t

· What is the difference between typeof(foo) and myFoo.GetType()?

· First 1 takes type name and return result at compile time whereas 2^nd 1 takes object and return type at runtime using reflection ofcourse.

· Explain what’s happening in the first constructor: public class c{ public c(string a) : this() {;}; public c() {;} } How is this construct useful?

· First one calls the base contructor.

· What is this? Can this be used within a static method?

· this keyword points to current object and as static methods can’t be invoked through object sooo

ASP.NET (UI) Developers

· Describe how a browser-based Form POST becomes a Server-Side event like Button1_OnClick.

· I am not certain but I think when we need to submit some information or manipulate data at server side we use POST method which transmit client side information to server side in Request object and send the information to server and server perform task according to information given by client so in this case Button1_OnClick is transferred to server and it’s handler called the relevant method.

· What is a PostBack?

· Postback is way to send client side information to server after loading it.

· What is ViewState? How is it encoded? Is it encrypted? Who uses ViewState?

· ViewState stores information so it could be accessible after postback and information could be persisted after any number of postbacks but only within the scope of page. It encoded into Base64 format. It can be encrypted. Controls uses viewstate to store control state and data to be preserved after postback.

· What is the <machinekey> element and what two ASP.NET technologies is it used for?

· machinekey defines unique key which could be use by session and cache so if site is cluster based or single sign on based then it’s very useful.

· What three Session State providers are available in ASP.NET 1.1? What are the pros and cons of each?

· In-proc, out-proc, sqlserver

· What is Web Gardening? How would using it affect a design?

· If server has multiple processors and requests traffic is dividing accordingly that is called web gardening. If server is using external resources (like sql server, web services, logging) then it could be very useful.

· Given one ASP.NET application, how many application objects does it have on a single proc box? A dual? A dual with Web Gardening enabled? How would this affect a design?

· HTTPApplication object with single key based would be only 1 per worker process so in case of single processor box ONLY 1, in case of dual processor box without webgardening there would be only 1 single worker process so again single object but in case of web gardening two worker process means 2 objects. So need to have machine key otherwise … :D

· Are threads reused in ASP.NET between reqeusts? Does every HttpRequest get its own thread? Should you use Thread Local storage with ASP.NET?

· ASP.NET is MTA based so multiple threads are possible but I remember once I tried to call methods through callback based async delegates which makes it run on separate thread so when I tried that I lost httpcontext L in that thread. So each thread gets its own thread and usage is depends upon need.

· Is the [ThreadStatic] attribute useful in ASP.NET? Are there side effects? Good or bad?

· I never used it but I think I got my just above mentioned problem’s solution that we can share httpContext through this attribute in multiple threads ;)

· Give an example of how using an HttpHandler could simplify an existing design that serves Check Images from an .aspx page.

· We can simply make httphandler for such specific requirements as .aspx are nto specialized for images based web page which we could make and make things efficient and manipulate response according to our need. If page is based upon images only and needs to show loads of images thumbnail and such features we can make specific httpHandler for such pages to customize response and have more command on request.

· What kinds of events can an HttpModule subscribe to? What influence can they have on an implementation? What can be done without recompiling the ASP.NET Application?

· HTTPModule subscribe to Request life cycle kinds of events like beginRequest,EndRequest,Session,… They are useful to manipulate Request and generate Response according to state and lifecycle. They are separate DLL which are referred by asp.net application and if we change HTTPModule and recompile it we don’t need to recompile our whole application. So they are plugged like plugins

· Describe ways to present an arbitrary endpoint (URL) and route requests to that endpoint to ASP.NET.

· I am sure either I interpreted this question in right way but here is the answer according to my understanding about this question. URL could be define in couple of ways relative path and absolute path and request could be route in multiple ways using Redirect, Transfer, URL Rewrite…

· Explain how cookies work. Give an example of Cookie abuse.

· Cookie stored at client side and readable by any user if it’s not encrypted, if you stored some important information about client data at server any other site could read cookies and get that information.

· Explain the importance of HttpRequest.ValidateInput()?

· It checks integrity of data in Request object (Form, Querystring, Cookies), you can prevented by XSS types of attacks and validate request data to see so there is no malicious input ;)

· What kind of data is passed via HTTP Headers?

· HTTP Header contains information about browser and some of page like browser name, version, page size, mime type, cookies

· Juxtapose the HTTP verbs GET and POST. What is HEAD?

· Get is used when we don’t need to do manipulation at server side and have nothing really secret information to send in querystring as it send information through querystring which is limited so input can’t be very long like article :D but it’s pretty fast as compare to POST as post sends information in hidden fields and preferred in case of manipulation at server side. Using Head we just send page header information not the actual contents/body.

· Name and describe at least a half dozen HTTP Status Codes and what they express to the requesting client.

· Very famous I just remember like 404 error page (page not found) 200 for OK, 500 Server not found

· How does if-not-modified-since work? How can it be programmatically implemented with ASP.NET?
Explain <@OutputCache%> and the usage of VaryByParam, VaryByHeader.

· No idea about the if-not-modified thingy but can tell about OutputCache which is directive used for caching contents and tells server that Header information could be change by VaryByHeader Param and Parameter could be change in query string using VaryByParam so it get different versions for different header (like browsers) and parameters respectively.

· How does VaryByCustom work?

· Can output different pages from cache on the basis of change of state of any control or value or object within that page

· How would one implement ASP.NET HTML output caching, caching outgoing versions of pages generated via all values of q= except where q=5 (as in http://localhost/page.aspx?q=5)?

· <@OutputCache VaryByParam=”q” %>