C# and VB.NET Interview Prep
E2 Series
C# and VB.NET Interview Prep
Language Basics
1.
What is the difference between String and StringBuilder? String is immutable set of characters whereas StringBuilder is mutable set of characters. String is used when fixed number of characters needs to be stored. StringBuilder is used when arbitrary number of strings needs to be stored. Note: String is immutable; means that each time it is being operated on, a new instance is created.
2.
Is C# a strongly typed language? C# is a strongly typed language. Conversions from one type to another type can be implicit or explicit. Conversion from larger type to smaller type requires explicit cast. This may not be always successful.
3.
Which is the base class for all the classes in .NET framework? System.Object class is the base class for all the classes in .NET framework.
4.
What is boxing and unboxing? Conversion of value type to reference type is called boxing. ArrayList is a non‐generic collection. Everything is stored as an object. When an integer is added in ArrayList collection, the value is said to be boxed. Conversion of reference type to value type is called unboxing. Explicit cast is required. When the same integer value is accessed from the ArrayList collection and some operation is performed, the value is said to be unboxed. C# Code static void Main(string[] args) { int number1 = 400; float rate = 9.5F; Display(number1); Display(rate); }
E2 Series
C# and VB.NET Interview Prep
Language Basics
public static void Display(object o) { Console.WriteLine(o.ToString()); int x = (int)o; // unboxing }
VB.NET Code Sub Main() Dim number1 As Integer = 400 Dim rate As Single = 9.5F Display(number1) Display(rate) End Sub Public Sub Display(ByVal o As Object) Console.WriteLine(o.ToString()) Dim x As Integer = CType(o, Integer)
‘ unboxing
End Sub
E2 Series
C# and VB.NET Interview Prep
Delegates and Events
1.
What is a delegate? Like a variable, every method also has a physical location in the memory. This address can be assigned to a delegate. Thus, a delegate is a reference to a method that matches with its signature. In other words, a delegate is equivalent to a type‐safe function pointer. Delegate plays a significant role in event handling in .NET by associating an event with the method that will handle the event.
2.
Is delegate a value type or a reference type? A delegate is a reference type. By default every delegate inherits from System.Delegate type. It is actually a reference to a method. When a delegate is defined, a class is defined internally. A delegate is always instantiated using “new” and a method to be referenced is associated with it.
3.
What are the rules for using a delegate? Rules for using delegates are: 1. A delegate is declared using the keyword “delegate”. a. The return type of the delegate should be same as that of the method that is to be referred. b. The signature of the delegate and the method to be referred should also match. c. Any method which has the same signature and return type as the delegate, can be invoked using the delegate. 2. The delegate is instantiated using “new” keyword. Name of the method is passed as an argument to the constructor. 3. The instance of delegate is used to invoke the method. If a method takes any argument, then it is passed to the instance of the delegate.
E2 Series
C# and VB.NET Interview Prep
1.
Exception Handling
What is exception handling? Exception handling mechanism is a structured way of handling run‐time errors. The errors like file not found, trying to open a connection which is already open, etc. are not known till the program executes. They often cause abnormal termination of program. So it becomes the responsibility of the developer to handle them in the code so that the program executes smoothly. Developer writes the code in “try” block that has the possibility of throwing error at run‐time. The error is caught in “catch” block. Any resources explicitly used in the “try” block can be freed in “finally” block. This block executes irrespective of whether the exception is thrown.
2.
What is the difference between Exception and Error? Writing programs and errors go hand in hand. Errors can occur due to incorrect syntax, incorrect logic or can occur at run‐time. Errors that occur at run‐time when the program gets executed are called run‐ time errors. Exceptions are runtime errors. If not handled cause the application to abort. These type of errors can also be predicted and handled. For example, accessing the array outside its bound, divide by zero error, unable to access the file, file not found etc. .NET provides a robust exception handling mechanism. Note: Refer question no. 4 for the syntax and details.
3.
What is the role of exception handling in a code snippet? A well designed error handling code block makes a program more robust and less prone to crashing because the application handles such errors using exception handling mechanism.
4.
How do you handle exception in .NET? ‘try’ block is used to define a block of code that is likely to throw exception. ‘catch’ block contains code that is expected to get executed when a particular exception occurs. One or more ‘catch’ blocks can be written to catch specific expected exceptions. The code written in ‘catch’ block is called handler code. E2 Series
C# and VB.NET Interview Prep
Exception Handling
C# Code try { int [] arr = new int[]{1,2,3}; Console.WriteLine(arr[4]); . . . // more code } catch(IndexOutOfRangeException ex) { Console.WriteLine(ex.Message); } catch (Exception ex) { Console.WriteLine(ex.Message); } VB.NET code Try Dim arr() As Integer =
New Integer() {1,2,3}
Console.WriteLine(arr(4)) . . . ' more code Catch ex As IndexOutOfRangeException Console.WriteLine(ex.Message) Catch ex As Exception Console.WriteLine(ex.Message) End Try
E2 Series
C# and VB.NET Interview Prep
Exception Handling
Base class for exception handling is “Exception” class. When an unknown exception occurs, it is caught with this class to avoid abnormal termination of program. Most generic exception is always handled in the last catch block. However; the developer should handle only those generic exceptions from which it can recover and smooth functioning takes place. For example, FileNotFoundException should be handled as the user can be informed to give some other file name. But exception that occurs due to some problem with execution engine should not be handled as the exact cause is not known and smooth functioning of application cannot be ensured.
E2 Series
C# and VB.NET Interview Prep
Reflection
1.
What is metadata in case of .NET application? The word metadata means “data about data”. In context with .NET applications, metadata contains information about the types, methods, events, properties, constructors, attributes, fields etc. This metadata information is present in .NET assembly.
2.
What is reflection? A .NET assembly contains manifest files, MSIL code, resources along with metadata. Metadata is in the form of types[Class/strutcture], their properties, methods, fields, events, attributes etc. A technique that is used to inspect this metadata at runtime is called reflection. Facilities provided by System.Reflection namespace, help a developer to instantiate any type, invoke its methods or even create new types. It also helps to access the attributes applied on any type. A developer studio feature of intellisense can be developed based on reflection mechanism.
3.
Can you create a type[Class/structure] dynamically in .NET? How?
With reflection, even a type[Class/structure] and an assembly can be dynamically created. Class TypeBuilder is used to create a type. Other classes ConstructorBuilder, FieldBuilder, EventBuilder, like MethodBuilder, etc. are used to generate constructor, fields, events, methods etc. Class AssemblyBuilder is used to create an assembly. These classes are part of System.Reflection.Emit namespace. 4.
How will you invoke a method of a type[Class/structure] using reflection in .NET? Following steps should be followed to invoke a method using reflection: 1. Assembly reference is first obtained using Assembly class. 2. A collection of types is obtained from assembly’s reference using GetTypes method. Required type is obtained from reference of Type class. 3. GetMethod method is used to obtain the reference of required method. MethodInfo class holds the reference of the method E2 Series
C# and VB.NET Interview Prep
Reflection
4. An object is created using CreateInstance method of Assembly class for a particular type. 5. Then method is invoked using Invoke method of MethodInfo class. C# Code MethodInfo method; object result = new object (); object[] ags = new object[] {30,15}; Assembly asmbly = Assembly.LoadFrom(@"C:\ SimpleCalc.dll"); // Step 1 Type[] types = asmbly.GetTypes();
// Step 2
foreach (Type t in types) { method = t.GetMethod("Subtract");
// Step 3
if (method != null) { string typeName = t.FullName; object obj = asmbly.CreateInstance(typeName); // Step 4 result = method.Invoke(obj, ags);
// Step 5
break; } } string res = result.ToString(); Console.WriteLine("Subtraction is: {0}", res);
E2 Series
C# and VB.NET Interview Prep
Reflection
VB.NET Code Dim method As MethodInfo Dim result As Object = New Object() Dim ags() As Object = New Object() {30, 15} Dim asmbly As Assembly = Assembly.LoadFrom("C:\SimpleCalc.dll") ’Step 1 Dim types() As Type = asmbly.GetTypes()
’Step 2
Dim t As Type For Each t In types method = t.GetMethod("Subtract")
’Step 3
If Not method Is Nothing Then Dim typeName As String = t.FullName Dim obj As Object = asmbly.CreateInstance(typeName) ’Step 4 result = method.Invoke(obj, ags)
’Step 5
Exit For End If Next Dim res As String = result.ToString() Console.WriteLine("Subtraction is: {0}", res)
E2 Series
C# and VB.NET Interview Prep
Project Experience
1.
Is your project dummy or real world? Possible intention
To know if you have really worked on projects that you claim. To know if you have experience of working on real projects with real deadlines and time pressure delivering expectations defined by a demanding customer.
Insights
State whatever the truth with confidence. Do not lie. There is no difference in learning, be it a real world project or dummy as far as processes are concerned at beginner level. It is the rigor that is critical, with which you follow the processes.
Example answer I have worked on two projects. One was a web‐based application for an overseas client. The project was in .NET technology. Other project was an in‐ house product, developed using SQL server and Visual Basic. In both the projects, my role was to write test cases and execute them. I have worked on two projects. One was a web‐based application for an overseas client. The project was in .NET technology. Other project was an in‐ house product, developed using SQL server and Visual Basic. My role was to do coding and unit testing along with creation of some stored procedures. Anti pattern
Do not lie. Tell the truth with confidence. Do not feel inferior if you believe that your project is not real world. What matters for the interviewer is the rigor with which it is executed.
Interviewer’s interpretation
Candidate with relevant experience is preferable because his time to get on to the project and become productive would be less. Confident and neat explanation shows that you have really worked on the project.
E2 Series
C# and VB.NET Interview Prep
C# and VB.NET Interview Prep
E2 Series
C# and VB.NET Interview Prep
