Q. Why we use “new” keyword for a function.
> To override the function.
> To create the new instances of an object.
Q. Explain DRY
Q. What is KISS
Q. What is attribute programming in c#, how to do it.?
Q. difference between IQuerable and IEnumerable ?
Q. Comapre Arraylist and List. Explain Generics.
Q.How’s method overriding different from overloading?
When overriding, you change the method behavior for a derived class. Overloading simply involves having a method with the same name within the class.
Q.Can you prevent your class from being inherited and becoming a base class for some other classes?
Yes, that’s what keyword sealed in the class definition is for. The developer trying to derive from your class will get a message: cannot inherit from Sealed class WhateverBaseClassName. It’s the same concept as final class in Java.
Q..Where do the reference-type variables go in the RAM?
The references go on the stack, while the objects themselves go on the heap. However, in reality things are more elaborate.
Q.. What is the difference between the value-type variables and reference-type variables in terms of garbage collection?
The value-type variables are not garbage-collected, they just fall off the stack when they fall out of scope, the reference-type objects are picked up by GC when their references go null.
Q.How do you convert a string into an integer in .NET?
Int32.Parse(string), Convert.ToInt32()
Q.Can you declare a C++ type destructor in C# like ~MyClass()?
Yes, but what’s the point, since it will call Finalize(), and Finalize() has no guarantees when the memory will be cleaned up, plus, it introduces additional load on the garbage collector. The only time the finalizer should be implemented, is when you’re dealing with unmanaged code.
Q..What’s the difference between const and readonly?
You can initialize readonly variables to some runtime values. Let’s say your program uses current date and time as one of the values that won’t change. This way you declare
public readonly string DateT = new DateTime().ToString().
Q..what is Yield :
Another often overlooked C# statement that was introduced in .NET 2.0 is yield. This keyword is used to return items from a loop within a method and retain the state of the method through multiple calls.
Q. What is C#.NET Generics?
The classes and the methods can treat the values of different types uniformly with the use if generics.
The usage of generics is advantageous as:
- They facilitate type safety
- They facilitate improved performance
- They facilitate reduced code
- They promote the usage of parameterized types
- The CLR compiles and stores information related to the generic types when they are instantiated. (The generic type instance refers to the location in memory of the reference type to which it is bound for all the instances of the generic type.)
Q. What is the difference between const and readonly in C#.NET?
The read only can be modified by the class it is contained in. However, the const cannot be modified. It needs to be instantiated only at the compile time.
Q. What is Constructor Chaining?
We can chain the call of constructor from child class to base class depending on our requirement. This concept makes sure that the matching base class constructor must be called based on the parameter passed to the child class constructor.
Q. What is the difference between Finalize() and Dispose()?
Dispose() is called by as an indication for an object to release any unmanaged resources it has held.
Finalize() is used for the same purpose as dispose however finalize doesn’t assure the garbage collection of an object.
Dispose() operates determinalistically due to which it is generally preferred.
Q. How does the XmlSerializer work? What ACL permissions does a process using it require?
The XmlSerializer constructor generates a pair of classes derived from XmlSerializationReader and XmlSerializationWriter by analysis of the classes using reflection.
Temporary C# files are created and compiled into a temporary assembly and then loaded into a process.
The XmlSerializer caches the temporary assemblies on a per-type basis as the code generated like this is expensive. This cached assembly is used after a class is created. Therefore the XmlSerialize requires full permissions on the temporary directory which is a user profile temp directory for windows applications
Q. What are circular references? Explain how garbage collection deals with circular references.
A circular reference is a run-around wherein the 2 or more resources are interdependent on each other rendering the entire chain of references to be unusable.
There are quite a few ways of handling the problem of detecting and collecting cyclic references.
1. A system may explicitly forbid reference cycles.
2. Systems at times ignore cycles when they have short lives and a small amount of cyclic garbage. In this case a methodology of avoiding cyclic data structures is applied at the expense of efficiency.
3. Another solution is to periodically use a tracing garbage collector cycles.
Other types of methods to deal with cyclic references are:
•Weighted reference counting
•Indirect reference counting
Q. Describe the accessibility modifier "protected internal" in C#.
The Protected Internal access modifier can be accessed by:
Members of the Assembly
The inheriting class
The class itself
Its access is limited to the types derived from the defining class in the current assembly or the assembly itself.
Q. Explain the use of virtual, sealed, override, and abstract.
The virtual keyword enables a class to be overridden. If it has to be prevented from being overridden, then the sealed keyword needs to be used. If the keyword virtual is not used, members of the class can even then be overridden. However, its usage is advised for making the code meaningful.
The override keyword is used to override the virtual method in the base class. Abstract keyword is used to modify a class, method or property declaration. You cannot instantiate an abstract class or make calls to an abstract method directly.
An abstract virtual method means that the definition of the method needs to be given in the derived class.
Q. Explain the use of static members with example using C#.NET.
Static members are not associated with a particular instance of any class.
They need to be qualified with the class name to be called.
Since they are not associated with object instances, they do not have access to non-static members.
i.e.: "this" cannot be used, which represents the current object instance.
Q. How to achieve polymorphism in C#.NET?
Polymorphism is when a class can be used as more than one type through inheritance. It can be used as its own type, any base types, or any interface type if it implements interfaces.
It can be achieved in the following ways:
Derived class inherits from a base class and it gains all the methods, fields, properties and events of the base class.
To completely take over a class member from a base class, the base class has to declare that member as virtual.
Q. What is Constructor Chaining?
We can chain the call of constructor from child class to base class depending on our requirement. This concept makes sure that the matching base class constructor must be called based on the parameter passed to the child class constructor.
Q. What is ref parameter? What is out parameter?
Ref Parameter: Used to pass a parameter as a reference so that the function called will set the value. This could be used to return more than 1 value by a function.
e.g.
public int AddMuliply( int a , int b, ref int c)
{
c = a*b;
return ( a+b);
}
The above function, returns the addition of two numbers as well as computes the multiplication result and passes to the calling function.
Out Parameter: Used to pass values from the aspx Code-behind to the aspx page.
The difference is that for a ref parameter, you have to assign a value before you call the function, while for OUT parameter, you dont have to assign a value, the calling function assumes that the called function would assign some value.
A ref parameter must first be initialized before being passed from the calling function to the called function. but a out parameter need not be initialized, we can pass it directly when we pass a parameter as ref to a method, the method refers to the same variable and changes made will affect the actual variable.
even the variable passed as out parameter is same as ref parameter, but implementation in c# is different, Arguement passed as ref parameter must be initialized before it is passed to the method. But in case of out parameter it is not necessary. But after a call to a method as out parameter it is necessary to initialize.
When to use out and ref parameter, out parameter is used when we want to return more than one value from a method. Ref parameter can be used as both input and o/p parameter out parameter can be used as only output parameter.
Q. Why multiple Inheritance is not possible in C#?
Multple inheritance is coneceptually wrong. It shouldn't be allowed in any language. Inheritance is the strongest relationship that can be expressed in OO languages.
It's used to express IS-A relationship. Aggregation is used to express IS CONSTRUCTED IN TERMS OF. If you're using multiple inheritance in C++ then you're design is wrong and you probably want to use aggregation. On the other hand it's plausible to want to use multiple interfaces. For instance you might have a class wheel and a class engine. You could say that your class car inherits from wheel and from engine but that's wrong. In fact car aggregates wheel and engine because it is built in terms of those classes. If wheel is an interface and engine is an interface then car must inherit both of these interfaces since it must implement the functionaity of wheel and engine .On this basis we can see that multiple inheritance for classes should not be allowed because it promotes mis-use of the strong IS-A relationship. C# enforces the correct concepts whilst C++ allows mis-use. multiple interface inheritance is permissible and C# allows this. It's all to do with properly understanding OO concepts.
Absolute Multiple Inheritance is not possible in c# but partially it supports multiple inheritance by the use of Interfaces. As interfaces force a class to implement same type of behaviour (as defined in interface) which classes implements that interface
Q. How to prevent a class from being inherited in C#.NET?
The sealed modifier is used to prevent derivation from a class. An error occurs if a sealed class is specified as the base class of another class. A sealed class cannot also be an abstract class
Q. Difference between a Class and Component?
Class is a datatype that encloses data and function members.
It can be used for implementing the various OOPS features.
Component is a particular class that must implement the IComponent interface .It is the base class for all components in the common language runtime that marshal by reference. Component is remotable and derives from the MarshalByRefObject class.
IComponent interface belongs to System.ComponentModel namespace.
So, we can say Component is subclassification of a class
Q. What does the modifier protected internal in C# mean?
The Protected Internal can be accessed by Members of the Assembly or the inheriting class, and of course, within the class itself.
Q. What is polymorphism?
Polymorphism means allowing a single definition to be used with different types of data (specifically, different classes of objects). For example, a polymorphic function definition can replace several type-specific ones, and a single polymorphic operator can act in expressions of various types. Many programming languages implement some forms of polymorphism.
The concept of polymorphism applies to data types in addition to functions. A function that can evaluate to and be applied to values of different types is known as a polymorphic function. A data type that contains elements of different types is known as a polymorphic data type.
Q. What is a static constructor?
Static Constructor - It is a special type of constructor, introduced with C#. It gets called before the creation of the first object of a class(probably at the time of loading an assembly).
Q. What is the difference between out and ref in C#?
1) out parameters return compiler error if they are not assigned a value in the method. Not such with ref parameters.
2) out parameters need not be initialized before passing to the method, whereas ref parameters need to have an initial value before they are passed to a method.
Q. What's the difference between IEnumerable<T> and List<T> ?
1. IEnumerable is an interface, where as List is one specific implementation of IEnumerable. List is a class.
2. FOR-EACH loop is the only possible way to iterate through a collection of IEnumerable, where as List can be iterated using several ways. List can also be indexed by an int index, element can be added to and removed from and have items inserted at a particular index.
3. IEnumerable doesn't allow random access, where as List does allow random access using integral index.
4. In general from a performance standpoint, iterating thru IEnumerable is much faster than iterating thru a List.
Q. LINQ interview questions: -What is the difference between LINQ to SQL and Entity framework?
Following is the LINQ interview questions asked in an interview: -
• LINQ to SQL is good for rapid development with SQL Server. EF is for enterprise scenarios and works with SQL server as well as other databases.
• LINQ maps directly to tables. One LINQ entity class maps to one table. EF has a conceptual model and that conceptual model map to storage model via mappings. So one EF class can map to multiple tables or one table can map to multiple classes.
• LINQ is more targeted towards rapid development while EF is for enterprise level where the need is to develop loosely coupled framework.
9. Delegtes and Events:
An interesting and useful property of a delegate is that it does not know or care about the class of the object that it references.
public delegate void SimpleDelegate ()
A delegate will allow us to specify what the function we'll be calling looks like without having to specify whichfunction to call.
Delegate and Event concepts are completely tied together. Delegates are just function pointers, That is, they hold references to functions.
A Delegate is a class. When you create an instance of it, you pass in the function name (as a parameter for the delegate's constructor) to which this delegate will refer.
