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100 Cards in this Set
- Front
- Back
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Does C# support multiple-inheritance?
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No. But you can use Interfaces.
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Where is a protected class-level variable available?
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It is available to any sub-class derived from base class
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Are private class-level variables inherited?
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Yes, but they are not accessible.
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Describe the accessibility modifier “protected internal”.
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It is available to classes that are within the same assembly and derived from the specified base class.
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Which class is at the top of .NET class hierarchy?
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System.Object.
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What does the term immutable mean?
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The data value may not be changed.
Note: The variable value may be changed, but the original immutable data value was discarded and a new data value was created in memory. |
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What’s the difference between System.String and System.Text.StringBuilder classes?
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System.String is immutable.
System.StringBuilder was designed with the purpose of having a mutable string where a variety of operations can be performed. |
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What’s the advantage of using System.Text.StringBuilder over System.String?
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StringBuilder is more efficient in cases where there is a large amount of string manipulation. Strings are immutable, so each time a string is changed, a new instance in memory is created.
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Can you store multiple data types in System.Array?
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No.
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What’s the difference between the System.Array.CopyTo() and System.Array.Clone()?
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The Clone() method returns a new array (a shallow copy) object containing all the elements in the original array. The CopyTo() method copies the elements into another existing array. Both perform a shallow copy. A shallow copy means the contents (each array element) contains references to the same object as the elements in the original array. A deep copy (which neither of these methods performs) would create a new instance of each element's object, resulting in a different, yet identacle object.
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.How can you sort the elements of the array in descending order?
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By calling Sort() and then Reverse() methods.
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What’s the .NET collection class that allows an element to be accessed using a unique key?
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HashTable.
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What class is underneath the SortedList class?
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A sorted HashTable.
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Will the finally block get executed if an exception has not occurred?
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Yes.
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What’s the C# syntax to catch any possible exception?
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A catch block that catches the exception of type System.Exception. You can also omit the parameter data type in this case and just write catch {}.
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Can multiple catch blocks be executed for a single try statement?
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No. Once the proper catch block processed, control is transferred to the finally block .
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Explain the three services model commonly know as a three-tier application?
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Presentation (UI), Business (logic and underlying code) and Data (from storage or other sources).
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What is the syntax to inherit from a class in C#?
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Place a colon and then the name of the base class.
Example: class MyNewClass : MyBaseClass |
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Can you prevent your class from being inherited by another class?
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Yes. The keyword “sealed” will prevent the class from being inherited.
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Can you allow a class to be inherited, but prevent the method from being over-ridden?
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Yes. Just leave the class public and make the method sealed.
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What’s an abstract class?
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A class that cannot be instantiated. An abstract class is a class that must be inherited and have the methods overridden. An abstract class is essentially a blueprint for a class without any implementation.
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When do you absolutely have to declare a class as abstract?
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1. When the class itself is inherited from an abstract class, but not all base abstract methods have been overridden.
2. When at least one of the methods in the class is abstract. |
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What is an interface class?
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Interfaces, like classes, define a set of properties, methods, and events. But unlike classes, interfaces do not provide implementation. They are implemented by classes, and defined as separate entities from classes.
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Why can’t you specify the accessibility modifier for methods inside the interface?
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They all must be public, and are therefore public by default.
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Can you inherit multiple interfaces?
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Yes. .NET does support multiple interfaces.
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What happens if you inherit multiple interfaces and they have conflicting method names?
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It’s up to you to implement the method inside your own class, so implementation is left entirely up to you. This might cause a problem on a higher-level scale if similarly named methods from different interfaces expect different data, but as far as compiler cares you’re okay.
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What’s the difference between an interface and abstract class?
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In an interface class, all methods are abstract - there is no implementation. In an abstract class some methods can be concrete. In an interface class, no accessibility modifiers are allowed. An abstract class may have accessibility modifiers.
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What is the difference between a Struct and a Class?
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Structs are value-type variables and are thus saved on the stack, additional overhead but faster retrieval. Another difference is that structs cannot inherit.
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What’s the implicit name of the parameter that gets passed into the set method/property of a class?
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Value. The data type of the value parameter is defined by whatever data type the property is declared .
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What does the keyword “virtual” declare for a method or property?
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The method or property can be overridden.
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How is method overriding different from method overloading?
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When overriding a method, you change the behavior of the method for the derived class. Overloading a method simply involves having another method with the same name within the class.
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Can you declare an override method to be static if the original method is not static?
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No. The signature of the virtual method must remain the same. (Note: Only the keyword virtual is changed to keyword override)
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What are the different ways a method can be overloaded?
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Different parameter data types, different number of parameters, different order of parameters.
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If a base class has a number of overloaded constructors, and an inheriting class has a number of overloaded constructors; can you enforce a call from an inherited constructor to a specific base constructor?
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Yes, just place a colon, and then keyword base (parameter list to invoke the appropriate constructor) in the overloaded constructor definition inside the inherited class.
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What’s a delegate?
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A delegate object encapsulates a reference to a method.
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What’s a multicast delegate?
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A delegate that has multiple handlers assigned to it. Each assigned handler (method) is called.
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What’s the implicit name of the parameter that gets passed into the class’ set method?
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Value, and it’s datatype depends on whatever variable we’re changing.
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How do you inherit from a class in C#?
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Place a colon and then the name of the base class.
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When you inherit a protected class-level variable, who is it available to?
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Classes in the same namespace.
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Are private class-level variables inherited?
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Yes, but they are not accessible, so looking at it you can honestly say that they are not inherited.
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Describe the accessibility modifier protected internal.?
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It’s available to derived classes and classes within the same Assembly (and naturally from the base class it’s declared in).
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C# provides a default constructor for me. I write a constructor that takes a string as a parameter, but want to keep the no parameter one. How many constructors should I write?
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Two. Once you write at least one constructor, C# cancels the freebie constructor, and now you have to write one yourself, even if there’s no implementation in it.
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What does the keyword virtual mean in the method definition?
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The method can be overridden.
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Can you declare the override method static while the original method is non-static?
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No, you can’t, the signature of the virtual method must remain the same, only the keyword virtual is changed to keyword override.
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Can you override private virtual methods?
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No, moreover, you cannot access private methods in inherited classes, have to be protected in the base class to allow any sort of access.
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Can you prevent your class from being inherited and becoming a base class for some other classes?
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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. |
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Can you allow class to be inherited, but prevent the method from being over-ridden?
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Yes, just leave the class public and make the method sealed.
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What’s an abstract class?
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A class that cannot be instantiated. A concept in C++ known as pure virtual method. A class that must be inherited and have the methods over-ridden.
Essentially, it’s a blueprint for a class without any implementation. |
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When do you absolutely have to declare a class as abstract (as opposed to free-willed educated choice or decision based on UML diagram)?
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When at least one of the methods in the class is abstract. When the class itself is inherited from an abstract class, but not all base abstract methods have been over-ridden.
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What’s an interface class?
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It’s an abstract class with public abstract methods all of which must be implemented in the inherited classes.
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Why can’t you specify the accessibility modifier for methods inside the interface?
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They all must be public. Therefore, to prevent you from getting the false impression that you have any freedom of choice, you are not allowed to specify any accessibility, it’s public by default.
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Can you inherit multiple interfaces?
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Yes, why not.
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And if they have conflicting method names?
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It’s up to you to implement the method inside your own class, so implementation is left entirely up to you.
This might cause a problem on a higher-level scale if similarly named methods from different interfaces expect different data, but as far as compiler cares you’re okay. |
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What’s the difference between an interface and abstract class?
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In the interface all methods must be abstract, in the abstract class some methods can be concrete. In the interface no accessibility modifiers are allowed, which is ok in abstract classes.
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How can you overload a method?
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Different parameter data types, different number of parameters, different order of parameters.
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If a base class has a bunch of overloaded constructors, and an inherited class has another bunch of overloaded constructors, can you enforce a call from an inherited constructor to an arbitrary base constructor?
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Yes, just place a colon, and then keyword base (parameter list to invoke the appropriate constructor) in the overloaded constructor definition inside the inherited class.
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Is it namespace class or class namespace?
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The .NET class library is organized into namespaces. Each namespace contains a functionally related group of classes so natural namespace comes first.
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What is the difference between public, static and void?
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All these are access modifiers in C#. Public declared variables or methods are accessible anywhere in the application. Static declared variables or methods are globally accessible without creating an instance of the class. The compiler stores the address of the method as the entry point and uses this information to begin execution before any objects are created. And Void is a type modifier that states that the method or variable does not return any value.
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Can multiple catch blocks be executed?
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No, Multiple catch blocks can’t be executed. Once the proper catch code executed, the control is transferred to the finally block and then the code that follows the finally block gets executed.
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What is an object?
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An object is an instance of a class through which we access the methods of that class. “New” keyword is used to create an object. A class that creates an object in memory will contain the information about the methods, variables and behavior of that class.
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Define Constructors?
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A constructor is a member function in a class that has the same name as its class. The constructor is automatically invoked whenever an object class is created. It constructs the values of data members while initializing the class.
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What is Jagged Arrays?
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The array which has elements of type array is called jagged array. The elements can be of different dimensions and sizes. We can also call jagged array as Array of arrays.
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What is the difference between ref & out parameters?
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An argument passed as ref must be initialized before passing to the method whereas out parameter needs not to be initialized before passing to a method.
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What is the use of using statement in C#?
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The using block is used to obtain a resource and use it and then automatically dispose of when the execution of block completed.
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What is serialization?
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When we want to transport an object through network then we have to convert the object into a stream of bytes. The process of converting an object into a stream of bytes is called Serialization. For an object to be serializable, it should inherit ISerialize Interface.
De-serialization is the reverse process of creating an object from a stream of bytes. |
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Can “this” be used within a static method?
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We can’t use ‘This’ in a static method because we can only use static variables/methods in a static method.
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What is difference between constants and read-only?
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Constant variables are declared and initialized at compile time. The value can’t be changed after wards. Read-only variables will be initialized only from the Static constructor of the class. Read only is used only when we want to assign the value at run time.
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What is an interface class?
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Interface is an abstract class which has only public abstract methods and the methods only have the declaration and not the definition. These abstract methods must be implemented in the inherited classes.
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What are value types and reference types?
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Value types are stored in the Stack whereas reference types stored on heap.
Value types: int, enum , byte, decimal, double, float, long Reference Types: string , class, interface, object. |
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What are Custom Control and User Control?
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Custom Controls are controls generated as compiled code (Dlls), those are easier to use and can be added to toolbox. Developers can drag and drop controls to their web forms. Attributes can be set at design time. We can easily add custom controls to Multiple Applications (If Shared Dlls), If they are private then we can copy to dll to bin directory of web application and then add reference and can use them.
User Controls are very much similar to ASP include files, and are easy to create. User controls can’t be placed in the toolbox and dragged – dropped from it. They have their design and code behind. The file extension for user controls is ascx. |
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What are sealed classes in C#?
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We create sealed classes when we want to restrict the class to be inherited. Sealed modifier used to prevent derivation from a class. If we forcefully specify a sealed class as base class then a compile-time error occurs.
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What is method overloading?
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Method overloading is creating multiple methods with the same name with unique signatures in the same class. When we compile, the compiler uses overload resolution to determine the specific method to be invoke.
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What is the difference between Array and Arraylist?
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In an array, we can have items of the same type only. The size of the array is fixed. An arraylist is similar to an array but it doesn’t have a fixed size.
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Can a private virtual method be overridden?
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No, because they are not accessible outside the class.
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Describe the accessibility modifier “protected internal”.
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Protected Internal variables/methods are accessible within the same assembly and also from the classes that are derived from this parent class.
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Write down the C# syntax to catch exception?
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To catch an exception, we use try catch blocks. Catch block can have parameter of system.Exception type.
Eg: try { GetAllData(); } catch(Exception ex) { } In the above example, we can omit the parameter from catch statement. |
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What is the difference between Finalize() and Dispose() methods?
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Dispose() is called when we want for an object to release any unmanaged resources with them. On the other hand Finalize() is used for the same purpose but it doesn’t assure the garbage collection of an object.
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What are circular references?
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Circular reference is situation in which two or more resources are interdependent on each other causes the lock condition and make the resources unusable.
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What are generics in C#.NET?
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Generics are used to make reusable code classes to decrease the code redundancy, increase type safety and performance. Using generics, we can create collection classes. To create generic collection, System.Collections.Generic namespace should be used instead of classes such as ArrayList in the System.Collections namespace. Generics promotes the usage of parameterized types.
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What is an object pool in .NET?
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An object pool is a container having objects ready to be used. It tracks the object that is currently in use, total number of objects in the pool. This reduces the overhead of creating and re-creating objects.
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List down the commonly used types of exceptions in .Net?
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ArgumentException, ArgumentNullException , ArgumentOutOfRangeException, ArithmeticException, DivideByZeroException ,OverflowException , IndexOutOfRangeException ,InvalidCastException ,InvalidOperationException , IOEndOfStreamException , NullReferenceException , OutOfMemoryException , StackOverflowException etc.
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What are Custom Exceptions?
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Sometimes there are some errors that need to be handeled as per user requirements. Custom exceptions are used for them and are used defined exceptions.
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What are delegates?
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Delegates are same are function pointers in C++ but the only difference is that they are type safe unlike function pointers. Delegates are required because they can be used to write much more generic type safe functions.
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How do you inherit a class into other class in C#?
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Colon is used as inheritance operator in C#. Just place a colon and then the class name.
public class DerivedClass : BaseClass |
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What is the difference between method overriding and method overloading?
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In method overriding, we change the method definition in the derived class that changes the method behavior. Method overloading is creating a method with the same name within the same class having different signatures.
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What are the different ways a method can be overloaded?
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Methods can be overloaded using different data types for parameter, different order of parameters, and different number of parameters.
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Why can’t you specify the accessibility modifier for methods inside the interface?
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In an interface, we have virtual methods that do not have method definition. All the methods are there to be overridden in the derived class. That’s why they all are public.
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How can we set class to be inherited, but prevent the method from being over-ridden?
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Declare the class as public and make the method sealed to prevent it from being overridden.
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What happens if the inherited interfaces have conflicting method names?
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Implement is up to you as the method is inside your own class. There might be problem when the methods from different interfaces expect different data, but as far as compiler cares you’re okay.
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What is the difference between a Struct and a Class?
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Structs are value-type variables and classes are reference types. Structs stored on the stack, causes additional overhead but faster retrieval. Structs cannot be inherited.
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How to use nullable types in .Net?
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Value types can take either their normal values or a null value. Such types are called nullable types.
Int? someID = null; If(someID.HasVAlue) { } |
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How we can create an array with non-default values?
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We can create an array with non-default values using Enumerable.Repeat.
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What is difference between is and as operators in c#?
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“is” operator is used to check the compatibility of an object with a given type and it returns the result as Boolean.
“as” operator is used for casting of object to a type or a class. |
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What’s a multicast delegate?
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A delegate having multiple handlers assigned to it is called multicast delegate. Each handler is assigned to a method.
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What are indexers in C# .NET?
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Indexers are known as smart arrays in C#. It allows the instances of a class to be indexed in the same way as array.
Eg: public int this[int index] // Indexer declaration |
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What is difference between the “throw” and “throw ex” in .NET?
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“Throw” statement preserves original error stack whereas “throw ex” have the stack trace from their throw point. It is always advised to use “throw” because it provides more accurate error information.
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What are C# attributes and its significance?
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C# provides developers a way to define declarative tags on certain entities eg. Class, method etc. are called attributes. The attribute’s information can be retrieved at runtime using Reflection.
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How to implement singleton design pattern in C#?
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In singleton pattern, a class can only have one instance and provides access point to it globally.
Eg: Public sealed class Singleton { Private static readonly Singleton _instance = new Singleton(); } |
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What is the difference between directcast and ctype?
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DirectCast is used to convert the type of an object that requires the run-time type to be the same as the specified type in DirectCast.
Ctype is used for conversion where the conversion is defined between the expression and the type. |
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Is C# code is managed or unmanaged code?
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C# is managed code because Common language runtime can compile C# code to Intermediate language.
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