जगदीश खोलिया: Few Object Oriented Question

Tuesday, May 15, 2012

Few Object Oriented Question

1. Can we call a base class method without creating instance?
Answer :
Its possible If its a static method.
Its possible by inheriting from that class also.
Its possible from derived classes using base keyword.

2. What is Method Overriding? How to override a function in C#?
Answer :
Use the override modifier to modify a method, a property, an indexer, or an event. An override method provides a new implementation of a member inherited from a base class. The method overridden by an override declaration is known as the overridden base method. The overridden base method must have the same signature as the override method.
You cannot override a non-virtual or static method. The overridden base method must be virtual, abstract, or override

3. What’s an abstract class?
Answer :
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.

4. When do you absolutely have to declare a class as abstract?
Answer :
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.

5. What is an interface class?
Answer :
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.

6. What happens if you inherit multiple interfaces and they have conflicting method names?
Answer :
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 it is okay.

7. What’s the difference between an interface and abstract class?
Answer :
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.

8. How is method overriding different from method overloading?
Answer :
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.

9. 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?
Answer :
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.

10. What are the different ways a method can be overloaded?
Answer :
Different parameter data types, different number of parameters, different order of parameters.

11. Can you prevent your class from being inherited by another class?
Answer :
Yes. The keyword “sealed” will prevent the class from being inherited.

12. What’s the C# syntax to catch any possible exception?
Answer :
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 {}

13. What’s the difference between the System.Array.CopyTo() and System.Array.Clone()?
Answer :
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.

14. What’s the advantage of using System.Text.StringBuilder over System.String?
Answer :
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.

15. What’s the difference between System.String and System.Text.StringBuilder classes?
Answer :
System.String is immutable. System.StringBuilder was designed with the purpose of having a mutable string where a variety of operations can be performed.

16. What does the term immutable mean?
Answer :
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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