1.Does C#
support multiple-inheritance?
No. But you can use Interfaces.
2.Where is a protected class-level variable available?
It is available to any sub-class derived from base class
3.Are private class-level variables inherited?
Yes, but they are not accessible.
4.Describe the accessibility modifier “protected internal”.
It is available to classes that are within the same assembly and derived from
the specified base class.
6.Which class is at the top of .NET class hierarchy?
System.Object.
7.What does the term immutable mean?
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.
8.What’s the difference between System.String and System.Text.StringBuilder
classes?
System.String is immutable.
System.StringBuilder was designed with the purpose of having a mutable string
where a variety of operations can be performed.
9.What’s the advantage of using System.Text.StringBuilder over System.String?
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.
10.Can you store multiple data types in System.Array?
No.
11.What’s the difference between the System.Array.CopyTo() and
System.Array.Clone()?
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.
12.How can you sort the elements of the array in descending order?
By calling Sort() and then Reverse() methods.
13.What’s the .NET collection class that allows an element to be accessed using
a unique key?
HashTable.
14.What class is underneath the SortedList class?
A sorted HashTable.
15.Will the finally block get executed if an exception has not occurred?
Yes.
16.What’s the C# syntax to catch any possible exception?
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 {}.
17.Can multiple catch blocks be executed for a single try statement?
No. Once the proper catch block processed, control is transferred to the
finally block .
18.Explain the three services model commonly know as a three-tier application?
Presentation (UI), Business (logic and underlying code) and Data (from storage
or other sources).
Class Questions
1.What is the syntax to inherit from a class in C#?
Place a colon and then the name of the base class.
Example: class MyNewClass : MyBaseClass
2.Can you prevent your class from being inherited by another class?
Yes. The keyword “sealed” will prevent the class from being inherited.
3.Can you allow a class to be inherited, but prevent the method from being
over-ridden?
Yes. Just leave the class public and make the method sealed.
4.What’s an abstract class?
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.
5.When do you absolutely have to declare a class as abstract?
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.
6.What is an interface class?
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.
7.Why can’t you specify the accessibility modifier for methods inside the
interface?
They all must be public, and are therefore public by default.
8.Can you inherit multiple interfaces?
Yes. .NET does support multiple interfaces.
9.What happens if you inherit multiple interfaces and they have conflicting
method names?
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.
10. What’s the difference between an interface and abstract class?
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.
11. What is the difference between a Struct and a Class?
Structs are value-type variables and are thus saved on the stack, additional
overhead but faster retrieval. Another difference is that structs cannot
inherit.
Method and Property Questions
1. What’s the implicit name of the parameter that gets passed into the set
method/property of a class?
Value. The data type of the value parameter is defined by whatever data type
the property is declared .
2. What does the keyword “virtual” declare for a method or property?
The method or property can be overridden.
3. How is method overriding different from method overloading?
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.
4. Can you declare an override method to be static if the original method is
not static?
No. The signature of the virtual method must remain the same. (Note: Only the
keyword virtual is changed to keyword override)
5. What are the different ways a method can be overloaded?
Different parameter data types, different number of parameters, different order
of parameters.
6. 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?
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.
Events and Delegates
1. What’s a delegate?
A delegate object encapsulates a reference to a method.
2. What’s a multicast delegate?
A delegate that has multiple handlers assigned to it. Each assigned handler
(method) is called.
3. What’s the implicit name of the parameter that gets passed into the class’
set method?
Value, and it’s datatype depends on whatever variable we’re changing.
4. How do you inherit from a class in C#?
Place a colon and then the name of the base class.
5. Does C# support multiple inheritance?
No, use interfaces instead.
6. When you inherit a protected class-level variable, who is it available to?
Classes in the same namespace.
7. Are private class-level variables inherited?
Yes, but they are not accessible, so looking at it you can honestly say that
they are not inherited.
8. Describe the accessibility modifier protected internal.?
It’s available to derived classes and classes within the same Assembly (and
naturally from the base class it’s declared in).
9. 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?
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.
10. What’s the top .NET class that everything is derived from?
System.Object.
11. 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.
12. What does the keyword virtual mean in the method definition?
The method can be over-ridden.
13. Can you declare the override method static while the original method is
non-static?
No, you can’t, the signature of the virtual method must remain the same, only
the keyword virtual is changed to keyword override.
14. Can you override private virtual methods?
No, moreover, you cannot access private methods in inherited classes, have to
be protected in the base class to allow any sort of access.
15. 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.
16. Can you allow class to be inherited, but prevent the method from being
over-ridden?
Yes, just leave the class public and make the method sealed.
17. What’s an abstract class?
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.
18. When do you absolutely have to declare a class as abstract (as opposed to
free-willed educated choice or decision based on UML diagram)?
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.
19. What’s an interface class?
It’s an abstract class with public abstract methods all of which must be
implemented in the inherited classes.
20. Why can’t you specify the accessibility modifier for methods inside the
interface?
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.
21. Can you inherit multiple interfaces?
Yes, why not.
22. And if they have conflicting method names?
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.
23. What’s the difference between an interface and abstract class?
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.
24. How can you overload a method?
Different parameter data types, different number of parameters, different order
of parameters.
25. 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?
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.
26. What’s the difference between System.String and System.StringBuilder
classes?
System.String is immutable, System.StringBuilder was designed with the purpose
of having a mutable string where a variety of operations can be performed.
27. Is it namespace class or class namespace?
The .NET class library is organized into namespaces. Each namespace contains a
functionally related group of classes so natural namespace comes first.
28. difference between stacks and heaps ?
‘Stack’ is a common name for the memory space in which
automatic variables (and often function parameters) are allocated.
‘Heap’ is a common name for the “free store”, the memory
space where dynamic objects are allocated (see “new” and “delete”).
The stack is used to
allocate temporary objects while the heap is used by a programmer to reserve
allocation. Basicly,
an object in a heap is not scope
dependent, it dies when you tell it to. Meanwhile, an object on the stack is
destroyed automatically when its scope ends.
The scope of memory allocated on the ‘stack’ is the scope
of the enclosing block. They get destroyed when the enclosing
block is finished. Thats why they are called ‘auto’ objects.
Example:
{
int i;
} // block ends, i gets destroyed
The scope of memory allocated on the ‘heap’ is different.
Objects
get allocated with new (or malloc) and get destroyed when a corresponding
delete (or free) is executed. Blocks do no longer influence the scope of
these objects.
Example:
int* pJ;
{
int* pI = new int [20];
// Note that
2 things are happening here:
// 1.) An int array is allocated on the free store (aka heap).
// This array will be there until a corresponding delete [] is
// executed
// 2.) A variable pI is created. Since pI was not dynamically created
// with new or malloc, it is an auto object (created on the stack)
// Thus the enclosing block determines its lifetime
pJ = pI;
} // block
ends. pI gets destroyed, but not so the int array. It
// will stay there in memory until a delete is done.
delete []
pJ; // now the memory in the free store (aka heap) gets released.
Free store allocation usually takes more time
