C# And .net Questions

Front 1

What is a Class?

Back 1

A class is a construct that enables you to create your own custom types by grouping together variables of other types, methods and events. A class is like a blueprint. It defines the data and behavior of a type. If the class is not declared as static, client code can use it by creating objects or instances which are assigned to a variable. The variable remains in memory until all references to it go out of scope. At that time, the CLR marks it as eligible for garbage collection. If the class is declared as static, then only one copy exists in memory and client code can only access it through the class itself, not an instance variable.

A class is a reference type.

public class Customer
{
//Fields, properties, methods and events go here...
}

Front 2

What members can a class contain?

Back 2

Constructors
Destructors
Fields
Methods
Properties
Indexers
Delegates
Events
Nested Classes

Front 3

What is a struct?

Back 3

A struct type is a value type that is typically used to encapsulate small groups of related variables, such as the coordinates of a rectangle or the characteristics of an item in an inventory.
The declaration of a struct takes the following form:

// keyword_struct.cs
// struct declaration and initialization
using System;
public struct Point
{
public int x, y;

public Point(int p1, int p2)
{
x = p1;
y = p2;
}
}

class MainClass
{
public static void Main()
{
// Initialize:
Point myPoint = new Point();
Point yourPoint = new Point(10,10);

// Display results:
Console.Write("My Point: ");
Console.WriteLine("x = {0}, y = {1}", myPoint.x, myPoint.y);
Console.Write("Your Point: ");
Console.WriteLine("x = {0}, y = {1}", yourPoint.x, yourPoint.y);
}
}

Front 4

What members can a struct contain?

Back 4

Structs can also contain constructors, constants, fields, methods, properties, indexers, operators, events, and nested types, although if several such members are required, you should consider making your type a class instead.

Front 5

What is a interface?

Back 5

Interfaces describe a group of related functionalities that can belong to any class or struct. You define an interface by using the interface keyword, as shown in the following example.

interface IEquatable<T>
{
bool Equals(T obj);
}
Interfaces consist of methods, properties, events, indexers, or any combination of those four member types. An interface cannot contain constants, fields, operators, instance constructors, destructors, or types. It cannot contain static members. Interfaces members are automatically public, and they cannot include any access modifiers.

When a class or struct implements an interface, the class or struct provides an implementation for all of the members defined by the interface. The interface itself provides no functionality that a class or struct can inherit in the way that base class functionality can be inherited. However, if a base class implements an interface, the derived class inherits that implementation. The derived class is said to implement the interface implicitly.

Classes and structs implement interfaces in a manner similar to how classes inherit a base class or struct, with two exceptions:

A class or struct can implement more than one interface.

When a class or struct implements an interface, it receives only the method names and signatures, because the interface itself contains no implementations,

Front 6

What members can a interface contain?

Back 6

Interfaces consist of methods, properties, events, indexers, or any combination of those four member types. An interface cannot contain constants, fields, operators, instance constructors, destructors, or types. It cannot contain static members. Interfaces members are automatically public, and they cannot include any access modifiers.

Front 7

Where are classes allocated?

Back 7

A Reference Type always goes on the Heap.

Front 8

Where are structs allocated?

Back 8

Now, Value Types are also sometimes placed on the Heap. Remember the rule, Value Types always go where they were declared? Well, if a Value Type is declared outside of a method, but inside a Reference Type it will be placed within the Reference Type on the Heap.

Front 9

What is an enum?

Back 9

The enum keyword is used to declare an enumeration, a distinct type consisting of a set of named constants called the enumerator list. Every enumeration type has an underlying type, which can be any integral type except char. The default underlying type of the enumeration elements is int. By default, the first enumerator has the value 0, and the value of each successive enumerator is increased by 1.

Front 10

What is an enum's default underlying type?

Back 10

The default underlying type of the enumeration elements is int. By default, the first enumerator has the value 0, and the value of each successive enumerator is increased by 1

Front 11

What is the difference between a property and a method?

Back 11

Properties are a useful way of expressing a feature of an object, allowing get/set in a common way that can be used by APIs like data-binding, reflection and serialization. So for simple values of the object, properties are handy. Properties can't take arguments, should not have significant side-effects*, and should return quickly and repeatably. Also, there is no such thing as an "extension property" (to mirror an extension method) nor a generic property.

(*=lazy loading etc isn't uncommon, however)

Methods (C# doesn't have functions) are better for expressing things that either change the state, or which have an expectation of taking some time and not necessarily being reproducible. They don't tend to work in binding / serialization etc.

Note that properties are actually just a special way of writing methods. There is little functional difference. It is all about expressing intent. The one thing you don't want to expose, however, is fields (the actual intEmployeeAge instance variable).

Front 12

What is a field?

Back 12

A field is a variable of any type that is declared directly in a class or struct. Fields are members of their containing type.

A class or struct may have instance fields or static fields or both. Instance fields are specific to an instance of a type. If you have a class T, with an instance field F, you can create two objects of type T, and modify the value of F in each object without affecting the value in the other object. By contrast, a static field belongs to the class itself, and is shared among all instances of that class. Changes made from instance A will be visibly immediately to instances B and C if they access the field.

Generally, you should use fields only for variables that have private or protected accessibility. Data that your class exposes to client code should be provided through methods, properties and indexers. By using these constructs for indirect access to internal fields, you can guard against invalid input values. A private field that stores the data exposed by a public property is called a backing store or backing field.

Fields typically store the data that must be accessible to more than one class method and must be stored for longer than the lifetime of any single method. For example, a class that represents a calendar date might have three integer fields: one for the month, one for the day, and one for the year. Variables that are not used outside the scope of a single method should be declared as local variables within the method body itself.

Fields are declared in the class block by specifying the access level of the field, followed by the type of the field, followed by the name of the field.

Front 13

What modifier is used to specify a variable argument list?

Back 13

The params keyword lets you specify a method parameter that takes an argument where the number of arguments is variable.
// cs_params.cs
using System;
public class MyClass
{

public static void UseParams(params int[] list)
{
for ( int i = 0 ; i < list.Length ; i++ )
Console.WriteLine(list[i]);
Console.WriteLine();
}

public static void UseParams2(params object[] list)
{
for ( int i = 0 ; i < list.Length ; i++ )
Console.WriteLine(list[i]);
Console.WriteLine();
}

public static void Main()
{
UseParams(1, 2, 3);
UseParams2(1, 'a', "test");

int[] myarray = new int[3] {10,11,12};
UseParams(myarray);
}
}

Front 14

What parameter types are used to contain the variable argument list?

Back 14

params int[] ints

Front 15

What is the difference between the ref and the out parameter modifiers?

Back 15

The ref keyword causes arguments to be passed by reference. The effect is that any changes to the parameter in the method will be reflected in that variable when control passes back to the calling method.
The out keyword causes arguments to be passed by reference. This is like the ref keyword, except that ref requires that the variable be initialized before it is passed. To use an out parameter, both the method definition and the calling method must explicitly use the out keyword.

Front 16

What is the reserve word this used for.

Back 16

The this keyword refers to the current instance of the class and is also used as a modifier of the first parameter of an extension method.

Front 17

What is the reserve word base used for.

Back 17

The base keyword is used to access members of the base class from within a derived class:

Call a method on the base class that has been overridden by another method.

Specify which base-class constructor should be called when creating instances of the derived class.

A base class access is permitted only in a constructor, an instance method, or an instance property accessor.

It is an error to use the base keyword from within a static method.

The base class that is accessed is the base class specified in the class declaration. For example, if you specify class ClassB : ClassA, the members of ClassA are accessed from ClassB, regardless of the base class of ClassA.