Understanding Interface

Interface used to establish contracts through which objects can interact with each other without knowing the implementation details.
  • Interfaces are defined by using the interface keyword.
  • An interface definition consists a set of signature for methods, delegates, events or indexers.
  • An interface cannot consist of any data fields or any implementation details such as methods body.

Icomparable interface

  • A common interface defined in the system namespace is the Icomparable. 
  • Icomparable definition:
 interface Icomparable 
{ 
        int compareTo(object obj);
}
  • The Icomparale has a single method that accepts an object and returns an int.
  • The return value of this method indicates the result of comparing the given parameter with the current object.

CompareTo method documentation

  • If the instance is equal to the parameter, CompareTo returns 0.
  • If the parameter value is less then the instance or if the parameter is equal to null then, CompareTo returns a positive value.
  • If the parameter value is greater then the instance, then a negative value is returned.
  • if the parameter is not of the compatible type, then an ArgumentException is thrown.
Interface vs Abstract
Interface and abstract are similar but there are some differences.
  • Implementation, abstract provide incomplete implemention, interface provides no implemention.
  • inherite, A class can inhirite a multiple interface but limit to one base class.
  • When you have an "is-a" relationship between the two concepts then you use abstract, on the other hand, if you there is no "is-a" relationship between then you can use interface.


You are creating a new class named Polygon. You write the following code:
class Polygon : IComparable
{
public double Length { get; set; }
public double Width { get; set; }
public double GetArea()
{
return Length * Width;
}
public int CompareTo(object obj)
{
// to be completed
}
}
You need to complete the definition of the CompareTo method to enable comparison of the
Polygon objects. Which of the following code segments should you use?
a) public int CompareTo(object obj)
{
Polygon target = (Polygon)obj;
double diff = this.GetArea() - target.GetArea();
if (diff == 0)
return 0;
else if (diff > 0)
return 1;
else return -1;
}

b) public int CompareTo(object obj)
{ Polygon target = (Polygon)obj;
double diff = this.GetArea() - target.GetArea();
if (diff == 0)
return 1;
else if (diff > 0)
return -1;
else return 0;
}

c) public int CompareTo(object obj)
{
Polygon target = (Polygon)obj;
if (this == target)
return 0;
else if (this > target)
return 1;
else return -1;
}

d) public int CompareTo(object obj)
{
Polygon target = (Polygon)obj;
if (this == target)
return 1;
else if (this > target)
return -1;
else return 0;
}

Answer: a
Difficulty: Medium
Section Reference: Understanding Interfaces
The return value of the CompareTo method indicates the result of comparing the given
parameter with the current object. According to the documentation of the CompareTo
method,
• If the instance is equal to the parameter, CompareTo returns 0.
• If the parameter value is less than the instance or if the parameter is null, a positive
value is returned.
• If the parameter value is greater than the instance, a negative value is returned.
• If the parameter is not of the compatible type, an ArgumentException is thrown.

5. You need to provide printing functionality to several of your classes. Each class’s algorithm for printing will likely be different. Also, not all the classes have an “is-a” relationship with each other. How should you support this functionality?

a) Add the print functionality to a base class with the public access modifier.
b) Have all classes inherit from an abstract base class and override the base-class method to provide their own print functionality.
c) Have all the classes inherit from a base class that provides the print functionality.
d) Create a common interface that all classes implement.


Answer: d
Difficulty: Medium
Section Reference: Understanding Interfaces
You should create a common interface that is implemented by all classes. Interfaces are used to establish contracts through which objects can interact with each other without knowing the implementation details.


  

Comments

Post a Comment

Popular posts from this blog

Understanding Encapsulation

Encapsulation Is an information-hiding mechanism that makes code easy to maintain and to understand.  Encapsulation is a mechanism to hide a class or members of a class in order to hide design decisions that are likely to change. Encapsulation gives the class designer the flexibility to change some section of the code without changing all of the other code that makes use of that code.  Properties are a great way to hide data fields. Understanding Access Modifiers Access modifiers control where a type or type member can be used. All types and type members have an access level that specifies where that class or its members can be used in your code. Public Access is not restricted. Private Access is restricted to the containing class. Protected Access is restricted to the containing class and to and class that derived directly or indirectly from the containing class. Internal Access is restricted to the ...
Read more

Understanding Polymorphism

Image
Polymorphism is the ability of the derived classes to share common functionality with base classes but still define their own unique behaviour. You are developing an application that allows users to work with a different kind of polygon.  You have a collection that store a different type of polygons, such as Rectangle, Triangle and square. Each polygon provides its own implementation of the method Draw. When working with the collection you don't necessarily know exactly which shape you are working with, but you would like the correct Draw method to be invoked each time.  polymorphism enable you to do it.    Polymorphism allows the objects of the derived class to be treated at runtime as objects of the base class. Understanding the Override and New Keywords The override keyword replaces a base class member in a derived class. 3. You created a class named GeoShape. You defined a method called Area in the Ge...
Read more

Understanding Static Members

Image
Static members  belong to the class itself rather than individual objects. Instance members They can be used only after an instance of a class is created. Static members Is used to declared members that do not belong to individual objects but to a class itself. one common example is the main method that serves as the entry point. Static members belong to the class itself, not the instance that created from the class.  When an instance of a class created A separate copy is created for each instance field. But only one copy of static field is shared by all instance. All things that you create are non-static by default. What can you make static Classes Method properties What static means: Does not belong to any object instance created, it belongs to the class itself. A class is a template and object is created from that template so it's instantiated from that template. that is the class. When we make som...
Read more