Chapter 6: OOPS
What is Object Oriented Programming?
It is a problem solving technique to develop software systems. It is a technique to think real world in terms of objects. Object maps the software model to real world concept. These objects have responsibilities and provide services to application or other objects.
What is a Class ?
A class describes all the attributes of objects, as well as the methods that implement the behavior of member objects. It’s a comprehensive data type which represents a blue print of objects. It’s a template of object.
What’s an Object?
It is a basic unit of a system. An object is an entity that has attributes, behavior, and identity. Objects are members of a class. Attributes and behavior of an object are defined by the class definition.
What is the relation between Classes and Objects?
They look very much same but are not same. Class is a definition, while object is a instance of the class created. Class is a blue print while objects are actual objects existing in real world.
What are different properties provided by Object-Oriented systems?
Following are characteristics of Object Oriented Systems:
- Abstraction It allows complex real world to be represented in simplified manner. Example color is
abstracted to RGB. By just making the combination of these three colors we can achieve any color in world. It’s a model of real world or concept.
- Encapsulation It is a process of hiding all the internal details of an object from the outside world.
- Communication using messages When application wants to achieve certain task it can only be done using combination of objects. A single object cannot do all the task. Example if we want to make order processing form. We will use Customer object, Order object, Product object and Payment object to achieve this functionality. In short these objects should communicate with each other. This is achieved when objects send messages to each other.
- Object lifetimeAll objects have life time.Objects are created ,and initialized, necessary functionalities
are done and later the object is destroyed. Every object have their own state and identity which differ from instance to instance.
- Class hierarchies (Inheritance and aggregation) In object-oriented world objects have relation and hierarchies in between them. There are basically three kind of relationship in Object Oriented world : association – the simplest relationship between objects. example every customer has sales. So Customer object and sales object have an association relation between them; aggregation – also called as composition model. example in order to make a “Accounts”class it has use other objects example “Voucher”, “Journal” and “Cash” objects. So accounts class is aggregation of these three objects.
- Inheritance Hierarchy is used to define more specialized classes based on a preexisting generalized
class. Example we have VEHICLE class and we can inherit this class make more specialized class like CAR, which will add new attributes and use some existing qualities of the parent class. Its shows more of a parent-child relationship. This kind of hierarchy is called inheritance.
- Polymorphism When inheritance is used to extend a generalized class to a more specialized class, it
includes behavior of the top class(Generalized class). The inheriting class often implement a behavior that can be somewhat different than the generalized class, but the name of the behavior can be same. It is important that a given instance of an object use the correct behavior, and the property of polymorphism allows this to happen automatically.
Chapter 4: Remoting and Webservices
Chapter 5: Caching Concepts