Object-oriented Concepts

Benefits of Object Technology

• It leads to reuse, and reuse (of program components) leads to faster software development and higher-quality programs. 
• It leads to higher maintainability of software modules because its structure is inherently decoupled.
• It leads to object-oriented system that are easier to adapt and easier to scale, ie, large systems are created by assembling reusable subsystems.

Object

• It is a representation of an entity either physical, conceptual, or software.
• It allows software developers to represent real-world concepts in their software design.
• It is an entity with a welldefined boundary and identity that encapsulates state and behavior.             

Object's State

• It is one of the possible conditions that an object may exists in.
• It is implemented by a set of properties called attributes, along with its values and the links it may have on other objects.

Object's Behavior

• It determines how an object acts and reacts.
• It is represented by the operations that the object can perform.

Object's Identity

• Although two objects may share the same state (attributes and relationships), they are separate, independent objects with their own unique identity.

Four Basic Principles of Object-orientation

• Abstraction
• Encapsulation
• Modularity
• Hierarchy

Abstraction

• Abstraction is a kind of representation that includes only the things that are important or interesting from a particular point of view.
• It is the process of emphasizing the commonalities while removing distinctions.
• It allows us to manage complexity systems by concentrating on the essential characteristics that distinguish it from all other kinds of systems.
• It is domain and perspective dependent.

Sample Abstraction

• An applicant submits a club membership application to the club staff.
• A club staff schedules an applicant for the mock try-outs.
• A coach assigns an athlete to a squad.
• A squad can be a training or competing squad.
• Teams are formed from a squad.

Encapsulation

• Encapsulation localizes features of an entity into a single blackbox abstraction, and hides the implementation of these features behind a single interface.
• It is also known as information-hiding; it allows users to use the object without knowing how the implementation fulfils the interface.
• It offers two kinds of protection: it protects the object's state from being corrupted and client code from changes in the object's implementation.

Encapsulation Illustrated

● Juan de la Cruz needs to change his year level.

● The key is in the message interface.

Modularity

• Modularity is the physical and logical decomposition of large and complex things into smaller and manageable components that achieve the software engineering goals.
• It is about breaking up a large chunk of a system into small and manageable subsystems. The subsystems can be independently developed as long as their interactions are well understood.

Hierarchy

• Any ranking or ordering of abstractions into a tree-like structure.
• Kinds of Hierarchy
• Aggregation
• Class
• Containment
• Inheritance
• Partition
• Specialization
• Type

Hierarchy Illustrated

Generalization

• It is a form of association wherein one class shares the structure and/or behavior of one or more classes.
• It defines a hierarchy of abstractions in which a subclass inherits from one or more superclasses.
• Single Inheritance
• Multiple Inheritance
• It is an is a kind of relationship.

Inheritance

• It is a mechanism by which more-specific elements incorporate the structure and behavior of moregeneral elements.
• A class inherits attributes, operations and relationship.

Polymorphism

• It is the ability to hide many different implementation behind a single interface.
• It allows the same message to be handled differently by different objects.

Interface

• It formalizes polymorphism. It defines polymorphism in a declarative way, unrelated to implementation.
• It is the key to the plug-n-play ability of an architecture.

Aggregation

• It is a special form of association that models a whole-part relationship between an aggregate (whole) and its parts.