Object Oriented Programming

Object Oriented Programming

1. Class

   • A class is a blueprint that helps create objects of similar types. All program elements in Java must be under a class.
   • Constructor
     • A constructor is used to construct an object. Every class must have at least one constructor. A constructor looks like a method, but does not have a return value. A constructor may have zero argument, in which case it is called a noargument constructor. Constructor arguments can be used to initialize the fields in the object.

2. Object

   • Objects have two features: attributes and actions that they are able to perform. Attributes are called fields and actions are called methods. Both fields and methods are optional; an object may have one, both, or neither. To create objects, you need classes.
   • Fields
     • Variables; can be primitives or references to other objects. The initial of each word in a field is capitalized, except for the first word (e.g. newAddress)
   • Methods
     • Methods define the actions that an object can perform. A method has a declaration part (which contains a return value, a method name, and a list of arguments) and a body (which contains the code that performs the action).
     • main
       • A special method that provides and entry point to the application.
     • null
       • When a reference variable does not have an output.

3. UML Class Diagram

   • A UML Class Diagram summarizes the fields and methods of the classes/objects of a program.