Object-Oriented Programming

Object-Oriented Programming

1. Objects

   • Two features: attributes (fields) and actions it can perform (methods)
     • An object could have one, none, or both of these

2. Models Applications on Real World Objects

3. Classes

   • Objects
     • An object can contain another object
     • "new" keyword creates new objects
     • A reference variable without an object must be assigned null
   • Template to create objects of that type
   • Tool to create abstractions of a problem
   • Consider the class name, fields, and methods when writing a class
     • Fields
       • Variable. Either primitive or reference to an object
     • Methods
       • Define actions that a class's objects can do
       • Has a declaration part and a body
         • Declaration consists of name, return type, list of arguments
         • Body contains code
       • Can return a primitive, object, or void
         • Void means it return nothing
       • The main method
         • Provides the entry point to a appliction
     • Constructors
       • Every class must have a constructor to construct its objects
       • Looks like a method, but returns nothing