OOP - Objects and Classes

OOP - Objects and Classes

1. Java Objects

   • have attributes
     • known as fields - fields are optional
   • can perform actions
     • known as methods - methods are optional
   • also called an instance

2. Class

   • a blueprint or template to create objects of a similar type
   • class name
     • capitalize the initial of each word - Pascal naming convention
   • fields
     • variables
       • primitives
       • references to other objects
     • follow the camel naming convention
       • first initial of each word, except the first, is capitalized
   • methods
     • define actions that a class's objects can do
     • declaration
       • return value
         • void
           • the method returns nothing
         • object
         • primitive
       • method name
       • list of arguments
     • body
       • contains code to perform an action
     • the special method main provides the entry point to an application
   • represented by a rectangle in UML class diagrams
   • constructors
     • used to construct an object
     • is sometimes called a constructor method
     • has no return
     • may have zero argument
   • creating an object from a class
     • "construct" or "instantiate"
     • new keyword following by the constructor of the class
     • can assign a created object to an object variable (or reference variable)
       • can call an object's methods and fields by using the object reference
       • null = when a reference variable does not have a value

3. UML Class Diagrams

   • provides a quick summary of fields and methods
     • can include field types and method signatures