Objects & Classes

Objects & Classes

1. Objects

   • Fields
     • Called by objectReference.fieldName
   • Methods
     • Called by objectReference.methodName
   • Instance
     • Keyword 'new' to create a new entry or instance of the object
   • Reference variable
     • Keyword 'null'; variable holds no value
       • Test 'null' by using '==' operator

2. Classes

   • Fields
     • Variables; Primitive or references to objects
   • Class name
     • camelCase naming convention
   • Methods
     • Declaration part; aka signature of the method
       • Return value
         • Primitive
         • Object
         • Void
           • Returns nothing
       • Method name
         • Method main invokes the class containing it
       • List of arguments
         • If more than 1, it is separated by a comma
     • Body
       • Code that performs the action
   • Constructors
     • Name
       • Same as the class
     • List of arguments
       • Can contain 0 args = 'no-arg'
   • UML diagram
     • Depicts fields & methods in a class
   • Reference variables are initialized once an instance is created
     • Keyword 'null' is not needed