OOP: object-oriented programming

OOP: object-oriented programming

1. objects

   • living eg: people
   • concrete eg: book

2. object

   • living eg: people
   • concrete eg: book
   • abstract eg: idea

3. class--serve as template in programming, to create identical type of objects

   • using Pascal naming convention
   • class definition, use the same name as class
     • eg: Employee.java for class Employee

4. field (attributes for objects), using Pascal naming convention, Capitalize the initials

   • variables : primitives/references to objects

5. method (actions for objects) , using camel naming convention, capitalize all initials except the first word

   • actions objects do
   • declaration of methods is called signature of methods
   • method main
     • entry to an application
     • arguments written as string

6. return type: primitive/ object/ void (nothing to return)

7. UML diagram

   • class name on the top, lists of fields in the middle and methods in the bottom
   • have to have a comma between field and type , arguments as a string , return type is written after colon

8. constructor

   • each class has to have a constructor
     • have to use the same name as class
   • no-argument constructor
     • constructor has no argument

9. the null keyword

   • not referencing any object
     • "null" will be assigned when declaring a local reference variable within a method but do not sign object to it
     • the "==" operator for testing if a reference variable is null

10. create objects

    • objects also refer to instance
    • instantiate
      • use "new" keyword, declare object reference with the same type as object, assign values