Types

Overview

• Data Types
• Object-type
• Variable Initialization / Assignment Statements
• Variable Declaration
• Variable Instantation
• Casting

Data Types

• In Object Oriented Programming (OOP) languages, “Everything is an Object”.
• The simplest program one could write is named the "Hello, World!" program

print("Hello, World!")

Object Type

• In Object Oriented Programming, an object is any value in memory referenced by an identifier.
• An object can be a
  • variable
  • data structure
  • function
  • method
• Because “everything is an object”, all variables can be assigned to the Object type.
• A type is the name of the class of an object.
• A class is a template, or blueprint from which objects are created
  • it is the cookie-cutter to a cookie
  • it is the classification of an object.
• An object is an instance of a class.
• All objects have the following three traits:
  • objects have a state
  • objects have behaviors
  • objects have an identity

age = 27
age_greeting = "My age is "        
age_output = age_greeting + age

print(nameOutput)

• Output

My age is 27

Variable Initialization

• Any expression which states a variable type, a variable name, an equal operator (=), followed by a variable value, is considered an assignment statement.
• All assignment statements result in variable initialization or reinitialization.
  • General Syntax: variable_name = ${some-value-here}
  • Example 1: age = 27;
  • Example 2: name = "Leon Hunter"
  • Example 3: account_balance = 999999.99

Why is Type relevant?

• The declared type of a variable determines which behaviors it will be able to perform.
• In OOP, methods denote behavior.
• Methods are functions defined within the scope of a class.
• In pure OOP languages, all functionality is achieved through methods, not functions.

Notable Object Behaviors

• The two most notable object behaviors are .toString() and .equals()

.toString()

• An Object can convert to string

age_as_integer = 27
age_as_string = age_as_integer.toString()

.equals()

• An Object can compare its equivalence

age_as_integer = 27
age_as_string = str(age_as_integer)
are_objects_equal = age_as_integer.equals(age_as_string)

What is Casting?

• Because the declared type of a variable determines which behaviors it will be able to perform, assigning variables to Object gives access to very few behaviors.
• An Object can be treated as a more-specific type through a mechanism called down-casting.
  • Downcasting gives access to more behaviors.
• An Object can be treated as a less-specific type through a mechanism called up-casting.
  • Upcasting restricts access to more-specific behaviors.

How to Cast

• Example 1:

age_as_string = "27"
age_as_integer = int(age_as_string)
age_as_integer_type = type(age_as_integer)
age_as_string_type = type(age_as_string)

print(age_as_integer_type)
print(age_as_string_type)

• Example 2:

is_name_leon = "true"
age_as_integer_type = type(age_as_integer)
age_as_string_type = type(age_as_string)

print(age_as_integer_type)
print(age_as_string_type)

• Example 2:

nameAsObject = object("Leon Hunter")
nameAsString = str(nameAsObject)

More Casting examples

• Example 1:

 ageAsInteger = int("27")

• Example 2:

isMaleBoolean = bool("true")

• Example 2:

nameAsString = str("Leon Hunter")