procedural - example

def power(a, b):
    r = a
    for _ in range(b - 1):
        r *= r
    return r

a = 3
a = power(a, 3)

1. abstraction

• hiding the complex reality while exposing only the necessary parts
• allows to focus on interactions at a higher level without needing to understand the details of the implementation
• often achieved through abstract classes and interfaces, which define a contract for what methods an object must implement without specifying how they should be implemented

2. encapsulation

• bundling data (attributes) and methods (functions) that operate on that data into a single unit
• this property restricts direct access to some of the object’s components
  • private, public, protected
• can preventing unintended interference and misuse of the methods and data
  • by exposing only the necessary parts of an object through public methods

3. inheritance

• a mechanism that allows one class (subclass or derived class) to inherit attributes and methods from another class (superclass or base class)
• this is said to promote code reusability, as common functionality can be defined in a base class and reused in derived classes
• results hierarchical relationship which can foster modular design
  • also increases dependency

class-based inheritance

• class-orientated, or class-based programming
  • inheritance via classes of objects,
  • instead of inheritance via the objects alone
• every object is defined by a class
  • which is like a definition or a blueprint
  • describes the structure and behavior of an object
• most common

prototype based inheritance

The object function untangles JavaScript’s constructor pattern, achieving true prototypal inheritance. It takes an old object as a parameter and returns an empty new object that inherits from the old one. If we attempt to obtain a member from the new object, and it lacks that key, then the old object will supply the member. Objects inherit from objects. What could be more object oriented than that?

Douglas Crockford

OO without inheritance

• Go does not support inheritance at all, though it is considered object-oriented
  • at least partially [Go FAQ]
• Bjarne Stroustrup (author of C++) has stated that it is possible to do OOP without inheritance [1]

4. polymorphism

• allows objects to be treated as instances of their parent class
• enables flexibility in code, allowing for methods to perform differently based on the object that invokes them
  • method defined in a base class can be overridden in a derived class to provide specific behavior

bounding together data and functions

class Something:
    foo = 0
    
    def increase(self, by):
        self.foo += by
    
something = Something()
print(something.foo)  # 0
something.increase(2)
print(something.foo)  # 2

why OO got popular?

elements of the use case diagram

use case diagram - example

use case diagram - example

use case diagram - example

(most common) elements of a class diagram

relations

• association: structural relationship
  • allows one object instance to cause another to perform an action on its behalf
• realization: e.g., class implements a interface
• aggregation: “has a” relation
  • without life cycle control
• composition: stronger form of aggregation
  • where the aggregate controls the lifecycle of the elements

class diagram - example

class diagram - example

state diagram elements

state diagram - example

parallel processing

a join synchronizes two inflows (waits for the slower)

merge after condition

swimlanes