OOP: Inheritance & Polymorphism

Table of Content

  1. Our Journey Thus Far...
  2. Inheritance
  3. Polymorphism
  4. Benefits & Use Cases

OUR OOP JOURNEY THUS FAR...

WHAT HAVE WE LEARNT SO FAR?

  • Intro to OOP Concepts by Asyrul
    • Understanding OOP
    • Why OOP
    • Encapsulation
    • Abstraction
    • Inheritance
    • Polymorphism

Inheritance

  • Build a class based on a another class

  • "Is-a" relationship

  • The child class inherit all methods & properties from the super class

  • Allows code re-usability & reduce code duplication

Inheritance

class RegexRemover extends Command {
  constructor(protected regex: RegExp) {
    super();
  }
  execute(text: string): string {
    return text.replace(this.regex, '');
  }
}
class RemoveExtraWhitespaces extends RegexRemover {
  constructor() {
    super(/\s\s+/g);
  }
}
const remover = new RemoveExtraWhitespaces();
const clean = remover.execute(
  'The dog      has a long   tail, and it     is RED!',
);
console.log(clean);
// prints 'The dog has a long tail, and it is RED!'

abstract class Command {
  abstract execute(text: string): string;
}

Types of Inheritance

However, just simply creating a subclass which inherit a superclass does not mean you're applying OOP correctly...

Polymorphism

  • Poly (many) morphism (forms).

  • Allows different data types to be handled using a uniform interface

  • Specify discrete logic for each specific child class

  • Program to interface instead of to concrete class

  • Allows Iterate through a list of child classes

Example

Overview Interfaces

let text = 'The dog      has a long   tail, and it    @ is RED!'

const commands: Commands[] = [];


commands.push(new RemoveWhitespaces());
commands.push(new RemoveInvalid());



for(const command of commands){
  text = command.execute(text);
}

console.log(text); 
// The dog has a long tail, and it is RED!

Program to Interface

interface / base class

derived classes

iteration & use common interface

BENEFITS &

USE CASES

So when should we use Inheritance & Polymorphism?

Summary

Use the right tools for the job..

Animal

Vehicle

is-a

implements ridable

Ridable

abstract class Command {
  abstract execute(text: string): string;
}
interface Hookable {
  onRead?: (text: string) => string;
  onProcess?: (text: string) => string;
  onWrite?: (text: string) => void;
}

Use Case: Hookable Interface

class RemoveExtraWhitespaces 
  extends Command 
  implements Hookable {
    
  execute(text: string): string {
    const regex = new RegExp(/\s\s+/g);
    return text.replace(regex, '');
  }
  
  onProcess(text: string): string {
    return text.toUpperCase();
  }
}
class MySqlWriter
  extends Writer 
  implements Hookable {
    
  protected client: MySqlClient;
  constructor(conn: MySqlConnection, 
               protected tableName: string) {
    this.client = new MySqlClient(con)
  }
    
  write(text: string) {
    this.client.write(this.tableName, text);
  }
  
  onWrite(text: string): void {
    this.logger.log('Wrote to ES')
  }
}
abstract class Writer {
  abstract write(text: string): void;
}
class RemoveExtraWhitespaces 
  extends Command {
    
    
  execute(text: string): string {
    const regex = new RegExp(/\s\s+/g);
    return text.replace(regex, '');
  }
  

    
    
}
class MySqlWriter
  extends Writer {
    
    
  protected client: MySqlClient;
  constructor(conn: MySqlConnection, 
               protected tableName: string) {
    this.client = new MySqlClient(con)
  }
    
  write(text: string) {
    this.client.write(this.tableName, text);
  }
  

    
    
}
const commands: Commands[] = [];
commands.push(new RemoveWhitespaces());
commands.push(new RemoveInvalid());
commands.push(new EsWriter());

const reader: Reader = new MySqlReader();
const stream = reader.stream();

stream.read('data', text => {
  
  for(const command of commands){
    
    if(command.onProcess) {
      text = command.onProcess(text);
    }
    
    text = command.execute(text);
    
    if(command.onWrite) {
      command.onWrite();
    }
    
  }
})

Putting the two together

Custom Hooks, if exists

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