Design Patterns Overview OOP

What You’ll Learn 📚

• Understand what design patterns are and why they are important.
• Learn about key design patterns in OOP with practical examples.
• Get familiar with common terminology and concepts.
• Explore troubleshooting tips for common issues.

Introduction to Design Patterns

Design patterns are like reusable solutions to common problems in software design. Think of them as blueprints that can help you solve coding challenges more efficiently. They are not specific to any programming language, which means you can apply these patterns in languages like Python, Java, JavaScript, and more.

💡 Lightbulb Moment: Design patterns are not code snippets, but rather templates that guide you in solving design problems.

Key Terminology

• Pattern: A general reusable solution to a commonly occurring problem.
• OOP (Object-Oriented Programming): A programming paradigm based on the concept of objects, which can contain data and code.
• Singleton: A design pattern that restricts the instantiation of a class to one single instance.

Simple Example: Singleton Pattern

class Singleton:    _instance = None    def __new__(cls):        if cls._instance is None:            cls._instance = super(Singleton, cls).__new__(cls)        return cls._instance# Usagefirst_instance = Singleton()second_instance = Singleton()print(first_instance is second_instance)  # Output: True

Progressively Complex Examples

Example 1: Factory Pattern in Java

interface Shape {    void draw();}class Circle implements Shape {    public void draw() {        System.out.println("Drawing a Circle");    }}class Square implements Shape {    public void draw() {        System.out.println("Drawing a Square");    }}class ShapeFactory {    public Shape getShape(String shapeType) {        if (shapeType == null) {            return null;        }        if (shapeType.equalsIgnoreCase("CIRCLE")) {            return new Circle();        } else if (shapeType.equalsIgnoreCase("SQUARE")) {            return new Square();        }        return null;    }}public class FactoryPatternDemo {    public static void main(String[] args) {        ShapeFactory shapeFactory = new ShapeFactory();        Shape shape1 = shapeFactory.getShape("CIRCLE");        shape1.draw();        Shape shape2 = shapeFactory.getShape("SQUARE");        shape2.draw();    }}

Example 2: Observer Pattern in JavaScript

class Subject {    constructor() {        this.observers = [];    }    subscribe(observer) {        this.observers.push(observer);    }    unsubscribe(observer) {        this.observers = this.observers.filter(obs => obs !== observer);    }    notify(data) {        this.observers.forEach(observer => observer.update(data));    }}class Observer {    update(data) {        console.log(`Observer received data: ${data}`);    }}const subject = new Subject();const observer1 = new Observer();const observer2 = new Observer();subject.subscribe(observer1);subject.subscribe(observer2);subject.notify('Hello Observers!');