What are design patterns?

Design patterns are typical, proven solutions to common problems encountered in object-oriented design. They are not ready-to-use libraries or frameworks, but rather concepts or "recipes" that can be adapted to specific tasks.

Patterns focus on relationships between classes and objects. They are divided into three main categories:

• Creational: Patterns for creating objects.
  • Factory Method
  • Abstract Factory
  • Singleton
  • Builder
  • Prototype
• Structural: Patterns for organizing classes and objects into larger structures.
  • Adapter
  • Bridge
  • Composite
  • Decorator
  • Facade
  • Flyweight
  • Proxy
• Behavioral: Patterns for algorithms and ways of interaction between classes and objects.
  • Chain of Responsibility
  • Command
  • Iterator
  • Mediator
  • Memento
  • Observer
  • State
  • Strategy
  • Template Method
  • Visitor

Applying design patterns allows creating more flexible, extendable, and maintainable code, improving readability and simplifying teamwork.

For example, the Singleton pattern guarantees that a class has only one instance and provides a global point of access to it.

// Singleton example in Java
class Singleton {
    private static Singleton instance; // Single instance

    private Singleton() {
        // Private constructor to prevent creating new instances
    }

    public static Singleton getInstance() {
        if (instance == null) { // Create instance on first call
            instance = new Singleton();
        }
        return instance; // Return the single instance
    }

    public void showMessage() {
        System.out.println("Hello from Singleton!");
    }
}