Can you name the main design patterns and explain their purpose?

Design patterns can be divided into three groups:

1. Creational — responsible for object creation.

   • Singleton: ensures a class has only one instance and provides a global point of access to it.
   • Factory Method: defines an interface for creating an object but allows subclasses to decide which class to instantiate.
   • Abstract Factory: provides an interface for creating families of related or dependent objects without specifying their concrete classes.
   • Builder: separates the construction of a complex object from its representation, allowing the same construction process to create different representations.
   • Prototype: creates new objects by copying existing ones.

2. Structural — help organize classes and objects into larger structures.

   • Adapter: allows objects with incompatible interfaces to work together.
   • Decorator: dynamically adds responsibilities to objects.
   • Facade: provides a simplified interface to a complex system.
   • Composite: allows grouping objects into tree structures and working with them uniformly.
   • Proxy: controls access to another object.

3. Behavioral — responsible for interactions between objects.

   • Observer: notifies dependent objects of changes in state.
   • Strategy: defines a family of algorithms and makes them interchangeable.
   • Command: encapsulates a request as an object, allowing parameterization of clients.
   • Iterator: provides a way to access elements of a collection sequentially.
   • State: allows an object to change its behavior when its internal state changes.

These patterns help create flexible, extensible, and maintainable code, solving common design problems.