What is the most commonly used design pattern?

The Factory Method Design Pattern is a creational design pattern that provides an interface for creating objects in a superclass but allows subclasses to alter the type of created object. This pattern is often used to encapsulate the instantiation logic in methods that return objects of a specific class.

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The Facade Design Pattern is a structural design pattern that provides a unified interface to a subsystem of classes, libraries, or services. This pattern is often used to simplify a complex subsystem by defining a single class that contains methods that delegate to the subsystem's classes.

The Singleton Design Pattern is a creational design pattern that ensures a class has only one instance and provides a global point of access to it. This pattern is useful when exactly one object is needed to coordinate actions across a system.

The Strategy Design Pattern is a behavioral design pattern that defines a family of algorithms, encapsulates each one, and makes them interchangeable. This pattern allows algorithms to be used interchangeably within the context of an application.