Which pattern allows new classes to be created without altering existing class structures?

The Prototype Pattern is designed to facilitate the creation of new objects by copying an existing object, known as the prototype. This approach is particularly useful when dealing with classes that are complex or costly to instantiate. By cloning an existing instance, it allows developers to create new instances without the need to modify the underlying class structure.

This pattern embraces the principles of object-oriented design by promoting a way to create new objects dynamically at runtime without the constraints typically associated with inheritance or modification of class hierarchies. It is effective in scenarios where classes evolve and where extensibility is a requirement. Additionally, it can simplify the initialization, as all defaults can be inherited from the prototype.

In contrast, the other patterns listed offer different functionalities. For example, the Template Method Pattern defines the skeleton of an algorithm in a method, allowing subclasses to provide specific implementations. The Constructor Pattern pertains to creating instances by employing a systematic approach, while the Factory Method Pattern provides an interface for creating objects in a superclass but allows subclasses to alter the type of objects that will be created. None of these patterns focus specifically on the cloning and creation of new class instances without altering existing structures as efficiently as the Prototype Pattern does.