Design patterns are categorized based on their purpose and scope. Understanding these classifications helps in identifying the right pattern for a specific problem. The three main categories of design patterns are Creational, Structural, and Behavioral patterns. Each category addresses different aspects of software design.

Creational patterns deal with object creation mechanisms, trying to create objects in a manner suitable to the situation. The basic form of object creation could result in design problems or added complexity to the design. Creational design patterns solve this problem by controlling the object creation process.

• Encapsulation of object creation: These patterns encapsulate knowledge about which concrete classes the system uses.
• Flexibility: They provide a way to decouple a client from the objects it needs to instantiate.

• 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 lets subclasses alter the type of objects that will be created.
• 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: Specifies the kinds of objects to create using a prototypical instance, and creates new objects by copying this prototype.

Structural patterns deal with object composition or the way to realize relationships between entities. They help ensure that if one part of a system changes, the entire system doesn't need to change.

• Composition over inheritance: These patterns use composition to extend functionalities.
• Simplification: They simplify the structure by identifying relationships.

• Adapter: Allows incompatible interfaces to work together.
• Bridge: Separates an object’s abstraction from its implementation so that the two can vary independently.
• Composite: Composes objects into tree structures to represent part-whole hierarchies.
• Decorator: Adds additional responsibilities to an object dynamically.
• Facade: Provides a simplified interface to a complex subsystem.
• Flyweight: Reduces the cost of creating and manipulating a large number of similar objects.
• Proxy: Provides a surrogate or placeholder for another object to control access to it.

Behavioral patterns are concerned with algorithms and the assignment of responsibilities between objects. They describe not just patterns of objects or classes but also the patterns of communication between them.

• Communication: These patterns are concerned with how objects interact and communicate with each other.
• Responsibility: They help in distributing responsibilities among objects.

• Chain of Responsibility: Passes a request along a chain of handlers.
• Command: Encapsulates a request as an object, thereby allowing for parameterization of clients with queues, requests, and operations.
• Interpreter: Implements a specialized language.
• Iterator: Provides a way to access the elements of an aggregate object sequentially without exposing its underlying representation.
• Mediator: Defines an object that encapsulates how a set of objects interact.
• Memento: Captures and externalizes an object’s internal state so that the object can be restored to this state later.
• Observer: Defines a one-to-many dependency between objects so that when one object changes state, all its dependents are notified and updated automatically.
• State: Allows an object to alter its behavior when its internal state changes.
• Strategy: Defines a family of algorithms, encapsulates each one, and makes them interchangeable.
• Template Method: Defines the skeleton of an algorithm in the superclass but lets subclasses override specific steps of the algorithm without changing its structure.
• Visitor: Represents an operation to be performed on the elements of an object structure.

Design patterns are classified into three main categories: Creational, Structural, and Behavioral patterns. Each category addresses different aspects of software design, from object creation to object composition and interaction. Understanding these classifications helps in selecting the appropriate pattern for solving specific design problems, leading to more flexible, reusable, and maintainable code.