What are the different categories of Java Design patterns?

Java design patterns are general reusable solutions to common problems encountered in software design. They represent best practices evolved over time by experienced developers. Design patterns are categorized into three main types:

1. Creational Patterns:

These patterns deal with the process of object creation. They provide mechanisms to create objects in a manner suitable to the situation.

Examples:

• Singleton Pattern: Ensures a class has only one instance and provides a global point of access to it.
• Factory Method Pattern: Defines an interface for creating an object, but leaves the choice of its type to the subclasses, creating instances of one or more derived classes.
• Abstract Factory Pattern: Provides an interface for creating families of related or dependent objects without specifying their concrete classes.

2. Structural Patterns:

These patterns deal with the composition of classes or objects to form larger structures.

Examples:

• Adapter Pattern: Allows the interface of an existing class to be used as another interface.
• Decorator Pattern: Attaches additional responsibilities to an object dynamically. Decorators provide a flexible alternative to subclassing for extending functionality.
• Composite Pattern: Composes objects into tree structures to represent part-whole hierarchies. It allows clients to treat individual objects and compositions of objects uniformly.

3. Behavioral Patterns:

These patterns deal with the interaction between objects, responsibilities, and algorithms.

Examples:

• Observer Pattern: Defines a one-to-many dependency between objects so that when one object changes state, all its dependents are notified and updated automatically.
• Strategy Pattern: Defines a family of algorithms, encapsulates each algorithm, and makes them interchangeable. Strategy lets the algorithm vary independently from clients that use it.
• Command Pattern: Encapsulates a request as an object, thereby allowing for parameterization of clients with different requests, queuing of requests, and logging of the parameters for requests.

These categories help organize design patterns based on their purpose and the problems they aim to solve. Each category consists of patterns that address specific concerns in the software development process. Applying design patterns appropriately can lead to more maintainable, flexible, and scalable software solutions.