The Singleton design pattern is used to ensure that a class has only one instance and to provide a global point of access to that instance. This can be useful in situations where it is important to have a single instance of a class that provides a shared resource.

The Adapter pattern is a design pattern used to convert the interface of one class into another interface that a client is expecting. This allows classes with incompatible interfaces to work together.

The Command pattern allows objects to be treated as commands that can be executed, deferred or queued

The Abstract Factory pattern is used to provide an interface for creating families of related or dependent objects, while the Factory pattern is used to create objects without specifying the exact class of object that will be created.

The Visitor pattern allows you to add new operations to existing object structures without modifying them, while the Iterator pattern provides a way to access the elements of a collection object in a sequential manner

The Front Controller pattern provides a centralized handler for requests coming from the client. It coordinates the work of different request handlers to provide a unified interface for the user.

J2EE Patterns are a set of design patterns that are specifically tailored to the Java 2 Platform, Enterprise Edition (J2EE) technology. These patterns provide a solution to common problems that arise in J2EE-based software development, such as implementing security, managing transactions, and integrating with other systems.

The Observer pattern involves a one-to-many relationship between objects, where one object (the subject) maintains a list of its dependents (observers) and notifies them of any changes, while the Pub-Sub pattern involves the publish and subscribe mechanism, where the publisher does not know the subscribers and the subscribers do not know the publishers.

Iterator pattern is a design pattern that allows the client to traverse a collection of objects, without exposing the underlying representation of the collection. The pattern involves creating an iterator class that implements the iterator interface, and provides a way for the client to access the elements of the collection one at a time, in a standardized manner. This pattern can be useful in situations where you want to provide a standard way for the client to access the elements of a collection, without exposing the internal representation of the collection.

The Builder pattern is used for creating complex objects step by step, using a builder object to abstract the process of creating the object from the client code