Java Design Patterns

Java Design Patterns are reusable, well-tested solutions to common design problems in object-oriented programming. They act as templates that guide how to structure classes, create objects, and manage interactions in a clean and efficient way. Instead of reinventing solutions, developers follow these established patterns to write flexible, maintainable, and scalable Java applications. They also improve communication by giving developers a shared vocabulary. Overall, design patterns help produce high-quality, organized, and adaptable software. Design patterns in Java are generally grouped into three main categories,

1. Creational Design Patterns

These patterns deal with object creation mechanisms, improving flexibility and reuse.

• Singleton   Ensures only one instance of a class exists, and provides a global access point.
• Factory Method  Defines an interface for creating objects, but lets subclasses decide which                                          object to create.
• Abstract Factory  Provides a way to create families of related objects without specifying their                                       concrete classes.
• Builder  Separates complex object construction from its representation; helps create objects                        step-by-step.
• Prototype  Creates new objects by copying an existing object (clone), useful when object                                    creation is expensive.

2. Structural Design Patterns

These patterns deal with class and object composition—how classes work together.

• Adapter  Allows incompatible interfaces to work together by converting one interface into                         another.
• Bridge  Separates abstraction from implementation, allowing both to vary independently.
• Composite  Treats individual objects and groups of objects uniformly (tree structures).
• Decorator Adds new functionality to an existing object dynamically without altering its                                  structure.
• Facade  Provides a simplified interface to a complex system of classes or libraries.
• Flyweight Reduces memory usage by sharing common object data instead of creating many                       similar objects.
• Proxy Provides a substitute or placeholder to control access to another object.

3. Behavioral Design Patterns

These patterns handle communication and interaction between objects.

• Strategy  Defines a family of algorithms and allows switching between them at runtime.
• Observer Defines a one-to-many relationship; when one object changes, dependents get                          notified.
• Command  Encapsulates a request or action as an object, useful for undo/redo operations.
• Chain of Responsibility Passes a request along a chain of handlers until one processes it.
• Iterator Provides a standard way to traverse elements of a collection without exposing                               internal   structure.
• State Allows an object to change its behavior when its internal state changes.
• Mediator Defines an object that centralizes communication between multiple objects,                                  reducing coupling.
• Memento Captures and restores an object’s state without exposing its internal structure.
• Template Method Defines the steps of an algorithm, allowing subclasses to override certain                                         steps.
• Visitor Separates operations from the object structure they operate on, allowing adding new                 operations easily.

more info - https://www.geeksforgeeks.org/system-design/software-design-patterns/