In software engineering, a design pattern is a general repeatable solution to a commonly occurring problem in software design. A design pattern isn't a finished design that can be transformed directly into code. It is a description or template for how to solve a problem that can be used in many different situations.
There are several types of design patterns in Java, including creational, structural, and behavioral patterns.
Creational patterns
Creational patterns deal with object creation mechanisms, trying to create objects in a manner suitable to the situation. Some examples of creational design patterns in Java are:
- Builder: Separates object construction from its representation, allowing the same construction process to create different representations.
- Factory Method: Creates an instance of several derived classes.
- Prototype: A fully initialized instance to be copied or cloned.
- Singleton: A class of which only a single instance can exist.
Structural patterns
Structural patterns deal with object composition, creating relationships between objects to form larger structures. Some examples of structural design patterns in Java are:
- Adapter: Match interfaces of different classes.
- Bridge: Separates an object's interface from its implementation.
- Composite: A tree structure of simple and composite objects.
- Decorator: Add responsibilities to objects dynamically.
- Facade: A single class that represents an entire subsystem.
- Flyweight: A fine-grained instance used for efficient sharing.
- Proxy: An object representing another object.
Behavioral patterns
Behavioral patterns focus on communication between objects, what goes on between objects and how they operate together. Some examples of behavioral design patterns in Java are:
- Chain of Responsibility: A way of passing a request between a chain of objects.
- Command: Encapsulate a command request as an object.
- Interpreter: A way to include language elements in a program.
- Iterator: Sequentially access the elements of a collection.
- Mediator: Defines simplified communication between classes.
- Memento: Capture and restore an object's internal state.
- Observer: A way of notifying change to a number of classes.
- State: Alter an object's behavior when its state changes.
- Strategy: Encapsulates an algorithm inside a class.
- Template Method: Defer the exact steps of an algorithm to a subclass.
- Visitor: Defines a new operation to a class without change.
It's important to note that design patterns are not a one-size-fits-all solution and should be used appropriately based on the specific requirements and constraints of a project.
