Design Patterns in Java are proven solutions to common software design problems. They provide developers with reusable and well-tested techniques to improve software development efficiency. By understanding and applying design patterns, Java programmers can build robust and flexible applications.
It all started with the publication of Design Patterns book of the very famous “GOF – Gang of Four”. Erich Gamma, Richard Helm, Ralph Johnson and John Vlissides were the four guys who created 23 design patterns as solutions to some of the common occurring problems in software design.
We can divide design patterns into three categories:
- Creational Design Patterns
- Structural Design Patterns
- Behavioral Design Patterns
Creational Design Patterns in Java:
Creational Design Patterns are a category of design patterns that focus on object creation mechanisms. They provide solutions for creating objects in a flexible and reusable manner, abstracting the process of object instantiation. Creational Design Patterns help decouple the client code from the specific classes it needs to create, promoting code maintainability and flexibility. Some common Creational Design Patterns are:
- Singleton – This pattern needs to be used wherein the number of instances of a class is restricted to one.
- Factory Method – Creates object of one of the sub classes based on certain conditions
- Abstract Factory – It provides one layer of abstraction over factory method pattern.It returns one of the factories based on certain conditions.
- Builder – builds a complex object stepwise.Separates the construction and representation of the object.
- Prototype – Creates the clone of an existing object.
Structural Design Patterns in Java:
Structural Design Patterns are a category of design patterns that deal with the composition of classes and objects to form larger structures and provide more complex functionalities. These patterns focus on how classes and objects can be combined to create flexible and efficient systems. Structural Design Patterns help in achieving proper object relationships, enhancing code organization, and enabling code reuse. Some common Structural Design Patterns are:
- Adapter – helps two incompatible interfaces to work together.
- Decorator – add/modifies the behaviour of an existing object dynamically.
- Composite– helps in creating part-whole hierarchy structures.
- Facade – provides simplified interface to a complex system with multiple sub-sytems.
- Flyweight – reduces cost of creation of large number of objects by reusing existing objects.
- Proxy – provides placeholder for another object to enforce access control, reduce expensive creation of original object,to enforce features like logging, instrumentation etc.
- Bridge – decouples an abstraction from its implementation so that the two can vary independently.
Behavioral Design Patterns in Java
Behavioral Design Patterns are a category of design patterns that focus on the interaction and communication between objects to provide solutions for complex behavioral patterns in software systems. These patterns address the responsibilities and behaviors of objects, ensuring efficient communication, flexibility, and maintainability. Behavioral Design Patterns help in achieving better encapsulation, decoupling, and extensibility of code. Some common Behavioral Design Patterns are:
- Chain of responsibility– decouples the sender of the request from the receiver of the request.
- Memento – enables an object to return back to some old state.
- Template – parent class provides the basic skeleton of an algorithm and the child classes provide the respective implementations.
- Observer – designs a publisher and subscriber model of communication.
- State – enables the object to change it’s behaviour on change of it’s state.
- Iterator – allows to traverse through a collection of objects without exposing the underlying representation.
- Mediator – provide loose coupling between communicating objects.
- Command – provides loose coupling in request-response model.
- Strategy – allows one of a family of algorithms to be selected on the fly at runtime.
- Visitor – lets you define a new operation without changing the classes of the objects on which it operates.It moves the operational logic from the objects to another class.
- Interpreter – implements a specialized language.It defines a grammatical representation for a language and provides an interpreter to deal with this grammar.
Incorporating design patterns in Java development can significantly boost software development efficiency. By leveraging established solutions to recurring design problems, developers can save time, improve code quality, and enhance maintainability. Design patterns empower Java programmers to build scalable and efficient software systems that meet the demands of modern applications.
Recommended Article: Design Principles
Here are some highly recommended books on design patterns in Java:
- “Design Patterns: Elements of Reusable Object-Oriented Software” by Erich Gamma, Richard Helm, Ralph Johnson, and John Vlissides (also known as the Gang of Four book)
- “Head First Design Patterns” by Eric Freeman, Elisabeth Robson, Bert Bates, and Kathy Sierra