Java design pattern or design pattern is not related to any specific language. Design patterns are very popular in the software industry. A design pattern is a solution to a common problem by software expertise. Design patterns are already defined and provide an industry-standard approach to solve a reoccurring problem while developing the application to save time. Design pattern promotes reusabilities that lead to more robust and highly maintainable code. It makes our code easy to understand and debug. It helps in faster development, and new members of the team understand it easily.
We’ll be covering the following topics in this tutorial:
Usage of Design Pattern
Design Patterns have two main usages in software development.
Common Platform for Developers
A design pattern provides standard terminology and applies to a specific situation. For example, a singleton pattern means that all programmers will use the same object or type of object and tell each other that their programs follow a singleton design pattern.
Design patterns have evolved over a long period and are the most effective solutions to specific problems. Studying these patterns will help the inexperienced software developer learn the necessary software design patterns.
Types of Design Patterns
The Design patterns can be classified according to three basic themes: Creational, Structural and Behavioral.
The creational design patterns deal with ways of creating objects that are ideally suited to the situation. To deliver the basic form of object creation, design problems may occur or could be added.
The singleton design pattern is used to ensure that only one instance of a class exists, preventing any other types from being instantiated. Special attention must be paid to the fact that a singleton class can only have a single object (instance) at a time per JVM instance.
The Factory Design Pattern is one of Java’s most used design patterns. According to GoF, this pattern is emphasized: “provides a standard interface for creating new objects, but let subclasses decide which class to instantiate. It’s the Factory Method that enables a class to defer instantiation to subclasses “.
Abstract Factory Pattern
In this, an interface is responsible for creating a factory of related objects without explicitly specifying their classes.
The Builder pattern builds a complex object by using simple objects and a step-by-step approach. This class is an ideal example of a creational pattern as it is the easiest way to create an object. A builder class builds the final object, step by step.
The prototype pattern enables cloning a wide variety of objects without linking any of them to particular classes. Objects of the same class are constructed in their entirety. They can both access one another’s private fields.
Structural Patterns focuses on developing effective solutions and efficient standards for data classes. They rely on inheritance and interfaces to allow multiple classes to cooperate and form a single working whole.
The adapter design pattern allows two different types of interface, which are not related to one another, to work together. This pattern enables the conversion of an incompatible interface of a class into an interface that clients require.
The Composite design pattern is meant to be used for easy organizational objects into a hierarchical tree structure.
Plus, Composite patterns allow us to apply the same treatments to both individual objects and compositions.
The proxy acts as a substitute for a real service object, providing a substitute object used by the client. A proxy is an object with the same interface as a real object passed into the client.
A flyweight pattern is used when a large number of similar objects are needed. One key characteristic of the flyweight object is that it cannot be modified. These cannot be modified once they have been built and installed.
A facade is a simplified (but limited) interface to a complex system of classes, library or framework. While Facade must be used, it can also be used to move unnecessary dependencies to one place.
Bridge divides a large class into smaller class hierarchies, creating independent hierarchies that can be developed separately. One of the hierarchies will be given a reference to an object of the other hierarchy (Implementation).
The decorator design pattern ensures that the capabilities of an object remain essentially the same while adding new capabilities. We use inheritance to extend the class’s functionality. The behaviour is applied at compile-time, so all of the instances get customized behaviour. Decorator patterns allow for the addition of new functionality before or after a class has been initialized. We can fully customize the setting of an individual object to meet an individual’s needs.
The study of behaviour patterns focuses on the interaction of objects, how objects and their surroundings are communicated, their dependency, and the ability to either be independent and dependent.
Template Method Pattern
Template Method pattern is a behavioural design pattern used to let subclasses define an algorithm’s steps without changing the overall algorithm’s structure.
When complex object communication begins to impede object reuse, a mediator is used. Complexity is found in view instances because it is found in any situation. The misuse of a mediator can cause crippling impacts on the interfaces of other class’s collaborators.
Chain of Responsibility Pattern
The Chain of Responsibility pattern eliminates coupling the sender of a request to the receiver by giving multiple objects the chance to handle the request. ATM requires the use of the Chain of Accountability in money transactions.
“Observer” describes a behavioural design pattern. It handles communication between objects: the observer and the observed. The observable is an object which changes its state for observers.
A behavioural design pattern turns a set of actions into objects and makes them interchangeable within the original context object. The original object holds a reference to an object that contains the behaviour code and delegates its execution.
A Command pattern is a type of object behavioural design pattern that clarifies the sender and receiver. In Java, we can use a Command pattern to implement callbacks.
State Design Pattern in Java describes an object with a state that can change along with different behaviours and actions. The state design pattern is a behavioural design pattern in which objects possess a state, and the state of the object can be altered over time.
A Visitor pattern aims to define a new operation without introducing modifications to an existing object structure. Imagine that we have a composite object which consists of components.
An interpreter design pattern solves problems specific to a given domain. Unspecialized non-domain-specific languages are designed to solve problems in many different ways. DSLs are used for, among others, ANT, CSS, regular expressions, SQL, HQL (Hibernate Query Language), and XML.
The Iterator pattern is a frequently used design pattern in Java-based systems and programmers’ Internet applications. This pattern allows you to access the elements of a collection object without knowing in advance how the collection is represented.
The Memento Design Pattern can restore an object, such as a computer file, to a previous state. The Memento design pattern involves three objects: the originator, the caretaker, and the memento.
Miscellaneous Design Patterns
DAO Design Pattern
A data access object is an abstract abstraction to an existing database that provides an interface to it in computer software. By mapping application calls to the persistence layer, the DAO allows for implementing specific data operations without revealing the database schema.
Dependency Injection Pattern
Dependency Injection (DI) is a design pattern used to implement Object-Oriented Design. It allows the creation of dependencies between classes that are not defined by the inheritance hierarchy of those classes. Use of Dependent Object, we move the creation and binding of the dependent objects outside of the class that uses them.
In the MVC design pattern, the view and controller use strategy design and the view and the model are synchronized using the observer design. Hence, we may say that MVC is a compound pattern. The controller and the view are loosely coupled, and multiple views can use one controller.
Advantage of Design Pattern
• They are reusable in various projects.
• They help to define the system architecture.
• They capture (some) software engineering experiences.
• They accurately describe the design of the application.
• They have been demonstrated to be effective solutions because experts in the field have shown them.
• Design patterns aren’t a panacea for all problems.
• They provide a clear and detailed architecture of the system that can be improved upon.