Design Patterns in Java with Real-time Examples
In this article series, I discussed all the Design Patterns in Java with Real-Time Examples using different types of Java Applications. It is very easy to understand and implement design patterns in our Real-Time Applications. Writing the code with Design Patterns will make our applications code more Reliable, Scalable, and Maintainable.
This Java Design Pattern Course is For Whom?
This Java Design Pattern tutorial is designed for Students, Beginners as well as Professional Developers who want to learn and enhance their knowledge of Design Patterns with Real-time Examples using Java Applications.
Here, we will explain all the Java Design Patterns step by step i.e. first we will discuss the definition of the particular design pattern, then we will give simple as well as multiple real-time examples of each design pattern, then we will discuss how to implement the same Design Pattern using Java Application, then we will compare the same example with the UML diagram of the design pattern so that you will understand the concept very easily.
What are Design Patterns?
Design patterns are programming constructs used by object-oriented programmers. They are programming language-independent strategies for solving common object-oriented design problems.
Design patterns are well-proven solutions for solving specific problems and hence help improve the flexibility, reusability, and maintainability of our code. They provide a common language and shared understanding among developers, making it easier to communicate and collaborate on software projects.
Design Patterns are nothing but, you can say, documented and tested solutions for recurring problems in a given context. So, in simple words, we can say that Design Patterns are reusable solutions to the problems that, as a developer, we encounter in our day-to-day programming. Design Patterns are basically used to solve the problems of Object Generation and Integration.
In Java, there are three types of design patterns: Creational, Structural, and Behavioral. Each of these types is further divided into their sub-parts.
Gang of Four (GOF)
In 1994, four authors Erich Gamma, Richard Helm, Ralph Johnson, and John Vlissides wrote a book called “Design Patterns – Elements of Reusable Object-Oriented Software”. Gang of Four (GoF) has divided the book into two parts with the first part explaining the Pros and Cons of Object-Oriented Programming and the second part describing the Evolution Of 23 Classic Software Design Patterns.
This book introduced the basic concept of Design Patterns in Object-Oriented Programming. These authors are commonly known as the Gang of Four (GOF). As per the content of the book, design patterns are based on the following principles:
- Program to an interface, not an implementation
- Favor object composition over inheritance
These principles help to create flexible and reusable software designs that can be easily adapted to changing requirements. Design patterns provide a common language and shared understanding among developers, making it easier to communicate and collaborate on software projects.
Types of Java Design Patterns
According to the book written by the Gang of Four (GOF), there are two main categories of design patterns: Core Java Design Patterns and J2EE Design Patterns. Core Java Design Patterns are further divided into three subcategories: Creational, Structural, and Behavioral.
- Creational Design Patterns: These provide a way to easily create objects while hiding the creation logic. This gives the program more flexibility in deciding which objects need to be created for a given use case.
- Structural Design Patterns: These work with class and object composition and use inheritance to write interfaces and obtain new functionality.
- Behavioral Design Patterns: These are concerned with communication between objects.
J2EE Design Patterns, on the other hand, are specifically concerned with the presentation tier. These patterns provide solutions for common problems that arise when developing enterprise applications using the Java 2 Platform, Enterprise Edition (J2EE).
Creational Design Pattern
The following patterns are included under creational design patterns:
- Factory Pattern: This is widely used in Java. It provides an interface for creating objects while allowing subclasses to determine which class should be instantiated. The factory pattern delegates the responsibility of instantiating a parent abstract class to its concrete sub-classes. When creating an object, the specific class type may not be known, so a creator class uses its factory method to separate the logic of identifying the class type.
- Abstract Factory Pattern: This pattern provides an interface for creating groups of related or dependent objects without specifying their concrete classes. It allows for the creation of objects that belong to the same family or theme without having to know their specific types.
- Singleton Pattern: This pattern ensures that only one instance of a class exists throughout the application and provides a global access point to that instance. It restricts the instantiation of a class to a single object and is useful when exactly one object is needed to coordinate actions across the system.
- Prototype Pattern: This pattern specifies the kind of object to create using a prototypical instance and creates new objects by copying this prototype. It allows for the creation of new objects by cloning an existing object, rather than creating a new object from scratch.
- Builder Pattern: This pattern constructs complex objects using a step-by-step approach and separates the construction of an object from its representation. It allows for the creation of complex objects with many parts by breaking down the construction process into smaller steps.
Structural Design Pattern
The following patterns are included under structural design patterns:
- Adapter Pattern: This pattern connects two incompatible interfaces by providing a wrapper for a class or object that uses a different interface, allowing it to be used with another interface.
- Bridge Pattern: This pattern separates an abstraction from its implementation so that it can change independently. It achieves this by separating the interface from the implementation without using inheritance.
- Composite Pattern: This pattern organizes objects into tree structures to represent part-whole hierarchies and allows clients to treat individual objects and compositions of objects in the same way.
- Decorator Pattern: This pattern adds new functionality to an existing object without changing its structure by wrapping it with additional functionality.
- Facade Pattern: This pattern simplifies access to a complex subsystem by providing a simplified interface that hides the complexities of the system.
- Flyweight Pattern: This pattern minimizes memory usage by sharing as much data as possible with other similar objects, reducing the number of objects created.
- Proxy Pattern: This pattern controls access to another object by providing a surrogate or placeholder for it. It creates an intermediary that acts as an interface to another resource.
Behavioral Design Pattern
The following patterns are included under behavioral design patterns:
- Chain of Responsibility Pattern: This pattern creates a chain of receiver objects for a request. It decouples the sender and receiver of a request based on the type of request and allows multiple objects to handle the request1.
- Command Pattern: This pattern encapsulates a request as an object, allowing it to be parameterized with different requests, queued or logged, and supports undoable operations.
- Interpreter Pattern: This pattern provides a way to evaluate language grammar or expression. It involves implementing an expression interface that interprets a particular context2.
- Iterator Pattern: This pattern provides a way to access the elements of an aggregate object sequentially without exposing its underlying representation.
- Mediator Pattern: This pattern defines an object that encapsulates how a set of objects interact. It promotes loose coupling by keeping objects from referring to each other explicitly and allows their interaction to vary independently.
- Memento Pattern: This pattern captures and externalizes an object’s internal state so that the object can be restored to this state later without violating encapsulation.
- Observer Pattern: This pattern defines a one-to-many dependency between objects so that when one object changes state, all its dependents are notified and updated automatically.
- State Pattern: This pattern allows an object to alter its behavior when its internal state changes. The object will appear to change its class.
- Strategy Pattern: This pattern defines a family of algorithms, encapsulates each one, and makes them interchangeable. It lets the algorithm vary independently from clients that use it.
- Template Pattern: This pattern defines the skeleton of an algorithm in an operation, deferring some steps to subclasses. It lets subclasses redefine certain steps of an algorithm without changing the algorithm’s structure.
- Visitor Pattern: This pattern represents an operation to be performed on the elements of an object structure. It lets you define a new operation without changing the classes of the elements on which it operates.
Advantages of Java Design Patterns
- They can be re-used.
- They capture the software engineering experiences.
- They provide transparency to the design of an application.
- They usually provide a foolproof method to solve a problem.
- Design patterns do not provide a complete solution to a problem. They only provide clarity to the application and provide an opportunity to build a better application.
Disadvantages of Java Design Patterns
- The code may remain disorganized.
- It can be difficult to determine where an exception is being handled.
- Additionally, programmers might use exceptions for regular control flow, leading to confusion and inefficiency.
- Implementing better design may require adding more code to the existing system, increasing its complexity and making it harder to understand.
Java Design Patterns Setup
Before Implementing design patterns in Java, let us do the setup in three simple steps
Step 1: Set up an IDE (Integrated Development Environment). We have used Microsoft Visual Studio (VS Code). You have options such as Eclipse or Theia.
Step 2: Install Java along with its extension packs. Download Java Development Kit (JDK) from https://learn.microsoft.com/en-us/java/openjdk/download. Select the appropriate OS from the available list as shown.
Step 3: Download the “Extension Pack for Java” extension to make it easier to code in Java using VS Code. This is found in the extensions tab, which is in the left sidebar of the VS Code window.
Congratulations‼ Your setup is now complete!
Pre-Requisites to Learn Java Design Patterns:
How easily you are going to learn the Design Patterns that basically depends on how strong you are in Object-Oriented Programming concepts. So, to take full advantage of this Java Design Patterns course, it is very important for you to have at least the basic knowledge of the following Object-Oriented Programming concepts.
This Design Patterns in Java with Real-Time Examples Course is definitely helping you to learn Design Patterns and definitely make you become a professional developer.
What do we expect from you?
We will try our level best to cover all the Java Design Patterns, but in the meantime, if you have any doubts or if you want to learn any Java Design Patterns which we missed in this course, then please give us a comment and we promised we will provide it as soon as possible. You can also contact us by email: firstname.lastname@example.org.
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