Design Patterns in Java

Design Patterns in Java

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Updated on Sep 27, 2023 18:23 IST

Design patterns in Java are reusable solutions to commonly occurring software development problems. They are general solutions that have been developed and proven over time to address common software design problems.

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Design patterns in Java can help software developers build more flexible applications by providing a common language and a set of best practices that can be applied to different situations.

Java is a popular programming language for developing various software applications. Therefore, Java design patterns refer to the specific design patterns commonly used in Java programming. 

Some common Java design patterns include the Singleton pattern, the Factory pattern, the Adapter pattern, the Observer pattern, the Decorator pattern, and the Strategy pattern, among others. These patterns can be used in various aspects of software design, such as object creation. 

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Need for Design Patterns in Java

Design patterns are an important part of software development in Java as they provide a way to solve common software design problems. Some of the benefits of using design patterns in Java  

  • Reusability: Design patterns provide a reusable solution to common software design problems. This saves developers from reinventing the wheel whenever they encounter a new problem. Instead, they can use a tried and tested pattern to solve the problem. 
  • Maintainability: Design patterns promote clean, organized and maintainable code. This makes it easier for developers to maintain and modify the code as the software evolves. 
  • Scalability: Design patterns provide a flexible and scalable solution to software design problems. This makes it easier to adapt to changes in the software requirements and add new features. 
  • Best Practices: Design patterns are based on best practices and design principles proven to work over time. This helps developers write better quality, more reliable, efficient and maintainable code. 
  • Faster Development: Design patterns provide a standard way of solving common software design problems. This saves time and effort in the development process, allowing developers to focus on other aspects of the software. 

In summary, using design patterns in Java can help developers write better-quality, more maintainable, scalable and reusable code. This results in more reliable and efficient software that can be adapted to changes in the software requirements over time. 

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Types of Design Patterns in Java

Creational Patterns 

Creational patterns provide a way to create objects in a controlled manner. These patterns define the best way to create an object in a particular situation. They include: 

Singleton Pattern 

The Singleton pattern ensures that a class has only one instance and provides a global access point to that instance. This pattern is useful when a single instance of a class is required to coordinate actions across the system. 

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Example: 

 
class Singleton {
private static Singleton singleton = new Singleton();
private Singleton() {}
public static Singleton getInstance() {
return singleton;
}
public static void main(String[] args) {
Singleton instance = Singleton.getInstance();
System.out.println("Singleton instance obtained: " + instance);
}
}
Copy code

Output

Singleton instance obtained: Singleton@77459877

Factory Pattern 

The Factory pattern provides an interface for creating objects in a superclass, but allows subclasses to alter the type of objects that will be created. This pattern is useful when there is a need to create multiple objects with the same interface, but different implementation. 

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Example

 
interface Shape {
void draw();
}
class Rectangle implements Shape {
public void draw() {
System.out.println("Inside Rectangle::draw() method.");
}
}
class Square implements Shape {
public void draw() {
System.out.println("Inside Square::draw() method.");
}
}
class ShapeFactory {
public Shape getShape(String shapeType){
if(shapeType == null){
return null;
}
if(shapeType.equalsIgnoreCase("RECTANGLE")){
return new Rectangle();
} else if(shapeType.equalsIgnoreCase("SQUARE")){
return new Square();
}
return null;
}
public static void main(String[] args) {
ShapeFactory shapeFactory = new ShapeFactory();
Shape shape1 = shapeFactory.getShape("RECTANGLE");
shape1.draw();
Shape shape2 = shapeFactory.getShape("SQUARE");
shape2.draw();
}
}
Copy code

Output

Inside Rectangle::draw() method.
Inside Square::draw() method.

Abstract Factory Pattern 

The Abstract Factory pattern provides an interface for creating families of related or dependent objects without specifying their concrete classes. This pattern is useful when there is a need to create related objects, but their implementation details vary. 

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Example

 
interface Color {
void fill();
}
class Red implements Color {
public void fill() {
System.out.println("Inside Red::fill() method.");
}
}
class Green implements Color {
public void fill() {
System.out.println("Inside Green::fill() method.");
}
}
interface AbstractFactory {
Color getColor(String color);
}
class ColorFactory implements AbstractFactory {
public Color getColor(String color) {
if (color == null) {
return null;
}
if (color.equalsIgnoreCase("RED")) {
return new Red();
} else if (color.equalsIgnoreCase("GREEN")) {
return new Green();
}
return null;
}
}
public class Main {
public static void main(String[] args) {
AbstractFactory colorFactory = new ColorFactory();
Color color1 = colorFactory.getColor("RED");
color1.fill();
Color color2 = colorFactory.getColor("GREEN");
color2.fill();
}
}
Copy code

Output

Inside Red::fill() method.
Inside Green::fill() method.

Structural Patterns 

Structural patterns provide a way to organize objects in a way that is efficient, flexible, and extension. 

Adapter Pattern 

The Adapter pattern allows objects with incompatible interfaces to work together by creating a bridge between them. This pattern is useful when there is a need to use an existing class, but its interface is not compatible with the system. 

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Example

 
interface MediaPlayer {
void play(String audioType, String fileName);
}
interface AdvancedMediaPlayer {
void playVlc(String fileName);
void playMp4(String fileName);
}
class VlcPlayer implements AdvancedMediaPlayer {
public void playVlc(String fileName) {
System.out.println("Playing vlc file. Name: " + fileName);
}
public void playMp4(String fileName) {
//do nothing
}
}
class Mp4Player implements AdvancedMediaPlayer {
public void playVlc(String fileName) {
//do nothing
}
public void playMp4(String fileName) {
System.out.println("Playing mp4 file. Name: " + fileName);
}
}
public class Main {
public static void main(String[] args) {
AdvancedMediaPlayer vlcPlayer = new VlcPlayer();
vlcPlayer.playVlc("example1.vlc");
AdvancedMediaPlayer mp4Player = new Mp4Player();
mp4Player.playMp4("example2.mp4");
}
}
Copy code

Output

Playing vlc file. Name: example1.vlc
Playing mp4 file. Name: example2.mp4

Softwares Used 

Design patterns in Java can be implemented and run in various software development environments, depending on the project’s needs and the development team’s preferences.

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Here are some common software tools and frameworks used in Java development that can support the implementation of design patterns: 

  • Integrated Development Environments (IDEs): 

IDEs such as Eclipse, IntelliJ IDEA, and NetBeans provide a comprehensive set of tools and features for developing Java applications, including support for code refactoring, code analysis, and code completion. These tools can make it easier to implement and use design patterns in Java, as they provide a user-friendly interface and a range of productivity features. 

  • Build tools: 

Build tools such as Apache Maven and Gradle can help manage the build process of a Java project, including the compilation, testing, and packaging of code. These tools can also be configured to support the use of design patterns, such as through the inclusion of external libraries and frameworks. 

  • Frameworks and libraries: 

Java frameworks such as Spring, Hibernate, and Struts provide a range of features and components that can be used to implement design patterns in Java code. For example, the Spring framework includes support for the Dependency Injection pattern, while Hibernate provides an Object-Relational Mapping (ORM) solution that can be used to implement the Data Access Object (DAO) pattern. 

  • Testing tools

Testing tools such as JUnit and TestNG can be used to write and run unit tests for Java code, including code that implements design patterns. These tools can help ensure that the implementation of a design pattern is correct and meets the requirements of the project. 

Overall, a wide range of software tools and frameworks are available to support the implementation and use of design patterns in Java development. The choice of tool or framework will depend on the specific needs and requirements of the project, as well as the preferences and expertise of the development team. 

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Real-Life Examples of Design Patterns in Java

  • Model-View-Controller (MVC) pattern 

This pattern is commonly used in web development to separate the presentation layer from the business logic and data storage. This pattern provides a clear separation between the user interface and the underlying code, making it easier to maintain and update the application. 

  • Singleton pattern: 

The Singleton pattern ensures that only one class instance is created and used throughout the application. This pattern is used when multiple class instances could cause resource contention or inconsistent behaviour. 

  • Factory pattern: 

The Factory pattern creates objects without specifying the exact class of the created object. This pattern creates an abstraction layer between the client code and the actual implementation of the created objects. 

  • Observer pattern: 

The Observer pattern is used to implement event-driven systems where changes in one part of the application trigger updates in other parts. This pattern is commonly used in user interfaces and event-driven systems. 

In summary, design patterns in Java provide developers with proven solutions to common software development problems and are used in a wide range of applications and scenarios to improve the quality and maintainability of software.  

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Use of  Design Patterns in AI

Artificial Intelligence (AI) is a rapidly growing field, and many AI applications utilize design patterns in Java. Here are some examples: 

  • Reinforcement Learning: Reinforcement Learning is a subfield of AI where agents learn to make decisions based on feedback from their environment. The State, Action, Reward, State (SARS) pattern is commonly used in Reinforcement Learning algorithms and can be implemented in Java. 
  • Neural Networks: Neural Networks are a type of AI that mimics the structure and function of the human brain. Design patterns like the Strategy and Template Method patterns can be used to implement neural network algorithms in Java. 
  • Natural Language Processing: Natural Language Processing (NLP) is a subfield of AI that focuses on the interaction between computers and human language. The Chain of Responsibility and Interpreter patterns can be used to implement NLP algorithms in Java. 
  • Robotics: Robotics is another application of AI that can use design patterns in Java. The Command pattern and the Observer pattern can be used to control robots’ behaviour and process data from their sensors. 
  • Machine Learning: Machine Learning is a subset of AI that focuses on creating algorithms to learn and make data-based decisions. Design patterns like the Factory and Builder patterns can be used to implement Machine Learning algorithms in Java. 

In summary, many applications of AI use design patterns in Java. Design patterns provide a proven solution to common problems in software development and can help improve the quality and maintainability of AI systems. 

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Future in Design Patterns in Java

Design patterns in Java have a wide scope in the software development industry. Here are some of the key areas where design patterns in Java are important: 

  • Code Reusability: Design patterns provide a way to encapsulate common solutions to software design problems. This makes it easier to reuse the same solution across multiple projects, saving time and effort for developers. 
  • Maintainability: Design patterns provide a structured and consistent approach to software design, making it easier to understand and modify code over time. This can help to reduce maintenance costs and increase the lifespan of software systems. 
  • Collaboration: Design patterns provide a common language and understanding for developers to work together on software development projects. This can help to improve communication and collaboration between team members. 
  • Performance: Design patterns can help improve software systems’ performance by providing optimized solutions to common problems. For example, the Flyweight pattern can be used to reduce the memory footprint of an application by sharing objects across multiple instances. 
  • Scalability: Design patterns can help to improve the scalability of software systems by providing solutions that are modular and easy to extend. For example, the Factory pattern can be used to create.

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Simple Exercises to Try

Here’s a basic flowchart illustrating the process of using design patterns in Java: 

Start:

  • Identify a problem in software design or a common pattern that can be reused.
  • Research existing design patterns and choose the most appropriate one for the problem.
  • Implement the design pattern in Java code, following best practices and established guidelines. 
  • Test and refine the implementation, making necessary adjustments to meet requirements.
  • Document the design pattern, including its purpose, implementation details, and any considerations or limitations. 
  • Incorporate the design pattern into the software development process, encouraging its use in future projects. 

End Notes

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Of course, the process of using design patterns in Java can vary depending on the specific pattern and the project’s needs. However, this flowchart provides a general overview of the key steps in using design patterns to improve software design and development.

Author: Sameer Chanda

FAQs

Can I create my own design patterns in Java?

Yes, you can create your own design patterns in Java. While there are well-established design patterns, every application has unique requirements, and you may encounter situations where existing patterns don't fully address your needs. In such cases, you can devise new patterns or modify existing ones to suit your specific scenario.

Are design patterns specific to Java, or can they be applied in other programming languages?

Design patterns are not specific to Java and can be applied in various programming languages. The concepts and principles behind design patterns are language-agnostic, focusing on software design and architecture. However, the implementation of design patterns may vary slightly depending on the features and syntax of each programming language.

How do I choose the right design pattern for my Java application?

Choosing the right design pattern depends on the specific problem you're trying to solve and the requirements of your application. Consider factors like the problem domain, scalability, maintainability, and flexibility. Study the characteristics and purposes of different design patterns and select the one that best fits your scenario.

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