What is Java Design Patterns?
- A Java design patterns is a general, reusable way to solve a software design-related problem that occurs frequently.
- Java design patterns are a template or blueprint that a person can use to solve the given software challenges.
- Java Design patterns do not provide a ready-to-use code, but rather a flexible set of rules and best practices, which developers can easily adjust to their own needs.
Why Are Java Design Patterns Important?
- Standardized solutions: They uncover the perfect and standard way of addressing the issues, which in turn boosts the code consistency and reliability.
- Reusability: Patterns push for code replication through the fostering of modular designs that are not restrictive and are also easy on the maintenance.
- Communication: Java Design patterns are a common vocabulary for developers, which in turn makes it easy for them to clearly and efficiently talk about solutions.
- Software architecture is greatly improved: Use of Java Design patterns brings such software development advantages as more flexible functionality, easy re-modifications, and low maintenance over the long run.
Types of Java Design Patterns:
Java Design patterns are normally separated into three main categories based on their function.
1.Creational Patterns:
- These patterns are about the process of object creation. They help with the implementation in creating the objects. For example one of the designs is:
- Singleton Pattern: Ensures that a class has only one instance and provides a global access point.
- Factory Method Pattern: Provides an interface for creating objects, but allows subclasses to alter the type of objects that will be created.
- Abstract Factory Pattern: Creates families of related or dependent objects without specifying their concrete classes.
2.Structural Patterns:
- These patterns are mainly about the aspect of object composition. They are facilitating the useful organization of the structure of the system. Among others, the following are especially:
- Adapter Pattern: Allows incompatible interfaces to work together.
- Decorator Pattern: Adds new responsibilities to an object dynamically without altering its structure.
- Facade Pattern: Provides a simplified interface to a complex system of classes.
3.Behavioral Patterns:
- These patterns are about the communication among objects and directly attaining the improvement of the interaction and responsibility delegation between them. These patterns happen through the below situations:
- Observer Pattern: The Observer Pattern is a software design pattern that is used to design an object that maintains a list of its dependents (observers that need to be notified of any change).
- Strategy Pattern: The Strategy Pattern is a software design pattern that can be used to extend a family of algorithms and encapsulate them so that they can be selected at runtime.
- Command Pattern: A design pattern that allows us to wrap a request into an object, thus allowing the separation of clients’ rules from requests. This also allows the reuse of the same code for other commands.
How to Implement Design Patterns in Java with Practical Examples
Design patterns give us the best options to the common problems and there are solutions that have already been proved capable. They offer best practices and reusable templates to tackle recurring challenges in software development. In this article, we will explore three widely used design patterns in Java: Singleton, Factory, and Observer patterns. These are going to have practical examples.
1. Singleton Pattern
Definition
- Singleton pattern allows ensuring that one class has only one object and that the object can be accessed by all the users of that system globally.
- The key purpose of the creation of the Singleton pattern is to make classes so that they don’t create duplicate objects when called from multiple users.
- It is common for such classes whose main task is to remind all the users of the shared resources of configuration details, logs, or database connections to be used in automation tests.
Implementation
Try out a procedure-by-procedure walkthrough of the Singleton pattern in Java.
Example: Logger Class
public class Logger {
// Step 1: Create a private static instance of the class
private static Logger instance;
// Step 2: Make the constructor private to prevent instantiation
private Logger() {
System.out.println(“Logger initialized.”);
}
// Step 3: Provide a public static method to access the instance
public static Logger getInstance() {
if (instance == null) {
instance = new Logger();
}
return instance;
}
// Method to log messages
public void log(String message) {
System.out.println(“Log: ” + message);
}
}
Usage:
public class Main {
public static void main(String[] args) {
Logger logger1 = Logger.getInstance();
Logger logger2 = Logger.getInstance();
logger1.log(“First log message.”);
logger2.log(“Second log message.”);
// Verify that both instances are the same
System.out.println(logger1 == logger2); // Output: true
}
}
Advantages:
- Only one instance is ensured: The Singleton pattern however guarantees that a class will be, one and only one object, that can be created, regardless of how many times the class is called.
- Memory efficient: This means the memory will not be wasted but only one instance is created.
- Centralized resource control: It acts as a centralized control point for shared resources, thus it is easier to be managed and maintained.
Best Practices:
- Bill Pugh Singleton: Instead of Eager Singleton, use the static inner class in Java to ensure lazy initialization and thread-safe nature of the code
- Thread-Safety: When a multi-threaded application is under consideration, the techniques for data synchronization (for instance, the “synchronized” keyword or ReentrantLock) are to be used to allow safe usage and access to Singleton.
2. Factory Pattern
Definition
- Factory pattern is the moment that an item having its interface is placed in another class and the subclasses that are between different types of the same category, in fact, are the ones that are determined to interact with the classes and not the superclass.
- This pattern separates the formation of objects from the main program logic.
Implementation
The Factory pattern is implemented by us in the way we create different types of shapes (Circle, Rectangle, and Square).
Example: Shape Factory
// Create an interface
interface Shape {
void draw();
}
// Implement concrete classes
class Circle implements Shape {
@Override
public void draw() {
System.out.println(“Drawing a Circle.”);
}
}
class Rectangle implements Shape {
@Override
public void draw() {
System.out.println(“Drawing a Rectangle.”);
}
}
class Square implements Shape {
@Override
public void draw() {
System.out.println(“Drawing a Square.”);
}
}
// Step 3: Create a Factory class
class ShapeFactory {
public Shape getShape(String shapeType) {
if(shapeType == null) {
return null;
}
switch (shapeType.toLowerCase()) {
case “circle”:
return new Circle();
case “rectangle”:
return new Rectangle();
case “square”:
return new Square();
default:
return null;
}
}
}
Usage:
public class Main {
public static void main(String[] args) {
ShapeFactory shapeFactory = new ShapeFactory();
// Create and use different shapes
Shape shape1 = shapeFactory.getShape(“circle”);
shape1.draw();
Shape shape2 = shapeFactory.getShape(“rectangle”);
shape2.draw();
Shape shape3 = shapeFactory.getShape(“square”);
shape3.draw();
}
}
Output:
Drawing a Circle.
Drawing a Rectangle.
Drawing a Square.
Advantages:
- Object creation is independent: The Factory pattern makes sure that the client code does not have to know how specifically object creation is done, therefore a more flexible design is achieved.
- More comfortable maintenance of code: If the creation logic is in one place (the factory), object creation changes can be made without affecting the client code.
- Scalable: New object types can be added more easily by just extending the factory class rather than changing the current code.
Best Practices:
- Abstract Factory: When the factory method involves the creation of families of related objects, the Abstract Factory pattern can be used.
- The factory method as a way to the complex creation logic: Use the Factory pattern when the object creation logic is not straightforward but a decision criteria or conditions must be satisfied.
3. Observer Pattern
Definition
- The Observer pattern, which is a behavioral design pattern, specifies that an object—the subject—preserves a list of its dependents (observers) and communicates any state changes to them.
- This layout is extensively applied to event-driven systems.
Implementation
Whe We will bring a creaking news Observer pattern to life in a news-agency that notifes the observers about the most recent news.
Example: News Agency
import java.util.ArrayList;
import java.util.List;
// Step 1: Create the Subject interface
interface Subject {
void registerObserver(Observer o);
void removeObserver(Observer o);
void notifyObservers(String news);
}
// Step 2: Create the Observer interface
interface Observer {
void update(String news);
}
// Step 3: Implement the Subject class
class NewsAgency implements Subject {
private List<Observer> observers = new ArrayList<>();
@Override
public void registerObserver(Observer o) {
observers.add(o);
}
@Override
public void removeObserver(Observer o) {
observers.remove(o);
}
@Override
public void notifyObservers(String news) {
for (Observer observer : observers) {
observer.update(news);
}
}
}
// Step 4: Implement Observer classes
class NewsSubscriber implements Observer {
private String name;
public NewsSubscriber(String name) {
this.name = name;
}
@Override
public void update(String news) {
System.out.println(name + ” received news: ” + news);
}
}
Usage
public class Main {
public static void main(String[] args) {
NewsAgency agency = new NewsAgency();
// Create observers
Observer subscriber1 = new NewsSubscriber(“Subscriber 1”);
Observer subscriber2 = new NewsSubscriber(“Subscriber 2”);
// Register observers
agency.registerObserver(subscriber1);
agency.registerObserver(subscriber2);
// Notify observers with news updates
agency.notifyObservers(“Breaking News: Observer Pattern Implemented Successfully!”);
// Remove an observer and notify again
agency.removeObserver(subscriber1);
agency.notifyObservers(“Second News Update: Singleton Pattern Rocks!”);
}
}
Output:
Subscriber 1 received news: Breaking News: Observer Pattern Implemented Successfully!
Subscriber 2 received news: Breaking News: Observer Pattern Implemented Successfully!
Subscriber 2 received news: Second News Update: Singleton Pattern Rocks!
Advantages:
- Loose coupling between subject and observers: Decoupled or decoupling equalizes the situation- the subject should not be aware of who its observers are, and they can be added and deleted at runtime.
- Real-time updates: The Observer pattern is the most appropriate in cases where real-time updates are required. It may include messages, stock prices, or sports scores.
- Scalable: It can easily scale to support multiple observers, even among different types of clients.
Best Practices:
- Use for real-time systems: The Observer pattern is often used for systems that need real-time notifications or updates such as messaging systems or event-driven architectures.
- Ensure proper memory management: For instance, take a good look at alerts caused by the observer pattern such as memory leaks especially in Java where the observer may not automatically be cleared if not handled properly.
Design patterns are essential in the solving common challenges of software engineering. The Singleton pattern guarantees that the class will be just in one instance; while the Factory pattern allows object creation to be independent of usage; and the Observer pattern enables one-to-many relationships between subjects and observers. The developers of these patterns are the ones who can produce the applications of the highest quality through their skill of making them more manageable, scalable, and flexible.
When software systems are getting complicated, design patterns maintain a standard approach for dealing with recurring issues that result in better software architecture. The inclusion of these patterns in Java would enable the developers to write cleaner and more efficient code which is also easier to test, maintain, and extend.