In 2025, Java continues to be one of the most popular programming languages, thanks to its versatility, portability, and wide range of libraries and frameworks. Understanding Java design patterns is crucial for building efficient, maintainable, and scalable applications. Design patterns are proven solutions to common design problems. This article explores some of the common Java design patterns used in 2025.

1. Singleton Pattern

The Singleton Pattern ensures that a class has only one instance and provides a global point of access to that instance. It is particularly useful when managing shared resources like configuration objects or connection pools. The following snippet demonstrates a simple implementation of a singleton in Java:

public class Singleton {
    private static Singleton instance;

    private Singleton() {}

    public static Singleton getInstance() {
        if (instance == null) {
            instance = new Singleton();
        }
        return instance;
    }
}

2. Factory Pattern

The Factory Pattern is a creational pattern used for creating objects. Instead of calling the constructor directly, a Factory class decides which subclass to instantiate based on given input. This pattern is particularly useful when the exact types of objects generated are unknown in advance.

public interface Shape {
    void draw();
}

public class Circle implements Shape {
    public void draw() {
        System.out.println("Drawing a Circle");
    }
}

public class ShapeFactory {
    public Shape getShape(String shapeType) {
        if (shapeType.equalsIgnoreCase("CIRCLE")) {
            return new Circle();
        }
        return null;
    }
}

3. Observer Pattern

The Observer Pattern is a behavioral pattern that defines a one-to-many dependency between objects. When one object changes state, all its dependents are notified and updated automatically. This pattern promotes a loose coupling between objects.

import java.util.ArrayList;
import java.util.List;

interface Observer {
    void update();
}

class Subject {
    private final List<Observer> observers = new ArrayList<>();

    public void addObserver(Observer observer) {
        observers.add(observer);
    }

    public void notifyObservers() {
        for (Observer observer : observers) {
            observer.update();
        }
    }
}

4. Decorator Pattern

The Decorator Pattern is a structural pattern that allows behavior to be added to individual objects, either statically or dynamically, without affecting the behavior of other objects from the same class. It is useful for adhering to the Open/Closed Principle.

interface Coffee {
    String getDescription();
    double getCost();
}

class SimpleCoffee implements Coffee {
    public String getDescription() {
        return "Simple coffee";
    }

    public double getCost() {
        return 1.0;
    }
}

class MilkDecorator implements Coffee {
    private final Coffee coffee;

    public MilkDecorator(Coffee coffee) {
        this.coffee = coffee;
    }

    public String getDescription() {
        return coffee.getDescription() + ", milk";
    }

    public double getCost() {
        return coffee.getCost() + 0.5;
    }
}

5. Strategy Pattern

The Strategy Pattern is used to create a family of algorithms, encapsulate each one, and make them interchangeable. It allows the algorithm behavior to be changed at runtime, promoting flexibility and reusability of code.

interface Strategy {
    void execute();
}

class ConcreteStrategyA implements Strategy {
    public void execute() {
        System.out.println("Executing strategy A");
    }
}

class Context {
    private Strategy strategy;

    public Context(Strategy strategy) {
        this.strategy = strategy;
    }

    public void executeStrategy() {
        strategy.execute();
    }
}

By leveraging these design patterns, Java developers can create more robust, efficient, and flexible applications. Understanding these patterns is essential for tackling complex software development challenges in 2025.

Additional Resources

For those interested in expanding their programming skills, consider reading about JavaScript bot development and learning how to run Java in PowerShell. Additionally, understanding how the p5.js draw function works and exploring recursive functions in JavaScript can further enhance your coding expertise.