What design patterns have you used most frequently in your projects?

Most commonly used design patterns in Java projects:

• Singleton — to ensure a class has only one instance.
• Factory Method — to create objects without specifying the exact class.
• Observer — for implementing subscription to events and notifications.
• Builder — for step-by-step creation of complex objects.
• Decorator — for dynamically adding functionality to objects.

Example of Singleton:

public class Singleton {
    private static Singleton instance;

    private Singleton() {}

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