What are the differences between Java design patterns?

What are the main differences between the Singleton and Factory design patterns in Java?

The Singleton pattern ensures a class has only one instance and provides a global point of access to it. In contrast, the Factory pattern is used to create objects without specifying the exact class of the object that will be created, allowing for more flexibility.

Can you give me an example of when to use the Builder pattern?

The Builder pattern is useful when you need to create an object with many optional parameters. For instance, when constructing a complex object like a Pizza, you can use a PizzaBuilder to set only the desired toppings and size.

How do the Observer and Strategy patterns differ?

The Observer pattern is used for a one-to-many dependency where changes in one object notify all dependent objects. The Strategy pattern, however, defines a family of algorithms, encapsulates each one, and makes them interchangeable, allowing the algorithm to vary independently from clients that use it.

Which design pattern would you recommend for a logging system?

For a logging system, the Singleton pattern is often recommended to ensure that there is only one instance of the logger throughout the application, while the Strategy pattern can be used to allow different logging strategies (e.g., file logging, console logging) to be implemented.