Java interview : Design Patterns Differences смотреть онлайн

What is the difference between Adapter vs Proxy vs Facade Design Patterns?

Adapter
let you connect two components, which wouldnt be working because of incompatible interfaces

Decorator pattern
adds new functionalities at runtime. It allows you to enrich object, even after its creation.

Facade
provides simpler interfaces. So instead of client directly accessing individual components of a system, it uses facade /ie REST/

Proxy
prevents client to directly accessing object, instead it act as real object and can provide alternate behavior /cache, delay / or forward request to original object

What is the difference between Singleton vs Static class ?

- static class provides better performance than Singleton pattern, because static methods are bonded on compile time.
- static methods in Java cannot be overridden
- static classes are hard to mock and consequently harder to test than Singletons,
which are pretty easy to mock and thus easy to test.
- should not maintain state in static class
- singleton classes can be lazy loaded if its an heavy object,
but static class doesnt have such advantages and are always eagerly loaded.

What is the difference between Flyweight vs Singleton vs Factory ?

Flyweight - array cache of immutable objects , creates the object if it does not exists
Factory - creates the mutable new instances of the object , return exception if no possibility found
Singleton - one instance of mutable object

What is the difference between Factory vs Dependency Injection Design Patterns?

Factory:
- your dependent class is dependent on factory
- need to mock factory to test the class

Dependency Injection:
- takes out the dependency completely, provides better decoupling
- gives simple unit testing of classes

Difference between Factory and Builder Design Pattern ?

Builder pattern is the extension of Factory pattern wherein the
Builder class builds a complex object in multiple steps.