DESIGN PATTERN
| Type : | Cr (Creational) |
| Intent : | Ensure a class only has one instance, and provide a global point of access to it. |
| Applicability : | Use the Singleton pattern when : - there must be exactly one instance of a class, and it must be accessible to clients from a well-known access point. - when the sole instance should be extensible by subclassing, and clients should be able to use an extended instance without modifying their code. |