Factory Design pattern common usage

Common Usage

Along with singleton pattern the factory is one of the most used patterns. Almost any application has some factories. Here are a some examples in java:
- factories providing an xml parser: javax.xml.parsers.DocumentBuilderFactory or javax.xml.parsers.SAXParserFactory
- java.net.URLConnection - allows users to decide which protocol to use

Factory pattern When to Use

Factory pattern should be used when: - a framework delegate the creation of objects derived from a common superclass to the factory - we need flexibility in adding new types of objects that must be created by the class

Singleton Design Pattern Common Usage

There are many common situations when singleton pattern is used:
- Logger Classes
- Configuration Classes
- Accesing resources in shared mode
- Other design patterns implemented as Singletons: Factories and Abstract Factories, Builder, Prototype

Factory(Simplified version of Factory Method) Design Pattern

Factory(Simplified version of Factory Method) - Creates objects without exposing the instantiation logic to the client andRefers to the newly created object through a common interface.

Singleton pattern how to use

Singleton pattern should be used when we must ensure that only one instance of a class is created and when the instance must be available through all the code. A special care should be taken in multithreading environments when multible threads must access the same resources throught the same singleton object.

Singleton Design Pattern

Singleton - Ensure that only one instance of a class is createdand Provide a global access point to the object.