Previously we learn JAVA : Singleton Pattern 

Factory pattern is one of the most used design pattern in Java. This type of design pattern comes under creational pattern as this pattern provides one of the best ways to create an object.

[Define an interface for creating an object, but let the subclasses decide which class to instantiate. The Factory method lets a class defer instantiation to subclasses. ]

Factory Method Pattern Definition Diagram:

Here we create a Shape interface and concrete classes implementing the Shape interface. A factory class ShapeFactory is defined.

FactoryPatternDemo is our demo class, it will use ShapeFactory to get a Shape object. It will pass information (CIRCLE / RECTANGLE / SQUARE) to ShapeFactory to get the type of object it needs.

Where Would I Use This Pattern?

The idea behind the Factory Method pattern is that it allows for the case where a client doesn't know what concrete classes it will be required to create at runtime, but just wants to get a class that will do the job. The FactoryMethod builds on the concept of a simple Factory but lets the subclasses decide which implementation of the concrete class to use. You'll see factories used in logging frameworks, and in a lot of scenarios where the client doesn't need to know about the concrete implementations. It's a good approach to encapsulation.

Next, we will learn about : JAVA - AbstractFactory Pattern