Learning record of java design patterns
Here we simply move the instantiation logic to a separate class and most commonly to a static method to this class. Some do not consider Simple Factory to be a 'design pattern', as it's simply a method that encapsulates object instantiation. Nothing complex goes on in the method. We are studying Simple Factory as it is often confused with "Factory Method" pattern.
java.text.NumberFormat.getInstance is an example of Simple Factory
a real example of Factory Method is java.util.Collection.iterator() method
Abstract Factory makes use of factory method pattern. You can think of abstract factory as an object with multiple factory methods.
Eager Singleton / Lazy Singleton / Enum Singleton java.lang.Runtime is a singleton In eager singleton implementation the singleton instance is created as soon the singleton class is referenced.