Static Factory Methods v.s. Constructor

Advantages to use Static Factory Methods

1. More descriptive - the name of the factory methods can explain more than a constructor

　　e.g.  v.s. 

2. Can have multiple static factory methods for separate purpose

3. Static factory methods can return existing instance instead of generate a new one everytime when it's invoked

　　- Good for immutable, singleton, uninstantiable

　　- Improve performance

　　e.g. 

4. Static factory method can return any subtype of their return type

　　- an API can return objects without making their classes public (can only make the interface public)

5. Static factory method can help guess type parameter

      e.g. Map<String, List<String>> m = HashMap.newInstance();

 

Disadvantages when only provide static factory method

1. Classes without Public/Protected constructor cannot be subclassed.

2. Not readily distinguishable from other static methods