Question

I am going through Effective Java and some of my things which I consider as standard are not suggested by the book, for instance creation of object, I was under the impression that constructors are the best way of doing it and books says we should make use of static factory methods, I am not able to few some advantages and so disadvantages and so am asking this question, here are the benefits of using it.

Advantages:

1. One advantage of static factory methods is that, unlike constructors, they
   have names.
2. A second advantage of static factory methods is that, unlike constructors,
   they are not required to create a new object each time they’re invoked.
3. A third advantage of static factory methods is that, unlike constructors,
   they can return an object of any subtype of their return type.
4. A fourth advantage of static factory methods is that they reduce the verbosity
   of creating parameterized type instances.

Disadvantages:

1. The main disadvantage of providing only static factory methods is that
   classes without public or protected constructors cannot be subclassed.
2. A second disadvantage of static factory methods is that they are not
   readily distinguishable from other static methods.

Reference: Effective Java, Joshua Bloch, Edition 2, pg: 5-10

I am not able to understand the fourth advantage and the second disadvantage and would appreciate if someone can explain those points. I would also like to understand how to decide to use whether to go for Constructor or Static Factory Method for Object Creation.

Answer 1

• Advantage 4: When using a constructor, you have

  Foo<Map<Key, Value>> foo = new Foo<Map<Key, Value>>();
  

  vs

  Foo<Map<Key, Value>> foo = Foo.createFoo(); // no need to repeat
  

  this advantage will be gone in Java 7, when the diamond syntax will be introduced

• Disadvantage 2. You can’t easily tell whether a given static method is used for constructor, or for something else.

As for how to choose – there is no single recipe for that. You can weigh all of the above advantages and disadvantages given a use-case, but most often it will just be a decision driven by experience.