The Singleton Pattern
¥Each execution of the expression
new Empty()
creates a new object. In principle, there is only one empty list, just like there is only one number 0. Hence, we would like to represent the empty list by a single library.
new Empty()creates a new object. In principle, there is only one empty list, just like there is only one number 0. Hence, we would like to represent the empty list by a single library.
¥The singleton pattern is the
mechanism that we use to create a unique
instance of a class. This pattern consists of two
chunks of code:
Ða static
final field in the class that holds the
single instance of the class
Ða private
attribute on the class constructor, so
no client can create another instance
of the class.