Prototype vs Singleton vs a Plain Constructor

Prototype, Singleton and a plain constructor each answer a different question about where an object comes from. Prototype answers "copy a configured one" when setting an object up is costly or its class is unknown. Singleton answers "share the only one" when exactly one object of a class may exist. A constructor answers "make a new one" when nothing about creation varies, and it is the default the other five patterns have to beat. This card sets those answers beside Factory Method, Abstract Factory and Builder, and ends at a flowchart for all six.

The flowchart asks the questions in an order that reaches the constructor fastest when nothing varies. Each "no" moves one question down, and the last "no" is the constructor.

The Singleton box offers an alternative because a global access point hides dependencies and carries state between tests: one object created at start-up and passed to the code that needs it gives the same single instance without the hidden state. Prototype and Singleton are opposites in one respect, since Prototype gives every caller a new object and Singleton gives every caller the same one.