Factory

Goal

• Classes of more abstract levels shall not depend on classes on more detailed levels
• Classes shall only depend on abstractions, e.g. interfaces

Solution

Move creation of objects to object factory class.

Object Factory

• The single responsibility of an object factory class is to create objects of other classes
• The factory decides if it provides the Singleton or a new object every time
• To prevent unwanted side effects due to the direct creation of the managed classes,

CLASS cl_managed DEFINITION
    PUBLIC
    CREATE PRIVATE "Define the constructor of the factory-managed class as private
    GLOBAL FRIENDS cl_factory "Declare the factory as a global friend of the factory-managed class

Factory using Friend Class

• Many programming languages support friend classes
• Friend class has access to the class's private constructor and hence can contain the factory method.

Testability advantage

Offers a single point of injection for Test Double (Private)s in unit tests and integration/system tests

• Create the Interface and multiple implementation of same interface.
• Factory method - used to hide the logic of object creation - loose coupling and high cohesion
• Create another class and initialize the object in a method over there. Return the object.

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Backlinks

• Test Isolation (cs)
• Do NOT create dependencies (cs)