Java Design Pattern Factory Approach (Factory method)

Type: Object-Creation pattern

Intent: defines an interface for creating objects, letting subclasses decide which class to instantiate. Factory method causes the instantiation of a class to be deferred to its subclasses.

Applicability:

• When a class does not know the class of the object it must create.
• When a class wants to specify the object it creates by its subclass.
• When a class delegates the responsibility of creating an object to one of several help subclasses, and you want the information to be localized for which helper subclasses are proxies.

Structure:

Participants:

Product (Document)
-Defines an interface for objects created by the factory method.
concreteproduct (MyDocument)
-Implements the product interface.
Creator (application)
-Declares a factory method that returns an object of type product. Creator can also define a factory side
The default implementation of the method, which returns a default Concreteproduct object.
-You can call the factory method to create a product object.
Concretecreator (MyApplication)
-Redefine the factory method to return a concreteproduct instance.

Example

Note: In the actual code, I have added several account interfaces. Factory method is: Getaccount ()

The code is as follows

Copy Code

Account.java Package Com.raysmond.factorymethod; Public interface Account { Interface to define objects created by the factory method Public Roletype getrole (); public void Setaccountid (Integer accountid); Public Integer Getaccountid (); public void Setaccountname (String name); Public String getaccountname (); } User.java Package Com.raysmond.factorymethod; public class User implements account{ Private Integer userId; Private String UserName; @Override Public Roletype Getrole () { return roletype.user; } @Override public void Setaccountid (Integer accountid) { This.userid = AccountId; } @Override Public Integer Getaccountid () { return userId; } @Override public void Setaccountname (String name) { This.username = name; } @Override Public String Getaccountname () { return userName; } } Admin.java Package Com.raysmond.factorymethod; public class Admin implements account{ Private Integer Adminid; Private String AdminName; @Override Public Roletype Getrole () { return roletype.admin; } @Override public void Setaccountid (Integer accountid) { This.adminid = AccountId; } @Override Public Integer Getaccountid () { return Adminid; } @Override public void Setaccountname (String name) { This.adminname = name; } @Override Public String Getaccountname () { return adminname; } } Accountfactory.java Package Com.raysmond.factorymethod; Public interface Accountfactory { Account Getaccount (); } Userfactory.java Package Com.raysmond.factorymethod; public class Userfactory implements accountfactory{ @Override Public account Getaccount () { return new User (); } } Adminfactory.java Package Com.raysmond.factorymethod; public class Adminfactory implements accountfactory{ @Override Public account Getaccount () { return new Admin (); } } Roletype.java Package Com.raysmond.factorymethod; public enum Roletype { Admin,user } Test.java Package Com.raysmond.factorymethod; public class Test { public static void Main (string[] args) { Accountfactory userfactory = new Userfactory (); User user = (user) userfactory.getaccount (); Accountfactory adminfactory = new Adminfactory (); Admin admin = (admin) adminfactory.getaccount (); System.out.println (User.getrole ()); System.out.println (Admin.getrole ()); } }