Factory Design Pattern in Java

Factory Design Pattern in Java

Intent

Define an interface for creating an object, but let subclasses decide which class to instantiate. Factory Method lets a class defer instantiation to subclasses.

Motivation

Factory Design pattern is also known as Virtual Constructor, the Factory Method is related to the idea on which libraries work: a library uses abstract classes for defining and maintaining relations between objects. One type of responsibility is creating such objects.

The library knows when an object needs to be created, but not what kind of object it should create, this being specific to the application using the library.

The Factory method works just the same way: it defines an interface for creating an object, but leaves the choice of its type to the subclasses, creation being deferred at run-time.

 A simple real life example of the Factory Method is the Bank Account.

A user wants to open an Account in a bank.  A user can open either a Saving Account, Current Account, Salary Account,  Demat Account based on their requirement.

Depending on the requirement the subclass object for any of the account type can be created can be created.

Applicability

Use the Factory Method pattern when

•          A class can't anticipate the class of objects it must create.
•          A class wants its subclasses to specify the objects it creates.
•          Classes delegate responsibility to one of several helper subclasses, and you want to localize the knowledge of which helper subclass is the delegate.

Consequences

•          Factory methods eliminate the need to bind application-specific classes into your code.
•           Provides hooks for subclasses. Creating objects inside a class with a factory method is always more flexible than creating an object directly. Factory Method gives subclasses a hook for providing an extended version of an object.
•          Connects parallel class hierarchies. Parallel class hierarchies result when a class delegates some of its responsibilities to a separate class.

 Implementation

We're going to create an Account interface and concrete classes implementing the Account interface.

A factory class AccountFactory would be responsible for returning object.

FactoryPatternDemo  class will use AccountFactory to get an Account object.

It will pass information (Saving / Current / Salary / Demat) to AccountFactory to get the type of object it needs.

Create an Interface Account

public interface Account {       public void openAccount(); }

Create Classes SavingAccount, SalaryAccount, CurrentAccount, DematAccount which implements the Account interface.

public class SavingAccount implements Account{       @Override       public void openAccount() {             System.out.println("Opening Savings Account");       } }

public class CurrentAccount implements Account{       @Override       public void openAccount() {             System.out.println("Opening Current Account");        } }

public class SalaryAccount implements Account{       @Override       public void openAccount() {             System.out.println("Opening Salary Account");       } }

public class DematAccount implements Account{       @Override       public void openAccount() {             System.out.println("Opening Demat Account");          } }

Create the AccountFactory Class which returns Objects of the Subclasses.

public class AccountFactory { public Account getAccountType(String accountType){       if(accountType==null){             return null;       }             if(accountType.equalsIgnoreCase("saving")){                   return new SavingAccount();             }             else if(accountType.equalsIgnoreCase("current")){                   return new CurrentAccount();             }             else if(accountType.equalsIgnoreCase("salary")){                   return new SalaryAccount();             }             else if(accountType.equalsIgnoreCase("demat")){                   return new DematAccount();             }       return null;      } }

Create the FactoryPatternDemo with the main method

public class FactoryPatternDemo { public static void main(String[] args) {       AccountFactory accountFactory=new AccountFactory();             Account saving=accountFactory.getAccountType("saving");       saving.openAccount();             Account current=accountFactory.getAccountType("current");       current.openAccount();             Account salary=accountFactory.getAccountType("salary");       salary.openAccount();             Account demat=accountFactory.getAccountType("demat");       demat.openAccount(); } }

Execute the above class , we get the following output.

Factory Design Pattern in Java