factory design pattern java code example

Example 1: java builder pattern example

public class BankAccount {
    public static class Builder {
        private long accountNumber; //This is important, so we'll pass it to the constructor.
        private String owner;
        private String branch;
        private double balance;
        private double interestRate;
        public Builder(long accountNumber) {
            this.accountNumber = accountNumber;
        }
        public Builder withOwner(String owner){
            this.owner = owner;
            return this;  //By returning the builder each time, we can create a fluent interface.
        }
        public Builder atBranch(String branch){
            this.branch = branch;
            return this;
        }
        public Builder openingBalance(double balance){
            this.balance = balance;
            return this;
        }
        public Builder atRate(double interestRate){
            this.interestRate = interestRate;
            return this;
        }
        public BankAccount build(){
            //Here we create the actual bank account object, which is always in a fully initialised state when it's returned.
            BankAccount account = new BankAccount();  //Since the builder is in the BankAccount class, we can invoke its private constructor.
            account.accountNumber = this.accountNumber;
            account.owner = this.owner;
            account.branch = this.branch;
            account.balance = this.balance;
            account.interestRate = this.interestRate;
            return account;
        }
    }
    //Fields omitted for brevity.
    private BankAccount() {
        //Constructor is now private.
    }
    //Getters and setters omitted for brevity.
}

BankAccount account = new BankAccount.Builder(1234L)
            .withOwner("Marge")
            .atBranch("Springfield")
            .openingBalance(100)
            .atRate(2.5)
            .build();
BankAccount anotherAccount = new BankAccount.Builder(4567L)
            .withOwner("Homer")
            .atBranch("Springfield")
            .openingBalance(100)
            .atRate(2.5)
            .build();

Example 2: simple factory pattern

enum FanType
{
    TableFan,
    CeilingFan,
    ExhaustFan
}

interface IFan
{
    void SwitchOn();
    void SwitchOff();
}

class TableFan : IFan {.... }

class CeilingFan : IFan {.... }

class ExhaustFan : IFan {..... }

interface IFanFactory
{
    IFan CreateFan(FanType type);
}

class FanFactory : IFanFactory
{
    public IFan CreateFan(FanType type)
    {
        switch (type)
        {
            case FanType.TableFan:
                return new TableFan();
            case FanType.CeilingFan:
                return new CeilingFan();
            case FanType.ExhaustFan:
                return new ExhaustFan();
            default:
                return new TableFan();
        }
    }
}

//The client code is as follows:

static void Main(string[] args)
{
        IFanFactory simpleFactory = new FanFactory();
        // Creation of a Fan using Simple Factory
        IFan fan = simpleFactory.CreateFan(FanType.TableFan);
        // Use created object
        fan.SwitchOn();

        Console.ReadLine();
 }