How to apply Simple Factory Pattern Java

Question

I am trying ot understand how to apply a the simple factory pattern to an assigment I have but I do not understand how to do it.

This is the request: Apply the Simple Factory pattern that creates the appropriate Strategy object. Remember, this is a Simple Factory pattern. Draw the UML diagram of the new design.

We already implemented the strategy pattern but I do not understand how to apply the simple factory pattern to the code. I understand that the simple factory pattern is supposed to provide encapsulation for the creation of the object but I do not see how the examples I have found show how to apply to this. Any help would be appreciated.

EDIT: Updated code EDIT: Changed code to make use of polymorphism

package Client;

import domain.Loan;
import factory.StrategyFactory;
import strategy.ComplexLoan;
import strategy.ICapitalStrategy;

public class Client {
    public static void main(String[] args){
        Loan complexLoan = new Loan(2.2, 2, 3.3, 4.4, 5, 6, 7, StrategyFactory.getComplexStrategy());
        System.out.print("hello");

    }

}

package factory;

import strategy.ComplexLoan;
import strategy.ICapitalStrategy;
import strategy.RevolvingLoan;
import strategy.TermLoan;



public class StrategyFactory {
    /*
    public static ICapitalStrategy getStrategy(String type) {       
        if (type.equals("Complex")){
            return new ComplexLoan();
        }
        else if (type.equals("Revolving")){
            return new RevolvingLoan();
        }
        else if (type.equals("Term")){
            return new TermLoan();
        }
        return null;
    }
    */

    public static ICapitalStrategy getComplexStrategy() {
        return new ComplexLoan();
    }
    public static ICapitalStrategy getRevolvingStrategy() {
        return new RevolvingLoan();
    }
    public static ICapitalStrategy getTermStrategy() {
        return new TermLoan();
    }
}

    package domain;
    import strategy.ICapitalStrategy;


    public class Loan {
        private ICapitalStrategy strategy;

        double commitment;
        int duration;
        double riskFactor;
        double unusedPercentage;
        int outstandingRiskAmount;
        int unusedRiskAmount;
        double unusedRiskFactor;
        double capital;

        public Loan(double commit, int dura, double rskFact, double unusedPer,
                    int outStandRskAmt, int unusedRskAmt, double unusedRskFac,
                    ICapitalStrategy strat) {
            this.commitment = commit;
            this.duration = dura;
            this.riskFactor = rskFact;
            this.outstandingRiskAmount = outStandRskAmt;
            this.unusedRiskAmount = unusedRskAmt;
            this.unusedRiskFactor = unusedRskFac;
            this.strategy = strat;

        }

        public double CalculateCapital() {
            return strategy.CapitalLoan(this);
        }

        public double getCommitment() {
            return commitment;
        }

        public void setCommitment(double c) {
            commitment = c;
        }

        public int getDuration() {
            return duration;
        }

        public void setDuration(int dur) {
            duration = dur;
        }

        public double getRiskFactor() {
            return riskFactor;
        }

        public void setRiskFactor(double rskFac) {
            riskFactor = rskFac;
        }

        public double getUnusedPercentage() {
            return unusedPercentage;
        }

        public void setUnusedPercentage(double unusedPercent) {
            unusedPercentage = unusedPercent;
        }

        public double getOutstandingRiskAmount() {
            return outstandingRiskAmount;
        }

        public void setOutstandingRiskAmount(int outStandingRskAmt) {
            outstandingRiskAmount = outStandingRskAmt;
        }

        public double getUnusedRiskAmount() {
            return unusedRiskAmount;
        }

        public void setUnusedRiskAmount(int UnusedRskAmt) {
            unusedRiskAmount = UnusedRskAmt;
        }

        public double getUnusedRiskFactor() {
            return unusedRiskFactor;
        }

        public void setUnusedRiskFactor(double unusedRskFac) {
            unusedRiskFactor = unusedRskFac;
        }

        public Loan(ICapitalStrategy strategy) {
            this.strategy = strategy;
        }

        /*public double executeStrategy() {
            return this.strategy.CapitalLoan(this);
        }
        */
    }

    package strategy;

    import domain.Loan;

    public class ComplexLoan implements ICapitalStrategy {

        @Override
        public double CapitalLoan(Loan l) {
            return ((l.getOutstandingRiskAmount() * l.getDuration() * l.getRiskFactor()) + (l.getUnusedRiskAmount() 
                    * l.getDuration() * l.getUnusedRiskFactor() ));
        }

    }

    package strategy;

    import domain.Loan;

    public interface ICapitalStrategy {
        public double CapitalLoan(Loan l);
    }

    package strategy;

    import domain.Loan;

    public class RevolvingLoan implements ICapitalStrategy {

        @Override
        public double CapitalLoan(Loan l) {
            return (l.getCommitment() * l.getUnusedPercentage() * l.getDuration() *l.getRiskFactor());  
        }

    }

    package strategy;

    import domain.Loan;

    public class TermLoan implements ICapitalStrategy {
        public TermLoan() {

        }
        public double CapitalLoan(Loan l) {
            return (l.getCommitment() * l.getDuration() * l.getRiskFactor());
        }

    }

Answer 1

Here's a likely helpful bit about Simple Factory Pattern[1]:

The simple factory isn't actually a pattern; it's more of a design principle. The simple factory encapsulates the object creation code, but keeps control over how the object is created. Simple factories are often designed as a class with a static method (aka static factory) that returns the object requested.

Here's an example, not suited directly to your example in order to make you think a bit hard for your homework :)

interface Foo{
  double calculateStuff();
}

class MyClass implements Foo{
  @Override
  public double calculateStuff(){
    //logic goes here
  }
}

class MyFactory {
  public static double getCalculatedStuff(){
    return new MyClass().calculateStuff();
  }
}

class RunCode {
  public static void main(String[] args){
     double stuff = MyFactory.getCalculatedStuff();
  }
}

• [1] - Learning Design Patterns - Factory Pattern

EDIT:

class LoanFactory{

    public static double getComplexLoan(Loan l){
        return new ComplexLoan().CapitalLoan(l);
    }
}

another way (which has its uses, but in this case I prefer the method above):

class ComplexLoan implements ICapitalStrategy{
    private ComplexLoan(){
    }

    public static double getLoan(Loan l){
        return new ComplexLoan().CapitalLoan(l);
    }
}

or this option that explicitly displays polymorphism:

class LoanFactory{

    public static ICapitalStrategy getComplexLoan(){
        return new ComplexLoan();
    }
}

One other thing that is important to note: convention says method names should start with a lowercase letter, so your CapitalLoan() would be capitalLoan().

Also, there's no need to prefix your interfaces with an I, so your ICapitalStrategy would become CapitalStrategy.

Answer 2

In the following example. The "Document" is abstract class and "html" document. "MyDocument" and "pdf" are concrete class. As long as you provide parameter with valid string, you will get the corresponding concrete class. For example if you put "pdf" as a parameter, you will get pdf document. Document type is all you need to accept whatever type of documents you want to create.

public Document CreateDocument(String type){
if (type.isEqual("html"))
    return new HtmlDocument();
if (type.isEqual("proprietary"))
    return new MyDocument();
if (type.isEqual("pdf"))
    return new PdfDocument ();
}

There is a better documented article thread in Examples of GoF Design Patterns in Java's core libraries

Answer 3

public interface PaymentMethod {
    public void makePayment();
}

class CreditCard implements PaymentMethod {
    public void makePayment() {
        System.out.println("Payment through credit card...");
    }
}

class NetBanking implements PaymentMethod {
    public void makePayment() {
        System.out.println("Payment through net banking...");
    }
}

public class PaymentMethodFactory {
    public static PaymentMethod getPaymentMethod(String method) {
        if ("creditcard".equalsIgnoreCase(method)) {
            return new CreditCard();
        } else if ("netbanking".equalsIgnoreCase(method)) {
            return new NetBanking();
        } else {
            throw new IllegalArgumentException("Payment method not supported!");
        }
    }
}

public class SimpleFactoryTest {

    public static void main(String[] args) {
        PaymentMethodFactory factory = new PaymentMethodFactory();
        PaymentMethod paymentMethod = factory.getPaymentMethod("creditcard");
        paymentMethod.makePayment();
    }

}