Template pattern - Example

A Loan application process may take several steps to finish.

Let's assume the steps are as follows : 

• Check client's bank balance history
• Check client's credit score from three different companies
• Check client's other loan information
• Check client's stock holding value
• Check client's income potential in the future etc.

You may use a template method to hold the process steps together without considering the real implementation in the subclass.

abstract class CheckBackground { 

    public abstract void checkBank();

    public abstract void checkCredit();

    public abstract void checkLoan();

    public abstract void checkStock();

    public abstract void checkIncome();

    // work as template method

    public void check() {

        checkBank();

        checkCredit();

        checkLoan();

        checkStock();

        checkIncome();

    }

}

class LoanApp extends CheckBackground {

    private String name;

    public LoanApp(String name) {

        this.name = name;

    }

    public String getName() {

        return name;

    }

    public void checkBank() {

        // check acct, balance

        System.out.println("check bank...");

    }

    public void checkCredit() {

        // check score from 3 companies

        System.out.println("check credit...");

    }

    public void checkLoan() {

        // check other loan info

        System.out.println("check other loan...");

    }

    public void checkStock() {

        // check how many stock values

        System.out.println("check stock values...");

    }

    public void checkIncome() {

        // check how much a family make

        System.out.println("check family income...");

    }

    //other methods

}

class TestTemplate {

    public static void main(String[] args) {       

        LoanApp mortgageClient = new LoanApp("Judy");

        System.out.println("\nCheck client " + 

          mortgageClient.getName()+ " Mortgage loan application. ");

        mortgageClient.check();

        

        LoanApp equityloanClient = new LoanApp("Mark");

        System.out.println("\nCheck client " + 

          equityloanClient.getName()+ " equity loan application. ");

        equityloanClient.check();

    }

}

Method overloading and method overriding are good examples of template method pattern.

For example,

Coercion polymorphism -- refers to a single operation serving several types through implicit type conversion.

Overloading polymorphism -- refers to using a single identifier for different operations.

Parametric polymorphism -- refers to a class declaration that allows the same field names and method signatures to associate with a different type in each instance of that class.