重構：Query Method

在重構：Replace Temp with Query中，用查詢函數（query method）來取代totalAmount 和frequentRentalPoints這兩個臨時變量。首先用getTotalCharge()取代totalAmount:

public class Customer {
    private String _name;
    private Vector<Rental> _rentals = new Vector<Rental>();;

    public Customer(String name) {
        _name = name;
    }

    public void addRental(Rental arg) {
        _rentals.addElement(arg);
    }

    public String getName() {
        return _name;
    }

    public String statement() {

        int frequentRenterPoints = 0;
        Enumeration<Rental> rentals = _rentals.elements();
        String result = "Rental Record For " + getName() + "\n";
        while (rentals.hasMoreElements()) {

            Rental each = (Rental) rentals.nextElement();


            frequentRenterPoints += each.getFrequentRenterPoints();

            result += "\t" + each.getMovie().getTitle() + "\t" + String.valueOf(each.getCharge()) + "\n";

        }
        result += "Amount owed is " + String.valueOf(getTotalCharge()) + "\n";
        result += "You earned " + String.valueOf(frequentRenterPoints) + " frequent renter points";
        return result;
    }
    private double getTotalCharge() {
        double result = 0;
        Enumeration<Rental> rentals = _rentals.elements();
        while (rentals.hasMoreElements()) {
            Rental each = (Rental) rentals.nextElement();
            result += each.getCharge();
        }
        return result;
    }

}

用getTotalFrequentRenterPoints（）取代frequentRenterPoints:

public class Customer {
    private String _name;
    private Vector<Rental> _rentals = new Vector<Rental>();;

    public Customer(String name) {
        _name = name;
    }

    public void addRental(Rental arg) {
        _rentals.addElement(arg);
    }

    public String getName() {
        return _name;
    }

    public String statement() {
        Enumeration<Rental> rentals = _rentals.elements();
        String result = "Rental Record For " + getName() + "\n";
        while (rentals.hasMoreElements()) {

            Rental each = (Rental) rentals.nextElement();
            result += "\t" + each.getMovie().getTitle() + "\t" + String.valueOf(each.getCharge()) + "\n";

        }
        result += "Amount owed is " + String.valueOf(getTotalCharge()) + "\n";
        result += "You earned " + String.valueOf(getTotalFrequentRenterPoints()) + " frequent renter points";
        return result;
    }
    private double getTotalCharge() {
        double result = 0;
        Enumeration<Rental> rentals = _rentals.elements();
        while (rentals.hasMoreElements()) {
            Rental each = (Rental) rentals.nextElement();
            result += each.getCharge();
        }
        return result;
    }
    private int getTotalFrequentRenterPoints() {
        int result = 0;
        Enumeration<Rental> rentals = _rentals.elements();
        while (rentals.hasMoreElements()) {
            Rental each = (Rental) rentals.nextElement();
            result += each.getFrequentRenterPoints();
        }
        return result;
    }
}