forgivingbuilder.java

java设计模式源码

package com.oozinoz.reservation;

/*
 * Copyright (c) 2001, 2005. Steven J. Metsker.
 * 
 * Steve Metsker makes no representations or warranties about
 * the fitness of this software for any particular purpose, 
 * including the implied warranty of merchantability.
 *
 * Please use this software as you wish with the sole
 * restriction that you may not claim that you wrote it.
 */

import com.oozinoz.utility.Dollars;

/**
*  This class builds a valid reservation from its attributes,
*  and fills in values where it can if the attributes are not
*  set. This builder must receive a city and a date, but it
*  will set reasonable values for the other reservation values.
*/
public class ForgivingBuilder extends ReservationBuilder {
    public Reservation build() throws BuilderException {
        boolean noHeadcount = (headcount == 0);
        boolean noDollarsPerHead = (dollarsPerHead.isZero());

        if (noHeadcount && noDollarsPerHead) {
            headcount = MINHEAD;
            dollarsPerHead = sufficientDollars(headcount);
        } else if (noHeadcount) {
            headcount = (int) Math.ceil(MINTOTAL.dividedBy(dollarsPerHead));
            headcount = Math.max(headcount, MINHEAD);
        } else if (noDollarsPerHead) {
            dollarsPerHead = sufficientDollars(headcount);
        }

        check();
        
        return new Reservation(date, headcount, city, dollarsPerHead, hasSite);
    }

    private Dollars sufficientDollars(int headcount) {
        Dollars dollars = MINTOTAL.dividedBy(headcount);
        if (dollars.times(headcount).isLessThan(MINTOTAL))
            dollars = dollars.plus(Dollars.cent);
        return dollars;
    }

    protected void check() throws BuilderException {
        if (date == null)
            throw new BuilderException("Valid date not found");

        if (city == null)
            throw new BuilderException("Valid city not found");

        if (headcount < MINHEAD)
            throw new BuilderException("Minimum headcount is " + MINHEAD);

        if (dollarsPerHead.times(headcount).isLessThan(MINTOTAL))
            throw new BuilderException("Minimum total cost is " + MINTOTAL);
    }
}