ch04/cashregister/CashRegister.java
 /**
 A cash register totals up sales and computes change due.
 */
 public class CashRegister
 {
 /**
 Constructs a cash register with no money in it.
 */
 public CashRegister()
 {
 purchase = 0;
 payment = 0;
 }

 /**
 Records the purchase price of an item.
 @param amount the price of the purchased item
 */
 public void recordPurchase(double amount)
 {
 purchase = purchase + amount;
 }

/**
 Enters the payment received from the customer.
 @param dollars the number of dollars in the payment
 @param quarters the number of quarters in the payment
 @param dimes the number of dimes in the payment
 @param nickels the number of nickels in the payment
 @param pennies the number of pennies in the payment
*/
 public void enterPayment(int dollars, int quarters,
 int dimes, int nickels, int pennies)
 {
 payment = dollars + quarters * QUARTER_VALUE + dimes * DIME_VALUE
 + nickels * NICKEL_VALUE + pennies * PENNY_VALUE;
 }

 /**
 Computes the change due and resets the machine for the next customer.
 @return the change due to the customer
 *
 public double giveChange()
 {
 double change = payment - purchase;
 purchase = 0;
 payment = 0;
 return change;
 }

 public static final double QUARTER_VALUE = 0.25;
public static final double DIME_VALUE = 0.1;
 public static final double NICKEL_VALUE = 0.05;
 public static final double PENNY_VALUE = 0.01;

 private double purchase;
 private double payment;
 }