change.java

package exceptiondemo;
import java.util.InputMismatchException;
import java.util.Scanner;

public class Change {
    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        double paid, toCharge;

        try {
            System.out.print("Enter amount paid by the customer: GBP");
            paid = scan.nextDouble();
            System.out.print("Enter amount to charge the customer: GBP");
            toCharge = scan.nextDouble();

            int[] coinCount = getChange(paid, toCharge);

            System.out.print("Custom has to be returned:");
            for (int i = 0; i < validChange.length; i++) {
                if (coinCount[i] == 0) {
                    continue;
                }

                System.out.print(" " + coinCount[i] + " * " + validChange[i] + "p");
            }
        } catch (InputMismatchException e) {
            System.out.println("Entered values are not valid");
        } catch (PaidLessThanToChargeException e) {
            System.out.println("Paid amount by the customer is less than the amount to charge");
        }
    }

    /**
     * Valid change in penny
     */
    protected static double[] validChange = {75, 15, 3, 1, 0.5, 0.25};

    /**
     * @param paid Amount paid by the customer
     * @param toCharge Actual amount to charge
     * @return Number of coins with respect to validChange
     */
    protected static int[] getChange(double paid, double toCharge) throws PaidLessThanToChargeException {
        if (paid - toCharge < 0.0001) {
            throw new PaidLessThanToChargeException();
        }

        double change = (paid - toCharge) * 100;
        int[] coinCount = new int[validChange.length];

        for (int i = 0; i < validChange.length; i++) {
            coinCount[i] = (int) (change / validChange[i]);
            change = change % validChange[i];
        }

        return coinCount;
    }
}

class PaidLessThanToChargeException extends Exception {
}