Question

I have this class determines how much petrol is being purchased and the cost. The gas is divided between regular, premium, and super unleaded. The program reads (R, P, or S) that designates which kind of gasoline was purchased.

class Petrol

{

private static final double Premium = 0;

private static final double Super = 0;

char gas;

String type;

double amount, cost;

private String free;

private double regular;

Petrol(char ch, double a)

{

gas = ch;

amount = a;

}

void calculateCost()

{

switch(gas)

{

case 'r':

case 'R':

      type = "Regular";

      cost = amount * regular;

      if (amount > 10)

            free = REGULAR_WASH1;

break;

case 'p':

case 'P':

      type = "Premium";

      cost = amount * Premium;

      if (amount > 10)

            free = REGULAR_WASH2;

break;

case 's':

case 'S':

      type = "Super";

      cost = amount * Super;

      if (amount > 10)

            free = REGULAR_WASH3;

break;

default:

            type = "Unkown";

            break;

}

}

public String toString()

{

      if (type.equals("Unknown"))

            return "Petrol is " + type + " cannot be served";

      else

            return "The type of petrol that will be served is " + type

                  +"\nYour bill is: $" + cost + "\n " + free;

}

I also have the test class below:

import javax.swing.JOptionPane;

class TestPetrol

{

public static void main(String[] arg)

{

String str = JOptionPane.showInputDialog("COP2210 Petrol Station"

+ "\nEnter the type of petrol"

+ "\nr/R - for regular gas"

+ "\np/P - for premium gas"

+ "\ns/S - for super gas");

char ch = str.charAt(0);

str = JOptionPane.showInputDialog("Enter the amount of gas to be purchased");

float amount = Float.parseFloat (str);

Petrol p = new Petrol(ch, amount);

p.calculateCost();

JOptionPane.showMessageDialog(null, p.toString());

}

}

The problem I’m having is the program needs to offer a reward after buying 10 gallons of gas. That reward being a car wash. I have to add the declarations below but I don’t know where to place them without getting an error or the amount coming out to zero.

static final float REGULAR_GAS                 = 2.99f;

static final float PREMIUM_GAS               = 3.15;

static final float SUPER_GAS                       = 3.25;

               

static final String REGULAR_WASH = "You get free wash excluding under carriage and wheels";

static final String REGULAR_WASH = "You get free wash excluding under carriage";

static final String REGULAR_WASH = "You get free super wash";

When I run the program, it should determine whether or not the customer gets a free wash

and it calculate the cost for petrol purchased. If I can get help on where the place these lines to get the program to run properly I’d appreciate it.

Answer 1

Solution: The variable should be placed above the Petrol Class Constructor as you can see in the below code.

Program Code to Copy:

Petrol.java

class Petrol {

    static final float REGULAR_GAS = 2.99f;

    static final float PREMIUM_GAS = (float) 3.15;

    static final float SUPER_GAS = (float) 3.25;

    final String REGULAR_WASH1 = "You get free wash excluding under carriage and wheels";

    final String REGULAR_WASH2 = "You get free wash excluding under carriage";

    final String REGULAR_WASH3 = "You get free super wash";


    char gas;

    String type;

    double amount, cost;

    private String free = "";

    Petrol(char ch, double a) {

        gas = ch;

        amount = a;

    }

    void calculateCost() {

        switch (gas) {

            case 'r':

            case 'R':

                type = "Regular";

                cost = amount * REGULAR_GAS;

                if (amount > 10)

                    this.free = REGULAR_WASH1;

                break;

            case 'p':

            case 'P':

                type = "Premium";

                cost = amount * PREMIUM_GAS;

                if (amount > 10)

                    this.free = REGULAR_WASH2;

                break;

            case 's':

            case 'S':

                type = "Super";

                cost = amount * SUPER_GAS;

                if (amount > 10)

                    this.free = REGULAR_WASH3;

                break;

            default:

                type = "Unknown";

                break;

        }

    }

    public String toString() {

        if (type.equals("Unknown"))

            return "Petrol is " + type + " cannot be served";

        else

            return "The type of petrol that will be served is " + type

                    + "\nYour bill is: $" + cost + "\n " + this.free;

    }
}
TestPetrol.java

import javax.swing.JOptionPane;

class TestPetrol {

    public static void main(String[] arg) {

        String str = JOptionPane.showInputDialog("COP2210 Petrol Station"

                + "\nEnter the type of petrol"

                + "\nr/R - for regular gas"

                + "\np/P - for premium gas"

                + "\ns/S - for super gas");

        char ch = str.charAt(0);

        str = JOptionPane.showInputDialog("Enter the amount of gas to be purchased");

        float amount = Float.parseFloat(str);

        Petrol p = new Petrol(ch, amount);

        p.calculateCost();

        JOptionPane.showMessageDialog(null, p.toString());


    }

}

Program Output Screenshots: