How do I get the total price from my carList?

Question

I am creating a class called Car with a method called TotalPrice which will take an array of Cars and calculate the total for the list. I have implemented a client method totalPrice, which accepts a list (ArrayUnsortedList carList) of cars and returns an integer equal to the total cost of the cars on the list.

I am stuck on writing the test driver so that I can test my actual Car class program.

Here's my code for the Car class:

public class Car
{
   int year;
   String make;
   String model;
   int price;

   public Car(int year, String make, String model, int price) {
      this.year = year;
      this.make = make;
      this.model = model;
      this.price = price;      
   }

   public int getYear() {
      return this.year;
   }

   public String getMake() {
      return make;
   }

   public String getModel() {
      return model;
   }

   public int getPrice() {
      return this.price;
   }

   public static int totalPrice(ArrayUnsortedList carList) {
      int totalPrice = 0;
      for(int i=carList.size(); i>0; i--)
      {

         totalPrice += ((Car)carList.getNext()).getPrice();
      }
      return totalPrice;
   }      
}

Here's my test drive class:

import java.util.Scanner;
import java.util.ArrayList;

public class CarList{

   public static void main (String [] args) {

      ArrayUnsortedList<Car> carList = new ArrayUnsortedList<Car>();  
      Car car1, car2;

      car1 = new Car(2016, "BMW", "M4", 65700);
      carList.add(car1);    
      car1 = new Car(2016, "Mercedes-Benz", "C300", 38950);
      carList.add(car1);    
      car2 = new Car(2016, "Lexus", "GS F", 84440);
      carList.add(car2);

      System.out.println(Car.totalPrice(carList));

   }   

}

UPDATE********

I have to use ArrayUnsortedList that is given.

Here are the rest of the codes: GITHUB

UPDATE Now I am getting the wrong totalPrice?

65700 + 38950 + 84440 = 189090

But I get 253320???

 ----jGRASP exec: java CarList

253320

 ----jGRASP: operation complete.

@skypjack I cannot use that because it is incompatible with my ArrayUnsortedList — pyuntae, Mar 06 '16 at 08:37
Well, build an `ArrayUnsortedList` from the other list or define a constructor that accepts a generic list, then use it. — skypjack, Mar 06 '16 at 08:38

score 1 · Accepted Answer · answered Mar 06 '16 at 09:10

For the code of the totalPrice function itself, I would use ArrayUnsortedList.size() and ArrayUnsortedList.getNext() to browse the list content. This list api is terrible (intentionally, I suppose) and it's understandable you had a little difficulties here. Learn to quickly browse a Java class, looking only at the function headers to determine which function can be useful.

int totalPrice = 0;
for(int i=carList.size(); i>0; i--)
{
  totalPrice += carList.getNext().getPrice();
}
return totalPrice;

You will notice I do not reference i inside the loop ; that's because there is no method of ArrayUnsortedList that expects an index. So I just rely on i to make sure I make the good number of calls to ArrayUnsortedList.getNext().

On other topics,

I don't think it's the job of the Car class to sum the price of cars. totalPrice should imo be implemented as a function on the ArrayUnsortedList or simply executed as is in your test class.
I think tests in Java environment should be run with JUnit. This might be a topic you'll soon encounter, but if you've already worked with JUnit then your test runner should use it.

If i change it to what you have posted, i get an error `Car.java:35: error: cannot find symbol` — pyuntae, Mar 06 '16 at 09:19
It looks like your function or code block currently accepts untyped ArrayUnsortedList. You should either change the signature to only accept `ArrayUnsortedList`, so the `carList.getNext()` naturally returns a `Car` on which you can call `.getPrice()`, or use a cast in the loop : `((Car)carList.getNext()).getPrice()` — Aaron, Mar 06 '16 at 09:30
If you look at the error you pasted in your question, you can see Java's trying to find a function `getPrice()` on the class `Object`, while it should be looking for it on the class `Car` — Aaron, Mar 06 '16 at 09:32

score 0 · Answer 2 · answered Mar 06 '16 at 08:42

In your main method, you can add cars to the given datatype (ArrayUnsortedList) itself. Then you can directly pass it to your static method.

Another alternative is to define a constructor for the ArrayUnsortedList to take in an ArrayList, and create its own instance with appropriate elements.

How do I get the total price from my carList?

2 Answers2