ArrayList Help

[socboy6579]

I am just asking for a little help if possible from the forums. In my program i am asked:
for a method returning the average number of miles of all cars in garage

a method returning"full" if the garage has 100 cars of more, "below minimum" if the garage has fewer than 25 cars, and "normal load" if the garage has between 25 and 100 cars in it

for a method returning the total number of gallons of gas used by all cars in garage

I know that i have to create an arraylist as a garage to hold cars with gallons of gas and miles. i have the miles and gas sorted out, but i am just stuck on how to put and relate the gallons of gas and the miles in the arrayList. If i could get any pointers, that would be appreciated. Here is my code

import java.util.ArrayList; //allows usage of ArrayLists


public class Garage {

	private int NumMiles;
	private int Gas;
	
	public Garage (int Miles, int GalsGas) 
	{
		NumMiles = Miles;
		Gas = GalsGas;
	}
	
	public int getMiles()
	{
		int returnMiles = NumMiles;
		return returnMiles;
	}
	
	public int getGalsGas()
	{
		int returnGalsGas = Gas;
		return returnGalsGas;
	}
	
	ArrayList<Integer> garage = new ArrayList<Integer>();
	
	{
		for(int i =0; i <garage.size(); i++);
	}
	
}

[Bertstar]

Why wouldn't the Garage class simply contain all of the cars? why does it contain miles and gas? Shouldn't miles and gas be instance variables in a car class?

[socboy6579]

it says to write a Garage class with one instance variable: an arraylist of autos which contains the gas and the miles

[Bertstar]

it says to write a Garage class with one instance variable: an arraylist of autos which contains the gas and the miles

Are you sure that doesnt mean that you have one ArrayList in your Garage class that contains car objects, which have instance variables miles and gas? It only makes sense that a garage holds cars. It makes no sense for a garage to have miles.

[socboy6579]

Yes i need to have an arrraylist in my garage class containing car objects which instance varaibles are miles and gas. am i even clear on the right path?

[Bertstar]

you are kind of on the right path since your Garage class contains the data for a Car. So you need to create a Garage class that has an instance variable that is an ArrayList of cars.

[socboy6579]

ArrayList<Integer> car = new ArrayList<Integer>();
could i use that for starters

[Bertstar]

No, you need to essentially rename your Garage class to Car and then create a Garage class that has an variable like this

ArrayList<Car> allCars = new ArrayList<Car>();

the ArrayList you are trying to create would contain Integers not Cars

[socboy6579]

is this at all correct

import java.util.ArrayList; //allows usage of ArrayLists


public class Car {

	private int NumMiles;
	private int Gas;
	
	public Car (int Miles, int GalsGas) 
	{
		NumMiles = Miles;
		Gas = GalsGas;
	}
	
	public int getMiles()
	{
		int returnMiles = NumMiles;
		return returnMiles;
	}
	
	public int getGalsGas()
	{
		int returnGalsGas = Gas;
		return returnGalsGas;
	}

	ArrayList<Car> allCars = new ArrayList<Car>();
	
}

[Bertstar]

You dont need the ArrayList of Cars in the Car class. You should create a Garage class that has an ArrayList of Cars as its instance variable.

[socboy6579]

could you show me that? im just very confused

[Bertstar]

I am not going to write the class for you, but here is what you need to do.

Create a new class called Garage that has one instance variable which is an ArrayList of Cars. You then need to add methods that will allow you to add Cars to your Garage. You will also probably need a method to remove Cars from your Garage. Keep in mind that the Cars in your Garage are held in your instance variable, which like I stated previously is an ArrayList of Cars. So, the implementation of your Garage's addCar and removeCar methods should be pretty simple.

[socboy6579]

we are given a source code file to build off of.

/* Auto class, Version 3
   Anderson, Franceschi
*/

public class Auto
{
    // instance variables
    private String model;          //  model of auto
    private int milesDriven;       //  number of miles driven
    private double gallonsOfGas;   //  number of gallons of gas

    // Default constructor:
    //  initializes model to "unknown";
    //  milesDriven is auto-initialized to 0
    //        and gallonsOfGas to 0.0
    public Auto( )
    {
       model = "unknown";
    }

    // Overloaded constructor:
    // allows client to set beginning values for
    //   model, milesDriven, and gallonsOfGas.
    public Auto( String startModel,
                 int startMilesDriven,
                 double startGallonsOfGas )
    {
       model = startModel;
       setMilesDriven( startMilesDriven );
       setGallonsOfGas( startGallonsOfGas );
    }

    // Accessor method:
    // returns current value of model
    public String getModel( )
    {
      return model;
    }

    // Accessor method:
    // returns current value of milesDriven
    public int getMilesDriven( )
    {
      return milesDriven;
    }

    // Accessor method:
    //  returns current value of gallonsOfGas
    public double getGallonsOfGas( )
    {
      return gallonsOfGas;
    }

    // Mutator method:
    // allows client to set model
    public void setModel( String newModel )
    {
      model = newModel;
    }

    // Mutator method:
    // allows client to set value of milesDriven;
    // prints an error message if new value is less than 0
    public void setMilesDriven( int newMilesDriven )
    {
      if ( newMilesDriven >= 0 )
        milesDriven = newMilesDriven;
      else
      {
        System.err.println( "Miles driven cannot be negative." );
        System.err.println( "Value not changed." );
      }
    }

    // Mutator method:
    // allows client to set value of gallonsOfGas;
    // prints an error message if new value is less than 0.0
    public void setGallonsOfGas( double newGallonsOfGas )
    {
      if ( newGallonsOfGas >= 0.0 )
        gallonsOfGas = newGallonsOfGas;
      else
      {
        System.err.println( "Gallons of gas cannot be negative." );
        System.err.println( "Value not changed." );
      }
    }
}

we are to create those various methods above^^

If i were to create an ArrayList could if start off as
ArrayList<Integer> autos = new ArrayList();
Any pointers on how to add gas and miles to the arraylist?

[Bertstar]

Please do not make multiple threads for this same problem...

Other thread

[gcalvin]

You don't want ArrayList<Integer> in your Garage class, you want ArrayList<Auto>.

I have to say this is a very poorly-designed exercise. It makes no sense to have a setModel() method -- is somebody going to change a Corolla into a Hummer2? setMilesDriven() makes some sense, as it can at least reflect a reading at some point in time -- but merely checking that it's a positive value is stupid. It should make sure the value is the same or higher than the previous reading, or else somebody is committing fraud. And setGallonsOfGas() makes no sense, as you can only add gasoline to a car's tank -- you can't just arbitrarily set a new value for how much it has used. But that's just me ranting.

You want an ArrayList<Auto>, and then your methods will all iterate through your list and sum up totals and compute averages. Basic stuff that's probably well covered in your text.

-Gary-