public class GasTank
{
  // Gas tank has two instance variables (fields, attributes etc)
  // that keeps track of the amount of gasoline
  // in the tank and it's total capacity. They can be decimals.

  private double capacity = 0;
  private double gas = 0;

  /**
   * Default constructor that sets the amount of gas to zero.
   */
  public GasTank(double capacity)
  {

    capacity = 0;

  }

  /**
   * bumps up the amount of gas in the gas tank by amount, but will not exceed
   * the capacity of the gas tank.
   *
   * @param amount
   */
  public void addGas(double amount)
  {
    gas += amount;

  }

  /**
   * Removes the gas from the gas tank by amountUsed. You can't have negative
   * gas!! so if the client uses more than what's in the tank then keep it zero.
   *
   * @param amountUsed
   */
  public void useGas(double amountUsed)
  {

    if (amountUsed <= gas)
    {
      gas -= amountUsed;
    }
    else
    {
      gas = 0;
    }

  }

  /**
   * Tank is empty if we have less than 0.1 gallons of gas. So person has chance
   * to run to the gas station before they are really out.
   *
   * @return
   */
  public boolean isEmpty()
  {

    if (gas < 0.1)
    {
      return true;
    }

    return false;
  }

  /**
   * The gas tank is full if the amount is within 0.1 gallons of the total
   * capacity of the tank.
   *
   * @return
   */
  public boolean isFull()
  {
    return gas >= 0.1 + capacity;
  }

  /**
   * Fills up the tank but ALSO returns the amount of gas it took to fill up the
   * tank to capacity. Remember there might already be some gas in the tank.
   *
   * @return
   */
  public double fillUp()
  {
    // TODO: Add code here.
    double gasDifference = capacity - gas;
    gas = capacity;
    return gasDifference;
  }

  /**
   * Just a simple getter that returns the amount of gas in the gas tank.
   *
   * @return
   */
  public double getGasLevel()
  {
    // TODO: Add code here.
    return gas;
  }

}