Answer:

Do the instance variables of an object hold values for the lifetime of the object?
- Yes—an object is a "thing" that has state (its unique characteristics.) The state is kept in instance variables.
Do the parameters of a constructor hold values for the lifetime of the object?
- No—the parameters of a constructor are part of a temporary "message" to the constructor. After the parameters have been used, they are gone.

Possible Errors

Here is an interesting program. Is anything wrong?

class Car
{
  // instance variables
  double startMiles;   // Stating odometer reading
  double endMiles;     // Ending odometer reading
  double gallons;      // Gallons of gas used between the readings

  // constructor
  Car( double first, double last, double gals )
  {
    startMiles = first ;
    endMiles   = last ;
    gallons    = gals ;
  }

  // methods
  double calculateMPG()
  {
    return  (last - first)/gals  ;
  }

}

Answer:

Possible Errors

QUESTION 17: