Complete Program

Here is the complete program. The calculateMPG() method returns a double value to the caller. Since it returns a value, there must be a return statement within its body that returns a value of the correct type.

In the complete program, the calculateMPG() method uses the instance variables of its object to calculate miles per gallon.

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 (endMiles - startMiles)/gallons ;
  }

}

class MilesPerGallon
{
  public static void main( String[] args ) 
  {
    Car car = new Car( 32456, 32810, 10.6 );
    System.out.println( "Miles per gallon is " + car.calculateMPG() );
  }
}