Initializing the Data

In this class, the parameter list uses three parameters to match the three instance variables that will be initialized.

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 )
  {
     = first;
     = last;
     = gals;
  }

  // methods

}

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() );
  }
}

Note: In most classes there is NOT an exact match between the parameters of a constructor and the instance variables. There may be fewer (or more) parameters than instance variables. Also, the constructor's parameters do not have to be in the same order as the instance variables (this might help keep things straight, but the compiler does not care).