Specifications for the Car class

Professional programmers carefully design the classes they need before any coding is done. With well-designed classes programming is much easier and the program has fewer bugs. Object oriented design consists of deciding what classes are needed, what data they will hold, and how they will behave. All these decisions are documented (written up) and then examined. If something doesn't look right, it is fixed before any programming is done. Let us do that with our Car class.

Car

A class that calculates miles per gallon.

Variables

• double startMiles; // Starting odometer reading
• double endMiles; // Ending odometer reading
• double gallons; // Gallons of gas used between the readings

Constructors

• Car( double startOdo, double endingOdo, double gallons )
  Creates a new instance of a Car object with the starting and ending odometer readings and the number of gallons of gas consumed.

Methods

• double calculateMPG()
  calculates and returns the miles per gallon for the car.

Look at the parameter list for the constructor:

Car( double startOdo, double endingOdo, double gallons );

This says that the constructor must be called with three items of data: three double precision values.