created 09/05/99; revised 06/13/00, 05/07/03
Modify the Car
class of the chapter by adding two methods:
The constructor and the calculateMPG()
method remain unchanged.
Each of these new methods should use the calculateMPG()
to get the
miles per gallon, not calculate it themselves.
An if-else
statement picks the correct boolean return value.
Put user interaction back into the main()
method method so the
user enters values for each car.
The main()
method uses these additional methods to write a message
to the user if the car is a gas hog or an economy car.
You might be tempted to make one of these common design errors:
startMiles, endMiles,
and gallons
.
Here is a sample run of the program:
C:\>java Miles Enter first reading: 10000 Enter second reading: 10400 Enter gallons: 10 Miles per gallon: 40 Economy Car!
Click here to go back to the main menu.
Change the constructor for the Car
class
so that it has only one parameter, the first reading of the
odometer.
The miles per gallon cannot yet be calculated.
Now add a method to the class:
void fillUp( int miles, double gallons )
This simulates filling up the tank at a gas station:
miles
is the current odometer reading and
gallons
is the number of gallons that filled the tank.
Save these values in instance variables.
With this information, miles per gallon can be calculated.
Write the method so that it
updates the instance variables each time it is called
(simulating another visit to the pumps).
After each call calculateMPG()
will
calculate the latest miles per gallon.
Write a testing class with a main()
/nobr>
that constructs a car and calls fillUp()
calculateMPG()
C:\>java MilesPerGallon New car odometer reading: 00000 Filling Station Visit odometer reading 00350 gallons to fill tank 10 Miles per gallon: 35 Economy Car! Filling Station Visit odometer reading 00450 gallons to fill tank 10 Miles per gallon: 10 Gas Hog!
Click here to go back to the main menu.
End of the Exercises