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Classes and Objects
Classes
The introduction to object-oriented concepts in
the lesson titled
Object-oriented Programming Concepts used a bicycle class as an example,
with racing bikes, mountain bikes, and tandem bikes as subclasses.
Here is sample code for a possible implementation of a
Bicycle class, to give you an overview of a
class declaration. Subsequent sections of this
lesson
will back up and explain class declarations
step by step. For the moment, don't concern yourself with the details.
public class Bicycle {
// the Bicycle class has three fields
public int cadence;
public int gear;
public int speed;
// the Bicycle class has one constructor
public Bicycle(int startCadence, int startSpeed, int startGear) {
gear = startGear;
cadence = startCadence;
speed = startSpeed;
}
// the Bicycle class has four methods
public void setCadence(int newValue) {
cadence = newValue;
}
public void setGear(int newValue) {
gear = newValue;
}
public void applyBrake(int decrement) {
speed -= decrement;
}
public void speedUp(int increment) {
speed += increment;
}
}
A class declaration for a MountainBike class that is a subclass of Bicycle might look like this:
public class MountainBike extends Bicycle {
// the MountainBike subclass has one field
public int seatHeight;
// the MountainBike subclass has one constructor
public MountainBike(int startHeight, int startCadence, int startSpeed, int startGear) {
super(startCadence, startSpeed, startGear);
seatHeight = startHeight;
}
// the MountainBike subclass has one method
public void setHeight(int newValue) {
seatHeight = newValue;
}
}
MountainBike inherits all the fields and methods of
Bicycle and adds the field
seatHeight and a method to set it (mountain bikes have seats that can be moved up and down
as the terrain demands).
