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).