Αντικειμενοστραφής Προγραμματισμός, Εφαρμογές με χρήση της γλώσσας προγραμματισμού JAVA

This page is read only. You can view the source, but not change it. Ask your administrator if you think this is wrong.

====== Παράδειγμα δυναμικού πολυμορφισμού σε μία ιεραρχία 3 κληρονομούμενων κλάσεων ======

Ας υποθέσουμε ότι έχετε την ιεραρχία των κλάσεων 
<code>
  Bycicle
    |
    |---------> MountainBike
                     |
                     |-----------> RacingMountainBike
</code>

Οι 3 κλάσεις δίνονται με την σειρά παρακάτω

<code java Bicycle.java>
public class Bicycle {
        
    public int cadence;
    public int gear;
    public int speed;
       
    public Bicycle(int startCadence, int startSpeed, int startGear) {
        gear = startGear;
        cadence = startCadence;
        speed = startSpeed;
    }
    
    public Bicycle() {
        gear = 0;
        cadence = 0;
        speed = 0;
    }
    
    public int getCadence() {
          return cadence;
    }
    
    public int getGear() {
          return gear;
    }
    
    public int getSpeed() {
          return speed;
    }

    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;
    }
    
    @Override
    public String toString() {
      return "cadence: "+ cadence+", gear: "+gear+", speed: "+speed;
    }       
}
</code>

<code java MountainBike.java>
public class MountainBike extends Bicycle {

    private int seatHeight;

    // the MountainBike subclass has
    // one constructor
    public MountainBike(int startHeight, int startCadence,
                        int startSpeed, int startGear) {
        //super(startCadence, startSpeed, startGear);
        super(startCadence, startSpeed, startGear);
        seatHeight = startHeight;
    }   
        
    // the MountainBike subclass has
    // one method
    public void setHeight(int newValue) {
        seatHeight = newValue;
    }
    
    public int getSeatHeight() {
        return seatHeight;
    }
    
    public String toString() {
     return super.toString() + ", seatHeight: " + seatHeight;
    }
}
</code>

<code java RacingMountainBike.java>
public class RacingMountainBike extends MountainBike {
  
  int racingNumber;
  
  public RacingMountainBike(int startHeight, int startCadence,
                        int startSpeed, int startGear, int num) {
    super(startHeight, startCadence, startSpeed, startGear);
    racingNumber = num;
  }
  
  public String toString() {
    return super.toString() + ", racing number: "+ racingNumber;
  }
  
}
</code>

<WRAP important 80% center round>
Στο παρακάτω παράδειγμα παρατηρήστε πως ο δυναμικός πολυμορφισμός λειτουργεί ανάμεσα σε κλάσεις που ανήκουν στην ίδια ιεραρχία.
</WRAP>

<code java PolymorphismExample.java>
public class PolymorphismExample {
  
  public static void main(String args[]) {
    MountainBike bike = new MountainBike(10,20,30,40);
    Bicycle bicycle = bike;
    
    System.out.println(bicycle);
    System.out.println("------");
    System.out.println(bike);
    
    bicycle = new Bicycle(15,25,35); 
    //bicycle = new MountainBike(15,25,35,45);
    
    if( bicycle instanceof MountainBike )
      bike = (MountainBike) bicycle;
    
    System.out.println("------");
    System.out.println(bike);
   
    System.out.println("------");
    RacingMountainBike rbike = new RacingMountainBike(10, 20, 30, 40, 100);
    
    bicycle = rbike;
    System.out.println(bicycle);
    
  }
  
}
</code>

Αντικειμενοστραφής Προγραμματισμός, Εφαρμογές με χρήση της γλώσσας προγραμματισμού JAVA

User Tools

Site Tools

Page Tools