Voilà ma classe abstraite

public abstract class MaForme implements Serializable{

  protected boolean selected = false;
 
    public abstract void dessine(Graphics g) ;
    
    public abstract void tourne (double a);
    
    public abstract boolean appartient (int x, int y);
    
    public abstract int nb();
 	
}

Et la classe MaForme1 avec juste la définition des méthodes de MaForme

public class MaForme1 extends Geometrie implements Serializable{

 private static final long serialVersionUID = 1L;

   public int x;

   public int y;

    public MaForme1(){
    }
 
    public MaForme1(int a, int o){
    	this.x=a;
    	this.y=o;
    }
   
    public int distance(MaForme1 p) {
        int dx = p.x - x ;
        int dy = p.y - y ;
        int res= dx*dx + dy*dy;
        return res ;         
    } 

   public void tourne(double a)
   { 
	 MaForme1 o = new MaForme1(0,0);
     int ox = this.x - o.x ;
     int oy = this.y - o.y ;
     double cosa = Math.cos (a) ;
     double sina = Math.sin (a) ;
     x = (int) (o.x + cosa * ox - sina * oy) ;
     y = (int) (o.y + sina * ox + cosa * oy) ;              
   }

	public void dessine(Graphics g) {
		// TODO Auto-generated method stub
		Graphics2D g2 = (Graphics2D)g;
		
		 if (selected)
	         g2.setColor(Color.green);
	      else
	         g2.setColor(Color.blue);		
    	
        g2.drawRect(x,y,1,1);
	}

	public boolean appartient(int x, int y) {
		MaForme1 p = new MaForme1(x,y);
		if(this.equals(p)){
			return false;
		}
		return true;
	}

	public int nb() {
		
		return 1;
}
}