Design pattern visitor en java (http://kandran.fr/design-pattern-visiteur)

visitor.java

interface IVisitable {
   void accept(IVisitor visitor);
}

class Book implements IVisitable
{
	public String support = "unknown";
    public void accept(IVisitor visitor) 
    {
    	visitor.visit(this);       
    }
}

class PaperBook extends Book
{
    public String support = "paper";
}

class EBook extends Book
{
    public String support = "numeric";
    public Float price = 5;
}



interface IVisitor {
    void visit(IVisitable o);
    void visit(EBook o);
    void visit(PaperBook o);
    void visit(Book o);
}

class DebugVisitor implements IVisitor
{
        public void visit(EBook o) 
        {      
            System.out.println("We have an ebook so it's support is " + o.support + " and it's price is" + o.price);
        }
 
        public void visit(PaperBook o) 
        {
            System.out.println("We have a classic book so it's support is made of " + o.support);
        }

        public void visit(Book o) 
        {
            System.out.println("We have a ebook - but we doesn't know this kind so it's support is " + o.support);
        }

        public void visit(IVisitable o) 
        {
                System.out.println("Not implemented yet");
        }


public class MainRun
{
    public static void main(String[] args) 
    {
        DebugVisitor visitor = new DebugVisitor();
    
        EBook ebook = new EBook();
    
        /* Display = We have an ebook so it's support is numeric and it's price is  5*/
        ebook.accept(visitor);
    
    
        PaperBook paperBook = new PaperBook();
    
        /* Display = We have a classic book so it's support is made of paper */
        paperBook.accept(visitor);
    
    
        Book book = new Book();
    
        /* Display = "We have a ebook - but we doesn't know this kind so it's support is unknown */
        book.accept(visitor);
    }
}