[中级偏下]想起一个面试题

//-------------------- Node.java -----------------------
public abstract class Node{
    public abstract String toXmlString();;
}


//-------------------- MenuItem.java ------------------
public class MenuItem extends Node{
    
    private String _name;
    
    public MenuItem(String name);{
        _name = name;
    }
    
    public String toXmlString();{
        return "<menuitem name='" + _name + "'/>";
    }        
}


//------------- Menu.java ------------------------
import java.util.*;
public class Menu extends Node{
    
    private String _name;
    private List _menuItems = new ArrayList();;
    
    public Menu(String name);{
        _name = name;
    }
    
    public void add(Node node);{
        _menuItems.add(node);;
    }
    
    public String toXmlString();{
        
        StringBuffer buffer = new StringBuffer("");;
        buffer.append("<menu name='");.append(_name);.append("'>");;
        for (Iterator iter = _menuItems.iterator();; iter.hasNext();; );
            buffer.append( ((Node);iter.next(););.toXmlString(); );;
        buffer.append("</menu>");;
        return buffer.toString();;            
    }
}


//----------------- TestMain.java ----------------------
public class TestMain{
    
    public static void main(String[] args);{
        
        Menu _menu = new Menu("Company");;
        Menu _menu1 = new Menu("Department #1");;
        MenuItem _gates = new MenuItem("Bill Gates");;
        
        _menu1.add(new MenuItem("Jim Johnson"););;
        _menu1.add(_gates);;
        
        
        _menu.add(_gates);;
        _menu.add(_menu1);;
        
        
        System.out.println("_menu := { "+_menu.toXmlString();+" }\n");;
        System.out.println("_menu1 := { "+_menu1.toXmlString();+" }\n");;
        System.out.println("_gates := { "+_gates.toXmlString();+" }\n");;
                
    }
}