Connection connexion = DriverManager.getConnection("jdbc:mysql://localhost:3306/bd","root","ali");

Statement instruction = connexion.createStatement();

ResultSet resultat = instruction.executeQuery("SELECT  date, count(*) as nb FROM traprecive group by date");

aliMap=new LinkedHashMap<String, Float>();

//Remplissage de la map
while(resultat.next())
{
    aliMap.put(resultat.getDate(1), Float.valueOf(resultat.getFloat(2)));
    }

//Affichage du contenu de la map
Iterator<Date> itKeys=aliMap.keySet().iterator();
while(itKeys.hasNext())
{
    String key=itKeys.next();
    System.out.println(key.toString()+"                 "+aliMap.get(key));
    }