public String toString(){
		String positif = "+ = ";
		String negatif = ", - = ";
		for(Entry<String, Boolean> entry : preferences.entrySet()){
			String cle = entry.getKey();
		    Boolean valeur = entry.getValue();
		    if(valeur){
		    	positif += cle+" ";
		    }
		    else{
		    	negatif += cle+" ";
		    }
		}
		return positif+negatif;
	}