public void quit(){
        if(PSTricksGraphEditor.graph.getNodes().isEmpty()){
            System.exit(0);
        } else {
            
            int reponse = getResponse();
            
            if(reponse == JOptionPane.YES_OPTION){
                saveFile();
                System.exit(0);
            } else if (reponse == JOptionPane.NO_OPTION){
                System.exit(0);
            } else {
                return;
            }
        }
    }