@Override
    public void delUser(String userDeSters) {
        BufferedReader fisier;
        BufferedWriter fisier_nou;
        BufferedReader fisier2;
        BufferedWriter fisier_nou2;
        try {            
            fisier = new BufferedReader(new FileReader("credentials"));
            
            ArrayList<String> vector = new ArrayList<>();
            for(String line; (line = fisier.readLine())!= null;){
                vector.add(line);                  
            }            
            for(int i=0;i<vector.size();i=i+5){               
                if(userDeSters.equals(vector.get(i))){
                        vector.remove(i+4);
                        vector.remove(i+3);
                        vector.remove(i+2);
                        vector.remove(i+1);
                        vector.remove(i);
                        fisier_nou = new BufferedWriter(new FileWriter("credentials"));
                        for(i=0;i<vector.size();i++){
                             fisier_nou.write(vector.get(i));
                             fisier_nou.newLine();
                        }
                        fisier_nou.close();
                    }
            }        
            
        } catch (FileNotFoundException ex) {
            Logger.getLogger(Administratorapp.class.getName()).log(Level.SEVERE, null, ex);
        } catch (IOException ex) {
            Logger.getLogger(Administratorapp.class.getName()).log(Level.SEVERE, null, ex);
        }
    }