public HashMap<String, Level> lees() throws AngryTanksException{
        HashMap<String, Level> levelMap = new HashMap<String, Level>();

        ArrayList<File> levelFiles = new ArrayList<File>();

        //bestanden vinden in folder
        File[] files = levelFolder.listFiles();
        if(files == null) files = new File[0];

        //bestanden selecteren
        for(File file : files){
            if(file.isFile()
               && file.getName().length() > EXTENSIE.length()
               && file.getName().substring(file.getName().length()-EXTENSIE.length()).equals(EXTENSIE)
               && !file.getName().substring(0,1).equals(".")){
                levelFiles.add(file);
            }
        }

        //bestanden uitlezen en toevoegen aan levelMap
        for(File file : levelFiles){
            try{
                String levelTitel = poetsNaam(file.getName());
                String levelText = new Scanner(file).useDelimiter("\\A").next();
                levelMap.put(levelTitel, decodeLevel(levelText));

            } catch(IOException e){
                throw new AngryTanksException("Bestand niet gevonden", e);
            }
        }
        return levelMap;
    }