String fileName = "file.txt";

    /**
     * SAUVEGARDE FICHIER TXT
     */
    public void saveFile(String file, String text)
    {
        try{
            FileOutputStream fos = openFileOutput(file, Context.MODE_WORLD_READABLE);
            fos.write(text.getBytes());
            fos.close();
            Toast.makeText(this, "Sauvegardé avec succès !", Toast.LENGTH_SHORT).show();
        }catch (Exception e){
            e.printStackTrace();
            Toast.makeText(this, "Erreur survenue ...", Toast.LENGTH_SHORT).show();
        }
    }

    /**
     * LECTURE FICHIER
     */
    public String readFile(String file)
    {
        String text = "";
        try{
            FileInputStream fis = openFileInput(file);
            int size = fis.available();
            byte[] buffer = new byte[size];
            fis.read(buffer);
            fis.close();
            text = new String(buffer);
            Toast.makeText(this, "Lecture avec succès !", Toast.LENGTH_SHORT).show();
        }catch (Exception e){
            e.printStackTrace();
            Toast.makeText(this, "Erreur survenue ...", Toast.LENGTH_SHORT).show();
        }
        return text;
    }