/** 修改班级 */
 public boolean modifyClass(Classes classes, String id) {
   ContentValues values = new ContentValues();
   values.put("class_id", classes.getClass_id());
   values.put("class_name", classes.getClass_name());
   values.put("class_date", classes.getClass_date());
   long l = db.update("class", values, "class_id=?", new String[] {id});
   return l == 1;
 }
 /**
  * 保存classes到数据库
  *
  * @param classes
  */
 public boolean saveClass(Classes classes) {
   if (classes != null) {
     ContentValues values = new ContentValues();
     values.put("class_id", classes.getClass_id());
     values.put("class_name", classes.getClass_name());
     values.put("class_date", classes.getClass_date());
     values.put("major_id", classes.getMajor_id());
     long l = db.insert("class", null, values);
     if (l == -1) {
       return false;
     } else {
       return true;
     }
   }
   return false;
 }