package seedu.ezdo.commons.core;

/**
 * Container for user visible messages.
 */
public class Messages {

    public static final String MESSAGE_UNKNOWN_COMMAND = "Unknown command";
    public static final String MESSAGE_INVALID_COMMAND_FORMAT = "Invalid command format! \n%1$s";
    public static final String MESSAGE_INVALID_TASK_DISPLAYED_INDEX = "The task index provided is invalid.";
    public static final String MESSAGE_TASKS_LISTED_OVERVIEW = "%1$d tasks listed!";
    public static final String MESSAGE_WRONG_LIST = "Please return to the task list "
                                                  + "if you want to mark a task as done.";

}

@@ -644,12 +644,105 @@
  done.%22;
+%0A    public static final String MESSAGE_TASK_DATES_INVALID = %22Start date is after due date!%22;
 %0A%0A%7D%0A

Add new messages for invalid task dates (start date after due date) in Messages.java