Java 和 SQL 比较日期

Question

我正在尝试获取客户到达日期并将其与我的 SQL 数据库进行比较，以查看我的数据库中是否存在相同的日期。但是我收到以下错误:The operator > is undefined for the argument type(s) java.lang.String, java.lang.String

P.S 我需要通过 java 比较它而不是使用 sql 查询

public void makeNewReservation() throws ParseException {
    // Enter informations

    System.out.println("Date of arrivel?");
    Scanner in = new Scanner(System.in);
    String date_entree = in.next();
    System.out.println("Date of exit? dd/MM/yyyy");
    String date_sortiee = in.next();
    calculateDaysDifference(date_sortiee, date_entree);



public  void calculateDaysDifference(String date_entree, String date_sortiee) throws ParseException{


ConnectionMySQL myConnection=new ConnectionMySQL();
    Connection conSQL=myConnection.startDBConnection();
    boolean connectionOK=myConnection.checkConnection(conSQL);

    String query = ("SELECT `START_DATE`,`END_DATE` FROM `room_booking");


    //if everything is fine with the connection, i try to execute a query
    if (connectionOK){
        try{
            ResultSet mesResultats=myConnection.executeQuery(conSQL, query);

            //the while loop is just for me to check the dates
            while (mesResultats.next()) {
                System.out.println("START_DATE: "+mesResultats.getString(1)+" END_DATE : "+ mesResultats.getString(2));


                if (date_entree > mesResultats.getString(1){
                    System.out.println("cant reserve room room reserved already");


                }
            }


            // je ferme la connexion
            conSQL.close();

        }

        catch(SQLException e){
            e.printStackTrace();


        }

    }

my data base

Answer 1

你需要比较2个日期

1) 将输入的字符串转换为日期

SimpleDateFormat df=new SimpleDateFormat("yyyy-MM-dd");
java.util.Date d=df.format(/*date String*/);

NOTE: df.format will throw parseException if the String format does not match "yyyy-MM-dd" . I leave it upto you to make sure the date string is of the specified format. 

2)从sql查询获取日期

java.util.Date sqlDate=new java.util.Date(resultset.getDate().getTime());

NOTE : resultset.getDate() will give you java.sql.Date class's object.

3) Compare 2 dates