我正在將客戶添加到數(shù)據(jù)庫(kù)中，但前提是數(shù)據(jù)庫(kù)中沒(méi)有其他 CustomerID 與我剛剛輸入的 CustomerID 相同。我在 Eclipse 中使用 JDBC 和 MySQL 來(lái)執(zhí)行此操作。有人能告訴我我的 while 循環(huán)是否正確設(shè)置來(lái)實(shí)現(xiàn)這一點(diǎn)嗎？我得到了很多奇怪的輸出，所以它可能不是。我已經(jīng)在網(wǎng)上環(huán)顧了幾個(gè)小時(shí)，但我無(wú)法讓它工作。我怎樣才能正確地做到這一點(diǎn)？我的一段代碼如下所示。public void addCust() {    String url = "jdbc:mysql://localhost:3306/northwind?useSSL=false&serverTimezone=EST";    String username = "root";    String password = "<password>";    String tempCustID, custID, comp, contName, contTitle, addr, city, reg, postCode, country, phone, fax;    System.out.println("Loading driver...");    try {        Class.forName("com.mysql.cj.jdbc.Driver");        System.out.println("Driver loaded!");    }catch (ClassNotFoundException e) {        throw new IllegalStateException("Cannot find the driver in the classpath!", e);    }    System.out.println("Connecting database...");    try {        Connection mycon = DriverManager.getConnection(url, username, password);        System.out.println("Database connected!");        Scanner keyboard1 = new Scanner(System.in);        System.out.println("Enter 5 letters to identify the customer as.");        tempCustID = keyboard1.nextLine();        custID = tempCustID.toUpperCase();        /**        if(custID == "") {            System.out.println("Must enter a value.");            addCust();        }        */        PreparedStatement stat = mycon.prepareStatement("SELECT CustomerID FROM customers");        ResultSet cust = stat.executeQuery();        while(cust.next()) {            String customerID = cust.getString("CustomerID");            if(custID == customerID) {                System.out.println("Customer ID already exists. Please enter a different sequence of 5 letters to identify the customer as.");                options();            }        }