输入错误的登录信息后，无法再登录Java应用程序

我的代码有这个问题，当我尝试输入错误的登录名时，在输入正确的登录名后，我无法再登录。这是我连接到数据库的登录身份验证方法。那么这里怎么了？这是我犯的JDBC错误还是在我的实际Java代码中

public void loginAuthentication(String getUsername, String getPassword) throws ClassNotFoundException {

    try {

        Class.forName("org.apache.derby.jdbc.EmbeddedDriver");
        final String dbURL = "jdbc:derby:myDB;",
                dbUsername = "adminUsername",
                dbPassword = "myPassword";

        Connection dbConnection = DriverManager.getConnection(dbURL, dbUsername, dbPassword);

        Statement queryStatement = dbConnection.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE, ResultSet.CONCUR_READ_ONLY);

        String SQL = "SELECT * FROM LOGIN_DETAILS WHERE USERNAME='" + getUsername + "'";
        ResultSet rs = queryStatement.executeQuery(SQL);

        while (rs.next()) {

            userName = rs.getString("USERNAME");
            passWord = rs.getString("PASSWORD");

        }

        if ((userName == getUsername) && (passWord == getPassword)) {

            loginSuccess = true;

        } else {

            System.out.println("Invalid login");

        }

    } catch (SQLException e) {

        String errorMessage = e.getMessage();
        JOptionPane.showMessageDialog(null, errorMessage);

    }

}

当我在第一次尝试时输入任何有效的登录凭据时，它工作正常

更新： 我现在使用的是.equals方法，即使输入错误的凭据，我也可以成功登录。然而，我仍然得到一个错误，这是

"Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException".

希望这能帮助你们找出我的代码有什么问题

更新： 下面是错误的完整堆栈跟踪

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at AppData.Login.loginAuthentication(Login.java:69)
at AppGUI.StartUIComponents$1.actionPerformed(StartUIComponents.java:105)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2022)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2346)
at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402)
at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:252)
at java.awt.Component.processMouseEvent(Component.java:6525)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3324)
at java.awt.Component.processEvent(Component.java:6290)
at java.awt.Container.processEvent(Container.java:2234)
at java.awt.Component.dispatchEventImpl(Component.java:4881)
at java.awt.Container.dispatchEventImpl(Container.java:2292)
at java.awt.Component.dispatchEvent(Component.java:4703)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4898)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4533)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4462)
at java.awt.Container.dispatchEventImpl(Container.java:2278)
at java.awt.Window.dispatchEventImpl(Window.java:2750)
at java.awt.Component.dispatchEvent(Component.java:4703)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:758)
at java.awt.EventQueue.access$500(EventQueue.java:97)
at java.awt.EventQueue$3.run(EventQueue.java:709)
at java.awt.EventQueue$3.run(EventQueue.java:703)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:75)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:86)
at java.awt.EventQueue$4.run(EventQueue.java:731)
at java.awt.EventQueue$4.run(EventQueue.java:729)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:75)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:728)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:201)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)

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不要使用e==检查字符串。用同样的方法，我刚才就是这么做的。我目前正在使用.equals方法。我现在登录，但当我尝试输入错误的凭据时仍然会出错。完整的stacktrace是什么？NullPointerException无法帮助您确定login.java的第69行是哪一行？而您必须提到第69行