Another problem - Login Page

Question

I can use this login page to log in to another page(MainFrame) successfully but got some problems. When i try to enter the username (which is not match the uppercase and lowercase rule with the data in database), but i still can successfully log in. Why? Actually the username should be case sensitive. Can somebody help me? thanks.
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void jButton1_actionPerformed(ActionEvent e) {
String userid = jTextField1.getText(); //username
char[] passwd = jPasswordField1.getPassword(); //password
System.out.println( "User ID is : " + userid);
try
connection = getDBConnection();
String query = "SELECT * FROM UserInfo WHERE UserID= '"+ userid +"' AND Password= '"+ passwd +"'";
Statement statement = connection.createStatement();
ResultSet resultSet = statement.executeQuery( query );
//displayResultSet ( resultSet );
resultSet.next();
String dbUserID = resultSet.getString("UserID");
if (dbUserID != null)
String dbUserPasswd = resultSet.getString("Password");
System.out.println("dbUserID: " + dbUserID);
System.out.println("dbUserPasswd: " + dbUserPasswd);
this.hide();
new MainFrameClass(); //to new page
else
System.out.println("dbUserID is null");
statement.close();
connection.close();
catch(SQLException sqlex)
System.out.println("DB Connection failed: " + sqlex);
//throw new SQLException("DB Connection failed");

Answer 1

somebody..please help! thanks!