Java SQL Select语句在WHERE子句中使用多个变量

I am writing a simple program using UDP Sockets.I need to input the name of a patient and retrieve its details from the database. The name of the patient is entered in the Doctor class and sent to the Server Class. The Server class then execute a query to retrieve the details of the patient. The problem is in the SQL statement. When I used only the variable firstname it is working fine, but when I put the second variable lastname the PatientRecord variable is NULL.I am writing a simple program using UDP Sockets