Errors in a Java class when calling other methods

Question

I am giving the code i have given the full class name . and now it is giving the following error :
Cannot reference a non-static method connectDB() in a static context.
I am also giving the code. Please do help me on this. i am a beginner in java.
import java.sql.*;
import java.util.*;
import DButil.*;
public class StudentManager {
/** Creates a new instance of StudentManager */
public StudentManager() {
Connection conn = null;
Statement cs = null;
public Vector getStudent(){
try{
dbutil.connectDB();
String Query = "Select St_Record, St_L_Name, St_F_Name, St_Major, St_Email_Address, St_SSN, Date, St_Company, St_Designation";
cs = conn.createStatement();
java.sql.ResultSet rs = cs.executeQuery(Query);
Vector Studentvector = new Vector();
while(rs.next()){
Studentinfo Student = new Studentinfo();
Student.setSt_Record(rs.getInt("St_Record"));
Student.setSt_L_Name(rs.getString("St_L_Name"));
Student.setSt_F_Name(rs.getString("St_F_Name"));
Student.setSt_Major(rs.getString("St_Major"));
Student.setSt_Email_Address(rs.getString("St_Email_Address"));
Student.setSt_Company(rs.getString("St_Company"));
Student.setSt_Designation(rs.getString("St_Designation"));
Student.setDate(rs.getInt("Date"));
Studentvector.add(Student);
if( cs != null)
cs.close();
if( conn != null && !conn.isClosed())
conn.close();
return Studentvector;
}catch(Exception ignore){
return null;
}finally {
dbutil.closeDB();
import java.sql.*;
import java.util.*;
public class dbutil {
/** Creates a new instance of dbutil */
public dbutil() {
Connection conn;
public void connectDB(){
conn = ConnectionManager.getConnection();
public void closeDB(){
try{
if(conn != null && !conn.isClosed())
conn.close();
}catch(Exception excep){
The main error is occuring at the following lines connectDB() and closeDB() in the class student manager. The class dbutil is in an another package.with an another file called connectionManager which establishes the connection with DB. The dbutil has the openconnection and close connection methods. I have not yet written the insert statements in StudentManager. PLease do Help me

Answer 1

You're doing quite a few things that will cause errors, I'm afraid. I'll see if I can help you.
The error you're asking about is caused by the following line:
dbutil.connectDB();
Now first of all please always ensure that your class names begin with capital letters and your instances of classes with lowercase letters. That's what everybody does, so it makes your code much easier to follow.
So re-write the couple of lines at the beginning of your dbutil class like this:
public class Dbutil {
/** Creates a new instance of Dbutil */
public Dbutil() {
Now you need to create an instance of dbutil before you can call connectDB() like this:
Dbutil dbutil = new Dbutil();
now you can call the method connectDB():
dbutil.connectDB();
The problem was that if you don't create an instance first then java assumes that you are calling a static method, because you don't need an instance of a class to call a static method. If it was static, the method code would have been:
public static void connectDB(){
You have a fine example of a static method call in your code:
ConnectionManager.getConnection();
If it wasn't a static method your code would have to look like this:
ConnectionManager connectionManager = new ConnectionManager();
connectionManager.getConnection();
See the difference? I also know that ConnectionManager.getConnection() is a call to a static method because it begins with a capital letter.
Anyway - now on to other things:
You have got two different Connection objects called conn. One is in StudentManager and the other is in Dbutils, and for the moment they have nothing to do with each other.
You call dbUtil.connectDb() and so if your connectDb method is working properly you have a live connection called conn in your dbUtil object. But the connection called conn in StudentManager is still null.
If your connection in the dbUtil object is working then you could just add a line after the call to connectDb() in StudentManager so that the StudentManager.conn object references the dbUtil.conn object like this:
dbutil.connectDB();
conn = dbUtil.conn;