Java Database Connectivity (JDBC)

I wrote the following class DBManager to access the mySQL DB server from java programs.
-----------------------------------------

// DBManager.java
import java.sql.*;

public class DBManager{   
  Connection connection=null;
  Statement statement=null; 
	
  public DBManager(){ // constructor
    initConnection();
  }

  void initConnection(){  // initialize DB connection and statement
    if(connection != null) return;
		try{ 
			Class.forName("com.mysql.jdbc.Driver");
			connection = DriverManager.getConnection("jdbc:mysql://localhost/cf?user=scott&password=tiger");			
			statement = connection.createStatement(); 
		} catch (ClassNotFoundException e){
		  	System.err.println(e);
		} catch (SQLException sqle){
			System.err.println(sqle);
		}
  }

  
  public void closeConnection(){
    try{
      if(statement != null){ statement.close(); }
      if(connection != null){ connection.close(); }
    } catch (SQLException sqle){
			System.err.println(sqle);
		}
  }

  public static void updateDB(String updateSQL){ // given the updateSQL, execute it
		try {
        	new DBManager().statement.executeUpdate(updateSQL);
		} catch (SQLException sqle){
			System.err.println(sqle);
		}
  }


	// given the querySQL, return the ResultSet
	public static ResultSet getQueryResultSet(String querySQL) {	
    	ResultSet resultSet=null;
		try {
        	resultSet = new DBManager().statement.executeQuery(querySQL);
		} catch (SQLException sqle){
			System.err.println(sqle);
		}
		return resultSet;
	}

} // class DBManager

-----------------------------------------

And use it in the following way:

 
	String sqlQuery = "SELECT age FROM users WHERE userID ='Mary'";
	ResultSet rs = DBManager.getQueryResultSet(sqlQuery);
	while(rs.next()){
		age = rs.getInt(1);
		//do something with age here...
	}

Is there any problem in this approach?
Will the connection created in getQueryResultSet() closed automatically after I call this method?
There seems to be a limit on the number of available connections. As my program query the DB using the above approach continously, I am concerned whether the available connections would be exhausted. I started my program this afternoon and went out for a hour or so, when I came back, I found the following error message:
--------------------------

java.sql.SQLException: Server configuration denies access to data source
** Exception
java.lang.NullPointerException
at DBManager.getQueryResultSet(DBManager.java:97)

--------------------------
What could be the reason of this error?
To see whether it's the problem of connections, I wrote the following code to test it,

 
		int count=1;
		String sql = "select userID from users";
		while(true){
			try{
				System.out.println("\ncount="+ count++);
				
				ResultSet rs = DBManager.getQueryResultSet(sql);
				while(rs.next()){
					System.out.print("  " + rs.getString(1));
				}
			
			}catch(Exception e){e.printStackTrace();}
			
		}

And it didn't generate any error so far: the count is already 68000!

I am confused. Anybody can help me?

Thanks.