Can someone look at program

[manishjain Jain]

Hi all,

I just made the new program which actully compiles with no error but if run this program it give me the error of :Exception in thread "main " java.lang,NullPointerException

My program is as below:

 
import java.sql.*;
 
public class EssentialJDBC
{
            public static void main(String[] args)
           {
EssentialJDBC SQLExample = new EssentialJDBC();

SQLExample.getResultsByColumnName();
SQLExample.getResultsByColumnPosition();
SQLExample.getAllColumns();
SQLExample.closeConnection();
           }
 
           //contructor to establish the connection and create a statement object......
           public EssentialJDBC()
           {
             try
             {
      Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
       
      Connection databaseConnection = DriverManager.getConnection(sourceURL);
      
      Statement statement = databaseConnection.createStatement();
             }
 
           catch(SQLException sqle)
            {
System.err.println("Error creating connection");
             }
 
           catch(ClassNotFoundException cnfe)
           {
System.err.println(cnfe.toString());
            }
        }
 
         //constructor to establish the connection and create a statement object.....
         void getResultsByColumnName()
         {
try
{
ResultSet authorResults = statement.executeQuery("SELECT  * FROM authors");
int row = 0;

while(authorResults.next())
   System.out.println("Row " + (++row) + " ) "+
authorResults.getString("authid") + " " +
authorResults.getString("lastname") + ", " +
authorResults.getString("firstname") );
  authorResults.close();
}
catch(SQLException sqle)
{
    System.err.println("\nSQLException------------------");
    System.err.println("SQLState: " + sqle.getSQLState());
    System.err.println("Message: " + sqle.getMessage());
}
 
        }
 
        void getResultsByColumnPosition()
        {
             try
             {
ResultSet authorResults = statement.executeQuery("SELECT authid, lastname, firstname FROM authors");
 
int row = 0;
while (authorResults.next())
{
  System.out.print("\nRow " + (++row) + ") ");
  for(int i = 1; i<=3; i++)
System.out.print( (i>1?", ":" ") + authorResults.getString(i));
}
authorResults.close();
             }
             
             catch(SQLException ex)
{
System.err.println("\nSQLException------------------\n");
System.err.println("SQLState: " + ex.getSQLState());
System.err.println("Message : " + ex.getMessage());
}
       }
 
       void getAllColumns()
       {
          try
          {
ResultSet authorResults = statement.executeQuery("SELECT  * FROM authors");

ResultSetMetaData metadata = authorResults.getMetaData();
int columns =  metadata.getColumnCount();
                int row = 0;
 
while(authorResults.next())
{
    
  System.out.print("\nRow " + (++row) + ") ");
  for(int i = 1; i<=columns; i++)
System.out.print( (i>1?", ":" ")+authorResults.getString(i));
  }
 
authorResults.close();

           }
             catch(SQLException ex)
{
System.err.println("\nSQLException------------------\n");
System.err.println("SQLState: " + ex.getSQLState());
System.err.println("Message : " + ex.getMessage());
}
       }
 
//close the connection
      void closeConnection()
     {
if(connection != null)
try
{
    connection.close();
    connection = null;
}

 catch(SQLException ex)
{
System.err.println("\nSQLException------------------\n");
System.err.println("SQLState: " + ex.getSQLState());
System.err.println("Message : " + ex.getMessage());
}
       }
 

Connection connection;
Statement statement;
String sourceURL = new String("jdbc :-o	 dbc:technical_library");
String queryIDandName = "SELECT authid, lastname, firstname FROM authors";
String queryWildCard = "SELECT  * FROM authors";
} 

Can someone plz look at it ....I will really appreciate if some one will help me.

Thanks
Manish Jain

[Paul Sturrock]

Post the full stack trace and people will help.

[Stefan Wagner]

We prefer a linenumber, and a mark, where this line is in the source-code, because we don't like counting to 297, and small differences in the layout may confuse our counting.

a = 7;
b = c.ddd ();
/* ------------- ex. next line --------------- */
e = f.foo ();

... but I found it without that.

You declare 'Statement statement' and 'Connection connection' in your class.
While initialising, you declare a new 'Statement statement' and 'Connection connection' in main, only locally visible, and hiding the class-attribut.
Later the local variable is out of scope - invalid, invisible, - and the class-member is used.
Which is null - has never been initialised.
[ July 28, 2004: Message edited by: Stefan Wagner ]

[manishjain Jain]

Hi Stefan,

Thankyou very much. It solved my problem. I must say you are very knowledgeble and very nice. Thanks for a such a great help from you.

Thanks
Manish