method always visible by other class  
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Mariano
PostPosted: 2007-3-19 3:55:00 Top
java-programmer, method always visible by other class Then I have a class called MyDBConn.java, inside this class there's a
method called GetResultFromPazienti():

MyDBConn.java:
==================================

package cc;

import java.sql.*;

public class MyDBConn {
private Connection myConnection;
private java.sql.Statement stmt;

// ...

public ResultSet getResultFromPazienti2(String query) {
ResultSet rs=null;
try{
rs=stmt.executeQuery(query);
}
catch(Exception e){
alerts.showErr(e.getMessage());
}
return rs;
}

// ...

==================================

After this, I have a class called Paziente.java, from this class I
would call method: getResultFromPazienti2(), class is something like
this:

File: Paziente.java
==================================
package cc;
import java.sql.*;

public class Paziente extends javax.swing.JFrame {
private MyDBConn mdbc;
private java.sql.Statement stmt;

// ...
// ...

private void formWindowOpened(java.awt.event.WindowEvent evt)
{
ResultSet rs=mdbc.getResultFromPazienti2("select ... from ...
where ...");

try {
rs.next();
// ...
txtNome.setText(rs.getString("NOME"));
// ...
} catch (SQLException ex) {
ex.printStackTrace();
}
}
}


==================================

At first moment seem that are not problems, infact there's no problem
in compile time, but when I execute project and method
formWindowOpened() is started an "Exception in thread "AWT-
EventQueue-0" java.lang.NullPointerException", where are the
problems???
Thank you to all....

 
Brandon McCombs
PostPosted: 2007-3-19 9:16:00 Top
java-programmer >> method always visible by other class Mariano wrote:
> Then I have a class called MyDBConn.java, inside this class there's a
> method called GetResultFromPazienti():

The method below is called GetResultFromPazienti2().

>
> MyDBConn.java:
> ==================================
>
> package cc;
>
> import java.sql.*;
>
> public class MyDBConn {
> private Connection myConnection;
> private java.sql.Statement stmt;
>
> // ...
>

the method below is not the same as you specify above.
You never instantiate stmt so maybe that is what is producing the null
pointer.

> public ResultSet getResultFromPazienti2(String query) {
> ResultSet rs=null;
> try{
> rs=stmt.executeQuery(query);
> }
> catch(Exception e){
> alerts.showErr(e.getMessage());
> }
> return rs;
> }
>
> // ...
>
> ==================================
>
> After this, I have a class called Paziente.java, from this class I
> would call method: getResultFromPazienti2(), class is something like
> this:
>
> File: Paziente.java
> ==================================
> package cc;
> import java.sql.*;
>
> public class Paziente extends javax.swing.JFrame {
> private MyDBConn mdbc;
> private java.sql.Statement stmt;

Is stmt ever used and initialized?
Is mdbc ever initialized? You leave out code that prevents full analysis
so we can't help you.

>
> // ...
> // ...
>
> private void formWindowOpened(java.awt.event.WindowEvent evt)
> {
> ResultSet rs=mdbc.getResultFromPazienti2("select ... from ...
> where ...");
>
> try {
> rs.next();
> // ...
> txtNome.setText(rs.getString("NOME"));
> // ...
> } catch (SQLException ex) {
> ex.printStackTrace();
> }
> }
> }
>
>
> ==================================
>
> At first moment seem that are not problems, infact there's no problem
> in compile time, but when I execute project and method
> formWindowOpened() is started an "Exception in thread "AWT-
> EventQueue-0" java.lang.NullPointerException", where are the
> problems???
> Thank you to all....
>

The exception should tell you what line the null pointer is on. Does it?
 
 
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