TableModel

[xin hao]

Hi all
I created a TableModel: ResultSetTableModel extends AbstractTableModel
the ResultSetTableModel use a Resultset in construct such as
public ResultSetTableModel(ResultSet re) {
this.resultset=re;
}
ResultSetTableModel's method getRowCount() is
public int getRowCount() {
try{
resultset.last();
return resultset.getRow();
}
catch(SQLException e)
{
e.printStackTrace();
return 0;
}
}
it compiled well but when i run it i get

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at com.xinhao.swing.ResultSetTableModel.getColumnCount(ResultSetTableModel.java:49)

How can I correct it?
the java version is jdk1.6
thanks!

[Romeo Son]

Hi Xin,

You posted the implementation of getRowCount method but the exception is in the implementation of the getColumnCount method.

Try to debug, put a breakpoint in that method and you will figure out which object is null. You are trying to do a method call on a null object in getColumnCount implementation.

Hope this helps,

Romeo

[xin hao]

thank you very much.

I changed nothing but add a JDBCConnection in the ResultSetTableModel such as followed:

public class ResultSetTableModel extends AbstractTableModel{
ResultSet resultset;
public ResultSetTableModel(){

Class.forName(driver).newInstance();
Connection connection = DriverManager.getConnection(url,user,pass);
Statement statement = connection.createStatement();
this.resultset = statement.executeQuery("some sql query ");

}
public int getRowCount() {
try{
this.resultset.last();
return this.resultset.getRow();
}catch(SQLException ex){
ex.printStackTrace();
}
return 0;
}

}
.....
every thing run well but when i just send a ResultSet in this ResultSetTableModel it can not run.

[Andrei Pat]

The JTable has to know how many rows and how many columns there are in the model. You need to write an implementation of the getColumnCount method that returns how many columns the table has. Also, you need an implementation of getValueAt

public int getColumnCount(){
 if (resultset!=null){
   return resultset.getMetaData().getColumnCount();
 }
 return 0;
}

[xin hao]

thinks Romeo Son ,thinks Andrei Pat .
I add "if (resultset!=null)" in my code ,it run well although there isn't any thing in my JTable.
Next i put a breakpoint in method and find the ResultSet i sent out is null.
I have corrected the wrong codes in geting results from database.
Now everything run well.
thanks very much.

[Romeo Son]

Voila