Init error

Question

Hi,
I have a this problem : I have JDBCTable and a JDBCTableModel classes, wich are extensions of JTable and AbstractTableModel respectively. JDBCTable has a constructor wich receive some strings containing a jdbc connection information and a sql command. Inside the JDBCTable constructor, this strings are used to create a new JDBCTableModel which is then used as JDBCTable model (with setModel()) .
Private JDBCTableModel data;
public JDBCTable(String dbDriver, String dbURL, String dbUser, String dbPass, String sql) throws DBTableException {
data = new JDBCTableModel(dbDriver, dbURL, dbUser, dbPass, sql);
Initialize(sql);
When creating a new JDBCTable, as usual, JTable() default creator gets called before anything else, including Jnew DBCTableModel creation. My problem is that JDBCTableModel.getModel() method is called from JTable code before model itself is created (data in this case).
I supposed that JTable() calls JTable(null, null, null) which creates default models, and this seem to be the case. I saw it debugging it under NetBeans. Finally, when program is still in JTable code I get a NullPointerException, because getModel() return null. It seems that getModel() is called to obtaing number of columns. What happens with default models created by JTable default constructor ?.
I had to change JDBCTabel getModel method as shown below and now it works, but I don't understand exactly why I have to do this. I did this because I saw that getModel() return "null".
public TableModel getModel() {
if (data==null) {
// when called before "actual" model setup
try {
System.out.println("getModel ---------------");
// creates a dummy model
return new JDBCTableModel("select * from accounts LIMIT 1");
} catch (DBTableException dbe) {
// error - I have to see what to do
return (TableModel)data;
// after creation of JDBCTable and model setup correctly
else return data;
With this modification, I saw that getModel() was called 11 times before actual model (data) is created.
As you may guess, I am somewhat new to Java and my Java debugging skills are limited. (I am switching from C to Java).
Maybe is something trivial but I can figure out where to find more info. Any hint will be very apreciatted.
Thanks.

Answer 1

I don't do GUIs, but the design is flawed.
Your data layer is part of the GUI layer. And I would say that should never be the case even in the smallest of applications.