Thread: JTable problem

When i create a JTable in this way:

JTable tab = new JTable(a,b);

where a is an String [][] and b String[]

The problem is set the TableModel, when i insert this line:

tab.setModel(new TabellaDati(a,b));

The table appears empty

This is the Table Model

public class DataTable extends TableModel{
    public static final int N_COL = 8;
    public static final int N_RIG = 20;
    private String[] heading;
    private String[][] data;
 
    public DataTable (String[] h, String[][] data){
        this.heading = h;
        this.data = data;
    }
    @Override
    public boolean isCellEditable(int rowIndex, int columnsIndex){
        return (rowIndex == 0) ? true : false;
    }
 
    public void removeTableModelListerner(TableModelListener s){
 
    }
 
    @Override
    public int getRowCount() {
        return data.length;
    }
 
    @Override
    public int getColumnCount() {
       return heading.length;
    }
 
    @Override
    public String getColumnName(int columnIndex) {
        return heading[columnIndex];
    }
 
    @Override
    public Class<?> getColumnClass(int columnIndex) {
        throw new UnsupportedOperationException("Not supported yet."); //To change body of generated methods, choose Tools | Templates.
    }
 
    @Override
    public Object getValueAt(int rowIndex, int columnIndex) {
        return data[rowIndex][columnIndex];
    }
 
    @Override
    public void setValueAt(Object aValue, int rowIndex, int columnIndex) {
         //To change body of generated methods, choose Tools | Templates.
        data[rowIndex][columnIndex] =(String) aValue;
    }
 
    @Override
    public void addTableModelListener(TableModelListener l) {
        //throw new UnsupportedOperationException("Not supported yet."); //To change body of generated methods, choose Tools | Templates.
 
    }
 
    @Override
    public void removeTableModelListener(TableModelListener l) {
        throw new UnsupportedOperationException("Not supported yet."); //To change body of generated methods, choose Tools | Templates.
    }
}

It might help to post a simple example that compiles and illustrates the problem.

---

private String[] heading;
private String[][] data;
 
public DataTable (String[] h, String[][] data){
    this.heading = h;
    this.data = data;
}

This code from the model could cause problems. The constructor sets data to the reference that is sent as an argument. Other methods will access this data array. But what if the caller of the constructor does something to the contents of the data array using its own reference to the array? Then the table's data will not "persist".

I don't know if it's related to what you're (not) seeing, but it might be a good idea to copy the data from the arrays used as arguments into newly created arrays in the model. (Also, that way you would actually be using the static final int values for some purpose.)

Ok, i found the error, the method public Class<?> getColumnClass(int columnIndex) was not implemented (throw new UnsupportedOperationException("Not supported yet."); ) but the program compiled and the table showed anyway.

Once i had implement the method getColumnClass:

public Class<?> getColumnClass(int columnIndex) {
         for (int row = 0; row < getRowCount(); row++)
            {
                Object o = getValueAt(row, columnIndex);
 
                if (o != null)
                {
                    return o.getClass();
                }
            }
 
            return Object.class;
    }

The table finally shows the data in it.
So it seems that first the program shows the table and only after fills it with data.

I got another question, i have to implement a Event Listener that catch the event of a edited cell in the tab.
Where and how i can implements this?

Listening for changes (strictly speaking, changes in the underlying data model not it's visual representation: the table cell) is covered in the Listening for Data Changes section of "How to Use Tables" in Oracle's Tutorial.

The section following that one, describes how to organise things so that the model fires such events. As mentioned there, you get that behaviour for free when you use a DefaultTable but in your case (a TableModel subclass) they suggest subclassing AbstractTableModel.

They illustrate this approach in the TableDemo.java example. Notice how the table model is a subclass of AbstractTabkeModel whose setValueAt() fires events when the table's contents change. Actually responding to such changes is illustrated in the "Listening for Data Changes" section itself.

---

Because of the many-way split between model and view (data, selection, how cells are rendered vs edited, etc) tables are a rather complex example of a gui component. (the most complex of the standard ones?). You might find it useful to go through the whole "How to Use Tables" page and see how they build up each element of the complexity in their example.

My table model implements:
public boolean isCellEditable(int rowIndex, int columnsIndex);
public void removeTableModelListerner(TableModelListener s);
public void removeTableModelListerner(TableModelListener s);
public int getRowCount();
public int getColumnCount();
public Class<?> getColumnClass(int columnIndex);
public Object getValueAt(int rowIndex, int columnIndex);
public void setValueAt(Object aValue, int rowIndex, int columnIndex);
public void addTableModelListener(TableModelListener l);
private void fireTableCellUpdated(int rowIndex, int columnIndex);

the problem that i have with this jtable is that when i write something inside the table, the method fireTableCellUpdated is called, this method get a new matrix and overwrite the data[][] of the table,
but the table do not change, is not refreshed

Write inside a cell -> call fireTableCellUpdated -> get new data to fill the table -> new data in not showed, the table remains the same

But when i move a side or i click on a certain cell, the table is refreshed and the new data is visible.

What could be the problem?

Check that you are invoking fireTableCellUpdated() with the right arguments.

If you continue to have problems post a small example that illustrates the problem. It needn't have all the rest of your program logic, but should compile and show the table not visually keeping up with the new data.

public class MyTable extends TableModel{
    public static final int C = 12;
    public static final int R = 25;
    public String[][] data;
 
    public MyTable(String[] h, String[][] data) {
        this.data = data;
    }
 
    public boolean isCellEditable(int rowIndex, int columnsIndex) {
             if (columnsIndex == 0) 
             return true;
         else 
            return false;      
    }
 
    public void removeTableModelListerner(TableModelListener s) {
    }
 
    public int getRowCount() {
        return data.length;
    }
    public int getColumnCount() {
        return heading.length;
    }
 
    public Class<?> getColumnClass(int columnIndex) {
        for (int row = 0; row < getRowCount(); row++) {
            Object o = getValueAt(row, columnIndex);
 
            if (o != null) {
                return o.getClass();
            }
        }
 
        return Object.class;
    }
 
    public Object getValueAt(int rowIndex, int columnIndex) {
        return data[rowIndex][columnIndex];
    }
 
    public void setValueAt(Object aValue, int rowIndex, int columnIndex) {
 
        data[rowIndex][columnIndex] = (String) aValue;
        try {
            fireTableCellUpdated(rowIndex, columnIndex);
        } catch (TException ex) {
            Logger.getLogger(TabellaDati.class.getName()).log(Level.SEVERE, null, ex);
        }
    }
 
 
    public void addTableModelListener(TableModelListener l) {
        //throw new UnsupportedOperationException("Not supported yet."); //To change body of generated methods, choose Tools | Templates.
    }
 
 
    public void removeTableModelListener(TableModelListener l) {
        throw new UnsupportedOperationException("Not supported yet."); //To change body of generated methods, choose Tools | Templates.
    }
 
    private void fireTableCellUpdated(int rowIndex, int columnIndex){
 
                String[][] newMatrix = Matrix.getMatrix();
                for(int i=0,j=0; i<N_RIG; i++,j++)
                    System.arraycopy(newMatrix[j], 0, data[i], 0, data[i].length);
   }   
}

in fireTableCellUpdated a new matrix is created and overwrite data[][]

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