JTable: Selecting rows in columns independently

Question

Dear all,
I have a JTable with two columns. I want the user to be able to select cells in columns independently. At present, the entire row gets marked as selected. Is it possible at all to, for instance, select row1 1 to 3 in column 1 and rows 4 to 5 in column 2? If so, where's the switch? Thanks a lot in advance!
Cheers,
Martin

Answer 1

Are you trying to use a seperate table for each column.
Thats not a good idear.
Here is what you have to do.
1. Create a sub class of JTable
2. You will have to redefine how the selection is done so. You will need some sort of a collection to store the list of selected cells indexes
2.1 Selecting a cell is simply adding the coordinations of the cell to the selection
2.2 de selecting is just removing it from the collection.
2.3 Here is what you have to override
     setColumnSelectionInterval()
     setColumnSelectionInterval()
     changeSelection()
     selectAll()
     getSelectedColumns()
     getSelectedColumn()
     getSelectedRows()
     getSelectedRow() You migh also need few new methods such as
     setCellSelected(int row, int column, boolean selected);
     boolean isCellSelected(int row, int column);
     clearSelection();
     int[][] getSelectedCells();You will have to implement the above in terms of your new data structure.
3. Handle mouse events.
Ex:- when user cicks on a cell if it is already selected it should be deselected (see 2.2)
other wise current selected should be cleared and the clicked cell should be selected
if your has pressed CTRL key while clicking the the cell should be selected without deselecting the old selection.
---you can use above using a MouseListener
When the user hold down a button and move the mouse accross multiple cell those need to be selected.
--- You will need a MouseMotionListener for this
You might also need to allow selection using key bord. You can do that using a KeyListener
4. Displaying the selection
You have to make sure only the selected cells are high lighted on the table.
You can do this using a simple trick.
(Just override getCellEditor(int row, int column) and getCellRenderer(int row, int column) )
Here is what you should do in getCellRenderer(int row, int column)
public TableCellRenderer getCellRenderer(int row, int column)
  TableCellRenderer realRenderer = super.getCellRenderer(int row, int);
  return new WrapperRenderer(realRenderer,selectedCellsCollection.isCellSelected(row,column));
static class WrapperRenderer implements TableCellRenderer{
    TableCellRenderer realRenderer;
    boolean selected;
    public WrapperRenderer(TableCellRenderer realRenderer, boolean selected){
       this.realRenderer = realRenderer;
       this.selected = selected;
    public Component getTableCellRendererComponent(JTable table,
                                               Object value,
                                               boolean isSelected,
                                               boolean hasFocus,
                                               int row,
                                               int column){       
        return realRenderer.getTableCellRendererComponent(table,value,selected,hasFocus,row,column);
}What the above code does is it simply created wrapper for the Renderer and when generating the rendering component it replaces the isSeleted flag with our on selected flag
and the original renderer taken from the super class will do the rest.
You will have to do the same with the TableCellEditor.
By the way dont use above code as it is becouse the getCellRenderer method create a new instance of WrapperRenderer every time.
If the table has 10000 cells above will create 10000 instances. So you should refine above code.
5. Finnaly.
Every time the selection is changes you should make the table rerender the respective cells in or der to make the changes visible.
I'll leave that part for you to figure out.
A Final word
When implementing th above make sure that you do it in the java way of doing it.
For the collection of selected cells write following classes
TableCellSelectionModel  // and interface which define what it does
DefaultTableCellSelectionModel //Your own implementation of above interface the table you create should use thisby default
//To communicate the selection changes
TableCellSelectionModelListener
TableCellSelectionModelEventif you read the javadoc about similer classes in ListSelectionModel you will get an idear
But dont make it as complex as ListSelectionModel try to keep the number of methods less than 5.
If you want to make it completly genaric you will have to resolve some issues such as handling changes to the table model.
Ex:- Rows and colums can be added and removed in the TableModle at the run time as a result the row and column indexes of some cells might change
and the TableCellSelectionModel should be updated with those changes.
Even though the todo list is quite long if you plan your implementation properly the code will not be that long.
And more importantly you will learn lots more by trying to implementing this.
Happy Coding :)