Swing Hacks

Add Column Selection to JTables #22

Chapter 3, Tables and Trees

|

107

HACK

When you run this version of ColumnResizer, the table should look like

Figure 3-3.

Having done this, it’s still possible to crush either table cells or headers if

you resize (programatically or by dragging the frame’s corner) to a point

where there’s just not enough room for all the content. If you really wanted

to keep header cells intact, you could alter the previous code to set the

TableColumn’s minimum width to the preferred width of the header cell,

assuming the header isn’t much wider than the content. Ultimately, it’s

really a question of what data you’re putting in the table and what looks

right to you.

Hacking the Hack

“But,” you might be saying, “what if I don’t have my table data in advance?”

If you have some idea of what the data is probably going to be like, you

could create your table, add this “prototype” data as a row, size the col-

umns, and then remove the prototype…all before ever making the table visi-

ble. That would give your users reasonable default sizing, and then they

could resize columns by dragging header borders as desired. Of course, you

could always hook up a

TableModelListener and resize the columns every

time data is inserted, deleted, or updated, but having the column widths

jump around magically can be very annoying.

H A C K

#22

Add Column Selection to JTables Hack #22

So, why can’t I select a column by clicking on its header?

Here’s something that seems strange about JTables: you can click on the col-

umn headers, but only for the purpose of reordering columns—not for

selecting the contents of that column. I don’t know about you, but consider-

ing that I almost never reorder columns, it seems like the default behavior is

Figure 3-3. Accounting for header width in JTable column resizing

108

|

Chapter 3, Tables and Trees

#22 Add Column Selection to JTables

HACK

backward. And if your users have had their expectations set by working with

Excel or other spreadsheets, they’ll surely expect the ability to select an

entire column.

The to-do list for adding column selectability to a

JTable

consists of two

items:

• Change which kinds of multiselection are allowed.

• Wire up a

MouseListener

.

Example 3-3 shows a very simple implementation.

The constructor is deliberately simple, taking only a two-dimensional array

of contents and a one-dimensional array of headers. Of course,

JTable has

many more constructor signatures than this, but this is the one that will be

easiest to expose to a test class (do I have to mention that building out the

other constructors is left to the reader as an exercise?).

The next step is changing the defaults for multi-cell selection. The default is

to allow row selection—exactly what you don’t want. So, enable column

selection and disable row selection. Next, you want to catch clicks on the

headers so you can select columns in response to them. Unfortunately, the

JTableHeader component doesn’t have an addActionListener( ) method, so

the best you can do is add a

MouseListener instead. Of its various methods,

you only need to override

mouseReleased( ), which signals the end of a click-

and-release.

Example 3-3. A JTable that allows column selection by clicking on column headers

public class ColumnSelectableJTable extends JTable {

public ColumnSelectableJTable (Object[][] items, Object[] headers) {

super (items, headers);

setColumnSelectionAllowed (true);

setRowSelectionAllowed (false);

// set up action listener on table header

final JTableHeader header = getTableHeader( );

header.addMouseListener (new MouseAdapter( ) {

public void mouseReleased (MouseEvent e) {

if (! e.isShiftDown( ))

clearSelection( );

int pick = header.columnAtPoint(e.getPoint( ));

addColumnSelectionInterval (pick, pick);

}

});

}

}