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Manipulating the Grid
To make it easy for users to distinguish among cells, the table component draws horizontal and vertical lines at regular intervals. Collectively, those lines form a grid. The table component's JTable class provides methods for manipulating a grid's color and showing/hiding grid lines. Table 3 describes the grid-manipulation methods.
Table 3 JTable Grid-Manipulation Methods
|
Method |
Description |
|
setGridColor(Color c) |
Establishes the object referenced by c as the color of grid lines. Redisplays the grid. |
|
setShowGrid(boolean isShown) |
Shows horizontal and vertical grid lines if isShown is true. Otherwise, hides horizontal and vertical grid lines. |
|
setShowHorizontalLines(boolean isShown) |
Shows horizontal grid lines if isShown is true. Otherwise, hides horizontal grid lines. |
|
setShowVerticalLines(boolean isShown) |
Shows vertical grid lines if isShown is true. Otherwise, hides vertical grid lines. |
As an example, assuming that you have a JTable variable jt that references a JTable object, jt.setGridColor (Color.cyan); establishes Color.cyan as the color of grid lines and redisplays the grid in the new color. Also, jt.setShowHorizontalLines (false); hides the grid's horizontal lines. Figure 3 shows the resulting grid.
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Figure 3 A table component's grid-manipulation methods make it easy to change a grid's color and show/hide the grid's horizontal and vertical lines.
Listing 3 presents source code to a TableDemo3 application that allows you to experiment with changing the grid's colors and hiding/showing horizontal and vertical grid lines. The only grid-manipulation method not present is setShowGrid(boolean isShown). I leave it as an exercise for you to incorporate that method into the source code.
Listing 3: TableDemo3.java
// TableDemo3.java
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.table.DefaultTableModel;
class TableDemo3 extends JFrame implements ActionListener
{
JTable jt;
boolean horizFlag;
boolean vertFlag;
TableDemo3 (String title)
{
// Pass the title to the JFrame superclass so that it appears in
// the title bar.
super (title);
// Tell the program to exit when the user either selects Close
// from the System menu or presses an appropriate X button on the
// title bar.
setDefaultCloseOperation (EXIT_ON_CLOSE);
// Create a table with a default table model that specifies 10
// rows by 10 columns dimensions.
jt = new JTable (new DefaultTableModel (10, 10));
// Add the table to the center portion of the frame window's
// content pane.
getContentPane ().add (jt);
// Create a panel for positioning buttons.
JPanel jp = new JPanel ();
// Create a "Change Grid Color" button, register the current
// TableDemo3 object as a listener to that button's action
// events, and add that button to the panel.
JButton jb = new JButton ("Change Grid Color");
jb.addActionListener (this);
jp.add (jb);
// Create a "Show/Hide Horizontal Lines" button, register the
// current TableDemo3 object as a listener to that button's
// action events, and add that button to the panel.
jb = new JButton ("Show/Hide Horizontal Lines");
jb.addActionListener (this);
jp.add (jb);
// Create a "Show/Hide Vertical Lines" button, register the
// current TableDemo3 object as a listener to that button's
// action events, and add that button to the panel.
jb = new JButton ("Show/Hide Vertical Lines");
jb.addActionListener (this);
jp.add (jb);
// Add the panel to the south portion of the frame window's
// content pane.
getContentPane ().add (jp, BorderLayout.SOUTH);
// Establish the frame's initial size as 600x250 pixels.
setSize (600, 250);
// Display the frame window and all contained components.
setVisible (true);
}
public void actionPerformed (ActionEvent e)
{
// Obtain a reference to the JButton object associated with the
// peer window from where an action event was fired.
JButton jb = (JButton) e.getSource ();
// Obtain the JButton's text label.
String label = jb.getText ();
// If the label equals "Change Grid Color," then change the grid
// color. If the label equals "Show/Hide Horizontal Lines," then
// show or hide those lines by calling setShowHorizontalLines()
// with the horizFlag Boolean argument value. Then toggle the
// state of horizFlag so the next call to that method undoes the
// current call. If label does not match the previous two
// strings,
// then show or hide vertical lines by calling
// setShowVerticalLines() with the vertFlag Boolean argument
// value. Then toggle the state of vertFlag so the next call to
// that method undoes the current call.
if (label.equals ("Change Grid Color"))
jt.setGridColor (new Color (rnd (256), rnd (256),
rnd (256)));
else
if (label.equals ("Show/Hide Horizontal Lines"))
{
jt.setShowHorizontalLines (horizFlag);
horizFlag = !horizFlag;
}
else
{
jt.setShowVerticalLines (vertFlag);
vertFlag = !vertFlag;
}
}
public static int rnd (int limit)
{
// Return a random number greater than or equal to 0 and less
// than limit.
return (int) (Math.random () * limit);
}
public static void main (String [] args)
{
// Create a TableDemo3 object, which creates the GUI.
new TableDemo3 ("Table Demo #3");
}
}