11.9 Displaying Tables
Now that we've seen
how to assemble a prototypical Swing GUI, we can move on and start
studying some more advanced Swing programming topics.
We'll start with examples of some of the more
powerful, and therefore complicated, components. The
JTable class displays tabular data. It is
particularly easy to use if your data happens to be organized into
arrays of arrays. If this is not the case, however, you must
implement the javax.swing.table.TableModel
interface to serve as a translator between your data and the
JTable component.
Example 11-19, which is
a listing of PropertyTable.java, does exactly
this. PropertyTable is a subclass of
JTable that uses a custom
TableModel implementation to display a table of
the properties defined by a specified JavaBeans class (it uses the
java.beans package, which we'll
see more of in Chapter 15). The example includes a
main( ) method so you can run it as a standalone
application. Figure 11-16 shows the
PropertyTable class in action. When studying this
example, pay particular attention to the
TableModel implementation: the
TableModel is the key to working with the
JTable component. Also note the
PropertyTable constructor method that uses the
TableColumnModel to modify the default appearance
of the columns in the table.
Example 11-19. PropertyTable.java
package je3.gui;
import java.awt.*;
import javax.swing.*;
import javax.swing.table.*; // TableModel and other JTable-related classes
import java.beans.*; // For JavaBean introspection
import java.util.*; // For array sorting
/**
* This class is a JTable subclass that displays a table of the JavaBeans
* properties of any specified class.
**/
public class PropertyTable extends JTable {
/** This main method allows the class to be demonstrated standalone */
public static void main(String[ ] args) {
// Specify the name of the class as a command-line argument
Class beanClass = null;
try {
// Use reflection to get the Class from the classname
beanClass = Class.forName(args[0]);
}
catch (Exception e) { // Report errors
System.out.println("Can't find specified class: "+e.getMessage( ));
System.out.println("Usage: java PropertyTable <bean class name>");
System.exit(0);
}
// Create a table to display the properties of the specified class
JTable table = new PropertyTable(beanClass);
// Then put the table in a scrolling window, put the scrolling
// window into a frame, and pop it all up on to the screen
JScrollPane scrollpane = new JScrollPane(table);
JFrame frame = new JFrame("Properties of JavaBean: " + args[0]);
frame.getContentPane( ).add(scrollpane);
frame.setSize(500, 400);
frame.setVisible(true);
}
/**
* This constructor method specifies what data the table will display
* (the table model) and uses the TableColumnModel to customize the
* way that the table displays it. The hard work is done by the
* TableModel implementation below.
**/
public PropertyTable(Class beanClass) {
// Set the data model for this table
try {
setModel(new JavaBeanPropertyTableModel(beanClass));
}
catch (IntrospectionException e) {
System.err.println("WARNING: can't introspect: " + beanClass);
}
// Tweak the appearance of the table by manipulating its column model
TableColumnModel colmodel = getColumnModel( );
// Set column widths
colmodel.getColumn(0).setPreferredWidth(125);
colmodel.getColumn(1).setPreferredWidth(200);
colmodel.getColumn(2).setPreferredWidth(75);
colmodel.getColumn(3).setPreferredWidth(50);
// Right justify the text in the first column
TableColumn namecol = colmodel.getColumn(0);
DefaultTableCellRenderer renderer = new DefaultTableCellRenderer( );
renderer.setHorizontalAlignment(SwingConstants.RIGHT);
namecol.setCellRenderer(renderer);
}
/**
* This class implements TableModel and represents JavaBeans property data
* in a way that the JTable component can display. If you've got some
* type of tabular data to display, implement a TableModel class to
* describe that data, and the JTable component will be able to display it.
**/
static class JavaBeanPropertyTableModel extends AbstractTableModel {
PropertyDescriptor[ ] properties; // The properties to display
/**
* The constructor: use the JavaBeans introspector mechanism to get
* information about all the properties of a bean. Once we've got
* this information, the other methods will interpret it for JTable.
**/
public JavaBeanPropertyTableModel(Class beanClass)
throws java.beans.IntrospectionException
{
// Use the introspector class to get "bean info" about the class.
BeanInfo beaninfo = Introspector.getBeanInfo(beanClass);
// Get the property descriptors from that BeanInfo class
properties = beaninfo.getPropertyDescriptors( );
// Now do a case-insensitive sort by property name
// The anonymous Comparator implementation specifies how to
// sort PropertyDescriptor objects by name
Arrays.sort(properties, new Comparator( ) {
public int compare(Object p, Object q) {
PropertyDescriptor a = (PropertyDescriptor) p;
PropertyDescriptor b = (PropertyDescriptor) q;
return a.getName( ).compareToIgnoreCase(b.getName( ));
}
public boolean equals(Object o) { return o == this; }
});
}
// These are the names of the columns represented by this TableModel
static final String[ ] columnNames = new String[ ] {
"Name", "Type", "Access", "Bound"
};
// These are the types of the columns represented by this TableModel
static final Class[ ] columnTypes = new Class[ ] {
String.class, Class.class, String.class, Boolean.class
};
// These simple methods return basic information about the table
public int getColumnCount( ) { return columnNames.length; }
public int getRowCount( ) { return properties.length; }
public String getColumnName(int column) { return columnNames[column]; }
public Class getColumnClass(int column) { return columnTypes[column]; }
/**
* This method returns the value that appears at the specified row and
* column of the table
**/
public Object getValueAt(int row, int column) {
PropertyDescriptor prop = properties[row];
switch(column) {
case 0: return prop.getName( );
case 1: return prop.getPropertyType( );
case 2: return getAccessType(prop);
case 3: return new Boolean(prop.isBound( ));
default: return null;
}
}
// A helper method called from getValueAt( ) above
String getAccessType(PropertyDescriptor prop) {
java.lang.reflect.Method reader = prop.getReadMethod( );
java.lang.reflect.Method writer = prop.getWriteMethod( );
if ((reader != null) && (writer != null)) return "Read/Write";
else if (reader != null) return "Read-Only";
else if (writer != null) return "Write-Only";
else return "No Access"; // should never happen
}
}
}
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