JList.
*
* A list of quotations is displayed using JList. The
* user selects a quotation and it appears in a separate text field.
*
* Creating a JList is straight forward. However,
* JList does not support scrolling directly; so,
* we also instantiate a JScrollpane object and make
* the JList its viewport.
*
* This program uses a command-line argument to specify the name of the
* file containing the quotations. This argument is passed on to the
* constructor of our extended JFrame class. The file
* is opened and the quotations are read into a Quotation
* array.
* A simple inner class named Quotation is defined to store
* a quotation.
*
* Although JList allows multiple items to be selected,
* this demo limits selection to a single item:
* *
* quoteList.setSelectionMode(ListSelectionModel.SINGLE_SELECTION); ** * A
JList fires a list selection event when an
* item is selected in the list. Our application is setup to process these
* events by adding a list selection listener to the JList
* component:
* * *
* quoteList.addListSelectionListener(this); ** * The extend
JFrame containing the JList
* must include "implements ListSelectionListener" in its signature
* and it must implement the valueChanged method of
* the ListSelectionListener.
*
* One small feature demonstrated in this program is dynamic updating
* of the application window's titlebar text.
* When a new quote is selected, the titlebar
* is updated with "DemoList - quote by name",
* where name is the
* person credited with the quotation. Updating the quotation and
* the titlebar are performed in the valueChanged method
* as follows:
* *
* Quotation q = (Quotation)quoteList.getSelectedValue();
* quoteField.setText(q.toString());
* this.setTitle("DemoList - quote from " + q.getName());
*
*
* Screen snap...
*
* @see source code
* @see quotations.txt
* @author Scott MacKenzie, 2002
*/
public class DemoList
{
public static void main(String[] args)
{
if (args.length != 1)
{
System.out.println("usage: java DemoList file");
System.exit(0);
}
// Hmmm... Java L&F looks better
//try {
// UIManager.setLookAndFeel(
// UIManager.getSystemLookAndFeelClassName());
//} catch (Exception e) {}
DemoListFrame frame = new DemoListFrame(args[0]);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setTitle("DemoList");
frame.pack();
frame.show();
}
}
class DemoListFrame extends JFrame implements ListSelectionListener
{
private JTextField quoteField;
private JList quoteList;
private Quotation[] q;
public DemoListFrame(String fileName)
{
final Color FOREGROUND = Color.blue;
final Color BACKGROUND = Color.pink;
final Font DEFAULT_FONT = new Font("Serif", Font.PLAIN, 18);
// get the quotes from a file and place in a Quotation array
q = getQuotes(fileName);
// exit if q is null (Note: an error message was sent to the console)
if (q == null)
System.exit(0);
// ----------------------------------
// construct and configure components
// ----------------------------------
quoteField = new JTextField("(please select a quotation)");
quoteField.setFont(DEFAULT_FONT);
quoteField.setEditable(false);
quoteField.setBackground(BACKGROUND);
quoteField.setForeground(FOREGROUND);
quoteField.setBorder(BorderFactory.createLineBorder(Color.black));
quoteField.setHorizontalAlignment(SwingConstants.CENTER);
quoteField.setPreferredSize(new Dimension(400, 100));
// create a JList of quotations
quoteList = new JList(q);
quoteList.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
quoteList.setSelectedIndex(0);
// put the JList in a JScrollPane
JScrollPane quoteScrollPane = new JScrollPane(quoteList);
quoteScrollPane.setPreferredSize(new Dimension(400, 100));
quoteScrollPane.setBorder(BorderFactory.createLineBorder(Color.black));
// -------------
// add listeners
// -------------
quoteList.addListSelectionListener(this);
// -----------------
// layout components
// -----------------
JPanel contentPane = new JPanel();
contentPane.setLayout(new BoxLayout(contentPane, BoxLayout.Y_AXIS));
contentPane.add(quoteScrollPane);
contentPane.add(Box.createRigidArea(new Dimension(0, 10)));
contentPane.add(quoteField);
contentPane.setBorder(BorderFactory.createEmptyBorder(30, 30, 30, 30));
// make panel this JFrame's content pane
this.setContentPane(contentPane);
}
// --------------------------------------
// implement ListSelectionListener method
// --------------------------------------
public void valueChanged(ListSelectionEvent lse)
{
Quotation q = (Quotation)quoteList.getSelectedValue();
quoteField.setText(q.toString());
this.setTitle("DemoList - quote from " + q.getName());
}
// -------------
// other methods
// -------------
/** Yet another do-the-dirty-work-here method. Open the specified
* file, read the quotations, and place them in a
* Quotation array.
* * Each line in the quotations file contains a quotation and the name * of the person credited with the quotation. A backward slash separates * the quotation from the name.
*
* @param fileArg a string specifying the name of the file containing the
* quotations
* @return a reference to an array of Quotation objects, or
* null if an error was encountered opening or reading the
* file.
*/
public Quotation[] getQuotes(String fileArg)
{
// prepare to read the quotations from a disk file
BufferedReader br = null;
try
{
br = new BufferedReader(new FileReader(fileArg));
} catch (FileNotFoundException e)
{
System.out.println("File not found: " + fileArg);
return null;
}
String line = null;
Vector v = new Vector();
StringTokenizer st;
while (true)
{
try
{
line = br.readLine();
} catch (IOException e)
{
System.out.println("Error reading file: " + fileArg);
return null;
}
if (line == null)
break;
if (line.length() == 0)
continue;
st = new StringTokenizer(line, "\\");
// exactly two entries per line required
if (st.countTokens() != 2)
{
System.out.println("Data format error in file: " + fileArg);
return null;
}
// get the quotation and name
String quotation = st.nextToken();
String name = st.nextToken();
// add to vector as a Quotation object
v.addElement(new Quotation(quotation, name));
}
// initialize quotation array with just the right amount of space
Quotation[] tmp = new Quotation[v.size()];
// copy elements from vector into array
v.copyInto(tmp);
// return a reference to the quotation array (whew!)
return tmp;
}
// -----------
// inner class
// -----------
/** A simple inner class to store a quotation
*/
class Quotation
{
private String quote;
private String name;
Quotation(String quoteArg, String nameArg)
{
quote = quoteArg;
name = nameArg;
}
public String getName() { return name; }
public String getQuote() { return quote; }
public String toString() { return quote + " --" + name; }
}
}