Text Components

Text Components

Text components are the most complex Swing components, but they are fun to use, and you need one for the assignment. The required user help is presented in one of these components, probably the JTextEditor. These are the five text components:

• JTextField ” This component is the simplest one for displaying and editing only one line of text.

• JPasswordField ” This component is the same control as JTextField, except the typed characters are displayed as asterisks to hide the password.

• JTextArea ” This component is the same as JTextField, except instead of only one line, JTextArea allows displaying and editing multiple lines of text, all in the same font.

• JEditorPane ” This component allows displaying and editing multiple lines of text and in multiple fonts.

• JTextPane ” This component also allows displaying and editing multiple lines of text in multiple fonts. JTextPane is a subclass of JEditorPane and has more functionality.

You must provide user help documentation, preferably in HTML format. Use the JEditorPane component to do this because that component is designed especially for HTML.

The following example shows how you might present user help information in HTML format. Listing 14.3 demonstrates how to display an HTML file using the JtextPane component.

Listing 14.3 How to Display an HTML File

 import javax.swing.*; import java.awt.*; public class UserHelp {     public UserHelp()     {         JTextPane pane = new JTextPane();         JScrollPane scroller = new JScrollPane();         scroller.getViewport().add(pane);         JFrame frame = new JFrame("Look-Feel");         frame.getContentPane().add(scroller, BorderLayout.CENTER);         frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);         frame.pack();         frame.setSize(800,500);         frame.setVisible(true);         String htmlDocument = "userHelp.html";         try         {             java.net.URL url = new java.net.URL("file:"                        + System.getProperty("user.dir")                        + System.getProperty("file.separator")                        + htmlDocument);             pane.setPage(url);         } catch (Exception ex)         {             ex.printStackTrace();         }     }     public static void main(String[] args)     {         try         {             UIManager.setLookAndFeel(                 UIManager.getCrossPlatformLookAndFeelClassName());         } catch (Exception e) {}         //Create the top-level container and add contents to it.         UserHelp app = new UserHelp();     } } 

Listing 14.3 produces a simple screen. (Refer to Figure 5.1 in Chapter 5, "Documentation and Javadoc Comments.") Be aware that the JTextPane is not an advanced browser tool. It displays plain HTML fine, but doesn't do well with advanced features, such as cascading style sheets (CSS), JavaScript, or Extensible Hypertext Markup Language (XHTML).

There are many interesting operations you can perform on text components. A few are shown in the following example:

 JTextComponent textComponent =            new JTextArea("Do not act like a knucklehead."); int textLength = textComponent.getDocument().getLength(); // grab all the text String allText = textComponent.getText(); try {     // grab first 5 characters     text = textComponent.getText(0, 5);     // grab last 5 characters     text = textComponent.getText(textLength-5, 5);     // delete characters     textComponent.remove(3, 4);     // replace characters     textComponent.insertString(3, "four", null); } catch (BadLocationException ble) {} 

The following is another way to programmatically manipulate the String in a text component:

 JTextPane textPane = new JTextPane(); // grab root element Element rootDoc = textPane.getDocument().getDefaultRootElement(); // How many paragraphs? int paragraphs = rootDoc.getElementCount(); // grab each paragraph for (int i=0; i<paragraphs; i++) {     Element para = section.getElement(i);     int start = para.getStartOffset();     int end = para.getEndOffset();     try     {         String text = rootDoc.getText(start, end-start);     } catch (BadLocationException ex)     {} } 

A text component stores the text as a Document object, which divides the content into a hierarchy of Element objects. Element objects are a contiguous span of characters with the same attributes. For example, a contiguous span of characters terminated by a single newline character is one paragraph element.