Using Text Components JTextComponent JTextTextFieldJEditorPane JTextPaneJPasswordField JTextArea Text Controls Plain Text Areas Styled Text Areas

Text Controls ● Also called text fields ● Can display and edit one line of text at a time ● Respond to action events, typically the user typing the Enter key ● Used to get a small amount of textual information from the user ● JPasswordField is an extension of JTextField that does not display typed text

Text Field Example ● Display a labeled text field with the following behavior: – User enters text followed by the Enter key – If the entered text is not '' quit '', the text is highlighted (selected) and then nothing is done ● Subsequent typing in the field will cause the highlighted text to be erased – If the entered text is ''quit'', the program exits

Display After the user enters some text and hits Enter:

Text Field Code... JLabel label = new JLabel("Enter a command:"); JTextField textField = new JTextField(20); textField.setPreferredSize(new Dimension(50,20)); textField.addActionListener(new ActionListener() { public void actionPerformed(ActionEvent e) { String command = textField.getText(); if (command.equals("quit")) { frame.dispose(); // frame is top-level System.exit(0); // JFrame } else { textField.selectAll(); } }); JPanel panel = new JPanel(); panel.setLayout(new BoxLayout(panel, BoxLayout.Y_AXIS)); panel.add(label); panel.add(textField); frame.getContentPane().add(panel); frame.setVisible(true);...

Notes On The Code ● The argument to the JTextField constructor is a preferred size for the visible area; the length of the string entered is not limited ● As with buttons, text fields are action-based ● The action listener is created using a constructor for an anonymous class that extends the action listener interface ● The getText method returns the entered string ● The selectAll method highlights the string ● The label and text field are put into a JPanel first; otherwise the text field would fill the frame

Plain Text Areas ● JTextArea can display and edit multiple lines of text ● Text can be displayed in any font, but all of the text is in the same font ● Use a text area to allow the user to enter unformatted text of any length ● Also can be used to display unformatted help information

JTextArea Example... JTextArea textArea = new JTextArea( "This is an editable JTextArea " + "that has been initialized with the setText method. " + "A text area is a \"plain\" text component, " + "which means that although it can display text " + "in any font, all of the text is in the same font." ); textArea.setFont(new Font("Serif", Font.ITALIC, 16)); textArea.setLineWrap(true); textArea.setWrapStyleWord(true); JPanel panel = new JPanel(); panel.setLayout(new BoxLayout(panel, BoxLayout.Y_AXIS)); panel.add(textArea); frame.getContentPane().add(panel); // frame is the top-level frame.setVisible(true); // JFrame...

Example Display Note that a default text area width was used, and that the text does not fit in the frame. It needs to have its text displayed within a scroll pane.

JTextArea Example Modified textArea = new JTextArea( "This is an editable JTextArea " + "that has been initialized with the setText method. " + "A text area is a \"plain\" text component, " + "which means that although it can display text " + "in any font, all of the text is in the same font." ); textArea.setFont(new Font("Serif", Font.ITALIC, 16)); textArea.setLineWrap(true); textArea.setWrapStyleWord(true); JScrollPane areaScrollPane = new JScrollPane(textArea); areaScrollPane.setVerticalScrollBarPolicy( JScrollPane.VERTICAL_SCROLLBAR_ALWAYS); areaScrollPane.setPreferredSize(new Dimension(200, 150)); panel = new JPanel(); panel.setLayout(new BoxLayout(panel, BoxLayout.Y_AXIS)); panel.add(areaScrollPane); frame.getContentPane().add(panel); frame.setVisible(true);

New Display

Styled Text Areas ● JEditorPane and JTextPane objects can display text in multiple fonts ● Some allow embedded images and even embedded components ● Require more up-front programming to set up and use ● Exception: JEditorPane can be easily used to display formatted text from a URL

Digression: The Model-View Approach to Software Architecture ● Like most Swing components, the text components use a model-view approach – The model is the data about the underlying component – The view is a presentation of the data ● E.g., underlying a JButton is a ButtonModel object that has: – whether it is enabled – whether it is selected – whether it is pressed – what its keyboard mnemonic is

The Model-View Approach to Software Architecture (cont'd) ● Why separate the model from its view? – So that different Look-and-Feels can be created for the same data – If you need the data for some processing, it is much more efficient to get it directly from the model than from the component that is presenting it ● All JTextComponent classes provide views of their associated models, called documents

Documents ● Each document is an instance of a class that implements the Document interface ● A document must provide the following services for a text component: – Contain the text – Provide support for text editing – Notify listeners of changes to the text – Manage a position within the text – Allow retrieval of information like text length, and of sub-portions of the text

Document Class and Interface Hierarchy AbstractDocument PlainDocument DefaultStyledDocumen t HTMLDocument Document StyledDocumen t implements Used by JTextField and JTextArea Used by JEditorPane Used by JTextPane

The JEditorPane Class ● JEditorPane is the foundation for Swing's styled text components ● A JEditorPane object becomes an editor for the type of content it is given: – text/plain: plain text – text/html: Hypertext Markup Language – text/rtf: Rich Text Format ● Uses an instance of the EditorKit class to accomplish editing tasks ● Can be used to display uneditable URLs

Loading Content into a JEditorPane ● setText : initializes the component from a String ● read : initializes the component from a Reader ● setPage : initializes the component from a URL ● Besides using these methods, similar loading can be accomplished using constructors

JEditorPane Example JFrame frame =... // make top-level window editorPane = new JEditorPane( "text/plain", "Here is a string of text\n" + "initialized in the constructor.\n" + "Note that we gave the type\n" + "\"text/plain\" as the first argument."); JScrollPane editorScrollPane = new JScrollPane(editorPane); editorScrollPane.setVerticalScrollBarPolicy( JScrollPane.VERTICAL_SCROLLBAR_ALWAYS); editorScrollPane.setPreferredSize(new Dimension(300, 300)); JPanel panel =... // make panel to hold editorPane and // add panel to frame

Example Display

Loading From URLs ● Consider the following HTML file, called Test.html : A Test HTML Page A Test HTML Page Fruits Vegetables Drinks Apples Broccoli Milk Bananas Spinach Juice Oranges Carrots Soda Grapes Squash Lemons

Loading From URLs (cont'd) ● A file URL is of the form: – file: ● There is a URL class constructor that takes a string representing a file URL specification as an argument ● We could code the specification directly: – new URL(''file:/home/cs/tcolburn.../Test.html'') ● Or we can use the System class to build the specification

System Class Properties ● Java maintains a list of system properties and their values, implemented as a hash table. Some of them: Property Value os.name Operating system name os.arch Operating system architecture os.version Operating system version file.separator ''/'' on Unix path.separator '':'' on Unix line.separator ''\n'' on Unix user.name User's account name user.home User's home directory user.dir User's current working directory Use Sytem.getProperty('' '') to retrieve a value

Example That Loads A File URL import java.io.*; import java.net.*;... editorPane = new JEditorPane(); editorPane.setEditable(false); try { url = new URL("file:" + System.getProperty("user.dir") + System.getProperty("file.separator") + "Test.html"); editorPane.setPage(url); } catch (IOException e) { System.err.println("Attempted to read a bad URL: " + url); } catch (Exception e) { System.err.println("Couldn't create URL: " + url); } JScrollPane editorScrollPane = new JScrollPane(editorPane);... panel = new JPanel();... panel.add(editorScrollPane); frame.getContentPane().add(panel); frame.setVisible(true);...

Notes On The Example ● The URL class is in the java.net package ● setEditable(false) is used to keep the HTML document from being edited ● new URL(...) can throw an exception if the file URL specification is malformed ● setPage(url) can throw an exception if the URL argument cannot be read for some reason

Example Output

Example That Loads A Network URL import java.io.*; import java.net.*;... editorPane = new JEditorPane(); editorPane.setEditable(false); try { url = new URL(" editorPane.setPage(url); } catch (IOException e) { System.err.println("Attempted to read a bad URL: " + url); } catch (Exception e) { System.err.println("Couldn't create URL: " + url); } JScrollPane editorScrollPane = new JScrollPane(editorPane);... panel = new JPanel();... panel.add(editorScrollPane); frame.getContentPane().add(panel); frame.setVisible(true);...

Example Output

The JTextPane Class ● The JTextPane class extends JEditorPane ● A text pane inherits the capabilities of an editor pane but insists that its document be a styled document ● You can embed images and components in a text pane ● You can embed images in an editor pane too, but only by including them in an HTML or RTF file