<!-- jEdit 4.0 Macro Guide, (C) 2001, 2002 John Gellene       -->
<!-- Wed Jun 20 16:56:26 EDT 2001 @914 /Internet Time/        -->
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<!-- This file covers the chapter "Macro tips and techniques" -->
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<chapter id="macro-tips"><title>Macro Tips and Techniques</title>

<sect1 id="macro-tips-input">
<title>Getting Input for a Macro</title>

  <para>
    The dialog-based macro discussed in <xref linkend="dialog-macro"/>
    reflects a conventional approach to obtaining input in a Java program.
    Nevertheless, it can be too lengthy or tedious for someone
    trying to write a macro quickly. Not every macro needs a user interface
    specified in such detail; some macros require only a single keystroke or
    no input at all. In this section we outline some other techniques for
    obtaining input that will help you write macros quickly.
  </para>

<sect2 id="macro-tips-input-single-line">
<title>Getting a Single Line of Text</title>

  <para>
    As mentioned earlier in <xref linkend="helpful-methods" />, the method
    <function>Macros.input()</function> offers a convenient way to obtain
    a single line of text input. Here is an example that inserts a pair
    of HTML markup tags specified by the user.
  </para>

<informalexample><programlisting>// Insert_Tag.bsh

void insertTag()
{
    caret = textArea.getCaretPosition();
    tag = Macros.input(view, <quote>Enter name of tag:</quote>);
    if( tag == null || tag.length() == 0) return;
    text = textArea.getSelectedText();
    if(text == null) text = <quote></quote>;
    sb = new StringBuffer();
    sb.append(<quote>&lt;</quote>).append(tag).append(<quote>&gt;</quote>);
    sb.append(text);
    sb.append(<quote>&lt;/</quote>).append(tag).append(<quote>&gt;</quote>);
    textArea.setSelectedText(sb.toString());
    if(text.length() == 0)
        textArea.setCaretPosition(caret + tag.length() + 2);
}

insertTag();

// end Insert_Tag.bsh</programlisting></informalexample>

  <para>
    Here the call to <function>Macros.input()</function> seeks the name
    of the markup tag. This method sets the message box title to a fixed string,
    <quote>Macro input</quote>, but the specific message <guilabel>Enter name
    of tag</guilabel> provides all the information necessary. The return value
    <varname>tag</varname> must be tested to see if it is null.  This would
    occur if the user presses the <guilabel>Cancel</guilabel> button or
    closes the dialog window displayed by <function>Macros.input()</function>.
  </para>
</sect2>

<sect2 id="macro-tips-input-multiple-data"><title>Getting Multiple Data Items</title>
  <para>
    If more than one item of input is needed, a succession of calls to
    <function>Macros.input()</function> is a possible, but awkward approach,
    because it would not be possible to correct early input after the
    corresponding message box is dismissed.  Where more is required,
    but a full dialog layout is either unnecessary or too much work,
    the Java method <function>JOptionPane.showConfirmDialog()</function>
    is available. The version to use has the following prototype:
  </para>

  <itemizedlist>
    <listitem>
      <funcsynopsis>
        <funcprototype>
          <funcdef>public static int <function>showConfirmDialog</function></funcdef>
          <paramdef>Component <parameter>parentComponent</parameter></paramdef>
          <paramdef>Object <parameter>message</parameter></paramdef>
          <paramdef>String <parameter>title</parameter></paramdef>
          <paramdef>int <parameter>optionType</parameter></paramdef>
          <paramdef>int <parameter>messageType</parameter></paramdef>
        </funcprototype>
      </funcsynopsis>
    </listitem>
  </itemizedlist>

  <para>
    The usefulness of this method arises from the fact that the
    <varname>message</varname> parameter can be an object of any
    Java class (since all classes are derived from
    <classname>Object</classname>), or any array of objects.  The
    following example shows how this feature can be used.
  </para>

  <informalexample><programlisting>// excerpt from Write_File_Header.bsh

title = <quote>Write file header</quote>;

currentName = buffer.getName();

nameField = new JTextField(currentName);
authorField = new JTextField(<quote>Your name here</quote>);
descField = new JTextField(<quote></quote>, 25);

namePanel = new JPanel(new GridLayout(1, 2));
nameLabel = new JLabel(<quote>Name of file:</quote>, SwingConstants.LEFT);
saveField = new JCheckBox(<quote>Save file when done</quote>,
    !buffer.isNewFile());
namePanel.add(nameLabel);
namePanel.add(saveField);


message = new Object[9];
message[0] = namePanel;
message[1] = nameField;
message[2] = Box.createVerticalStrut(10);
message[3] = <quote>Author's name:</quote>;
message[4] = authorField;
message[5] = Box.createVerticalStrut(10);
message[6] = <quote>Enter description:</quote>;
message[7] = descField;
message[8] = Box.createVerticalStrut(5);

if( JOptionPane.OK_OPTION !=
    JOptionPane.showConfirmDialog(view, message, title,
        JOptionPane.OK_CANCEL_OPTION,
        JOptionPane.QUESTION_MESSAGE))
    return null;

// *****remainder of macro script omitted*****

// end excerpt from Write_File_Header.bsh</programlisting></informalexample>

  <para>
    This macro takes several items of user input and produces a formatted
    file header at the beginning of the buffer. The full macro is included in
    the set of macros installed by jEdit. There are a number of input
    features of this excerpt worth noting.
  </para>

  <itemizedlist>
    <listitem>
      <para>
        The macro uses a total of seven visible components. Two of them are
        created behind the scenes by <function>showConfirmDialog()</function>,
        the rest are made by the macro. To arrange them, the script creates an
        array of <classname>Object</classname> objects and assigns components to
        each location in the array. This translates to a fixed, top-to-bottom
        arrangement in the message box created by
        <function>showConfirmDialog()</function>.
      </para>
    </listitem>

    <listitem>
      <para>
        The macro uses <classname>JTextField</classname> objects to
        obtain most of the input data.  The fields <varname>nameField</varname>
        and <varname>authorField</varname> are created with constructors
        that take the initial, default text to be displayed in the field as a
        parameter.  When the message box is displayed, the default text
        will appear and can be altered or deleted by the user.
      </para>
    </listitem>

    <listitem>
      <para>
        The text field <varname>descField</varname> uses an empty string for its
        initial value. The second parameter in its constructor sets the width of
        the text field component, expressed as the number of characters of
        <quote>average</quote> width. When
        <function>showConfirmDialog()</function> prepares the layout of the
        message box, it sets the width wide enough to accommodate the
        designated with of <varname>descField</varname>. This technique produces
        a message box and input text fields that are wide enough for your data
        with one line of code.
      </para>
    </listitem>

    <listitem>
      <para>
        The displayed message box includes a <classname>JCheckBox</classname>
        component that determines whether the buffer will be saved to disk
        immediately after the file header is written. To conserve space
        in the message box, we want to display the check box to the
        right of the label <guilabel>Name of file:</guilabel>. To do that,
        we create a <classname>JPanel</classname> object and populate it with
        the label and the checkbox in a left-to-right
        <classname>GridLayout</classname>.  The <classname>JPanel</classname>
        containing the two components is then added to the beginning of
        <varname>message</varname> array.
      </para>
    </listitem>

    <listitem>
      <para>
        The two visible components created by
        <function>showConfirmDialog()</function> appear at positions 3 and 6 of
        the <varname>message</varname> array. Only the text is required; they
        are rendered as text labels.
      </para>
    </listitem>

    <listitem>
      <para>
        There are three invisible components created by
        <function>showConfirmDialog()</function>.  Each of them involves
        a call to <function>Box.createVerticalStrut()</function>.  The
        <classname>Box</classname> class is a sophisticated layout class
        that gives the user great flexibility in sizing and positioning
        components. Here we use a <function>static</function> method of
        the <classname>Box</classname> class that produces a vertical
        <glossterm>strut</glossterm>.  This is a transparent component
        whose width expands to fill its parent component (in this case,
        the message box).  The single parameter indicates the height
        of the strut in pixels.  The last call to
        <function>createVerticalStrut()</function> separates the
        description text field from the <guilabel>OK</guilabel> and
        <guilabel>Cancel</guilabel> buttons that are automatically added
        by <function>showConfirmDialog()</function>.
      </para>
    </listitem>

    <listitem>
      <para>
        Finally, the call to <function>showConfirmDialog()</function> uses
        defined constants for the option type and the message type.  The
        constants are the same as those used with the
        <function>Macros.confirm()</function> method; see
        <xref linkend="helpful-methods" />. The
        option type signifies the use of <guilabel>OK</guilabel>
        and <guilabel>Cancel</guilabel> buttons. The
        <constant>QUERY_MESSAGE</constant> message type causes the message box
        to display a question mark icon.
      </para>
      <para>
        The return value of the method
        is tested against the value <constant>OK_OPTION</constant>.  If
        the return value is something else (because the
        <guilabel>Cancel</guilabel> button was pressed or because the
        message box window was closed without a button press), a
        <constant>null</constant> value is returned to a calling function,
        signaling that the user canceled macro execution.  If the return
        value is <constant>OK_OPTION</constant>, each of the input components
        can yield their contents for further processing by calls to
        <function>JTextField.getText()</function> (or, in the case of
        the check box, <function>JCheckBox.isSelected()</function>).
      </para>
    </listitem>

  </itemizedlist>
</sect2>

<sect2 id="tips-macro-input-combo"><title>Selecting Input From a List</title>
<para>
  Another useful way to get user input for a macro is to use a combo box
  containing a number of pre-set options. If this is the only input
  required, one of the versions of <function>showInputDialog()</function>
  in the <classname>JOptionPane</classname> class provides a shortcut.
  Here is its prototype:
</para>

  <itemizedlist>
    <listitem>
      <funcsynopsis>
        <funcprototype>
          <funcdef>public static Object <function>showInputDialog</function></funcdef>
          <paramdef>Component <parameter>parentComponent</parameter></paramdef>
          <paramdef>Object <parameter>message</parameter></paramdef>
          <paramdef>String <parameter>title</parameter></paramdef>
          <paramdef>int <parameter>messageType</parameter></paramdef>
          <paramdef>Icon <parameter>icon</parameter></paramdef>
          <paramdef>Object[] <parameter>selectionValues</parameter></paramdef>
          <paramdef>Object <parameter>initialSelectionValue</parameter></paramdef>
        </funcprototype>
      </funcsynopsis>
    </listitem>
  </itemizedlist>

  <para>
    This method creates a message box containing a drop-down list of the
    options specified in the method's parameters, along with
    <guilabel>OK</guilabel> and <guilabel>Cancel</guilabel> buttons.
    Compared to <function>showConfirmDialog()</function>, this method lacks
    an <varname>optionType</varname> parameter and has three additional
    parameters: an <varname>icon</varname> to display in the dialog
    (which can be set to <constant>null</constant>), an array of
    <varname>selectionValues</varname> objects, and a reference to one
    of the options as the <varname>initialSelectionValue</varname> to be
    displayed. In addition, instead of returning an <classname>int</classname>
    representing the user's action, <function>showInputDialog()</function>
    returns the <classname>Object</classname> corresponding to the user's
    selection, or <constant>null</constant> if the selection is canceled.
  </para>

  <para>
    The following macro fragment illustrates the use of this method.
  </para>

  <informalexample>
  <programlisting>// fragment illustrating use of showInputDialog()
options = new Object[5];
options[0] = "JLabel";
options[1] = "JTextField";
options[2] = "JCheckBox";
options[3] = "HistoryTextField";
options[4} = "-- other --";

result = JOptionPane.showInputDialog(view,
    "Choose component class",
    "Select class for input component",
    JOptionPane.QUESTION_MESSAGE,
    null, options, options[0]);</programlisting>
  </informalexample>

  <para>
    The return value <varname>result</varname> will contain either the
    <classname>String</classname> object representing the selected text
    item or <constant>null</constant> representing no selection.  Any
    further use of this fragment would have to test the value of
    <varname>result</varname> and likely exit from the macro if the value
    equaled <constant>null</constant>.
  </para>

  <para>
    A set of options can be similarly placed in a
    <classname>JComboBox</classname> component created as part of a larger
    dialog or <function>showMessageDialog()</function> layout.  Here are some
    code fragments showing this approach:
  </para>

  <informalexample>
  <programlisting>// fragments from Display_Abbreviations.bsh
// import statements and other code omitted

// from main routine, this method call returns an array
// of Strings representing the names of abbreviation sets

abbrevSets = getActiveSets();

...

// from showAbbrevs() method

combo = new JComboBox(abbrevSets);
// set width to uniform size regardless of combobox contents
Dimension dim = combo.getPreferredSize();
dim.width = Math.max(dim.width, 120);
combo.setPreferredSize(dim);
combo.setSelectedItem(STARTING_SET); // defined as "global"

// end fragments</programlisting>
  </informalexample>

</sect2>


<sect2 id="macro-tips-single-char"><title>Using a Single Keypress as Input</title>

  <para>
    Some macros may choose to emulate the style of character-based text
    editors such as <application>emacs</application> or
    <application>vi</application>. They will require only a single keypress
    as input that would be handled by the macro but not displayed on the
    screen. If the keypress corresponds to a character value, jEdit can pass
    that value as a parameter to a BeanShell script.
  </para>

  <para>
    The jEdit class <classname>InputHandler</classname> is an abstract class
    that that manages associations between keyboard input and editing
    actions, along with the recording of macros. Keyboard input
    in jEdit is normally managed by the derived class
    <classname>DefaultInputHandler</classname>. One of the methods in
    the <classname>InputHandler</classname> class handles input from a
    single keypress:
  </para>

  <itemizedlist>
    <listitem>
      <funcsynopsis>
        <funcprototype>
          <funcdef>public void <function>readNextChar</function></funcdef>
          <paramdef>String <parameter>prompt</parameter></paramdef>
          <paramdef>String <parameter>code</parameter></paramdef>
        </funcprototype>
      </funcsynopsis>
    </listitem>
  </itemizedlist>

  <para>
    When this method is called, the contents of the <varname>prompt</varname>
    parameter is shown in the view's status
    bar. The method then waits for a key press, after which
    the contents of the <varname>code</varname> parameter will be run as
    a BeanShell script, with one important modification. Each time the
    string <varname>__char__</varname> appears in the parameter script, it
    will be substituted by the character pressed. The key press
    is <quote>consumed</quote> by <function>readNextChar()</function>.
    It will not be displayed on the screen or otherwise processed by jEdit.
  </para>

  <para>
    Using <function>readNextChar()</function> requires a macro within the
    macro, formatted as a single, potentially lengthy string literal. The
    following macro illustrates this technique. It selects a line of text
    from the current caret position to the first occurrence of the character
    next typed by the user. If the character does not appear on the line, no
    new selection occurs and the display remains unchanged.
  </para>

  <informalexample>
  <programlisting>// Next_Char.bsh

script = new StringBuffer(512);
script.append( "start = textArea.getCaretPosition();"         );
script.append( "line = textArea.getCaretLine();"              );
script.append( "end = textArea.getLineEndOffset(line) + 1;"   );
script.append( "text = buffer.getText(start, end - start);"   );
script.append( "match = text.indexOf(__char__, 1);"           );
script.append( "if(match != -1) {"                            );
script.append(   "if(__char__ != '\\n') ++match;"             );
script.append(   "textArea.select(start, start + match - 1);" );
script.append( "}"                                            );

view.getInputHandler().readNextChar("Enter a character",
    script.toString());

// end Next_Char.bsh</programlisting>
  </informalexample>

  <para>
    Once again, here are a few comments on the macro's design.
  </para>

  <itemizedlist>
    <listitem>
      <para>
        A <classname>StringBuffer</classname> object is used for efficiency; it
        obviates multiple creation of fixed-length <classname>String</classname>
        objects. The parameter to the constructor of <varname>script</varname>
        specifies the initial size of the buffer that will receive the contents
        of the child script.
      </para>
    </listitem>

    <listitem>
      <para>
        Besides the quoting of the script code, the formatting of the macro is
        entirely optional but (hopefully) makes it easier to read.
      </para>
    </listitem>

    <listitem>
      <para>
        It is important that the child script be self-contained.  It does
        not run in the same namespace as the <quote>parent</quote> macro
        <filename>Next_Char.bsh</filename> and therefore does not share
        variables, methods, or scripted objects defined in the parent
        macro.
      </para>
    </listitem>

    <listitem>
      <para>
        Finally, access to the <classname>InputHandler</classname> object used
        by jEdit is available by calling
        <function>getInputHandler()</function> on the current view.
      </para>
    </listitem>

  </itemizedlist>

</sect2>

</sect1>


<sect1 id="startup-scripts"><title>Startup Scripts</title>

  <para>
    On startup, jEdit runs any BeanShell scripts located in the
    <filename>startup</filename> subdirectory of the jEdit installation and
    user settings directories (see <xref linkend="settings-directory" />). As
    with macros, the scripts must have a <filename>.bsh</filename> file name
    extension. Startup scripts are run near the end of the startup sequence,
    after plugins, properties and such have been initialized, but before the
    first view is opened.
  </para>

  <para>
    Startup scripts can perform initialization tasks that cannot be handled
    by command line options or ordinary configuration options, such as
    customizing jEdit's user interface by
    changing entries in the Java platform's
    <classname>UIManager</classname> class.
  </para>

  <para>
    Startup scripts have an additional feature lacking in ordinary macros
    that can help you further customize jEdit. Variables and methods
    defined in a startup script are available in all instances of the BeanShell
    interpreter created in jEdit. This allows you to create a personal
    library of methods and objects that can be accessed at any time during
    the editing session in another macro, the BeanShell shell of the Console
    plugin, or menu items such as
    <guimenu>Utilities</guimenu>&gt;<guisubmenu>BeanShell</guisubmenu>&gt;<guimenuitem>Evaluate
    BeanShell Expression</guimenuitem>.
  </para>

  <para>
    The startup script routine will run script files in the installation
    directory first, followed by scripts in the user settings directory. In
    each case, scripts will be executed in alphabetical order, applied
    without regard to whether the file name contains upper or lower case
    characters.
  </para>

  <para>
    If a startup script throws an exception (because, for example,
    it attempts to call a method on a <constant>null</constant> object).
    jEdit will show an error dialog box and move on to the next
    startup script. If script bugs are causing jEdit to crash or
    hang on startup, you can use the
    <userinput>-nostartupscripts</userinput> command line option to
    disable them for that editing session.
  </para>

  <para>
    Another important difference between startup scripts and ordinary
    macros is that startup scripts cannot use the pre-defined variables
    <varname>view</varname>, <varname>textArea</varname>,
    <varname>editPane</varname> and <varname>buffer</varname>. This is
    because they are executed before the initial view is created.
  </para>

  <para>
    If you are writing a method in a
    startup script and wish to use one of the above variables, pass
    parameters of the
    appropriate type to the method, so that a macro calling them after
    startup can supply the appropriate values. For example, a startup script
    could include a method
  </para>

  <informalexample><programlisting>void doSomethingWithView(View v, String s)  {
    ...
}</programlisting></informalexample>

  <para>
    so that during the editing session another macro can call the method
    using
  </para>

  <informalexample><programlisting>doSomethingWithView(view, "something");</programlisting></informalexample>

  <sidebar><title>Reloading startup scripts without restarting</title>
   <para>
    It is actually possible to reload startup scripts or load other scripts
    without restarting
    jEdit, using a BeanShell statement like the following:
   </para>
   <programlisting>BeanShell.runScript(view,<replaceable>path</replaceable>,null,false);</programlisting>
   <para>
    For <replaceable>path</replaceable>, you can substitute any string,
    or a method call such as <function>buffer.getPath()</function>.
   </para>
  </sidebar>
</sect1>

<sect1 id="scripts-command-line"><title>Running Scripts from the Command
Line</title>

<para>
  The <userinput>-run</userinput> command line switch specifies a BeanShell
  script to run on startup:
</para>

<screen><prompt>$ </prompt><userinput>jedit -run=test.bsh</userinput></screen>

<para>
  Note that just like with startup scripts, the <varname>view</varname>,
  <varname>textArea</varname>, <varname>editPane</varname> and
  <varname>buffer</varname> variables are not defined.
</para>

<para>
  If another instance is already running, the script will be run in that
  instance, and you will be able to use the
  <function>jEdit.getLastView()</function> method to obtain a view.
  However, if a new instance of jEdit is being started, the script will
  be run at the same time as all other startup scripts; that is, before
  the first view is opened.
</para>

<para>
  If your script needs a view instance to operate on, you can use the
  following code pattern to obtain one, no matter how or when the script is
  being run:
</para>

<programlisting>void doSomethingUseful()
{
    void run()
    {
        view = jEdit.getLastView();

        // put actual script body here
    }

    if(jEdit.getLastView() == null)
        VFSManager.runInAWTThread(this);
    else
        run();
}

doSomethingUseful();</programlisting>

<para>
  If the script is being run in a loaded
  instance, it can be invoked to perform its work immediately.
  However, if
  the script is running at startup, before an initial view exists, its
  operation must be delayed to allow the view object first to be created
  and displayed.
  In order to queue the macro's operation, the scripted <quote>closure</quote>
  named <function>doSomethingUseful()</function> implements the
  <classname>Runnable</classname> interface of the Java platform.
  That interface contains only
  a single <function>run()</function> method that takes no parameters
  and has no return value. The macro's implementation of the
  <function>run()</function> method contains the <quote>working</quote>
  portion of the macro.  Then the scripted object, represented by a
  reference to <varname>this</varname>, is passed to the
  <function>runInAWTThread()</function> method. This schedules the
  macro's operations for execution after the startup routine is complete.
</para>

<para>
  As this example illustrates, the <function>runInAWTThread()</function>
  method can be used to ensure that a macro will perform operations
  after other operations have
  completed. If it is invoked during startup, it schedules the specified
  <classname>Runnable</classname> object to run after startup is complete.
  If invoked when jEdit is fully loaded, the <classname>Runnable</classname>
  object will execute after
  all pending input/output is complete, or immediately if there are no
  pending I/O operations. This will delay operations on a new buffer,
  for example, until after the buffer is loaded and displayed.
</para>

</sect1>

<sect1 id="macro-tips-BeanShell"><title>Advanced BeanShell Techniques</title>

<para>
  BeanShell has a few advanced features that we haven't mentioned yet.
  They will be discussed in this section.
</para>

<sect2 id="macro-tips-BeanShell-convenience">
<title>BeanShell's Convenience Syntax</title>

<para>
  We noted earlier that BeanShell syntax does not require that variables
  be declared or defined with their type, and that variables that are
  not typed when first used can have values of differing types assigned
  to them. In addition to this <quote>loose</quote> syntax, BeanShell
  allows a <quote>convenience</quote> syntax for dealing with the
  properties of JavaBeans.  They may be accessed or set as if they were
  data members. They may also be accessed using the name of the property
  enclosed in quotation marks and curly brackets.  For example, the following
  statement are all equivalent, assuming <varname>btn</varname> is
  a <classname>JButton</classname> instance:
</para>

<informalexample><programlisting>b.setText("Choose");
b.text = "Choose";
b{"text"} = "Choose";
</programlisting></informalexample>

<para>
  The last form can also be used to access a key-value pair of a
  <classname>Hashtable</classname> object.
</para>

<!-- actually, the following requires the bsh.classpath package, which
     is not included with jEdit at this point in time.

     a future release of jEdit will use bsh.classpath, and hence support
     'import *'

<para>
  Finally, when importing classes, BeanShell permits the following form
  to import all classes lying within the interpreter's classpath:
</para>

<informalexample><programlisting>import *;
</programlisting></informalexample>

-->

</sect2>


<sect2 id="macro-tips-BeanShell-keywords">
<title>Special BeanShell Keywords</title>

<para>
  BeanShell uses special keywords to refer to variables or methods defined in
  the current or an enclosing block's scope:
</para>

<itemizedlist>
  <listitem>
    <para>
      The keyword <function>this</function> refers to the current scope.
    </para>
  </listitem>
  <listitem>
    <para>
      The keyword <function>super</function> refers to the immediately
      enclosing scope.
    </para>
  </listitem>
  <listitem>
    <para>
      The keyword <function>global</function> refers to the top-level
      scope of the macro script.
    </para>
  </listitem>
</itemizedlist>

<para>
  The following script illustrates the use of these keywords:
</para>

<informalexample><programlisting>a = "top\n";
foo() {
    a = "middle\n";
    bar() {
        a = "bottom\n";
        textArea.setSelectedText(global.a);
        textArea.setSelectedText(super.a);
        // equivalent to textArea.setSelectedText(this.a):
        textArea.setSelectedText(a);
    }

    bar();
}
foo();</programlisting></informalexample>

<para>
  When the script is run, the following text is inserted in the current
  buffer:
</para>

<screen>top
middle
bottom</screen>

</sect2>

<sect2 id="macro-tips-BeanShell-interface">
<title>Implementing Interfaces</title>

<para>
  As discussed in the macro example in <xref
  linkend="dialog-macro"/>, scripted objects can implement Java
  interfaces such as <classname>ActionListener</classname>.  Which
  interfaces may be implemented varies depending upon the
  version of the Java runtime environment being used. If running under
  Java 1.1 or 1.2, BeanShell objects can only implement the AWT or
  Swing event listener interfaces contained in the
  <literal>java.awt.event</literal> and <literal>javax.swing.event</literal>
  packages, along with the <classname>java.lang.Runnable</classname> interface.
  If BeanShell is running under Java 1.3 or 1.4, which jEdit 4.0 requires, any
  interface can be implemented.
</para>

<para>
  Frequently it will not be necessary to implement all of the methods of
  a particular interface in order to specify the behavior of a scripted
  object. Under Java 1.3 and above, the virtual machine's reflection
  mechanism will throw an exception for any
  missing interface methods.  This will bring macro execution to a
  halt unless the exception is trapped and handled.  The solution
  is to implement the <function>invoke()</function> method,
  which is called when an undefined method is invoked on a scripted
  object. Typically, the implementation of this method will do nothing,
  as in the following example:
</para>

<informalexample><programlisting>invoke(method, args) {}</programlisting>
</informalexample>

</sect2>

</sect1>

<sect1 id="macro-tips-debugging"><title>Debugging Macros</title>

  <para>
    Here are a few techniques that can prove helpful in debugging
    macros.
  </para>

<sect2 id="macro-tips-debugging-exceptions">
<title>Identifying Exceptions</title>

  <para>
    An <glossterm>exception</glossterm> is a condition reflecting an error
    or other unusual result of program execution that requires interruption
    of normal program flow and some kind of special handling. Java has a
    rich (and extensible) collection of exception classes which represent
    such conditions.
  </para>

  <para>
    jEdit catches exceptions thrown by BeanShell scripts and displays
    them in a dialog box. In addition, the full traceback is written to
    the activity log (see <xref linkend="activity-log"/> for more
    information about the activity log).
  </para>

  <para>
    There are two broad categories of errors that will result in
    exceptions:
  </para>

  <itemizedlist>
   <listitem>
    <para>
     <emphasis>Interpreter errors</emphasis>, which may arise from typing
     mistakes like mismatched brackets or missing semicolons, or from
     BeanShell's failure to find a class corresponding to a particular
     variable.
    </para>
    <para>
     Interpreter errors are usually accompanied by the line number in
     the script, along with the cause of the error.
    </para>
   </listitem>
   <listitem>
    <para>
     <emphasis>Execution errors</emphasis>, which result from
     runtime exceptions thrown by the Java platform when macro code is
     executed.
    </para>
    <para>
     Some exceptions thrown by the Java platform can often seem
     cryptic. Nevertheless, examining the
     contents of the activity log may reveals clues as to the cause of
     the error.
    </para>
   </listitem>
  </itemizedlist>

</sect2>

<sect2 id="macro-tips-debugging-log">
<title>Using the Activity Log as a Tracing Tool</title>

  <para>
    Sometimes exception tracebacks will say
    what kind of error occurred but not where it arose in the script.
    In those cases, you can insert calls that log messages to the
    activity log in your macro. If the logged messages appear when the
    macro is run, it means that up to that point the macro is fine;
    but if an exception is logged first, it means the logging call is
    located after the cause of the error.
  </para>

  <para>
   To write a message to the activity log,
   use the following method of the <classname>Log</classname>
   class:
  </para>

  <itemizedlist>
    <listitem>
      <funcsynopsis>
        <funcprototype>
          <funcdef>public static void <function>log</function></funcdef>
          <paramdef>int <parameter>urgency</parameter></paramdef>
          <paramdef>Object <parameter>source</parameter></paramdef>
          <paramdef>Object <parameter>message</parameter></paramdef>
        </funcprototype>
      </funcsynopsis>
    </listitem>
  </itemizedlist>

  <para>
   The parameter <varname>urgency</varname> can take one of the
   following constant values:
  </para>

  <itemizedlist>
   <listitem><para><constant>Log.DEBUG</constant></para></listitem>
   <listitem><para><constant>Log.MESSAGE</constant></para></listitem>
   <listitem><para><constant>Log.NOTICE</constant></para></listitem>
   <listitem><para><constant>Log.WARNING</constant></para></listitem>
   <listitem><para><constant>Log.ERROR</constant></para></listitem>
  </itemizedlist>

  <para>
   Note that the <varname>urgency</varname> parameter merely changes
   the string prefixed to the log message; it does not change the logging
   behavior in any other way.
  </para>

  <para>
   The parameter <varname>source</varname> can be either an object or a
   class instance. When writing log messages from macros, set
   this parameter to <literal>BeanShell.class</literal> to make macro
   errors easier to spot in the activity log.
  </para>

  <para>
    The following code sends a typical debugging message to the
    activity log:
  </para>

    <informalexample><programlisting>Log.log(Log.DEBUG, BeanShell.class,
    "counter = " + counter);</programlisting></informalexample>

  <para>
    The corresponding activity log entry might read as follows:
  </para>

    <informalexample>
    <programlisting>[debug] BeanShell: counter = 15</programlisting>
    </informalexample>

  <sidebar><title>Using message dialog boxes as a tracing tool</title>
    <para>
      If you would prefer not having to deal with the activity log, you
      can use the <function>Macros.message()</function> method as a
      tracing tool. Just insert calls like the following in the macro
      code:
    </para>

    <programlisting>Macros.message(view,"tracing");</programlisting>

    <para>
      Execution of the macro is halted until the message dialog box is
      closed. When you have finished debugging the macro, you should
      delete or comment out the debugging calls to
      <function>Macros.message()</function> in your final source code.
    </para>
  </sidebar>

</sect2>

</sect1>

</chapter>