Analysis of the Macro

Import Statements

// import statement
import javax.swing.border.*;

This macro makes use of classes in the javax.swing.border package, which is not automatically imported. As we mentioned previously (see the section called “The Mandatory First Example”), jEdit's implementation of BeanShell causes a number of classes to be automatically imported. Classes that are not automatically imported must be identified by a full qualified name or be the subject of an import statement.

Create the Dialog

// create dialog object
title = Add prefix and suffix to selected lines;
dialog = new JDialog(view, title, false);
content = new JPanel(new BorderLayout());
content.setBorder(new EmptyBorder(12, 12, 12, 12));

To get input for the macro, we need a dialog that provides for input of the prefix and suffix strings, an OK button to perform text insertion, and a Cancel button in case we change our mind. We have decided to make the dialog window non-modal. This will allow us to move around in the text buffer to find things we may need (including text to cut and paste) while the macro is running and the dialog is visible.

The Java object we need is a JDialog object from the Swing package. To construct one, we use the new keyword and call a constructor function. The constructor we use takes three parameters: the owner of the new dialog, the title to be displayed in the dialog frame, and a boolean parameter (true or false) that specifies whether the dialog will be modal or non-modal. We define the variable title using a string literal, then use it immediately in the JDialog constructor.

A JDialog object is a window containing a single object called a content pane. The content pane in turn contains the various visible components of the dialog. A JDialog creates an empty content pane for itself as during its construction. However, to control the dialog's appearance as much as possible, we will separately create our own content pane and attach it to the JDialog. We do this by creating a JPanel object. A JPanel is a lightweight container for other components that can be set to a given size and color. It also contains a layout scheme for arranging the size and position of its components. Here we are constructing a JPanel as a content pane with a BorderLayout. We put a EmptyBorder inside it to serve as a margin between the edge of the window and the components inside. We then attach the JPanel as the dialog's content pane, replacing the dialog's home-grown version.

A BorderLayout is one of the simpler layout schemes available for container objects like JPanel. A BorderLayout divides the container into five sections: North, South, East, West and Center. Components are added to the layout using the container's add method, specifying the component to be added and the section to which it is assigned. Building a component like our dialog window involves building a set of nested containers and specifying the location of each of their member components. We have taken the first step by creating a JPanel as the dialog's content pane.

Create the Text Fields

// add the text fields
fieldPanel = new JPanel(new GridLayout(4, 1, 0, 6));
prefixField = new HistoryTextField("macro.add-prefix");
prefixLabel = new JLabel(Prefix to add:);
suffixField = new HistoryTextField(macro.add-suffix);
suffixLabel = new JLabel(Suffix to add:);
content.add(fieldPanel, Center);

Next we shall create a smaller panel containing two fields for entering the prefix and suffix text and two labels identifying the input fields.

For the text fields, we will use jEdit's HistoryTextField class. It is derived from the Java Swing class JTextField. This class offers the enhancement of a stored list of prior values used as text input. When the component has input focus, the up and down keys scroll through the prior values for the variable.

To create the HistoryTextField objects we use a constructor method that takes a single parameter: the name of the tag under which history values will be stored. Here we choose names that are not likely to conflict with existing jEdit history items.

The labels that accompany the text fields are JLabel objects from the Java Swing package. The constructor we use for both labels takes the label text as a single String parameter.

We wish to arrange these four components from top to bottom, one after the other. To achieve that, we use a JPanel container object named fieldPanel that will be nested inside the dialog's content pane that we have already created. In the constructor for fieldPanel, we assign a new GridLayout with the indicated parameters: four rows, one column, zero spacing between columns (a meaningless element of a grid with only one column, but nevertheless a required parameter) and spacing of six pixels between rows. The spacing between rows spreads out the four grid elements. After the components, the panel and the layout are specified, the components are added to fieldPanel top to bottom, one grid cell at a time. Finally, the complete fieldPanel is added to the dialog's content pane to occupy the Center section of the content pane.

Create the Buttons

// add the buttons
buttonPanel = new JPanel();
buttonPanel.setLayout(new BoxLayout(buttonPanel,
buttonPanel.setBorder(new EmptyBorder(12, 50, 0, 50));
ok = new JButton(OK);
cancel = new JButton(Cancel);
content.add(buttonPanel, South);

To create the dialog's buttons, we follow repeat the nested container pattern we used in creating the text fields. First, we create a new, nested panel. This time we use a BoxLayout that places components either in a single row or column, depending on the parameter passed to its constructor. This layout object is more flexible than a GridLayout in that variable spacing between elements can be specified easily. We put an EmptyBorder in the new panel to set margins for placing the buttons. Then we create the buttons, using a JButton constructor that specifies the button text. After setting the size of the OK button to equal the size of the Cancel button, we designate the OK button as the default button in the dialog. This causes the OK button to be outlined when the dialog if first displayed. Finally, we place the buttons side by side with a 6 pixel gap between them (for aesthetic reasons), and place the completed buttonPanel in the South section of the dialog's content pane.

Register the Action Listeners

// register this method as an ActionListener for
// the buttons and text fields

In order to specify the action to be taken upon clicking a button or pressing the Enter key, we must register an ActionListener for each of the four active components of the dialog - the two HistoryTextField components and the two buttons. In Java, an ActionListener is an interface - an abstract specification for a derived class to implement. The ActionListener interface contains a single method to be implemented:

public void actionPerformed(ActionEvent e);

BeanShell does not permit a script to create derived classes. However, BeanShell offers a useful substitute: a method can be used as a scripted object that can include nested methods implementing a number of Java interfaces. The method prefixSuffixDialog() that we are writing can thus be treated as an ActionListener object. To accomplish this, we call addActionListener() on each of the four components specifying this as the ActionListener. We still need to implement the interface. We will do that shortly.

Make the Dialog Visible

// locate the dialog in the center of the
// editing pane and make it visible

Here we do three things. First, we activate all the layout routines we have established by calling the pack() method for the dialog as the top-level window. Next we center the dialog's position in the active jEdit view by calling setLocationRelativeTo() on the dialog. We also call the setDefaultCloseOperation() function to specify that the dialog box should be immediately disposed if the user clicks the close box. Finally, we activate the dialog by calling setVisible()with the state parameter set to true.

At this point we have a decent looking dialog window that doesn't do anything. Without more code, it will not respond to user input and will not accomplish any text manipulation. The remainder of the script deals with these two requirements.

The Action Listener

// this method will be called when a button is clicked
// or when ENTER is pressed
void actionPerformed(e)
    if(e.getSource() != cancel)

The method actionPerformed() nested inside prefixSuffixDialog() implements the implicit ActionListener interface. It looks at the source of the ActionEvent, determined by a call to getSource(). What we do with this return value is straightforward: if the source is not the Cancel button, we call the processText() method to insert the prefix and suffix text. Then the dialog is closed by calling its dispose() method.

The ability to implement interfaces like ActionListener inside a BeanShell script is one of the more powerful features of the BeanShell package. this technique is discussed in the next chapter; see the section called “Implementing Classes and Interfaces”.

Get the User's Input

// this is where the work gets done to insert
// the prefix and suffix
void processText()
    prefix = prefixField.getText();
    suffix = suffixField.getText();
    if(prefix.length() == 0 && suffix.length() == 0)

The method processText() does the work of our macro. First we obtain the input from the two text fields with a call to their getText() methods. If they are both empty, there is nothing to do, so the method returns. If there is input, any text in the field is added to that field's stored history list by calling addCurrentToHistory(). We do not need to test the prefixField or suffixField controls for null or empty values because addCurrentToHistory() does that internally.

Call jEdit Methods to Manipulate Text

    // text manipulation begins here using calls
    // to jEdit methods
    selectedLines = textArea.getSelectedLines();
    for(i = 0; i < selectedLines.length; ++i)
        offsetBOL = textArea.getLineStartOffset(
        text = textArea.getSelectedText();
        if(text == null) text = "";
        textArea.setSelectedText(prefix + text + suffix);

The text manipulation routine loops through each selected line in the text buffer. We get the loop parameters by calling textArea.getSelectedLines(), which returns an array consisting of the line numbers of every selected line. The array includes the number of the current line, whether or not it is selected, and the line numbers are sorted in increasing order. We iterate through each member of the selectedLines array, which represents the number of a selected line, and apply the following routine:

  • Get the buffer position of the start of the line (expressed as a zero-based index from the start of the buffer) by calling textArea.getLineStartOffset(selectedLines[i]);

  • Move the caret to that position by calling textArea.setCaretPosition();

  • Find the first and last non-whitespace characters on the line by calling textArea.goToStartOfWhiteSpace() and textArea.goToEndOfWhiteSpace();

    The goTo... methods in JEditTextArea take a single parameter which tells jEdit whether the text between the current caret position and the desired position should be selected. Here, we call textArea.goToStartOfWhiteSpace(false) so that no text is selected, then call textArea.goToEndOfWhiteSpace(true) so that all of the text between the beginning and ending whitespace is selected.

  • Retrieve the selected text by storing the return value of textArea.getSelectedText() in a new variable text.

    If the line is empty, getSelectedText() will return null. In that case, we assign an empty string to text to avoid calling methods on a null object.

  • Change the selected text to prefix + text + suffix by calling textArea.setSelectedText(). If there is no selected text (for example, if the line is empty), the prefix and suffix will be inserted without any intervening characters.

The Main Routine

// this single line of code is the script's main routine

The call to prefixSuffixDialog()is the only line in the macro that is not inside an enclosing block. BeanShell treats such code as a top-level main method and begins execution with it.

Our analysis of Add_Prefix_and_Suffix.bsh is now complete. In the next section, we look at other ways in which a macro can obtain user input, as well as other macro writing techniques.