Analysis of the Macro
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## 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));
    dialog.setContentPane(content);

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:”);
    fieldPanel.add(prefixLabel);
    fieldPanel.add(prefixField);
    fieldPanel.add(suffixLabel);
    fieldPanel.add(suffixField);
    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,
        BoxLayout.X_AXIS));
    buttonPanel.setBorder(new EmptyBorder(12, 50, 0, 50));
    buttonPanel.add(Box.createGlue());
    ok = new JButton(“OK”);
    cancel = new JButton(“Cancel”);
    ok.setPreferredSize(cancel.getPreferredSize());
    dialog.getRootPane().setDefaultButton(ok);
    buttonPanel.add(ok);
    buttonPanel.add(Box.createHorizontalStrut(6));
    buttonPanel.add(cancel);
    buttonPanel.add(Box.createGlue());
    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
    ok.addActionListener(this);
    cancel.addActionListener(this);
    prefixField.addActionListener(this);
    suffixField.addActionListener(this);

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
    dialog.pack();
    dialog.setLocationRelativeTo(view);
    dialog.setDefaultCloseOperation(JDialog.DISPOSE_ON_CLOSE);
    dialog.setVisible(true);

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)
        {
            processText();
        }
        dialog.dispose();
    }

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)
            return;
        prefixField.addCurrentToHistory();
        suffixField.addCurrentToHistory();

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
        buffer.beginCompoundEdit();
        selectedLines = textArea.getSelectedLines();
        for(i = 0; i < selectedLines.length; ++i)
        {
            offsetBOL = textArea.getLineStartOffset(
                selectedLines[i]);
            textArea.setCaretPosition(offsetBOL);
            textArea.goToStartOfWhiteSpace(false);
            textArea.goToEndOfWhiteSpace(true);
            text = textArea.getSelectedText();
            if(text == null) text = "";
            textArea.setSelectedText(prefix + text + suffix);
        }
        buffer.endCompoundEdit();
    }

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
    prefixSuffixDialog();

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.

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