LimitLinesDocumentListener.java

package robotinterface.gui.panels.console;

import javax.swing.*;
import javax.swing.event.*;


import javax.swing.text.*;

/*
 *  A class to control the maximum number of lines to be stored in a Document
 *
 *  Excess lines can be removed from the start or end of the Document
 *  depending on your requirement.
 *
 *  a) if you append text to the Document, then you would want to remove lines
 *     from the start.
 *  b) if you insert text at the beginning of the Document, then you would
 *     want to remove lines from the end.
 * 
 *  @author Rob Camick {http://tips4java.wordpress.com/2008/10/15/limit-lines-in-document/} 2008
 */
public class LimitLinesDocumentListener implements DocumentListener {

    private int maximumLines;
    private boolean isRemoveFromStart;

    /*
     *  Specify the number of lines to be stored in the Document.
     *  Extra lines will be removed from the start of the Document.
     */
    public LimitLinesDocumentListener(int maximumLines) {
        this(maximumLines, true);
    }

    /*
     *  Specify the number of lines to be stored in the Document.
     *  Extra lines will be removed from the start or end of the Document,
     *  depending on the boolean value specified.
     */
    public LimitLinesDocumentListener(int maximumLines, boolean isRemoveFromStart) {
        setLimitLines(maximumLines);
        this.isRemoveFromStart = isRemoveFromStart;
    }

    /*
     *  Return the maximum number of lines to be stored in the Document
     */
    public int getLimitLines() {
        return maximumLines;
    }

    /*
     *  Set the maximum number of lines to be stored in the Document
     */
    public void setLimitLines(int maximumLines) {
        if (maximumLines < 1) {
            String message = "Maximum lines must be greater than 0";
            throw new IllegalArgumentException(message);
        }

        this.maximumLines = maximumLines;
    }

    //  Handle insertion of new text into the Document
    public void insertUpdate(final DocumentEvent e) {
        //  Changes to the Document can not be done within the listener
        //  so we need to add the processing to the end of the EDT

        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                removeLines(e);
            }
        });
    }

    public void removeUpdate(DocumentEvent e) {
    }

    public void changedUpdate(DocumentEvent e) {
    }

    /*
     *  Remove lines from the Document when necessary
     */
    private void removeLines(DocumentEvent e) {
        //  The root Element of the Document will tell us the total number
        //  of line in the Document.

        Document document = e.getDocument();
        Element root = document.getDefaultRootElement();

        while (root.getElementCount() > maximumLines) {
            if (isRemoveFromStart) {
                removeFromStart(document, root);
            } else {
                removeFromEnd(document, root);
            }
        }
    }

    /*
     *  Remove lines from the start of the Document
     */
    private void removeFromStart(Document document, Element root) {
        Element line = root.getElement(0);
        int end = line.getEndOffset();

        try {
            document.remove(0, end);
        } catch (BadLocationException ble) {
            System.out.println(ble);
        }
    }

    /*
     *  Remove lines from the end of the Document
     */
    private void removeFromEnd(Document document, Element root) {
        //  We use start minus 1 to make sure we remove the newline
        //  character of the previous line

        Element line = root.getElement(root.getElementCount() - 1);
        int start = line.getStartOffset();
        int end = line.getEndOffset();

        try {
            document.remove(start - 1, end - start);
        } catch (BadLocationException ble) {
            System.out.println(ble);
        }
    }
}