Custom caret for JTextArea in Java

/*  w  ww .  j a v a 2s.  com*/
/*
 Java Swing, 2nd Edition
 By Marc Loy, Robert Eckstein, Dave Wood, James Elliott, Brian Cole
 ISBN: 0-596-00408-7
 Publisher: O'Reilly 
 */
// FancyCaret.java
//Another (fancier) custom caret class.
//
import java.awt.BorderLayout;
import java.awt.Graphics;
import java.awt.Rectangle;

import javax.swing.JFrame;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.text.BadLocationException;
import javax.swing.text.DefaultCaret;
import javax.swing.text.JTextComponent;

public class Main {
  public static void main(String args[]) {
    JFrame frame = new JFrame("FancyCaret demo");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    JTextArea area = new JTextArea(8, 32);
    area.setCaret(new FancyCaret());
    area.setText("VI\tVirgin Islands \nVA      Virginia\nVT\tVermont");
    frame.getContentPane().add(new JScrollPane(area), BorderLayout.CENTER);
    frame.pack();
    frame.setVisible(true);
  }

}

class FancyCaret extends DefaultCaret {

  protected synchronized void damage(Rectangle r) {
    if (r == null)
      return;

    // give values to x,y,width,height (inherited from java.awt.Rectangle)
    x = r.x;
    y = r.y;
    height = r.height;
    // A value for width was probably set by paint(), which we leave alone.
    // But the first call to damage() precedes the first call to paint(), so
    // in this case we must be prepared to set a valid width, or else
    // paint()
    // will receive a bogus clip area and caret will not get drawn properly.
    if (width <= 0)
      width = getComponent().getWidth();

    repaint(); // calls getComponent().repaint(x, y, width, height)
  }

  public void paint(Graphics g) {
    JTextComponent comp = getComponent();
    if (comp == null)
      return;

    int dot = getDot();
    Rectangle r = null;
    char dotChar;
    try {
      r = comp.modelToView(dot);
      if (r == null)
        return;
      dotChar = comp.getText(dot, 1).charAt(0);
    } catch (BadLocationException e) {
      return;
    }

    if ((x != r.x) || (y != r.y)) {
      // paint() has been called directly, without a previous call to
      // damage(), so do some cleanup. (This happens, for example, when
      // the
      // text component is resized.)
      repaint(); // erase previous location of caret
      x = r.x; // Update dimensions (width gets set later in this method)
      y = r.y;
      height = r.height;
    }

    g.setColor(comp.getCaretColor());
    g.setXORMode(comp.getBackground()); // do this to draw in XOR mode

    if (dotChar == '\n') {
      int diam = r.height;
      if (isVisible())
        g.fillArc(r.x - diam / 2, r.y, diam, diam, 270, 180); // half
      // circle
      width = diam / 2 + 2;
      return;
    }

    if (dotChar == '\t')
      try {
        Rectangle nextr = comp.modelToView(dot + 1);
        if ((r.y == nextr.y) && (r.x < nextr.x)) {
          width = nextr.x - r.x;
          if (isVisible())
            g.fillRoundRect(r.x, r.y, width, r.height, 12, 12);
          return;
        } else
          dotChar = ' ';
      } catch (BadLocationException e) {
        dotChar = ' ';
      }

    width = g.getFontMetrics().charWidth(dotChar);
    if (isVisible())
      g.fillRect(r.x, r.y, width, r.height);
  }

}