Basic Text Components - The Definitive Guide to Java Swing - page 544

Listing 15-11. Restricting Caret Movement
import javax.swing.*;
import javax.swing.text.*;
import javax.swing.event.*;
import java.awt.*;
public class NavigationSample {
private static final String START_STRING = "Start\n";
private static final int START_STRING_LENGTH = START_STRING.length();
public static void main(String args[]) {
Runnable runner = new Runnable() {
public void run() {
JFrame frame = new JFrame("Navigation Example");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JTextArea textArea = new JTextArea(START_STRING);
textArea.setCaretPosition(START_STRING_LENGTH);
JScrollPane scrollPane = new JScrollPane(textArea);
frame.add(scrollPane, BorderLayout.CENTER);
NavigationFilter filter = new NavigationFilter() {
public void setDot(NavigationFilter.FilterBypass fb, int dot,
Position.Bias bias) {
if (dot < START_STRING_LENGTH) {
fb.setDot(START_STRING_LENGTH, bias);
} else {
fb.setDot(dot, bias);
}
}
public void moveDot(NavigationFilter.FilterBypass fb, int dot,
Position.Bias bias) {
if (dot < START_STRING_LENGTH) {
fb.setDot(START_STRING_LENGTH, bias);
} else {
fb.setDot(dot, bias);
}
}
};
textArea.setNavigationFilter(filter);
frame.setSize(250, 150);
frame.setVisible(true);
}
};
EventQueue.invokeLater(runner);
}
}