Basic Text Components - The Definitive Guide to Java Swing - page 534

Listing 15-7. Custom Document Filter
import javax.swing.text.*;
import java.awt.Toolkit;
public class IntegerRangeDocumentFilter extends DocumentFilter {
int minimum, maximum;
int currentValue = 0;
public IntegerRangeDocumentFilter(int minimum, int maximum) {
this.minimum = minimum;
this.maximum = maximum;
}
public void insertString(DocumentFilter.FilterBypass fb, int offset,
String string, AttributeSet attr) throws BadLocationException {
if (string == null) {
return;
} else {
String newValue;
Document doc = fb.getDocument();
int length = doc.getLength();
if (length == 0) {
newValue = string;
} else {
String currentContent = doc.getText(0, length);
StringBuffer currentBuffer = new StringBuffer(currentContent);
currentBuffer.insert(offset, string);
newValue = currentBuffer.toString();
}
currentValue = checkInput(newValue, offset);
fb.insertString(offset, string, attr);
}
}
public void remove(DocumentFilter.FilterBypass fb, int offset, int length)
throws BadLocationException {
Document doc = fb.getDocument();
int currentLength = doc.getLength();
String currentContent = doc.getText(0, currentLength);
String before = currentContent.substring(0, offset);
String after = currentContent.substring(length+offset, currentLength);
String newValue = before + after;
currentValue = checkInput(newValue, offset);
fb.remove(offset, length);
}