A document filter which can support a regular expression

RegularExpressionDocumentFilter.java

import java.util.regex.Matcher;
import java.util.regex.Pattern;
import javax.swing.text.AttributeSet;
import javax.swing.text.BadLocationException;
import javax.swing.text.DocumentFilter;

public class RegularExpressionDocumentFilter extends ChainedDocumentFilter {
    
    // Useful for every kind of input validation !
    // this is the insert pattern
    // The pattern must contain all subpatterns so we can enter characters into a text component !
    private Pattern pattern;

    public RegularExpressionDocumentFilter(DocumentFilter filter, Pattern pattern) {
        super(filter);
        this.pattern = pattern;
    }

    public RegularExpressionDocumentFilter(Pattern p) {
        this(null, p);
    }

    public void insertString(FilterBypass fb, int offset, String string, AttributeSet attr) throws BadLocationException {
        String newStr = fb.getDocument().getText(0, fb.getDocument().getLength()) + string;
        Matcher m = pattern.matcher(newStr);
        if (m.matches()) {
            super.insertString(fb, offset, string, attr);
        } else {
        }
    }

    public void replace(FilterBypass fb, int offset, int length, String string, AttributeSet attr) throws BadLocationException {
        if (length > 0) {
            fb.remove(offset, length);
        }
        insertString(fb, offset, string, attr);
    }
    
}