A document filter which can change the case of the input to either upper or lower case

CaseModificationDocumentFilter.java

import javax.swing.text.AttributeSet;
import javax.swing.text.BadLocationException;
import javax.swing.text.DocumentFilter;

// Original source https://tips4java.wordpress.com/2009/10/18/chaining-document-filters/
public class CaseModificationDocumentFilter extends ChainedDocumentFilter {

    public enum Case {
        UPPER, LOWER
    }
    private Case desiredCase;

    /**
     * Standard constructor for stand alone usage
     */
    public CaseModificationDocumentFilter(Case desiredCase) {
        this(null, desiredCase);
    }

    /**
     * Constructor used when further filtering is required after this filter
     * has been applied.
     */
    public CaseModificationDocumentFilter(DocumentFilter filter, Case desiredCase) {
        super(filter);
        this.desiredCase = desiredCase;
    }

    public void insertString(FilterBypass fb, int offs, String str, AttributeSet a) throws BadLocationException {
        replace(fb, offs, 0, str, a);
    }

    public void replace(FilterBypass fb, final int offs, final int length, String text, final AttributeSet a) throws BadLocationException {
        if (text != null) {
            switch (getDesiredCase()) {
                case UPPER:
                    text = text.toUpperCase();
                    break;
                case LOWER:
                    text = text.toLowerCase();
                    break;
            }
            super.replace(fb, offs, length, text, a);
        }
    }

    public Case getDesiredCase() {
        return desiredCase;
    }
    
}