How to know whether text in JEditPane is modified?

I'm working to build a editor; so I'd like to know whether the test in JEditPane is modified or not? The following code seems not work :(

        JEditorPane editorConfig = new JEditorPane();

        editorConfig.getDocument().addDocumentListener(new DocumentListener(){

            @Override
            public void insertUpdate(DocumentEvent e) {
                System.out.println("a");
                Dialogc.this.refreshTitle();

            }

            @Override
            public void removeUpdate(DocumentEvent e) {
                System.out.println("b");
                Dialogc.this.refreshTitle();
            }

            @Override
            public void changedUpdate(DocumentEvent e) {
                System.out.println("c");
                Dialogc.this.refreshTitle();

            }

        });

Thanks Klaus Ma