button doesn't turn disabled when textArea is empty

I added a documentListener to a jTextArea, which should set a button disabled whenever the textArea is empty. This works just at the starting point when the textArea is empty, but when I type something and then delete all the text until textArea.getText() == "", the button still doesn't turn disabled again. This is what I wrote:

textArea.getDocument().addDocumentListener(new DocumentListener() {
            @Override
            public void insertUpdate(DocumentEvent e) {

                if (textArea.getText() == null) {
                    disableButton();
                } else {
                    enableButton();
                } 



            }

            @Override
            public void removeUpdate(DocumentEvent e) {

                if (textArea.getText() == null) {
                    disableButton();
                } else {
                    enableButton();
                }

            }

            @Override
            public void changedUpdate(DocumentEvent e) {

                if (textArea.getText() == null) {
                    disableButton();
                } else {
                    enableButton();
                }
            }

            public void enableButton() {
                clearModelMenuItem.setEnabled(true);
                discardModel.setEnabled(true);
                increaseFontSize.setEnabled(true);
                decreaseFontSize.setEnabled(true);
                incMenuItem.setEnabled(true);
                decMenuItem.setEnabled(true); 
            }

What is the problem here? Thanks for helping!

It's because you're not actually checking whether the text is empty; you're checking whether it's null. There's a difference between a String that's empty and a String that's null.

You need to be checking

if ("".equals(textArea.getText())) ...

if you want to check whether it's empty.

(You might also want to check for null.)