Can't figure out error with ActionListener

Question

The following is my program. the goal is to convert from a roman numeral to an Arabic number after a user types in the numeral and presses the enter key.

This is a

Answer 1

For a better answer, see @MadProgrammer 's answer.

My solution:

There is no ActionListener for JTextArea.

So just use KeyListener instead

HandlerForTextArea handler = new HandlerForTextArea();
enterRomanNumber.addKeyListener(handler);

Implements KeyListener

private class HandlerForTextArea implements KeyListener
{

    @Override
    public void keyPressed(KeyEvent arg0) {
        // TODO Auto-generated method stub
    }

    @Override
    public void keyReleased(KeyEvent arg0) {
        // TODO Auto-generated method stub
        if (arg0.getKeyCode() == VK_ENTER){
            // TODO Your bussiness
        }
    }

    @Override
    public void keyTyped(KeyEvent arg0) {
        // TODO Auto-generated method stub
    }
}