In Java, best way to check if Selenium WebDriver has quit

If quit() has been called, driver.toString() returns null:

>>> FirefoxDriver: firefox on XP (null))

Otherwise, it returns a hashcode of the object:

>>> FirefoxDriver: firefox on XP (9f897f52-3a13-40d4-800b-7dec26a0c84d)

so you could check for null when assigning a boolean:

boolean hasQuit = driver.toString().contains("(null)");