How to know if web-page is open or closed?

After calling driver.close() the value of driver is set to

FirefoxDriver: firefox on WINDOWS(4b4ffb1e-7c02-4d9c-b37b-310c771492ac)

But if you call driver.quit() then it sets the value of driver to

FirefoxDriver: firefox on WINDOWS (null)

So if you're checking the browser window after calling driver.quit() then you will be able to know by below implementation.

WebDriver driver = new FirefoxDriver();
driver.get("http://www.google.com");
driver.quit();              
if(driver.toString().contains("null"))
{

System.out.print("All Browser windows are closed ");
}
else
{
//open a new Browser
}