driver getwindowhandles vs driver.getwindowhandles() in selenium webdriver code example

Example 1: difference between driver.getwindowhandle() and driver.getwindowhandles()

driver.getWindowHandle() – It returns a handle (String) of the current 
page (a unique identifier)
driver.getWindowHandles() – It returns a set of handles (Set) 
of the all the pages available

Example 2: what is difference between getwindowhandle and getwindowhandles

driver.getWindowHandle() – It returns a handle (String) of the current 
page (a unique identifier)
driver.getWindowHandles() – It returns a set of handles (Set) 
of the all the pages available