How to resize current browser window in Selenium WebDriver with Java?

You can get a reference to the current window with driver.manage().window(). And the window has a setSize() method, so you could try

Dimension dimension = new Dimension(800, 600);
driver.manage().window().setSize(dimension)

If nothing works (to make tab in full screen only) for you, go for it:

driver.maximize_window()

where

driver = webdriver.Chrome(executable_path="D:\softwares\chromedriver.exe")

or could be any other webdriver locations.

For Responsive Design it's better if you don't use fixed data, in this case screen resolution - users need most often (cause it's much less prone to errors) :

_driver.manage().window().maximize();

or

_driver.manage().window().fullScreen();