How to handle Pop-up in Selenium WebDriver using Java

To switch to a popup window, you need to use getWindowHandles() and iterate through them.

In your code you are using getWindowHandle() which will give you the parent window itself.

String parentWindowHandler = driver.getWindowHandle(); // Store your parent window
String subWindowHandler = null;

Set<String> handles = driver.getWindowHandles(); // get all window handles
Iterator<String> iterator = handles.iterator();
while (iterator.hasNext()){
    subWindowHandler = iterator.next();
}
driver.switchTo().window(subWindowHandler); // switch to popup window

// Now you are in the popup window, perform necessary actions here

driver.switchTo().window(parentWindowHandler);  // switch back to parent window