Handling the  multiple windows or window based alert pop ups is beyond web driver capabilities. To handle this we need some third party utilities(alerts API).

• Web driver interface provides two methods to handle this:
• To access the window pop up,  getWindowHandles() and getWindowHandle()  methods are used.
• If there are multiple windows are opened by web driver and we need to access all windows we use "Driver.getWindowHandles()", using this method we can switch from one window to another window.

When we have to handle only main window we used  "Driver.getWindowHandles()" method and it will handle only current window.

Example:-

Steps:

1. Launch the application(http://toolsqa.com/automation-practice-switch-windows/)
2. Click on 'New browsers window' button, it will open in new window
3. Maximize the new child window
4. Verify the text(Selenium Online Training) on new window
5. Click on 'Enroll Your self' button
5. close the child window and return to main window.

Code:

import java.util.Iterator;
import java.util.Set;
import java.util.concurrent.TimeUnit;

import org.openqa.selenium.By;
import org.openqa.selenium.WebDriver;
import org.openqa.selenium.firefox.FirefoxDriver;


public class Multiplewindowhandling {

  public static void main(String[] args) {
  
  

  WebDriver driver = new FirefoxDriver();

  //launch the application

  driver.navigate().to("http://toolsqa.com/automation-practice-switch-windows/");
  driver.manage().timeouts().implicitlyWait(20L, TimeUnit.SECONDS);
 

  
  driver.findElement(By.xpath(".//*[@id='button1']")).click();
  
  String MainWindow=driver.getWindowHandle();
  

   //To handle all new open window

  Set<String> windowids = driver.getWindowHandles();
  Iterator<String> iterate = windowids.iterator();

  while(iterate.hasNext())   
        {  
            String ChildWindow=iterate.next();  
              
            if(!MainWindow.equalsIgnoreCase(ChildWindow))   
            {      
                 
                    // Switching to Child window
                    driver.switchTo().window(ChildWindow);
                    driver.manage().window().maximize();
                                                                                         
                                                                                             
                driver.findElement(By.xpath(".//*[@id='rev_slider_8_1']/ul/li[1]/div[2]")).isDisplayed();
  
  driver.findElement(By.xpath(".//*[@id='rev_slider_8_1']/ul/li[1]/div[6]/a")).click();   
                                           
                       
                                
   // Closing the Child Window.
                        driver.close();  
            }  
        }
  
        // Switching to Parent window i.e Main Window.
            driver.switchTo().window(MainWindow);
}

}