How to handle multiple windows in selenium webdriver?

You can use below code-

String mainwindow=driver.getWindowHandle(); //get parent(current) window name
    for(String popup :driver.getWindowHandles()) //iterating on child windows
    {
    driver.switchTo().window(popup);
    System.out.println("Popup values: "+popup);
    // Perform any operations on child window
    }
    driver.switchTo().window(mainwindow); //switch back to main window & continue further execution

Try this.

 public void SwitchToAnotherWindow(Webdriver driver,int window_number){

     List<String> windowlist = null;

    Set<String> windows = driver.getWindowHandles();

    windowlist = new ArrayList<String>(windows);

   String currentWindow = driver.getWindowHandle();

 if (!currentWindow.equalsIgnoreCase(windowlist.get(window_number - 1))) 
    {
        driver.switchTo().window(windowlist.get(window_number - 1));
     }

}

just pass window number which window you want execute for example if you want switch to 3 window just pass 3 to this method,it can directly shuffle to any window (for ex:1 to 9 window,or 9 to 4 window )

public static void main(String[] args) throws InterruptedException
  {

   WebDriver d = new FirefoxDriver();
   d.get("url");
   String prntwin = d.getWindowHandle();
   System.out.println("Parent window's handle -> " + prntwin);
   WebElement clkElement = d.findElement(By.id("button1")); 

  for(int i = 0; i < 3; i++)
    {
    clkElement.click();
    Thread.sleep(3000);
    }

    Set<String> allWindowHandles = d.getWindowHandles();

   for(String handle : allWindowHandles)
      {
      System.out.println("Window handle - > " + handle);
   }

}

public static void main(String[] args) throws InterruptedException {
    ChromeOptions chromeOption = new ChromeOptions();
    ChromeDriverManager.chromedriver().setup();
    ChromeDriver driver = new ChromeDriver(chromeOption);
    driver.get("https://the-internet.herokuapp.com/");
    driver.manage().window().maximize();
    driver.findElement(By.xpath("//a[contains(text(),'Multiple Windows')]")).click();
    driver.findElement(By.xpath("//a[@target='_blank']")).click();
    Set<String>id=driver.getWindowHandles();
    Iterator<String> ids=id.iterator();
    String Parent=ids.next();
    String Child=ids.next();
    driver.switchTo().window(Child);
    System.out.println(driver.getTitle());
    driver.switchTo().window(Parent);
    System.out.println(driver.getTitle());
}

}