Switch between two browser windows using Selenium WebDriver

you can use following code to switch between windows based on the window title

 private void handleMultipleWindows(String windowTitle) {
            Set<String> windows = driver.getWindowHandles();

            for (String window : windows) {
                driver.switchTo().window(window);
                if (driver.getTitle().contains(windowTitle)) {
                    return;
                }
            }
        }

Similary you could use URL or some other criteria to switch windows.

I have added scope of switching back to mainWindowHandle as well.

You may try using below function provided that you are handeling windows with different titles.

private String mainWindowsHandle; // Stores current window handle
 public static boolean swithToWindow(WebDriver driver,String title){
  mainWindowsHandle = driver.getWindowHandle();
  Set<String> handles = driver.getWindowHandles(); // Gets all the available windows
  for(String handle : handles)
  {
    driver.switchTo().window(handle); // switching back to each window in loop
    if(driver.getTitle().equals(title)) // Compare title and if title matches stop loop and return true
     return true; // We switched to window, so stop the loop and come out of funcation with positive response
  }
  driver.switchTo().window(mainWindowsHandle); // Switch back to original window handle
  return false; // Return false as failed to find window with given title.
 }