As I understand, you said "You do not know on which occurrence popup will come. so first you shall verify if current popup is the right one or not if yes then verify something on that"
Approach should be like this
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
if (driver.gettitle).equals("expected") if true then
{
// perform operations on popup
}
driver.switchTo().window(parentWindowHandler); // switch back to parent window
if