我找到了上述程序的解决方案，其目标是登录http://rediff.com
public class Handle_popupNAlert
{
public static void main(String[] args ) throws InterruptedException
{
WebDriver driver= new FirefoxDriver();
driver.get("http://www.rediff.com/");
WebElement sign = driver.findElement(By.xpath("//html/body/div[3]/div[3]/span[4]/span/a"));
sign.click();
Set windowId = driver.getWindowHandles(); // get window id of current window
Iterator itererator = windowId.iterator();
String mainWinID = itererator.next();
String newAdwinID = itererator.next();
driver.switchTo().window(newAdwinID);
System.out.println(driver.getTitle());
Thread.sleep(3000);
driver.close();
driver.switchTo().window(mainWinID);
System.out.println(driver.getTitle());
Thread.sleep(2000);
WebElement email_id= driver.findElement(By.xpath("//*[@id='c_uname']"));
email_id.sendKeys("hi");
Thread.sleep(5000);
driver.close();
driver.quit();
}
}