Selenium:How to handle web based popups in selenium webdriver

package New;

import java.util.concurrent.TimeUnit;

import org.openqa.selenium.Alert;
import org.openqa.selenium.NoAlertPresentException;
import org.openqa.selenium.WebDriver;
import org.openqa.selenium.firefox.FirefoxDriver;
import org.testng.annotations.Test;
import org.testng.annotations.BeforeClass;
import org.testng.annotations.AfterClass;

public class PopUps {
    WebDriver driver;
     Alert alert;
  @Test
  public void poupup() {
     
     /* switching to alert
      * Alert alert=driver.switchTo().alert();
      * accepting the alert
      alert.accept();
      dismissing
      alert.dismiss();
      authenticating
      alert.authenticateUsing(null);*/
      try{
      alert=driver.switchTo().alert();
      }
      catch(NoAlertPresentException ex){
          ex.printStackTrace();
      }
      alert.accept();
      alert.dismiss();
      alert.authenticateUsing(null);
  }
  @BeforeClass
  public void beforeClass() {
      driver = new FirefoxDriver();
        driver.manage().window().maximize();
        driver.manage().timeouts().implicitlyWait(30, TimeUnit.SECONDS);
     
  }

  @AfterClass
  public void afterClass() {
   
      driver.quit();
  }

}