Handling Java script..in Selenium

import static org.junit.Assert.*;

import java.util.Arrays;
import java.util.List;

import org.junit.Test;
import org.openqa.selenium.JavascriptExecutor;
import org.openqa.selenium.WebDriver;
import org.openqa.selenium.WebElement;
import org.openqa.selenium.firefox.FirefoxDriver;


public class check_box {

@SuppressWarnings("unchecked")
@Test
public void testDefaultSelectedCheckbox() {

WebDriver driver=new FirefoxDriver();
driver.get("http://dl.dropbox.com/u/55228056/Locators.html");
//Expected list of selected Checkbox
List<String> checked = Arrays.asList(new
String[]{"user1_admin", "user3_browser"});
//Create an instance of JavaScript Executor from driver
JavascriptExecutor js = (JavascriptExecutor) driver;
//Locate all the Checkbox which are checked by calling jQuery
//find() method.
//find() method returns elements in array
List<WebElement> elements = (List<WebElement>)
js.executeScript("return jQuery.find(':checked')");
//Verify two Checkbox are selected

assertEquals(elements.size(),2);
//Verify correct Checkbox are selected
for (WebElement element : elements)
assertTrue(checked.contains(element.getAttribute("id")));
driver.close();



}

}