ways to drag n drop elements using selenium

There are several web applications that provides services for drag an element and drop on certain element on browser.

Some examples:
Can customize menu bar items by drag child elements on parent element.
Drag and drop files/folders in some hierarchy manner.

There are several ways we can automate drag and drop, any one of the following methods can be used:

-click and hold on the child element and release the element on parent element.

action.clickAndHold(child).moveToElement(parent).release(child).build().perform();

-drag an element and drop  on parent element.

action.dragAndDrop(child, parent).build().perform();

-click and hold the child element and drop on a particular co-ordinate on web application

Point p = parent.getLocation();
    int px=p.getX();
    int py=p.getY();
action.dragAndDropBy(child, px, py).build().perform();

Let's see the full code implementation:

public class DragnDrop {
 
public static void main(String[] args) throws InterruptedException, AWTException {
 WebDriver driver = new FirefoxDriver();
 driver.manage().window().maximize();
 driver.get("http://dhtmlx.com/docs/products/dhtmlxTree/");
 System.out.println(driver.getTitle());
 
 Thread.sleep(5000);
 WebElement parent = driver.findElement(By.xpath("//div[@id='treebox2']//span[text()='Ian Rankin']"));
 
 WebElement child = driver.findElement(By.xpath("//div[@id='treebox2']//span[text()='James Johns']"));
 
 Actions action = new Actions(driver);
 //action.clickAndHold(child).moveToElement(parent).release(child).build().perform();
 action.dragAndDrop(child, parent).build().perform();
        System.out.println("Done");
   }
}

one more site to practice drag and drop:
http://html5demos.com/drag
https://www.dartlang.org/samples/dnd/