How to check whether the selectbox is singleListbox or multipleListBox.

Note- use the method getAttribute("multiple") , if it return 'true' then it is multipleListBox else if return null then it is singleListBox.

Sample html code- 

<select id="sdd">   //in this select box only one option can be selected

<option>idly</option>

<option>dosa</option>

<option>vada</option>

<option>tea</option>

</select>

<br>

Combo

<select id="mdd" multiple>  //in this select box only multiple option can be selected

<option>idly</option>

<option>dosa</option>

<option>vada</option>

<option>tea</option>

</select>

Script Code-

import org.openqa.selenium.By;
import org.openqa.selenium.WebDriver;
import org.openqa.selenium.firefox.FirefoxDriver;

public class MultipleListBox {
    public static void main(String[] args) {
        WebDriver driver = new FirefoxDriver();
        driver.get("C:\\selenium\\Selenium_web.html"); 
/*here the url is my personal page, you can try for any url which has such scenario or you can develop your own html page having the above html code.*/
        System.out.println(driver.findElement(By.xpath("//select[@id='mdd']")).getAttribute("multiple")); // this will print true, which means it is multipleListBox
        System.out.println(driver.findElement(By.xpath("//select[@id='sdd']")).getAttribute("multiple"));//
// this will print null, which means it is singleListBox       
    }
}