Exception in thread "main" java.lang.NoClassDefFoundError: org/openqa/selenium/firefox/FirefoxDriver [duplicate]

package com.Pack;

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

public class TextBoxDemo {
    //Launch the browser
    //enter valid url
    //enter data in to text box

    public static void main(String[] args)
    {
        // System.setProperty("webdriver.c  rome.driver",
        //  "/Users/adeshpansuriya/Downloads/chromedriver");
        WebDriver driver = new FirefoxDriver();
    }   
}