错误：尝试运行Java程序时看到无法初始化主类

Question

以下程序给出了错误：

import org.openqa.selenium.WebDriver;
import org.openqa.selenium.chrome.ChromeDriver;

public class demo {    
    public static void main(String[] args) {
        // TODO Auto-generated method stub

        //Create a new object driver for class Web driver
    System.setProperty("webdriver.chrome.driver", "C:\\Roshan_Work\\chromedriver.exe"); 
    WebDriver driver = new ChromeDriver();
    driver.get("http://google.com");

    }    
}

返回的错误是：

Error: Unable to initialize main class demo
Caused by: java.lang.NoClassDefFoundError: org/openqa/selenium/WebDriver