Unable to launch firefox browser

Hi,

    Below is sample code i used to launch firefox browser.

Please help me out to resolve this issue.

package webpackage;
import org.openqa.selenium.firefox.FirefoxDriver;

public class First {

public static void main(String[] args) {

System.out.println("Hello browser launch test");

// declaration and instantiation of objects/variables
System.setProperty("webdriver.firefox.marionette","D:\\test\\testing\\Auto\\Browserdrivers\\firefox\\geckodriver-v0.23.0-win64\\geckodriver.exe");
WebDriver driver = new FirefoxDriver();
//comment the above 2 lines and uncomment below 2 lines to use Chrome
//System.setProperty("webdriver.chrome.driver","G:\\chromedriver.exe");
//WebDriver driver = new ChromeDriver();

String baseUrl = "www.google.com";

// launch Fire fox and direct it to the Base URL
driver.get(baseUrl);
//close Fire fox
driver.close();
}
}

exception:

Exception in thread "main" java.lang.Error: Unresolved compilation problems:
WebDriver cannot be resolved to a type
FirefoxDriver cannot be resolved to a type

at webpackage.First.main(First.java:12)

Below is test environment:

firefox 62

selenium 3.11

Windows7