WebDriver as Singleton

import org.openqa.selenium.WebDriver;
import org.openqa.selenium.firefox.FirefoxDriver;
 
public class Driver {
 
    private static WebDriver driver = null;
 
    // Private constructor prevents instantiation from other classes
    private Driver() {
        System.out.println("Driver()");
    }
    /** author Bill Pugh
     * LazyHolder is loaded on the first execution of Driver.getInstance()
     * or the first access to LazyHolder.INSTANCE, not before.
     * minus: It is impossible to use for not static fields of a class
     */
    private static class LazyHolder  {
        private static final Driver INSTANCE = new Driver();
    }
 
    public static Driver instance() {
        System.out.println("instance()");
        return LazyHolder.INSTANCE;
    }
 
    public WebDriver getDriver() {
        System.out.println("getDriver()");
        return driver;
    }
 
    public void init() {
        System.out.print("init(): ");
        driver = new FirefoxDriver();
        System.out.println("FirefoxDriver()");
    }
 
    public void close() {
        System.out.print("close(): ");
        if (driver!=null) {
            driver.quit();
            System.out.println("driver.quit()");
        }
        else
            System.out.println("null error");
    }
}
 
public class Main {
    public static void main(String[] args) throws InterruptedException {
        System.out.println("get instance ...");
        Driver drv = Driver.instance();
        drv.init();
        drv.getDriver().get("http://yandex.ru");
        Thread.sleep(5000);
        drv.close();
    }
}

public class WebBrowser {
    private static WebDriver instance;
 
    private WebBrowser() { }
 
    public static WebDriver getInstance() {
        if (instance==null) {
            instance = new FirefoxDriver();
            System.out.println("get instance FirefoxDriver()");
        }
        return instance;
    }
 
    public void close() {
        System.out.println("close ");
        if (instance!=null) {
            instance.quit();
            instance = null;
        }
        else
            System.out.println("null error at close()");
    }
}

public class Driver {
    private static WebDriver driver = null;
 
    private Driver() {
        driver = new FirefoxDriver();
    }
 
    private static class LazyHolder  {
        private static final Driver INSTANCE = new Driver();
    }
 
    public static WebDriver instance() {
        return LazyHolder.INSTANCE.driver;
    }
 
    public static void close() {
        if (driver!=null) {
            driver.quit();
        }
    }
}
 
    public static void main(String[] args) throws InterruptedException {
        WebDriver drv1 = Driver.instance();
        WebDriver drv2 = Driver.instance();
        drv1.get("http://yandex.ru");
        drv2.get("http://mail.ru");
        Thread.sleep(5000);
        Driver.close();
    }