How to open and close tab in selenium webdriver using java?.

 import java.util.concurrent.TimeUnit;  
 import org.openqa.selenium.By;  
 import org.openqa.selenium.Keys;  
 import org.openqa.selenium.WebDriver;  
 import org.openqa.selenium.firefox.FirefoxDriver;  
 public class OpenandClosenewtab {  
   public static void main(String[] a) throws InterruptedException {  
     // Initialize driver   
     WebDriver dr = new FirefoxDriver();  
     //Maximize browser window    
     dr.manage().window().maximize();  
     //Go to URL   
     dr.get("http://www.google.com");  
     //Set timeout   
 dr.manage().timeouts().implicitlyWait(10, TimeUnit.SECONDS);  
     // Open new tab   
 dr.findElement(By.cssSelector("body")).sendKeys(Keys.CONTROL + "t");  
     //Go to URL   
     dr.get("http://www.gmail.com");  
     //Set new tab timeout   
 dr.manage().timeouts().implicitlyWait(10, TimeUnit.SECONDS);  
     // Do some operation       
     dr.findElement(By.id("gmail-sign-in")).click();  
     dr.findElement(By.id("Email")).sendKeys("WebDriver");  
     dr.findElement(By.id("Passwd")).sendKeys("WebDriver");  
     dr.findElement(By.id("signIn")).click();  
     Thread.sleep(2000);  
     // Close new tab   
 dr.findElement(By.cssSelector("body")).sendKeys(Keys.CONTROL + "w");  
     // Switch first tab   
     dr.switchTo().defaultContent();  
     Thread.sleep(2000);  
     // Write search String   
     dr.findElement(By.id("gbqfq")).sendKeys("WebDriver");  
     // Click on Search button       
     dr.findElement(By.id("gbqfb")).click();  
     Thread.sleep(2000);  
     // Browser close    
     dr.close();  
   }  
 }