How can open and close browser tabs in selenium Webdriver on Mac 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 Openandclosetabhandler {  
   public static void main(String[] a) throws InterruptedException {  
     // Initialize driver   
     WebDriver driver = new FirefoxDriver();  
     //Maximize browser window    
     driver.manage().window().maximize();  
     //Go to URL   
     driver.get("http://www.google.com");  
     //Set timeout   
     driver.manage().timeouts().implicitlyWait(10, TimeUnit.SECONDS);  
     // Open new tab   
     driver.findElement(By.cssSelector("body")).sendKeys(Keys.COMMAND + "t");  
     //Go to URL   
     driver.get("http://www.yahoo.com/");  
     //Set new tab timeout   
     driver.manage().timeouts().implicitlyWait(10, TimeUnit.SECONDS);  
     // Do some operation       
     driver.findElement(By.partialLinkText("Sign in")).click();  
     Thread.sleep(2000);  
     // Switch first tab   
     driver.findElement(By.cssSelector("body")).sendKeys(Keys.COMMAND + "w");  
     driver.switchTo().defaultContent();  
     Thread.sleep(2000);  
     // Operation   
     driver.findElement(By.partialLinkText("Gmail")).click();  
     Thread.sleep(2000);  
     // Browser close    
     driver.close();  
   }  
 }