How to get all valid urls from a website in selenium webdriver using java.

import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.TimeUnit;
import org.openqa.selenium.By;
import org.openqa.selenium.Keys;
import org.openqa.selenium.WebDriver;
import org.openqa.selenium.WebElement;
import org.openqa.selenium.firefox.FirefoxDriver;
import static selenium.practice.BdJobsQARelatdJobsHtmlUnitDriver.m;


public class Getallurlsfromwebsite {

    static WebDriver driver;

    static List<WebElement> mainurl, suburl;
    static List<String> uniqueurl;

    public static void main(String[] a) throws InterruptedException {
        // Initialize Firefox driver 
        driver = new FirefoxDriver();
        //Maximize browser window 
        driver.manage().window().maximize();

        String websiteaddress = "http://www.google.com";
        //Go to website  
        uniqueurl = new ArrayList();
        driver.get(websiteaddress);
     driver.manage().timeouts().implicitlyWait(10, TimeUnit.SECONDS);
        //get all url of page
        mainurl = driver.findElements(By.tagName("a"));

for (int k = 0; k < mainurl.size(); k++) {
            // check url not null, empty and only current website 
            if (!(mainurl.get(k).getText().trim().equals("")) && !(mainurl.get(k).getText().trim() == null) && !(mainurl.get(k).getAttribute("href").trim() == null) && !(mainurl.get(k).getAttribute("href").trim().equals("")) && (mainurl.get(k).getAttribute("href").contains("google.com")) && !(mainurl.get(k).getAttribute("href").contains("@"))) {

       if (!(uniqueurl.contains(mainurl.get(k).getAttribute("href").trim()))) {
   uniqueurl.add(mainurl.get(k).getAttribute("href").trim());
//Print urls
 System.out.println(mainurl.get(k).getAttribute("href"));

                    // Open new tab
  driver.findElement(By.cssSelector("body")).sendKeys(Keys.CONTROL + "t");
  driver.get(mainurl.get(k).getAttribute("href").trim());
  driver.manage().timeouts().implicitlyWait(10, TimeUnit.SECONDS);
// get all sub page url
     suburl = driver.findElements(By.tagName("a"));

      /get all sub page url
      for (int m = 0; m < suburl.size(); m++) {
        if (!(suburl.get(m).getText().trim().equals("")) && !(suburl.get(m).getText().trim() == null) && !(suburl.get(m).getAttribute("href").equals("")) && !(suburl.get(m).getAttribute("href") == null)) {

     if (!(uniqueurl.contains(suburl.get(m).getAttribute("href").trim()))) {
  uniqueurl.add(suburl.get(k).getAttribute("href").trim());
       //Print urls
System.out.println(suburl.get(m).getAttribute("href"));
                            }

                        }
                    }
  // close open tab
driver.findElement(By.cssSelector("body")).sendKeys(Keys.CONTROL + "w");
// Move default window
driver.findElement(By.cssSelector("body")).sendKeys(Keys.CONTROL + "\t");
driver.switchTo().defaultContent();
                    Thread.sleep(7000);

                }
            }
        }
        driver.quit();
    }

}