How I Can Print Credentials In Login Form Using Prompt Window In Selenium Webdriver?

Hello Ryan,
I want to create a script of login/logout for gmail account.As you know for login we have to enter username and password for that in java we use this snippet.
driver.findElement(By.name("Email")).clear();
driver.findElement(By.name("Email")).sendKeys("username");
driver.findElement(By.name("password")).clear();

driver.findElement(By.name("password")).sendKeys("xxxxx");

driver.findElement(By.cssSelector("input.button")).click();

But this code can send only fixed username and password which is filled in code.I want to enter new credentials in each run with prompt.We can do this in IDE using prompt and type commands from this in each run in selenium IDE a prompt window open for username and password.How can we do this in selenium webdriver??