Selenium java Browser session reuse

My question is as follows: How can I reuse a browser session for tests that are in different java classes? I have the browser open like this:

public class OpenBrowser {

    public static WebDriver driver;

    @BeforeSuite
    public static void openb() {
        // Create a new instance of the Firefox driver
        driver = new FirefoxDriver();
        driver.manage().timeouts().implicitlyWait(10, TimeUnit.SECONDS);
    }
}

Then I have to log into a website using some credentials and after it's logged I want to perform other tests, I do not want to log in for every test because there are a lot of them that I need to make and logging in for each will take a decade. For example a flow looks like : Log In->Push some component->add some values->Generate a report. Than after this i would like to generate other report on another component but when I try to it gives a null pointer exception. Any ideas? :)