import org.openqa.selenium.By;
import org.openqa.selenium.WebDriver;
import org.openqa.selenium.WebElement;
import org.openqa.selenium.chrome.ChromeDriver;
import org.openqa.selenium.support.ui.ExpectedConditions;
import org.openqa.selenium.support.ui.WebDriverWait;

import java.util.List;

class Scratch {
    public static WebElement findElement(WebDriver webDriver, By selector) {
        List<WebElement> elements = webDriver.findElements(selector);
        if (elements.size() > 0) {
            return elements.get(0);
        }
        return null;
    }

    public static void main(String[] args) {
        // you could use FirefoxDriver, PhantomJSDriver, SafariDriver here
        WebDriver webDriver = new ChromeDriver();
        webDriver.get("https://the-internet.herokuapp.com/dynamic_loading/2");
        webDriver.findElement(By.id("start")).click();
        WebElement finishElement = findElement(webDriver, By.id("finish"));
        if (finishElement != null) {
            System.out.println("it loaded");
        }

        // you can also use expected conditions
        new WebDriverWait(webDriver, 60).until(ExpectedConditions.visibilityOfElementLocated(By.id("finish")));
    }
}