org.testng.TestNGException：无法实例化类TestNG.DemoTestNG

Question

这是我的问题。
 执行testNG脚本后，我收到错误说明 org.testng.TestNGException： 无法实例化类TestNG.DemoTestNG。任何人都可以给我解决我的问题的方法。

public class DemoTestNG {
        WebDriver driver = new FirefoxDriver();
        String appUrl = "http://192.168.1.116:9090/soxaudit/login";
       @Test
        public void Sox_Login() {
            driver.get(appUrl);
        driver.manage().window().maximize();
        String expectedTitle = "SOX ADMIN - LOGIN";

                String actualTitle = driver.getTitle();
                Assert.assertEquals(expectedTitle,actualTitle);
        WebElement username = driver.findElement(By.id("j_username"));
        username.clear();
        username.sendKeys(new String[]{"sox"});
        WebElement password = driver.findElement(By.id("j_password"));
        password.clear();
        password.sendKeys(new String[]{"welcome@123"});      
        WebElement SignInButton = driver.findElement(By.xpath("//*[@id='login-page']/div/form/div/button"));
        SignInButton.click();               
// close the web browser
        driver.close();
        System.out.println("Test script executed successfully.");

// terminate the program
        System.exit(0);
    }
}