Selenium Java WebDriver中的空指針異常

Question

我的代碼：

public class Testlogin {

    WebDriver driver;

    public Testlogin(WebDriver driver) {
        this.driver=driver;
    }

    WebElement userName = driver.findElement(By.id("username"));
    WebElement Password = driver.findElement(By.id("password"));
    WebElement login = driver.findElement(By.xpath("//button"));

    public void loginpages(String user,String pass) {
        userName.sendKeys(user);
        Password.sendKeys(pass);
        login.click();
    }
}

---

public class Testclass {

    public static void main(String[] args) {
        WebDriver driver = new FirefoxDriver(); 
        driver.get("https://the-internet.herokuapp.com/login");
        Testlogin test = new Testlogin(driver);
        test.loginpages("tomsmith","SuperSecretPassword!");
    }
}

出現以下錯誤：

Exception in thread "main" java.lang.NullPointerException
    at Test.Testlogin.<init>(Testlogin.java:18)
    at Test.Testclass.main(Testclass.java:14)

Answer 1

必須首先將驅動程序對象實例化。 例如，將其移動到構造器內部：

public Testlogin(WebDriver driver)
{
    this.driver=driver;

    WebElement userName = driver.findElement(By.id("username"));
    WebElement Password = driver.findElement(By.id("password"));
    WebElement login = driver.findElement(By.xpath("//button"));

}

Answer 2

如果尚未設置驅動程序，請使testlogin類如下所示，它將指向null並在您嘗試運行driver.findElement(By.id("username")); 驅動程序為null，這將無法解決此問題，因為艾登·格羅斯曼（Aiden Grossman）表示，在設置驅動程序后會初始化

public class Testlogin {

    WebDriver driver;

    public Testlogin(WebDriver driver) {
        this.driver=driver;
        WebElement userName = driver.findElement(By.id("username"));
        WebElement Password = driver.findElement(By.id("password"));
        WebElement login = driver.findElement(By.xpath("//button"));
    }

    public void loginpages(String user,String pass) {
        userName.sendKeys(user);
        Password.sendKeys(pass);
        login.click();
    }
}