为什么我们需要将Firefox驱动程序强制转换为javascript执行程序？

Question

I'm a beginner in Java and Selenium and I came across JavascriptExecutor while working.

Wanted to know: though Remote webdriver and Firefox driver implement javascript executor, why can't I acess the method executeScript() directly and why should it be typecasted to get acessed?

Here is the program for javascript executor:

public class entertextwithoutsendkeys
{
    WebDriver driver;

    public entertextwithoutsendkeys()
    {
        driver = new FirefoxDriver();
    }

    @Test
    public void entertextpgm()
    {
        driver.get("https://www.gmail.com/");
        JavascriptExecutor executor = (JavascriptExecutor) driver;
        executor.executeScript("document.getElementById('Email').value='sh'");
    }
}

Answer 1

Your driver variable (field, actually) is declared as of type WebDriver .

Since FirefoxDriver implements WebDriver , you can assign a new FirefoxDriver() to driver without problems.

Now you want to execute some JavaScript command. To do that, you must use the executeScript() method of the JavascriptExecutor interface.

JavascriptExecutor has nothing to do with the WebDriver interface (this one doesn't extend that one, for example), but FirefoxDriver happens to implement both.

So, even though your driver variable is seen as a WebDriver (due to its declaration), it actually holds as value an instance of FirefoxDriver - thus its value is a JavascriptExecutor as well (because FirefoxDriver implements JavascriptExecutor ).

Still, you have to find a way of "looking at" that driver variable as if it were a JavascriptExecutor , so you can execute this interface's methods (like executeScript() ). The way to do this , this "looking at", is casting , just as you did.

You wouldn't have to do any cast if you declared driver as of type FirefixDriver . Try it yourself.