如何解释运算符关联性？(How to interpret the operator associativity?)

 您的代码需要2个小的更改。 
 
 变化1： 
 WebElement loc=driver.findElement(By.className("input1")); 
 
 指向页面上的三个Web元素，而不是在下面使用 
 
WebElement loc=driver.findElement(By.xpath("//input[@class='input1' and @name='pin_no']"));
 
 改变2：它是一个文本字段，所以代替 
 
a.moveToElement(loc)
 
 使用 
 
 a.click(loc)
 
 所以您的代码应如下所示： 
 
    public static void main(String[] args) {
        WebDriver driver=new FirefoxDriver();
        driver.get("http://fleet.idrivesafely.com");
        driver.manage().window().maximize();
        driver.findElement(By.linkText("Student Login")).click();
        WebElement loc=driver.findElement(By.xpath("//input[@class='input1' and @name='pin_no']"));
        Actions a= new Actions(driver);
        a.click(loc).keyDown(Keys.SHIFT).sendKeys("wel").keyUp(Keys.SHIFT).sendKeys("co").keyDown(Keys.SHIFT).sendKeys("me").perform();

Your code requires 2 small changes.
 
Change 1:
 WebElement loc=driver.findElement(By.className("input1"));
 
is pointing to three Web-elements on the page, Instead use below 
 
WebElement loc=driver.findElement(By.xpath("//input[@class='input1' and @name='pin_no']"));
 
Change 2: Its a Text field, so Instead of 
 
a.moveToElement(loc)
 
Use 
 
 a.click(loc)
 
So you code should be as below : 
 
    public static void main(String[] args) {
        WebDriver driver=new FirefoxDriver();
        driver.get("http://fleet.idrivesafely.com");
        driver.manage().window().maximize();
        driver.findElement(By.linkText("Student Login")).click();
        WebElement loc=driver.findElement(By.xpath("//input[@class='input1' and @name='pin_no']"));
        Actions a= new Actions(driver);
        a.click(loc).keyDown(Keys.SHIFT).sendKeys("wel").keyUp(Keys.SHIFT).sendKeys("co").keyDown(Keys.SHIFT).sendKeys("me").perform();