Exception in thread "main" org.openqa.selenium.WebDriverException: Build info: version: '4.0.0-alpha-1', revision: 'd1d3728cae', time: '2019-04-24T16:14:53'
System info: host: 'DESKTOP-Q0ODJRV', ip: '192.168.154.1', os.name: 'Windows 10', os.arch: 'x86', os.version: '10.0', java.version: '1.8.0_144'
Driver info: driver.version: FirefoxDriver
at java.util.Optional.orElseThrow(Optional.java:290)
at org.openqa.selenium.firefox.FirefoxDriver.toExecutor(FirefoxDriver.java:174)
at org.openqa.selenium.firefox.FirefoxDriver.<init>(FirefoxDriver.java:149)
at org.openqa.selenium.firefox.FirefoxDriver.<init>(FirefoxDriver.java:127)
at seleniumdemo.FirstDemo.main(FirstDemo.java:16)

1、浏览器驱动文件没下载，
2、selenium jar包和浏览器版本不兼容
应该就是这2个问题之一