java 这是什么错误：在 com.google.common.base.Preconditions.checkNotNull
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/42936414/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
What is this Error: at com.google.common.base.Preconditions.checkNotNull
提问by Vishvesh Savant
I am a new automation tester, Working on sample test scripts, Need some help from you guys, I have tried to use POM and basic TestNG.
我是一名新的自动化测试人员，正在编写示例测试脚本，需要你们的帮助，我尝试使用 POM 和基本的 TestNG。
I have created 2 packages - pages and testcases.
我创建了 2 个包 - 页面和测试用例。
I am getting some error when I am trying to access the "ClickJoin, Enterusername" methods from my pages packages. I had tried figuring out the issue, but was unable to get to why this error is occurring.
当我尝试从我的页面包访问“ClickJoin, Enterusername”方法时遇到一些错误。我曾尝试找出问题所在，但无法弄清楚为什么会发生此错误。
Below is the Error: java.lang.NullPointerException at com.google.common.base.Preconditions.checkNotNull
下面是错误：com.google.common.base.Preconditions.checkNotNull 上的 java.lang.NullPointerException
My Code from the "pages" package:package com.gptoday.pages;
“页面”包中的我的代码：包 com.gptoday.pages;
import org.openqa.selenium.By;
import org.openqa.selenium.WebDriver;
import org.openqa.selenium.support.ui.ExpectedConditions;
import org.openqa.selenium.support.ui.WebDriverWait;
public class Login {
public WebDriver driver;
public WebDriverWait wait;
By join = By.xpath("//*[@id='members']/a[1]");
By username = By.id("username");
By password = By.id("password");
By loginButton = By.xpath("//*[@id='normallogin']/div[4]/p/input[2]");
public Login (WebDriver driver){
this.driver=driver;
}
public void ClickJoin(){
wait = new WebDriverWait(driver,10);
//driver.findElement(join).click();
wait.until(ExpectedConditions.visibilityOfElementLocated(join)).click();
}
public void EnterUsername(){
wait = new WebDriverWait(driver, 10);
wait.until(ExpectedConditions.visibilityOfElementLocated(username)).click();
wait.until(ExpectedConditions.visibilityOfElementLocated(username)).sendKeys("Test username");
System.out.println("Username Entered");
}
public void EnterPassword(){
driver.findElement(password).clear();
driver.findElement(password).click();
System.out.println("Password Entered");
}
public void ClickButton(){
wait = new WebDriverWait(driver, 10);
//driver.findElement(loginButton).click();
wait.until(ExpectedConditions.visibilityOfElementLocated(loginButton)).click();
System.out.println("Login Button Clicked");
}
}
My Code from the "TestCases" package: This code is of my base class.
“TestCases”包中的我的代码：此代码属于我的基类。
package com.gptoday.com.gptoday.testcases;
import org.testng.annotations.Test;
import org.testng.annotations.BeforeMethod;
import org.openqa.selenium.WebDriver;
import org.openqa.selenium.firefox.FirefoxDriver;
import org.openqa.selenium.firefox.FirefoxProfile;
import org.openqa.selenium.firefox.internal.ProfilesIni;
import org.testng.annotations.AfterMethod;
import org.openqa.selenium.firefox.internal.ProfilesIni;
public class Base {
public WebDriver driver;
@BeforeMethod
public void BaseSetup(){
ProfilesIni prof = new ProfilesIni();
FirefoxProfile ffProfile= prof.getProfile ("vishvesh");
ffProfile.setAcceptUntrustedCertificates(true);
ffProfile.setAssumeUntrustedCertificateIssuer(false);
String BaseUrl = "https://www.gptoday.com";
System.setProperty("webdriver.gecko.driver", "G:/Workplace/AutomationSetupFiles/Geckdriver/geckodriver.exe");
driver = new FirefoxDriver (ffProfile);
driver.get(BaseUrl);
driver.manage().window().maximize();
}
@AfterMethod
public void afterTest() {
System.out.println("Success");
}
}
**Below the the code for the test case.**
package com.gptoday.com.gptoday.testcases;
import org.testng.annotations.Test;
import com.gptoday.pages.Login;
import org.openqa.selenium.WebDriver;
public class LoginVerification extends Base {
public WebDriver driver;
public Login obj = new Login(driver);
@Test
public void Verify()
{
obj.ClickJoin();
obj.EnterUsername();
}
}
**Error:**
Success
FAILED: Verify
java.lang.NullPointerException
at com.google.common.base.Preconditions.checkNotNull(Preconditions.java:770)
at org.openqa.selenium.support.ui.FluentWait.<init>(FluentWait.java:96)
at org.openqa.selenium.support.ui.WebDriverWait.<init>(WebDriverWait.java:71)
at org.openqa.selenium.support.ui.WebDriverWait.<init>(WebDriverWait.java:45)
at com.gptoday.pages.Login.ClickJoin(Login.java:22)
at com.gptoday.com.gptoday.testcases.LoginVerification.Verify(LoginVerification.java:16)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at org.testng.internal.MethodInvocationHelper.invokeMethod(MethodInvocationHelper.java:108)
at org.testng.internal.Invoker.invokeMethod(Invoker.java:661)
at org.testng.internal.Invoker.invokeTestMethod(Invoker.java:869)
at org.testng.internal.Invoker.invokeTestMethods(Invoker.java:1193)
at org.testng.internal.TestMethodWorker.invokeTestMethods(TestMethodWorker.java:126)
at org.testng.internal.TestMethodWorker.run(TestMethodWorker.java:109)
at org.testng.TestRunner.privateRun(TestRunner.java:744)
at org.testng.TestRunner.run(TestRunner.java:602)
at org.testng.SuiteRunner.runTest(SuiteRunner.java:380)
at org.testng.SuiteRunner.runSequentially(SuiteRunner.java:375)
at org.testng.SuiteRunner.privateRun(SuiteRunner.java:340)
at org.testng.SuiteRunner.run(SuiteRunner.java:289)
at org.testng.SuiteRunnerWorker.runSuite(SuiteRunnerWorker.java:52)
at org.testng.SuiteRunnerWorker.run(SuiteRunnerWorker.java:86)
at org.testng.TestNG.runSuitesSequentially(TestNG.java:1301)
at org.testng.TestNG.runSuitesLocally(TestNG.java:1226)
at org.testng.TestNG.runSuites(TestNG.java:1144)
at org.testng.TestNG.run(TestNG.java:1115)
at org.testng.remote.AbstractRemoteTestNG.run(AbstractRemoteTestNG.java:132)
at org.testng.remote.RemoteTestNG.initAndRun(RemoteTestNG.java:230)
at org.testng.remote.RemoteTestNG.main(RemoteTestNG.java:76)
回答by DebanjanB
Here's the reason behind the error you are getting:
这是您收到错误背后的原因：
In both Login & EnterUsername methods while you defined the wait you have passed the instance of Webdriver & interval. Now whenever Selenium detects this particular type of argument Selenium treats this as FluentWait. Now when you actually implement a FluentWait you have to import those two libraries "com.google.common.base.Function" which will address the error you are facing. Of course you have to import "FluentWait" as well.
在 Login 和 EnterUsername 方法中，当您定义等待时，您已经传递了 Webdriver & interval 的实例。现在，每当 Selenium 检测到这种特定类型的参数时，Selenium 都会将其视为 FluentWait。现在，当您实际实现 FluentWait 时，您必须导入这两个库“com.google.common.base.Function”，这将解决您面临的错误。当然，您还必须导入“FluentWait”。
Let me know if this helps you.
如果这对您有帮助，请告诉我。
回答by Vishvesh Savant
By modifying the code in the "Login.Java" class.. The issue was related to driver being null as I did not extend "Base" in the "Login" class.
通过修改“Login.Java”类中的代码。问题与驱动程序为空有关，因为我没有在“Login”类中扩展“Base”。
