Cannot Instantiate class error - Selenium WebDriver

Question 1

I am facing this 'Cannot insantiate class' error on running one of my test cases in Selenium webdriver using Java.

Below is the class of the functionality of the test,

package Pages;
import java.util.List;
import org.openqa.selenium.By;
import org.openqa.selenium.WebDriver;
import org.openqa.selenium.WebElement;
import org.openqa.selenium.support.ui.ExpectedConditions;
import org.openqa.selenium.support.ui.Select;
import org.openqa.selenium.support.ui.WebDriverWait;
import Lib.lib;
public class KnowledgeBase extends lib{
 By sortBylink = By.xpath("html/body/div[1]/featured-studies-grid/div[2]/featured-studies-toolbar/div/div[2]/div[2]/div/div");
 By featuredOption = By.xpath("html/body/div[1]/featured-studies-grid/div[2]/featured-studies-toolbar/div/div[2]/div[2]/div/ul/li[1]");
 By mostRcnt = By.xpath("html/body/div[1]/featured-studies-grid/div[2]/featured-studies-toolbar/div/div[2]/div[2]/div/ul/li[2]");
 String featOption = driver.findElement(By.xpath("html/body/div[1]/featured-studies-grid/div[2]/featured-studies-toolbar/div/div[2]/div[2]/div/ul/li[1]")).getText();
 String mostRecent = driver.findElement(By.xpath("html/body/div[1]/featured-studies-grid/div[2]/featured-studies-toolbar/div/div[2]/div[2]/div/ul/li[2]")).getText();
 public void initSBy() throws Exception
 {
 driver.findElement(sortBylink).click();
 Thread.sleep(1500);
 }
 public void selectfO() throws Exception
 {
 driver.findElement(featuredOption).click();
 Thread.sleep(5000);
 }
 public void selectMr() throws Exception
 {
 driver.findElement(mostRcnt).click();
 Thread.sleep(5000);
 }
 public void sortBy(String sProp) throws Exception
 {
 this.initSBy();
 if (sProp == "featOption") {
 this.selectfO();
 }
 else if (sProp == "mostRecent"){
 this.selectMr();
 }
 else {
 System.out.println("Incorrect option. Test failed.");
 }
 }
}

Below is my Test Case Class

package TestCases;
import org.testng.annotations.Test;
import Lib.lib;
import Pages.KnowledgeBase;
import Pages.LoginPage;
public class sortingTextKB extends lib {
 LoginPage uLogin = new LoginPage();
 KnowledgeBase sortObj = new KnowledgeBase();
 //Logging In
 @Test (priority = 1)
 public void loggingIn() throws Exception
 {
 uLogin.loginToKB("[email protected]", "uziiiii");
 }
 //Sorting
 @Test (priority = 2)
 public void sortIn() throws Exception
 {
 sortObj.sortBy("Most Recent");
 }
}

Below is my Lib class, that contains the chrome driver configuration

package Lib;
import org.openqa.selenium.WebDriver;
import org.openqa.selenium.chrome.ChromeDriver;
import org.openqa.selenium.chrome.ChromeOptions;
import org.testng.annotations.BeforeTest;
import org.testng.annotations.AfterTest;
public class lib {
 protected static WebDriver driver = null;
 @BeforeTest
 public void chrome_extension()
 {
 System.setProperty("webdriver.chrome.driver", "chromedriver.exe");
 ChromeOptions options = new ChromeOptions();
 options.addArguments("--start-maximized");
 driver = new ChromeDriver(options);
 driver.get("http://www.testsite.com");
 }
 @AfterTest
 public void quit()
 {
 driver.quit();
 }
}

When I run my test case class, I am getting the following error,

org.testng.TestNGException: 
Cannot instantiate class TestCases.sortingTextKB
 at org.testng.internal.ObjectFactoryImpl.newInstance(ObjectFactoryImpl.java:38)
 at org.testng.internal.ClassHelper.createInstance1(ClassHelper.java:387)
 at org.testng.internal.ClassHelper.createInstance(ClassHelper.java:299)
 at org.testng.internal.ClassImpl.getDefaultInstance(ClassImpl.java:110)
 at org.testng.internal.ClassImpl.getInstances(ClassImpl.java:186)
 at org.testng.internal.TestNGClassFinder.<init>(TestNGClassFinder.java:120)
 at org.testng.TestRunner.initMethods(TestRunner.java:409)
 at org.testng.TestRunner.init(TestRunner.java:235)
 at org.testng.TestRunner.init(TestRunner.java:205)
 at org.testng.TestRunner.<init>(TestRunner.java:160)
 at org.testng.remote.RemoteTestNG1ドル.newTestRunner(RemoteTestNG.java:141)
 at org.testng.remote.RemoteTestNG$DelegatingTestRunnerFactory.newTestRunner(RemoteTestNG.java:271)
 at org.testng.SuiteRunner$ProxyTestRunnerFactory.newTestRunner(SuiteRunner.java:561)
 at org.testng.SuiteRunner.init(SuiteRunner.java:157)
 at org.testng.SuiteRunner.<init>(SuiteRunner.java:111)
 at org.testng.TestNG.createSuiteRunner(TestNG.java:1299)
 at org.testng.TestNG.createSuiteRunners(TestNG.java:1286)
 at org.testng.TestNG.runSuitesLocally(TestNG.java:1140)
 at org.testng.TestNG.run(TestNG.java:1057)
 at org.testng.remote.RemoteTestNG.run(RemoteTestNG.java:111)
 at org.testng.remote.RemoteTestNG.initAndRun(RemoteTestNG.java:204)
 at org.testng.remote.RemoteTestNG.main(RemoteTestNG.java:175)
Caused by: java.lang.reflect.InvocationTargetException
 at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
 at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
 at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
 at java.lang.reflect.Constructor.newInstance(Unknown Source)
 at org.testng.internal.ObjectFactoryImpl.newInstance(ObjectFactoryImpl.java:29)
 ... 21 more
Caused by: java.lang.NullPointerException
 at Pages.KnowledgeBase.<init>(KnowledgeBase.java:22)
 at TestCases.sortingTextKB.<init>(sortingTextKB.java:12)
 ... 26 more

Following is line 22 of KnowledgeBase class,

String featOption = driver.findElement(By.xpath("html/body/div[1]/featured-studies-grid/div[2]/featured-studies-toolbar/div/div[2]/div[2]/div/ul/li[1]")).getText();

Please let me know why I am facing this 'cannot instantiate class' error. Thanks

Question 2

BTW, package names should be lower case, and class names should start from Capital letter in Java.

Question 3

Rename ClassName of Lib to another. I also got an error.This can be resolved by changing Classname.

Question 4

It looks like your driver instance is created in one class(lib, (should start with Capital letter BTW)) but you are trying to access it in another class(KnowledgeBase).

If you want to use a class instance in another class, you have options. Some of them are:

Add a getter method. Add a public getDriverInstance() method in the class where the instance is created that will just return the driver instance.
Keep everything in the same class. Keep the driver initialization method as well as the tests themselves in the same class. That's obviously a messy solution but it will work.
Use a Dependency Injection framework. You can use a DI framework like Spring, PicoContainer, etc.., which is probably the cleanest solution but has some learning curve to it.

Question 5

Use @BeforeMethod annotation in place of @BeforeTest.

Question 6

Just curious, what does this do? What other impacts does this change make?

Question 7

It’s purely intuitive; there aren’t any issues in the code. So either user14403 has made a logical error in loginToKB method (for which code isn’t shared) or since details are specified in BeforeTest and it is expected to call this before each Test (priority=1) and Test2 (priority=2), to achieve this BeforeMethod has to be used (this being a common mistake made).

Question 8

The explanation of the difference between @BeforeMethod and @BeforeTest needs to be in your answer.

Question 9

@KatePaulk Explaining the difference would be a great idea, because it's a confusing concept in TestNG. @BeforeMethod runs before each @Test method. @BeforeTest runs before each test, which is not the same thing as a @Test method. A TestNG test is defined in the XML or JSON file that defines what to run. It's essentially a sub-suite, and can invoke many test methods. Yeah, like I said, confusing. That said, explaining the difference would not help this answer, because (while it may be a good idea) it does not solve the problem described in the question.

Question 10

There are a few problems here. The construction of your classes is confusing and will give you issues if not corrected. First, @BeforeTest is run once before the entire suite of tests (This is a common error). You would instead want either @BeforeClass or @BeforeMethod. @BeforeMethod would be a better choice as it would ensure a fresh browser before each test method. You'll need a matching @AfterMethod as well.

Next, you are extending all of your Classes from the same Lib class. This is a very unwieldy design pattern. Instead create a class with all of your test setup and tear down. Extend the classes with the actual tests from this.

From here you can pass the driver to the Page objects and Knowledgebase object using a getdriver() method as suggested by Eugene.

public class ChromeTest {
 private ChromeDriver driver;
 @BeforeMethod
 public void beforeMethod(){
 driver = new ChromeDriver();
 //additional setup
 }
 @AfterMethod
 public void afterMethod(){
 driver.quit();
 //additional tear down 
 }
 public ChromeDriver getDriver (){
 return driver;
 }
}

Test Classes

public class UiTest extends ChromeTest {
 @Test
 public void test1(){
 KnowledgeBase kb = new KnowledgeBase(getDriver());
 //Rest of your test code
 }
}

Refactor your page and KnowledgeBase classes to use the passed in driver instance.

public class KnowledgeBase{
 private WebDriver driver;
 public KnowledgeBase( WebDriver webDriver ) {
 driver = webDriver;
 }
 //rest of your methods
}

By refactoring your classes and methods as noted above it will vastly simplify your code which will make the logical errors easier to find if not fix it outright.

Question 11

The problem is this:

TestNG must finish instantiating a KnowledgeBase object before it calls any of the configuration methods (annotated with @BeforeTest and @BeforeMethod).
Instantiating a KnowledgeBase includes initializing all of its members.
One of the members it must initialize is featOption, on line 22.
In order to initialize featOption, the initialization tries to call driver.findElement(...).
Because the chrome_extension() method in Lib hasn't been called yet, driver is still null.
Kaboom

To fix this, either:

Initialize driver in a constructor (probably in Lib), and only then initialize featOption (probably in KnowledgeBase's constructor). This means you'll have a single driver instance for all of your tests. Given that you're currently launching a new driver for each TestNG test (confusingly, in TestNG a "test" is not at all the same thing as a test method, even though test methods are annotated with @Test), that may or may not be what you want.
Initialize driver at the point where you declare it in Lib. This is more or less like initializing it in a constructor. So again, this may or may not be what you want.
Initialize featOption in a configuration method (annotated as @BeforeTest or @BeforeMethod) in KnowledgeBase. This will be called after the chrome_extension() method in Lib, so the driver will have have been constructed and launched. So when you call driver.findElement(...), driver will be valid.

Question 12

Can you change:

protected static WebDriver driver = null;

to

 public static WebDriver driver;

Maybe that works. Just a try.

Eugene S Eugene S 4291 gold badge6 silver badges18 bronze badges · Answer 1 · 2015-12-14 03:25:01Z

It looks like your driver instance is created in one class(lib, (should start with Capital letter BTW)) but you are trying to access it in another class(KnowledgeBase).

If you want to use a class instance in another class, you have options. Some of them are:

Add a getter method. Add a public getDriverInstance() method in the class where the instance is created that will just return the driver instance.
Keep everything in the same class. Keep the driver initialization method as well as the tests themselves in the same class. That's obviously a messy solution but it will work.
Use a Dependency Injection framework. You can use a DI framework like Spring, PicoContainer, etc.., which is probably the cleanest solution but has some learning curve to it.

JustARandomGuy JustARandomGuy 8498 silver badges21 bronze badges · Answer 2 · 2015-09-14 01:58:03Z

0

Use @BeforeMethod annotation in place of @BeforeTest.

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edited Sep 14, 2015 at 14:19

user246

answered Sep 14, 2015 at 1:58

JustARandomGuy's user avatar

JustARandomGuy JustARandomGuy

8498 silver badges21 bronze badges

4

Just curious, what does this do? What other impacts does this change make?

corsiKa
– corsiKa ♦

2015年09月14日 04:15:51 +00:00
Commented Sep 14, 2015 at 4:15
It’s purely intuitive; there aren’t any issues in the code. So either user14403 has made a logical error in loginToKB method (for which code isn’t shared) or since details are specified in BeforeTest and it is expected to call this before each Test (priority=1) and Test2 (priority=2), to achieve this BeforeMethod has to be used (this being a common mistake made).

JustARandomGuy
– JustARandomGuy

2015年09月14日 04:36:32 +00:00
Commented Sep 14, 2015 at 4:36
1

The explanation of the difference between @BeforeMethod and @BeforeTest needs to be in your answer.

Kate Paulk
– Kate Paulk

2015年09月14日 11:12:51 +00:00
Commented Sep 14, 2015 at 11:12
@KatePaulk Explaining the difference would be a great idea, because it's a confusing concept in TestNG. @BeforeMethod runs before each @Test method. @BeforeTest runs before each test, which is not the same thing as a @Test method. A TestNG test is defined in the XML or JSON file that defines what to run. It's essentially a sub-suite, and can invoke many test methods. Yeah, like I said, confusing. That said, explaining the difference would not help this answer, because (while it may be a good idea) it does not solve the problem described in the question.

Dale Emery
– Dale Emery

2018年01月26日 22:09:11 +00:00
Commented Jan 26, 2018 at 22:09

Add a comment |

CodeBreaker CodeBreaker 2961 silver badge5 bronze badges · Answer 3 · 2015-12-14 09:49:27Z

There are a few problems here. The construction of your classes is confusing and will give you issues if not corrected. First, @BeforeTest is run once before the entire suite of tests (This is a common error). You would instead want either @BeforeClass or @BeforeMethod. @BeforeMethod would be a better choice as it would ensure a fresh browser before each test method. You'll need a matching @AfterMethod as well.

Next, you are extending all of your Classes from the same Lib class. This is a very unwieldy design pattern. Instead create a class with all of your test setup and tear down. Extend the classes with the actual tests from this.

From here you can pass the driver to the Page objects and Knowledgebase object using a getdriver() method as suggested by Eugene.

public class ChromeTest {
 private ChromeDriver driver;
 @BeforeMethod
 public void beforeMethod(){
 driver = new ChromeDriver();
 //additional setup
 }
 @AfterMethod
 public void afterMethod(){
 driver.quit();
 //additional tear down 
 }
 public ChromeDriver getDriver (){
 return driver;
 }
}

Test Classes

public class UiTest extends ChromeTest {
 @Test
 public void test1(){
 KnowledgeBase kb = new KnowledgeBase(getDriver());
 //Rest of your test code
 }
}

Refactor your page and KnowledgeBase classes to use the passed in driver instance.

public class KnowledgeBase{
 private WebDriver driver;
 public KnowledgeBase( WebDriver webDriver ) {
 driver = webDriver;
 }
 //rest of your methods
}

By refactoring your classes and methods as noted above it will vastly simplify your code which will make the logical errors easier to find if not fix it outright.

Dale Emery Dale Emery 4,4851 gold badge19 silver badges20 bronze badges · Answer 4 · 2018-01-26 20:06:25Z

The problem is this:

TestNG must finish instantiating a KnowledgeBase object before it calls any of the configuration methods (annotated with @BeforeTest and @BeforeMethod).
Instantiating a KnowledgeBase includes initializing all of its members.
One of the members it must initialize is featOption, on line 22.
In order to initialize featOption, the initialization tries to call driver.findElement(...).
Because the chrome_extension() method in Lib hasn't been called yet, driver is still null.
Kaboom

To fix this, either:

Initialize driver in a constructor (probably in Lib), and only then initialize featOption (probably in KnowledgeBase's constructor). This means you'll have a single driver instance for all of your tests. Given that you're currently launching a new driver for each TestNG test (confusingly, in TestNG a "test" is not at all the same thing as a test method, even though test methods are annotated with @Test), that may or may not be what you want.
Initialize driver at the point where you declare it in Lib. This is more or less like initializing it in a constructor. So again, this may or may not be what you want.
Initialize featOption in a configuration method (annotated as @BeforeTest or @BeforeMethod) in KnowledgeBase. This will be called after the chrome_extension() method in Lib, so the driver will have have been constructed and launched. So when you call driver.findElement(...), driver will be valid.

joan joan 1 · Answer 5 · 2018-02-23 05:53:34Z

0

Can you change:

protected static WebDriver driver = null;

to

 public static WebDriver driver;

Maybe that works. Just a try.

Share

Improve this answer

edited Feb 23, 2018 at 7:09

Bharat Mane's user avatar

Bharat Mane ♦

6,78512 gold badges42 silver badges69 bronze badges

answered Feb 23, 2018 at 5:53

joan's user avatar

joan joan

1

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