Getting java.lang.NullPointerException while finding a table with Selenium Webdriver - selenium

Question

I am new to Selenium Webdriver. I am getting Null Pointer exception while trying to find the rows present in the table. Can anyone please help me to resolve this? Please find the below scenario and code that I am using for this.
URL: http://newtours.demoaut.com/
Scenario: To click on each link that present in the table present in the left hand side of the page. Just under Mercury Tours image.
Here is code that I am using,
public class HomePage {
private WebDriver driver = null;
public HomePage(WebDriver driver){
this.driver = driver;
}
public void VerifyTableLink() throws InterruptedException{
List<WebElement> rowObj = driver.findElements(By.xpath("//td[p[img[#alt='Mercury Tours']]]/table/tbody/tr"));
System.out.println("testttt");
for(int i=0;i<rowObj.size();i++){
WebElement we = driver.findElement(By.xpath("//td[p[img[#alt='Mercury Tours']]]/table/tbody/tr["+i+"]/td[2]/a"));
we.click();
Thread.sleep(5);
driver.navigate().back();
String text = we.getText();
System.out.println(text);
}
}
}
public class VerifyNavigationTable {
WebDriver driver = null;
#Parameters({"bname","appurl"})
#BeforeMethod
public void preCondition(#Optional("Chrome")String brow, #Optional("http://newtours.demoaut.com/")String url){
driver = BrowserSelection.getBrowser(brow);
BrowserSelection.openURL(url);
}
#Test
public void verifyTableLink() throws InterruptedException{
HomePage hp = new HomePage(driver);
hp.VerifyTableLink();
}
}
Exception Message:
[Utils] Directory D:\My Selenium Training\Practical\SeleniumLearning\SeleniumPractice4\test-output\Default suite exists: true
FAILED: verifyTableLink
org.openqa.selenium.NoSuchElementException: no such element: Unable to locate element: {"method":"xpath","selector":"//td[p[img[#alt='Mercury Tours']]]/table/tbody/tr[0]/td[2]/a"}
(Session info: chrome=54.0.2840.99)
(Driver info: chromedriver=2.24.417431 (9aea000394714d2fbb20850021f6204f2256b9cf),platform=Windows NT 6.2.9200 x86_64) (WARNING: The server did not provide any stacktrace information)
Command duration or timeout: 10.07 seconds
For documentation on this error, please visit: http://seleniumhq.org/exceptions/no_such_element.html
Build info: version: 'unknown', revision: '1969d75', time: '2016-10-18 09:43:45 -0700'
System info: host: 'Bishnu', ip: '192.168.0.107', os.name: 'Windows 8', os.arch: 'amd64', os.version: '6.2', java.version: '1.8.0_111'
Driver info: org.openqa.selenium.chrome.ChromeDriver
Capabilities [{applicationCacheEnabled=false, rotatable=false, mobileEmulationEnabled=false, networkConnectionEnabled=false, chrome={chromedriverVersion=2.24.417431 (9aea000394714d2fbb20850021f6204f2256b9cf), userDataDir=C:\Users\Bishnu\AppData\Local\Temp\scoped_dir10480_1335}, takesHeapSnapshot=true, pageLoadStrategy=normal, databaseEnabled=false, handlesAlerts=true, hasTouchScreen=false, version=54.0.2840.99, platform=WIN8, browserConnectionEnabled=false, nativeEvents=true, acceptSslCerts=true, locationContextEnabled=true, webStorageEnabled=true, browserName=chrome, takesScreenshot=true, javascriptEnabled=true, cssSelectorsEnabled=true}]
Session ID: c1401a5ed7966a2f15d6570c612b2449
*** Element info: {Using=xpath, value=//td[p[img[#alt='Mercury Tours']]]/table/tbody/tr[0]/td[2]/a}
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.openqa.selenium.remote.ErrorHandler.createThrowable(ErrorHandler.java:216)
at org.openqa.selenium.remote.ErrorHandler.throwIfResponseFailed(ErrorHandler.java:168)
at org.openqa.selenium.remote.RemoteWebDriver.execute(RemoteWebDriver.java:635)
at org.openqa.selenium.remote.RemoteWebDriver.findElement(RemoteWebDriver.java:368)
at org.openqa.selenium.remote.RemoteWebDriver.findElementByXPath(RemoteWebDriver.java:473)
at org.openqa.selenium.By$ByXPath.findElement(By.java:361)
at org.openqa.selenium.remote.RemoteWebDriver.findElement(RemoteWebDriver.java:360)
at in.prolearn.newtours.pages.HomePage.VerifyTableLink(HomePage.java:20)
at in.prolearn.newtours.testcases.VerifyNavigationTable.verifyTableLink(VerifyNavigationTable.java:26)
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:100)
at org.testng.internal.Invoker.invokeMethod(Invoker.java:646)
at org.testng.internal.Invoker.invokeTestMethod(Invoker.java:811)
at org.testng.internal.Invoker.invokeTestMethods(Invoker.java:1137)
at org.testng.internal.TestMethodWorker.invokeTestMethods(TestMethodWorker.java:129)
at org.testng.internal.TestMethodWorker.run(TestMethodWorker.java:112)
at org.testng.TestRunner.privateRun(TestRunner.java:753)
at org.testng.TestRunner.run(TestRunner.java:607)
at org.testng.SuiteRunner.runTest(SuiteRunner.java:368)
at org.testng.SuiteRunner.runSequentially(SuiteRunner.java:363)
at org.testng.SuiteRunner.privateRun(SuiteRunner.java:321)
at org.testng.SuiteRunner.run(SuiteRunner.java:270)
at org.testng.SuiteRunnerWorker.runSuite(SuiteRunnerWorker.java:52)
at org.testng.SuiteRunnerWorker.run(SuiteRunnerWorker.java:86)
at org.testng.TestNG.runSuitesSequentially(TestNG.java:1284)
at org.testng.TestNG.runSuitesLocally(TestNG.java:1209)
at org.testng.TestNG.runSuites(TestNG.java:1124)
at org.testng.TestNG.run(TestNG.java:1096)
at org.testng.remote.AbstractRemoteTestNG.run(AbstractRemoteTestNG.java:132)
at org.testng.remote.RemoteTestNG.initAndRun(RemoteTestNG.java:236)
at org.testng.remote.RemoteTestNG.main(RemoteTestNG.java:81)
===============================================
Default test
Tests run: 1, Failures: 1, Skips: 0
===============================================
Any suggestion will help me to understand the tool in better way.
Thanks

Answer 1

To find each row of the table you can use this xpath: //tr[#class='mouseOut']
Since you are interested only on links("a" nodes), I suggest to write your code like this:
List<WebElement> linksInTable = driver.findElements(By.xpath("//tr[#class='mouseOut']//a"));
for(WebElement a : linksInTable){
// write what you want to do with each link
}
You might also encounter a problem because you are using "back" in your codes. Probably(you should test it to become sure) you should find web elements again each time you back to the main page. Something similar to:
for(int i=0;i<linksInTable.size();i++) {
String text = linksInTable[i].getText();
System.out.println(text);
linksInTable[i].click();
driver.navigate().back();
linksInTable = driver.findElements(By.xpath("//tr[#class='mouseOut']//a"));
}