java.lang.NullPointerException for TestNG classes

Question

大家好，我在TestNG测试下面运行时出错。

public class BaseTest {
WebDriver driver;
@BeforeClass
public void LaunchBrowser() throws InterruptedException {
System.setProperty("webdriver.chrome.driver", "c://chromedriver.exe");
WebDriver driver = new ChromeDriver();
Thread.sleep(5000);
driver.get("https://stackoverflow.com/questions/26032149/selenium-testng-java-lang-nullpointerexception");
System.out.println("1");
driver.manage().window().maximize();
Thread.sleep(10000);
}
}

public class Homepage extends BaseTest 
{
WebDriver driver;
@Test
public void Discover() {
driver.findElement(By.xpath("/html/body/header/div/ol[1]/li/a")).click();
}
}

Error:
1
FAILED: Discover
java.lang.NullPointerException
at pages.Homepage.Discover(Homepage.java:16)


===============================================
Default test
Tests run: 1, Failures: 1, Skips: 0
===============================================

Answer 1

Null point exception occurring because of driver instance you are initiating begin differently than later.
Please create and use driver instance as a global variable 
static WebDriver driver;
-------------------------------------------------------------------------------------------
OR
Singleton is solution for null point exception in your test automation 
Create class and by using method you can use driver instance any where without any issue like null point 
import org.openqa.selenium.By;
import org.openqa.selenium.WebDriver;
import org.openqa.selenium.WebElement;
import org.openqa.selenium.chrome.ChromeDriver;
import org.openqa.selenium.chrome.ChromeOptions;
import org.openqa.selenium.support.ui.ExpectedConditions;
import org.openqa.selenium.support.ui.WebDriverWait;
import java.io.File;
import java.net.URISyntaxException;
import java.net.URL;
import java.nio.file.Paths;
public class TestApp {
private WebDriver driver;
private static TestApp myObj;
// public static WebDriver driver;
utils.PropertyFileReader property = new PropertyFileReader();
public static TestApp getInstance() {
if (myObj == null) {
myObj = new TestApp();
return myObj;
} else {
return myObj;
}
}
//get the selenium driver
public WebDriver getDriver()
{
return driver;
}
//when selenium opens the browsers it will automatically set the web driver
private void setDriver(WebDriver driver) {
this.driver = driver;
}
public static void setMyObj(TestApp myObj) {
TestApp.myObj = myObj;
}
public void openBrowser() {

//String chromeDriverPath = property.getProperty("config", "chrome.driver.path");
//String chromeDriverPath = property.getProperty("config", getChromeDriverFilePath());
System.setProperty("webdriver.chrome.driver", getChromeDriverFilePath());
ChromeOptions options = new ChromeOptions();
options.addArguments("--disable-notifications");
options.addArguments("disable-infobars");
driver = new ChromeDriver(options);
driver.manage().window().maximize();
try {
Thread.sleep(2000);
} catch (InterruptedException e) {
e.printStackTrace();
}
}

public void navigateToURL() {
String url =property.getProperty("config","url");
;
driver.get(url);
}
public void closeBrowser()
{
driver.quit();
}
public WebElement waitForElement(By locator, int timeout)
{
WebElement element = new WebDriverWait(TestApp.getInstance().getDriver(), timeout).until
(ExpectedConditions.presenceOfElementLocated(locator));
return element;
}
private String getChromeDriverFilePath()
{
// checking resources file for chrome driver in side main resources
URL res = getClass().getClassLoader().getResource("chromedriver.exe");
File file = null;
try {
file = Paths.get(res.toURI()).toFile();
} catch (URISyntaxException e) {
e.printStackTrace();
}
return file.getAbsolutePath();
}
}

//If you want call driver instance you can use following line 
**TestApp.getInstance().getDriver();**