java.lang.NullPointerException while invoking driver.quit() within #AfterClass annotated method through Selenium WebDriver and JUnit - selenium

Question

I created a test using JUnit and in class #AfterClass I put the driver.quit () command to shut down the browser when the tests are finished but the eclipse displays the java.lang.NullPointerException message.
The test class populates several fields and then makes a query in the base, displays the result in the Eclipse console and should close the browser but displays the java.lang.NullPointerException message.
Below is the log and test script.
public class validarStatus {
private static WebDriver driver;
#Before
public void setUp() throws Exception {
System.setProperty("webdriver.chrome.driver", "E:\\Selenium\\chromedriver.exe");
}
#Test
public void validarStatusOs() throws InterruptedException {
WebDriver driver = new ChromeDriver();
driver.get("http://10.5.9.45/BKOMais_S86825EstrategiaBackOfficeClaroFixo");
driver.manage().window().maximize();
// Logar BkoMais
driver.findElement(By.id("matricula_I")).sendKeys("844502");
driver.findElement(By.id("senha_I")).sendKeys("Pw34Jdt#*");
driver.findElement(By.id("bt_entrar")).click();
// Logar na Estratégia
driver.findElement(By.id("mn_backoffice")).click();
driver.findElement(By.id("mn_bkoffice_prod_203")).click();// Produto
driver.findElement(By.id("mn_bkoffice_est_57")).click();// Estratégia
// Selecionado a atividade
Select atividade = new Select(driver.findElement(By.id("cboAtividade")));
atividade.selectByIndex(3);
// Registro >> Novo
Thread.sleep(500);
driver.findElement(By.id("mn_registro")).click();
driver.findElement(By.id("mn_novo_caso")).click();
driver.manage().timeouts().implicitlyWait(5, TimeUnit.SECONDS);
// Cod Os Estratégia VREL
String CodOs = driver.findElement(By.xpath("//*[#id=\"content\"]/div[1]/fieldset[1]/div[2]/div[3]/span"))
.getText();
// Campo Análise de Contrato
Select analiseContrato = new Select(driver.findElement(By.id("cboMotivo")));
analiseContrato.selectByIndex(5);
try {
// Campo Ação
Select acao = new Select(driver.findElement(By.id("cboSubMotivo")));
acao.selectByIndex(3);
// Status
WebDriverWait wait = new WebDriverWait(driver, 10);
WebElement ele = wait.until(ExpectedConditions.presenceOfElementLocated(By.id("cboStatus")));
String valorStatus = ele.getText();
// driver.findElement(By.id("cboStatus")).getText();
Assert.assertEquals(" R", valorStatus);
// Chamado
driver.findElement(By.id("txtChamado")).sendKeys("Teste");
// Observação
driver.findElement(By.id("txtObservacao")).sendKeys("Teste 07/06/2018");
// Botão Salvar
driver.findElement(By.id("btnSalvar")).click();
} catch (StaleElementReferenceException e) {
// Campo Ação
Select acao = new Select(driver.findElement(By.id("cboSubMotivo")));
acao.selectByIndex(3);
// Status
WebDriverWait wait = new WebDriverWait(driver, 10);
WebElement ele = wait.until(ExpectedConditions.presenceOfElementLocated(By.id("cboStatus")));
String valorStatus = ele.getText();
// String valorStatus = driver.findElement(By.id("cboStatus")).getText();
Assert.assertEquals(" R", valorStatus);
// Chamado
driver.findElement(By.id("txtChamado")).sendKeys("Teste");
// Observação
driver.findElement(By.id("txtObservacao")).sendKeys("Teste 07/06/2018");
// Botão Salvar
driver.findElement(By.id("btnSalvar")).click();
} catch (Exception e) {
// Campo Ação
Select acao = new Select(driver.findElement(By.id("cboSubMotivo")));
acao.selectByIndex(3);
// Status
String valorStatus = driver.findElement(By.id("cboStatus")).getText();
Assert.assertEquals(" R", valorStatus);
// Chamado
driver.findElement(By.id("txtChamado")).sendKeys("Teste");
// Observação
driver.findElement(By.id("txtObservacao")).sendKeys("Teste 07/06/2018");
// Botão Salvar
driver.findElement(By.id("btnSalvar")).click();
}
// Select na base para validar o status da NU_OS
ValidarEstrategiaPage p = new ValidarEstrategiaPage();
p.returnNuOs(CodOs);
// Saindo do Bko+
Thread.sleep(1000);
driver.findElement(By.linkText("Sair")).click();
}
#AfterClass
public static void closeBrowser() {
driver.quit();
}}

Answer 1

You clearly defined your WebDriver object as local variable inside the method:
#Test
public void validarStatusOs() throws InterruptedException {
WebDriver driver = new ChromeDriver();
In order for both the 'After' and 'Test' methods to interact with the global variable, change to:
#Test
public void validarStatusOs() throws InterruptedException {
driver = new ChromeDriver();
And BTW, change your class name from 'validarStatus' to 'ValidarStatus'. Starting a class name in upper case letter is a major best practice in Java.

Answer 2

As per your code block you have defined a global instance of WebDriver as:
private static WebDriver driver;
Within validarStatusOs() method you have initialized another local instance of WebDriver as:
WebDriver driver = new ChromeDriver();
When the control of your program comes out of validarStatusOs() method, the local instance of WebDriver is no more accessible.
So, when the control of your program enters within closeBrowser() method it tries to use the global instance of WebDriver and throws java.lang.NullPointerException.
Solution
As you have declared a global instance of WebDriver, use the same instance throughout your program. So you need to change the line:
WebDriver driver = new ChromeDriver();
To:
driver = new ChromeDriver();