Null Pointer Exception using TestNG - selenium-webdriver

Question

I am trying to automate and have integrated Selenium with Appium and I am using Eclipse with TestNG for execution.
Now within a project I have a package with two classes; the first class is for login into the App and the second class is for logout
First class code -
package com.gma.test;
import java.io.File;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.concurrent.TimeUnit;
import org.openqa.selenium.By;
import org.openqa.selenium.remote.DesiredCapabilities;
import org.testng.annotations.BeforeClass;
import org.testng.annotations.BeforeSuite;
import org.testng.annotations.Test;
import io.appium.java_client.AppiumDriver;
import io.appium.java_client.android.AndroidDriver;
import java.text.SimpleDateFormat;
import java.util.Calendar;
public class LoginApp {
public AppiumDriver driver;
#BeforeSuite
public void beforeMethod() throws InterruptedException {
File app = new File("C:\\Users\\mc30058\\Downloads\\gma-QA-RELEASE-QRCode-07022015_v4.5.4028.apk");
DesiredCapabilities capabilities = new DesiredCapabilities();
capabilities.setCapability("deviceName","Android Emulator");
capabilities.setCapability("platformVersion", "4.4");
capabilities.setCapability("app", app.getAbsolutePath());
try {
driver = new AndroidDriver(new URL("http://127.0.0.1:4723/wd/hub"), capabilities);
} catch (MalformedURLException e) {
e.printStackTrace();
}
driver.manage().timeouts().implicitlyWait(100, TimeUnit.SECONDS);
driver.findElement(By.xpath("//android.widget.Button[#resource-id='com.mcdonalds.app:id/button_choose_closest']")).click();
driver.findElement(By.xpath("//android.widget.Button[#text='Continue']")).click();
driver.findElement(By.xpath("//android.widget.Button[#text='OK']")).click();
}
#Test (priority=1)
public void Login() {
driver.manage().timeouts().implicitlyWait(100, TimeUnit.SECONDS);
driver.findElement(By.xpath("//android.widget.TextView[#text='Sign In']")).click();
driver.findElement(By.xpath("//android.widget.EditText[#resource-id='com.mcdonalds.app:id/signin_edittext_email']")).sendKeys("anuj.shrivastava#us.mcd.com");
driver.findElement(By.xpath("//android.widget.EditText[#resource-id='com.mcdonalds.app:id/signin_edittext_password']")).sendKeys("Anujtest2");
currentTime();
driver.findElement(By.xpath("//android.widget.Button[#text='Sign In']")).click();
driver.manage().timeouts().implicitlyWait(100, TimeUnit.SECONDS);
driver.findElement(By.xpath("//android.widget.Button[#text='Yeah, count me in!']")).isDisplayed();
currentTime();
driver.findElement(By.xpath("//android.widget.Button[#text='No, thanks. I like to be out of the loop']")).click();
}
private void currentTime() {
Calendar cal = Calendar.getInstance();
SimpleDateFormat sdf = new SimpleDateFormat("HH:mm:ss");
System.out.println( sdf.format(cal.getTime()) );
}
}
Second class code:
package com.gma.test;
import java.io.File;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.concurrent.TimeUnit;
import org.openqa.selenium.By;
import org.openqa.selenium.remote.DesiredCapabilities;
import org.testng.annotations.BeforeClass;
import org.testng.annotations.Test;
import io.appium.java_client.AppiumDriver;
import io.appium.java_client.android.AndroidDriver;
import java.text.SimpleDateFormat;
import java.util.Calendar;
public class Logout {
public AppiumDriver driver;
#Test (priority=3)
public void LogoutApp() {
driver.findElement(By.xpath("//android.widget.TextView[#content-desc='Navigation Button']")).click();
driver.findElement(By.xpath("//android.widget.TextView[#text='Sign Out']")).click();
driver.findElement(By.xpath("//android.widget.Button[#text='Sign Out']")).click();
}
}
Contents from Testng.xml
<suite name = "GMA Automation">
<test name = "GMA Automation">
<classes>
<class name = "com.gma.test.LoginApp"/>
<class name = "com.gma.test.Logout"/>
</classes>
</test>
</suite>
I receive Null Pointer exception after execution of first class. Appium server stops saying no more commands received. Please help.

Answer 1

You are getting NPE b'coz you have declared one more driver reference public AppiumDriver driver; in your Logout class.
And you are using this driver reference without instantiation.

Answer 2

In logout class you forget to instantiate your AppiumDriver driver.
try this:
public AppiumDriver driver;
driver = new AndroidDriver();