How to remove null pointer exception while calling different class method into main class?

Question

I tried many times to remove null pointer exception while calling a different class method into main class.

public class Demo {
    
    WebDriver driver;
    
    int x;
    public static void main(String[] args) throws InterruptedException {
    System.setProperty("webdriver.chrome.driver", "D:\\Software\\chromedriver.exe");
    WebDriver driver = new ChromeDriver();
    driver.manage().timeouts().pageLoadTimeout(60, TimeUnit.SECONDS);
    driver.manage().timeouts().implicitlyWait(60, TimeUnit.SECONDS);
    String Url = "https://www.worldometers.info/coronavirus/#countries";
    driver.get(Url);
    Thread.sleep(5000);
        
    Demo_Methods DM = new Demo_Methods(); **(Demo.java:31)**
    DM.addCountryName();
    System.out.println(DM.Countries);
}

Here is the another class which I want to call in main class

public class Demo_Methods
{
    public WebDriver driver;
    public  List<String> Countries = new ArrayList<String>();
    public  List<String> TotalCases = new ArrayList<String>();
    public  List<String> NewCases = new ArrayList<String>();
    public  List<String> TotalDeaths = new ArrayList<String>();

    public void addCountryName() throws InterruptedException
    {
        //List<WebElement> Count = driver.findElements(By.xpath(("//table[@id='main_table_countries_today']//tbody[1]//tr")));
        for(int z=1;z<12;z++)
        {
            List<WebElement> CountryName = driver.findElements(By.xpath(("//table[@id='main_table_countries_today']//tbody[1]//tr["+z+"]//td")));
            //System.out.println(CountryName.size());
            Thread.sleep(5000);
            for(int x=2;x<6;x++)
            {
                if(CountryName.get(1).getText().isEmpty())
                {
                    break;
                    
                }
                else {
                    WebElement Country=driver.findElement(By.xpath(("//table[@id='main_table_countries_today']//tbody[1]//tr["+x+"]//td[2]")));
                    {
                        if(Country.getText().isEmpty())
                        {
                            Countries.add("000");
                            break;
                        }
                        else {
                            Countries.add(Country.getText());
                            }
                        }
                    WebElement TotalCase =driver.findElement(By.xpath(("//table[@id='main_table_countries_today']//tbody[1]//tr["+x+"]//td[3]")));
                    if(TotalCase.getText().isEmpty())
                    {
                        TotalCases.add("000"); 
                        break;
                    }
                    else {
                        TotalCases.add(TotalCase.getText());
                    }
                }
                WebElement NewCase =driver.findElement(By.xpath(("//table[@id='main_table_countries_today']//tbody[1]//tr["+x+"]//td[4]")));
                if(NewCase.getText().isEmpty())
                {
                    NewCases.add("000");
                    break;
                }
                else {
                    NewCases.add(NewCase.getText());
                }
                
                WebElement TotalDeath =driver.findElement(By.xpath(("//table[@id='main_table_countries_today']//tbody[1]//tr["+x+"]//td[5]")));
                if(TotalDeath.getText().isEmpty())
                {
                    TotalDeaths.add("000");
                    break;
                }
                else {
                    TotalDeaths.add(TotalDeath.getText());
                }
            }
        }
    }
}

Exception in thread "main" java.lang.NullPointerException
  at myInfoModule.Demo_Methods.addCountryName(Demo_Methods.java:23)
  at myInfoModule.Demo.main(Demo.java:31)

I tried this call concept of class in the main class for different practices but I faced the same issues again and again. I'm sure that I had missed some conceptual thing to attach in my code.

If you can post the stacktraces that would help, but generally if you're trying to catch NPE's, you're better off testing for null/using an ```Optional```, and throwing a different exception or returning a different error. Printing out "NullPointerException thrown!" doesn't really help. You're masking bad data and losing everything about the exception. — Gryphon, Aug 30 '20 at 06:23
Does this answer your question? [What is a NullPointerException, and how do I fix it?](https://stackoverflow.com/questions/218384/what-is-a-nullpointerexception-and-how-do-i-fix-it) — Thiyagu, Aug 30 '20 at 06:27
Demo methods doesn't know what your webdriver value is. Create a constrictor and pass in webdriver when you create. — RichEdwards, Aug 30 '20 at 07:22

score 0 · Answer 1 · answered Aug 30 '20 at 07:30

Null Pointer means you're trying to access a something which has no (a null) value - basically meaning it's not been instantiated or set.

At the moment you do this to create your webdriver in your Demo class:

WebDriver driver = new ChromeDriver();

Then, when you do this:

Demo_Methods DM = new Demo_Methods(); **(Demo.java:31)**
DM.addCountryName();

You're creating a new instance of Demo_Methods - but this has NO idea what your VALUE of webdriver is.

The simple solution is to pass and set webdrvier in your demo_methods when you create demo methods with a constructor.

A constructor is special method that is called when you create an instance the class.

Add this to your Demo_Methods:

public Demo_Methods(WebDriver _driver){
driver = _driver;
}

This means, when you create demo_methods, you pass in your webdriver to demo_methods knows the value of it.

Then, you now create your instance like this:

    Demo_Methods DM = new Demo_Methods(driver); 
    DM.addCountryName();

How to remove null pointer exception while calling different class method into main class?

1 Answers1