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My test automation returns NullPointerException.

What are Null Pointer Exceptions (java.lang.NullPointerException) and what causes them?

What methods/tools can be used to determine the cause so that you stop the exception from causing the program to terminate prematurely?

You may think this too generic and lacks details but similar question exists on Stackoverflow and given the number of votes it appears helpful to others.

Also, we have plenty of questions about this topic on this site:

While I understand that many of our posters here have little coding experience (see similar discussion on SQA Meta), I also notice that such questions are very specific to the author code base and environment. This makes answers to such questions very specific and thus hard to generilize to other setups.

With such a generic question I am looking for answers that will provide basic troubleshooting steps that can be used in many custom setups.

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    I appreciate the effort to write a reference question. Perhaps you could make it Community Wiki to prevent the reference being downvoted to oblivion or closed?
    – Kate Paulk
    May 8, 2023 at 12:18
  • @KatePaulk Thanks for reading my intentions. I turned my answer into a community wiki. Not sure if I can do the same with my question.
    – dzieciou
    May 8, 2023 at 16:16

3 Answers 3

1

It can be frustrating to encounter NullPointerException, but there are a few steps you can take to identify and fix the issue:

1 Look at the stack trace in the console. It will tell you which line of code is causing the issue. Look for the line that starts with "Caused by: java.lang.NullPointerException" and examine the code on that line.

2 Once you have identified the line of code causing the issue, check to see if any variables or objects being used in that line are null. You can use debugger in your IDE or add print statements to check the values of that variables.

3 If you find a null value, you will need to fix it. This might involve initializing the variable or object properly, checking for null values before using them, or changing the logic of your code.

4 After you have made changes to your code, be sure to test it thoroughly to ensure that the NullPointerException has been resolved.

Here is an example of how you might use these steps to identify and fix a NullPointerException:

public class MyClass {
    private String myString;

    public void doSomething() {
        int length = myString.length(); // This line throws a NullPointerException
        System.out.println("The length of myString is " + length);
    }

    public static void main(String[] args) {
        MyClass myClass = new MyClass();
        myClass.doSomething();
    }
}

In this example, the NullPointerException occurs because the myString variable has not been initialized. To fix this issue, we need to add an initialization statement for myString.

public class MyClass {
    private String myString = "";

    public void doSomething() {
        int length = myString.length();
        System.out.println("The length of myString is " + length);
    }

    public static void main(String[] args) {
        MyClass myClass = new MyClass();
        myClass.doSomething();
    }
}

By initializing myString to an empty string, we prevent the NullPointerException from occurring.

2

A NullPointerException generally means there's a variable somewhere in your code that hasn't been initialized and you are trying to perform operations on null.

In test automation code, this often happens when an element is not found, and a fluent coding style is used, such as in the pseudocode below:

driver.findElement(By.Id("myElement")).Click();

If driver.findElement() fails to find myElement, the value will be null, which means that the attempt to click actually resolved to:

null.Click();

Obviously this can't work, so a null pointer exception is thrown.

1

A NullPointerException (often abbreviated as NPE) is a common runtime error in programming languages like Java, C++, and others. It occurs when a program attempts to access or manipulate an object that has not been initialized or is set to

"null." In simple terms, it means that the program is trying to perform an operation on an object that doesn't exist or has not been assigned any value.

For Example:

#include <iostream>

int main() {
    int* ptr = nullptr; // Initializing a pointer to Null
    
    if (ptr != nullptr) {
        // Attempting to access the value of the pointer, which is Null
        std::cout << "Value of ptr: " << *ptr << std::endl;
    } else {
        std::cout << "Pointer is Null." << std::endl;
    }

    return 0;
}

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