In this post, we provide 3 fixes For The “exception in thread “main” java.lang.nullpointerexception” error.
As you can see, over on Twitter lots of people experience this frustrating error:
Exception in thread “main” java.lang.NullPointerException
[error] at org.apache.spark.rdd.RDD.(RDD.scala:79)Today’s a bad day :/
— Mario Pastorelli (@mapastr) December 1, 2015
JVM: Exception in thread “main” java.lang.NullPointerException
ME: Ah, no— i stan birds 🎵🎷🐓 (@_ardeej) November 7, 2015
cat ~/.bash_aliases
alias java = echo “Exception in thread “main” java.lang.NullPointerException.”— Жизнь Убогая (@grepdev) February 4, 2016
The exception in thread “main”java.lang.nullpointerexception error is probably the first exception you will encounter when using java. It is challenging to solve since the name has a pointer, yet Java does not support pointers such as multiple inheritances.
In this article, we include a comprehensive guide on what the error is and how you can fix it. In Java, a null value is allocated to an object as reference. It shows that the object is pointing to a piece of data that is unknown.
Any NullPointerExceptions error means that you are pointing to something non-existent. For instance, it is like searching for a 5th spot when there are only four spots. It comes about when you fail to fill your array of types. Therefore, it happens when the reference does not point to any location.
Failing to provide value to every index of your array will cause java to assign the array with default values. Java will give each array a default value – null. That is how a nullPointerExceptions comes about since Java does not allow null.
While it is a real nightmare for beginners, it is an error that is quite easy to solve. Before discussing various ways to address the error, it is essential to understand what it is, why the error comes about, and how to avoid it.
Quick Video Fix
What is the Exception in thread main java.lang.nullpointerexception Error?
The exception in thread “main”java.lang.nullpointerexception error is an error or an exception which comes about when you try to conduct an operation with an object that has a null value. The “main” part means that the exception is in the main thread.
Since it is a runtime exception, don’t expect to find a NullPointerException in a program. Being a runtime exception implies that the program ends at the runtime instead of at the compile time.
The error occurs when:
- You call on an instance method on any null object
- Calling the length of an array if the array is null
- You access or change any variable on a null object
- You throw a null when an exception is expecting to throw
- Changing or accessing slots of null similar to an array
- Trying to synchronize a null object or when you use null in a synchronized java block
Like we have mentioned earlier, null is a unique value that Java uses. It is essential when coding using some design patterns such as the Singleton pattern or Null Object pattern. That is why we need a null value.
A null object pattern acts as a surrogate for a missing object in a particular type; while the singleton pattern makes sure an instance of a class is created once. For example, declaring constructors to be private, and later forming a public method which returns a unique example of the entire type.
How to Fix the Exception in thread main java.lang.nullpointerexception java Error
To successfully solve a NullPointerException error in Java, you first need to identify the cause. It is quite easy to know the cause of the error. Just check the stack-trace of the exception. The stack-case will show you the exact line where the NPE has occurred.
Now, go to the line with the error and check for possible object operations. For instance, check an accessing field, throwing an exception, or calling methods. These will give you a hint on the null object.
After identifying the null object, we are halfway done. Understand why the object is invalid, and use the fixes below to solve the exception. Note that the second part of identifying the error may vary. The null may be from a factory or a thread.
Since there are different causes of the thread “main”java.lang.nullpointerexception, we cannot narrow down to one solution. However, these different fixes will help you avoid the error:
1st Fix: Hash Tables
Check your coding practice. If you are coding using a “Hash Table” class, a user from DevShed forums recommends the following:
- Instead of using HashTable, it’s better to use HashMap since the former is really old.
- Use a file with “Properties file format.”
Video Overview: Data Structures: Hash Tables
2nd Fix: Cryptography Extension Update
According to Symantec, if you encounter the problem when trying to run Java LiveUpdate ConfigEditor, it could be that the JCE- Java Cryptography Extension files need to be updated, or that the LiveUpdate Configuration file is unreadable. You can fix this by following these steps:
- Update your JCE policy files
- Delete LiveUpdate.conf files then create a new one
- Alternatively, you can also correct the Java Path
Note that this fix is only applicable to Windows 2003 and 2008.
Video Overview: Java Cryptography Architecture (JCA)
3rd Fix: Argument Method
Java Code Geeks recommend checking the argument of a method. Before performing the body of a method, it is essential to check the argument of the process for any null values. Only proceed with the execution after making sure there aren’t any null values.
Alternatively, you can send an “IllegalArguementException” and let the calling method know that something is wrong with previously passed arguments.
For instance:
public static int getLength(String s) {
if (s == null)
throw new IllegalArguementException (“The argument cannot be null”);
return s. length ( ) ;
}
Forum Feedback
To find more about the Exception in thread “main” java.lang.NullPointerException error and what troubles people have with it, we search through Java boards and forums. In general, users were interested in Exception in thread “main” java.lang.NullPointerException in Java, Selenium Eclipse, and Glassfish. They also wanted to know about Exception in thread main java.lang.NullPointrException at java.io.file. init (unknown source).
A computer user shared that he had been stuck for hours trying to solve the error message “Exception in thread “main” java.lang.NullPointerException” and that he was at his wit’s ends. He asked fellow JavaScript forum member for advice, and they said that he had made a common JavaScript mistake. They explained that he had a variable with a null value somewhere in his code and as a result, his method was throwing the NullPointerException.
Another forum poster remarks that you should learn to read your stack trace if you want to be able to find and fix your code mistakes. He points out that after Exception in thread “main” java.lang.NullPointerException, you will see java: (line number), which indicates in which line you should look for the error. Then you should go over that line and find the variable, which is null and fix it in the code.
A poster explains that NullPointerException occurs when you declare an object reference, but do not create the object. For example, if you create an array of a list, it doesn’t create the objects in the list. In other words, when you get NullPointerException, you’re trying to point something to something that has a null value and therefore, doesn’t exist. The individual reminds that you can’t call a method on null in JavaScript and that it’s important not to code around the error.
A person stated that if you have problems with NullPointerException you might want to start checking whether your variables are null before calling them.
- He mentioned that you could use @Nullable and @NotNull annotations.
- The user explains that @Nullable remind you that you have to check for NullPointerExpceptions when you call a method that could return a null value and when you’re differencing values that could be null. On the other hand, @NotNull declares that a method shouldn’t be null and that a variable cannot have a null value.
- The user pointed out that you have to think about two phases if you want to use an object.
- First, you have to declare it, and then you have to initialize it.
- If you do not initialize an object, then you’ll get the error Exception in thread “main” java.lang.NullPointerException.
- The poster recommends that when you’re in doubt to use print to see what’s inside your variable.
A forum user shared that the code he had written was throwing the error Exception in thread “main” java.lang.NullPointerException.
- He had checked his variable, and it wasn’t null, so he wasn’t sure how to proceed.
- When he got in touch with other JavaScript users, they pointed out that he had a problem with his manager array because he had forgotten to set one element in the array.
- As a result, one of his elements was null, which was triggering the NullPointerException.
Another Java expert says that in Java you don’t work with an array of objects. Instead, you deal with arrays of references to objects, and that’s why your references must point to an object before you call a method.
- He explains that NullPointerException is a Runtime Exception, a programmatic error. The poster points out that you can assign a null value to a reference, but you can’t use such a reference.
- He also remarks that you might get the NullPointerException if you’re trying to access or modify a variable with a null value.
A person observed that dealing with Null Pointers is easier if you use Java 8 or above because you can use Optional. It’s a new class in Java, which encapsulated an optional value and helps you avoid NullPointerExceptions altogether. On the other hand, some Java users are against using the Optional class because it doesn’t make your code more correct and they advise that you rely on the regular methods in Java to check for a null value.
A person also comments that you’ll get Exception in thread “main” java.lang.NullPointerException if you’re attempting to throw null as if it were a Throwable value or when you try to access/modify slots of nulls as if you’re trying to access/modify an array.
Conclusion
Remember that any NullPointerException comes about when you use a method on a variable which has not been initialized. Therefore, you can avoid the error by always setting a default value for every variable.
Other ways to avoid exception in thread main java.lang.nullpointerexception include using String.valueOf () method as opposed to toString () method. For instance, if an application code needs a string representation, use the static method instead of the toString method which throws an NPE.
Consider using the ternary operator which is in the form of Boolean expression seven value1: value2. Alternatively, you can avoid the error by creating methods which return to an empty collection, rather than those which return to null. Lastly, use Apache`s StringUtils class. Apache is a library which provides utilities for APU; for example, string manipulation methods.
Now that we have discussed what the error is, how it comes about, remedies to fix, and how to avoid it, you are in a better position to enjoy coding using Java.
