Posted 7-Apr am OriginalGriff. Member 9-Apr pm. OriginalGriff 9-Apr pm. You're welcome! To fix a null-ref error you need to know 1.

What is actually "null" 2. Why that variable is not being set to something First: Check objfile. Length objfile is an object so could be null files is a property of the that's an array.

It's possible for this to be null Length is a scalar a number and can't be null So the code is trying to get the Length of files of objfile. If files is null you're trying to get objfile of "null". If files is null you're trying to get Length of null. So to protect your code you can do C. Posted 7-Apr am Chris Maunder Member 7-Apr pm. I am trying to learn rest to create a service that just gets pass a file and I have not used rest.

Add your solution here. OK Paste as. Treat my content as plain text, not as HTML. Existing Members Sign in to your account. This email is in use. Why dont you use a simple if.. Can you not have Null return a non-nullable string and call it as part of the assignment to variable? Sure, I thought about it. Null parameter, nameof parameter ; so I would have to make a variable for every parameter that I have.

This is the cleanest solution so far, but I wonder if there's a better option — Andreas Koder. How do you define "clean? While ultimately it depends on the circumstance, some might argue that's not very clean, especially when the alternative is a simple null check inside an if statement.

What does clean mean to you in this context? What makes a solution more or less clean than any other? Please try this out: docs. Add a comment. Active Oldest Votes. This means you don't need the! Null argument ; Think of the? Improve this answer. Drew Noakes Drew Noakes k gold badges silver badges bronze badges. Thanks Drew, this is really cleaner than the! I used to work with Resharper before, good to see that I can now use this attribute without it.

The short answer is to apply logical inference to the evidence provided by the stack trace, the source code, and the relevant API documentation. Let's illustrate with the simple example above first. We start by looking at the line that the stack trace has told us is where the NPE happened:.

In fact, there is only one way: it can only happen if foo has the value null. We then try to run the length method on null and Well, if that happened, the stack trace would look different. The first "at" line would say that the exception was thrown in some line in the java.

String class and line 4 of Test. So where did that null come from? In this case, it is obvious, and it is obvious what we need to do to fix it. Assign a non-null value to foo. OK, so let's try a slightly more tricky example. This will require some logical deduction. Next, we need to figure out which of those scenarios explains what is actually happening.

We will start by exploring the first one:. Where does bar come from? It is a parameter to the test method call, and if we look at how test was called, we can see that it comes from the foo static variable. In addition, we can see clearly that we initialized foo to a non-null value. That is sufficient to tentatively dismiss this explanation. In theory, something else could change foo to null So what about our second scenario?

Well, we can see that pos is 1 , so that means that foo[1] must be null. Is this possible? After that, we have not changed the contents of foo On Android, tracking down the immediate cause of an NPE is a bit simpler.

The exception message will typically tell you the compile time type of the null reference you are using and the method you were attempting to call when the NPE was thrown. This simplifies the process of pinpointing the immediate cause. But on the flipside, Android has some common platform-specific causes for NPEs. A very common is when getViewById unexpectedly returns a null. At this time you have just declared this object but not initialized or instantiated.

And whenever you try to access any property or method in it, it will throw NullPointerException which makes sense. A null pointer exception is thrown when an application attempts to use null in a case where an object is required. A null pointer is one that points to nowhere. When you dereference a pointer p , you say "give me the data at the location stored in "p". When p is a null pointer, the location stored in p is nowhere , you're saying "give me the data at the location 'nowhere'".

Obviously, it can't do this, so it throws a null pointer exception. A lot of explanations are already present to explain how it happens and how to fix it, but you should also follow best practices to avoid NullPointerException s at all. See also: A good list of best practices. I would add, very important, make a good use of the final modifier. Using the "final" modifier whenever applicable in Java. Because you are using student , but you forgot to initialize it like in the correct code shown below:.

If you are not giving the initialization section then the NullPointerException arise. In Java all the variables you declare are actually "references" to the objects or primitives and not the objects themselves. When you attempt to execute one object method, the reference asks the living object to execute that method.

But if the reference is referencing NULL nothing, zero, void, nada then there is no way the method gets executed. Then the runtime let you know this by throwing a NullPointerException. The object lives in the VM memory space and the only way to access it is using this references. Take this example:. This an important thing to know - when there are no more references to an object in the example above when reference and otherReference both point to null then the object is "unreachable".

There is no way we can work with it, so this object is ready to be garbage collected, and at some point, the VM will free the memory used by this object and will allocate another. Another occurrence of a NullPointerException occurs when one declares an object array, then immediately tries to dereference elements inside of it.

This particular NPE can be avoided if the comparison order is reversed; namely, use. All elements inside of an array are initialized to their common initial value ; for any type of object array, that means that all elements are null. You must initialize the elements in the array before accessing or dereferencing them. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Collectives on Stack Overflow. Learn more.

What is a NullPointerException, and how do I fix it? Ask Question. Asked 13 years, 2 months ago. Active 6 months ago.

Viewed 3. Active Oldest Votes. Note, it is possible to call the method like this: doSomething null ; In which case, obj is null , and the statement obj. Improve this answer. Silently ignoring invalid input and doing nothing in the method is extremely poor advice because it hides the problem. There are cases where this is confusing to debug. Is it possible to capture NPE thrown by a webapp from the web browser?

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