a sample code is something like this.
String s = null ;
if (today is monday){
s = "Monday" ;
else if (today is tuesday){
s = "Tuesday" ;
}
System.out.println(s.length()); //Will throw a null pointer if today is not monday or tuesday.
a sample code is something like this.
String s = null ;
if (today is monday){
s = "Monday" ;
else if (today is tuesday){
s = "Tuesday" ;
}
System.out.println(s.length()); //Will throw a null pointer if today is not monday or tuesday.
It says here
NP: Possible null pointer dereference (NP_NULL_ON_SOME_PATH)
There is a branch of statement that, if executed, guarantees that a null value will be dereferenced, which would generate a NullPointerException when the code is executed. Of course, the problem might be that the branch or statement is infeasible and that the null pointer exception can't ever be executed; deciding that is beyond the ability of FindBugs.
If you would have posted some code it would be easier to answer.
EDIT I don't see a lot of documentation but here is one example! Hope this helps!
sessionTarget = jsch.getSession(backupUser, backupHost, backupPort); Here in this line, getSession() method can throw an Exception, and hence the variables sessionTarget and channelTarget will be null, and in the finally block, you are accessing those variables, which may cause null pointer exception.
To avoid this, in the finally block check for null before accessing the variable.
finally {
if (channelTarget != null) {
channelTarget.exit();
channelTarget.disconnect();
}
if (sessionTarget != null ) {
sessionTarget.disconnect();
}
}
That means: what if your channelTarget and sessionTarget are null in your finally block? Check them for null to avoid the warning.
If it's really pointing to that line, it looks like a bug in the code review tool to me.
As it's a local variable, there's no chance that it'll be changed by anything else between the nullity check and the size() call - so there's no way it'll throw a NullPointerException.
There is a branch of statement that, if executed, guarantees that a null value will be dereferenced, which would generate a NullPointerException when the code is executed. Of course, the problem might be that the branch or statement is infeasible and that the NullPointerException cannot ever be thrown. Deciding that is beyond the ability of FindBugs.
So if you throw an exception on your first line, your variable will not be assigned to a File, and will retain it's previous value (null if not formerly assigned). Your exception is caught, and then you continue to use that unassigned variable. Hence the warning. See the commented code below.
try {
fileFile = // exception thrown. Variable not assigned
} catch (URISyntaxException | NullPointerException e) {
// exception caught
}
finally {
// unassigned variable used here...
if (fileFile.getPath()!= null){
strPathName = fileFile.getPath();
}
if (fileFile.getName() != null){
strFileName = fileFile.getName();
}
}
I would rather scope and use the variable within the try block, if at all practical. In your finally block, you need to be as careful as you can, since you could have come to it from most anywhere in your try block.
As an aside, this:
Main.class.getProtectionDomain().getCodeSource().getLocation().toURI();
will cause you enormous problems if you do get an NPE. Which of the above resolved to null ? I would perhaps be more explicit, such that you can check for nulls from each invocation and unambiguously determine which invocation gave you a null. Tiresome ? Unfortunately so.
A "null pointer dereference" is computer speak for trying to call a method on a null value. It's a little more complicated, but you said you were a novice, so I wanted to keep it simple.
Let's see an example:
String s = null;
s = s.toUpperCase();
This is a simple example of what a null pointer dereference is. s is a null reference (its value is null), when we derefrence is (get the value of it) we have null, when we call toUpperCase() on null, something goes horribly wrong because null doesn't have any methods, at all! Java throws a NullPointerException to be specific.
Now, back to your code, because fileFile is assigned in the try-block I assume it was set to null before it to avoid Java yelling about an uninitialized variable. (This is all fine and correct.) In this try-block, if any of the exceptions for your catch-block occur it will stop the try-block (meaning fileFile will not get a new value, meaning it will still be null).
Now you'll notice the warning is possible null pointer dereference. That means it won't necessarily be null, but could be! (In my above example, it's always a null pointer dereference for comparison.) Specifically, if the catch catches an exception it will be null.
To be clear, the issue is this: fileFile.getPath(). It's like saying it might be null.getPath(), gross. It looks like you were trying to avoid the null pointer issue, what you should have done was if (fileFile != null) { instead. Then inside of the if do what you want.
Also, because it seems like you included it to avoid this warning, I would seriously remove the NullPointerException from the catch-block. That's not helping you avoid the warning. If you want me to explain more why it's bad you can leave a comment and I will, otherwise just take my word for it, it's not helping you.