I'm adding model to Jtable. Error message is showing NullPointerException. And I can't find the object that is null
What is a NullPointerException, and how do I fix it?
Why did Snape need to appear well-informed? "You will have to give Voldemort the correct date of Harry's departure from his aunt and uncle's," said Dumbledore. "Not to do so will raise suspicion, when Voldemort believes you so well informed."   Snape had just killed Dumbledore, why would it raise suspicion about the movements of Harry's departure? it would seem likely that once Dumbledore died at the hands of Snape the Order would surely have changed any plans they would have had in place for Harry's exit from Privet Drive? Problem: Evaluate $$ L=\displaystyle \lim_{n \to \infty} \frac{1}{n} \sum_{k=1}^{n} \left(  \left\lfloor \frac{2n}{k} \right\rfloor -2\left\lfloor \frac{n}{k}\right \rfloor \right).$$  Please help me with this one.  I tried using the sandwich theorem by first constructing the following  $$ 2 \geq \left\lfloor \frac{2n}{k} \right\rfloor -2\left\lfloor \frac{n}{k} \right\rfloor \geq -1 $$ and then summing over. But the limit of the two bounds are different so sandwich theorem doesn't help!. Is it possible to construct sharper bounds?  Also I observed that if we ignore question of continuity, etc. then we can write,  $L= \displaystyle \int ^{1}_{0}\left\lfloor \frac{2}{x} \right\rfloor -2\left\lfloor \frac{1}{x} \right\rfloor dx$  Now I am able to compute the above integral. But is the above process correct? If then how can make it rigorous? Or if any other approach is possible, please tell. Why is it called John Dies at the End? The 2012 adaptation of David Wong's "John Dies at the End" ends without John dying at the end at all. While the core of the film espouses the belief that time is not linear, the word "end" suggests there is a beginning and an end to things.  Why is the movie called John Dies at the End? Why "hide" Luke from his father somewhere Anakin knows? Selenium + FF : How to fix error, Unable to connect to host 127.0.0.1 on port 7055 after 45000 ms? How to make specifics apps password protected even after passcode in iPhone? Unresolved external symbol on static class members Very simply put:  I have a class that consists mostly of static public members, so I can group similar functions together that still have to be called from other classes/functions.  Anyway, I have defined two static unsigned char variables in my class public scope, when I try to modify these values in the same class' constructor, I am getting an "unresolved external symbol" error at compilation.  class test  { public:     static unsigned char X;     static unsigned char Y;      ...      test(); };  test::test()  {     X = 1;     Y = 2; }   I'm new to C++ so go easy on me. Why can't I do this? What's the legal way to stream music online? It's really hard getting a definite answer on this so I'm going to ask it here. Is there a legal way to stream new music on a website without getting artist consent first. There seems to be a lot of popular sites like hotnewhiphop.com doing this that are hosting from both the US and Canada so I'm guessing there is a grey area that allows it. For the record I don't allow downloads of the music and simply stream each song in a player. Distribution of $-\log X$ if $X$ is uniform. How do I copy a property from an active object to selected objects? I have been using the Copy Attributes add-on to copy some properties from active object to selected objects. This add-on is not enabled by default and must be explicitly enabled. But its a very useful workflow enhancing tool.    There is a limitation though. Not all properties can be copied and even those that can be copied are copied in groups (Its hard-coded in to the add-on).  My question is if there is a built-in feature or any another other way to copy any property from the active object to the selected objects? Make Chrome always execute with flags, for eg., directly opening an HTML file I want to run Chrome with a given set of flags, always  I created a shortcut and added the flag to it in the following way, so my target of the shortcut says:  C:\&lt;application-path&gt;\chrome.exe --user-data-dir=D:\Chrome   But when I double click an HTML file, or if any other application triggers Chrome, it looses the flag value. The result - A new chrome window opens with Default profile directory.  I want to make the flag permanent, so that its active irrespective of however Chrome executes.  I tried changing the following registry key:  HKEY_CLASSES_ROOT\ChromeHTML\shell\open\command   It was this earlier:  "C:\&lt;application-path&gt;\chrome.exe" -- "%1"    I changed to following attempts which did not work:  1. "C:\&lt;application-path&gt;\chrome.exe" -- "%1" --user-data-dir=D:\Chrome 2. "C:\&lt;application-path&gt;\chrome.exe" -- "%1" -- "user-data-dir=D:\Chrome" 3. "C:\&lt;application-path&gt;\chrome.exe" -- "%1 user-data-dir=D:\Chrome"   Conclusively, when I try to open a link from any application, it doesn't open in my current Chrome as a new tab, rather opens a new Chrome window with no plugins and extensions since its from other directory.  Why I have changed my default directory? - because the OS drive was getting low on memory due to heave Chrome caches and apps. Plot $|z - i| + |z + i| = 16$ on the complex plane I have a Storex eZee Tab 702 tablet. My Google Play Store was working very well until a few weeks ago, when it started saying,     Error while retrieving information from server [DF-DFERH-01]   I tried to clear the cache, clear the data, force stop, and downloading another Google Play Store, but I'm still having the same problem.  How can I fix this issue? Recently I found a claim saying that  $$  \int_0^\infty \left( \frac{\sin ax}{x}\right)\left( \frac{\sin bx}{x}\right) \mathrm{d}x= \pi \min(a,b)/2  $$ from what I can see this seems to be true. I already know that $\int_{0}^\infty \operatorname{sinc}xy\,\mathrm{d}y = \pi/2$, and so independant of $y$. My suspicion is that this is closely related to the integral above.   Can someone give me some suggestions for evaluating the integral above? Also are there any generalizations for the integral? Eg $$ \int_{0}^{\infty} \left( \prod_{k=1}^N \frac{\sin (a_k \cdot x)}{x} \right) \,\mathrm{d}x $$ Where $a_k, \cdots, a_N$ are arbitrary positive constants. It seems related to the , but there are some subtle differences. In FreeBSD and also in Linux, how can I get the numerical chmod value of a file? For example, 644 instead of -rw-r--r--? I need an automatic way for a Bash script. General formula for evaluating integrals of the form $\displaystyle\int_0^\infty x^ae^{-bx}dx$ What are the Windows A: and B: drives used for? In Windows you have a C-drive. Everything labeled beyond that is with the following letter.   So your second drive is D, your DVD is E and if you put in a USB stick it becomes F and the following drive G. And so on and so forth.  But then, what and where are A and B-drives? Why are POSIX Find Parameters Different from Other Program styles? Is it okay to board only the second flight of a return ticket? The return ticket is much cheaper than buying one way I was browsing flight price at Singapore Airlines website, and a one-way flight from SIN to SFO cost this much:    That's quite expensive. I tried browsing around and found that a return flight from SFO to SIN and back to SFO cost much cheaper:    It's really weird because the second ticket includes the exact same flight that cost 1900+, but it's almost half the price. The reason for this counter-intuitive situation is explained in the answers this question   If I am located in Singapore and my intention is to fly one-way to SFO, is it safe to book the flight in the second picture and only board SFO-SIN leg? Will they deny me because I miss the SIN-SFO flight? Automorphism group of direct product of groups I was working on a problem in group theory, which asks about the automorphism group of a direct product of groups.  Okay, so I know that if $G,H$ are two groups whose orders are relatively prime, then $\operatorname{Aut}(G\times H)\cong\operatorname{Aut}(G)\times \operatorname{Aut}(H)$.  I also know that if $G,H$ are abelian and simple and isomorphic, then $\operatorname{Aut}(G\times H)\cong \operatorname{GL}_2(\mathbf{Z}_p)$ where $p$ is the order of $G$.  What I don't know is the following: what if $G,H$ are simple, yet not abelian? Let us for now focus on a more restricted case where $G\cong H$, in particular, $G=H$. What can we say about the group $\operatorname{Aut}(G\times H)$? (I heard something about this group being related to what is called "wreath product", which I do not know...)  Thanks bunch in advance!