When I run the app, the build is successful but the app is crashing. Please help me with that. Below is the error I'm receiving in the run tab
What is a NullPointerException, and how do I fix it?
How to check whether a string contains a substring in JavaScript? Counter with 4 flip flops jk synchronous from 3 to 13! I have to create a counter with 4 flip flops jk synchronous. The counter shall count in this order: 3 to 13 and then to 3 to 13 and so on..  I have to use logisim simulator.   Ok. So i think its solved. I realized that the circuit needs to start at 0 ou 1 and stabilize after the 13 and then it goes to 3. Thanks for your help.  Hope this will help for somebody else too.  Thank you all for your help! Change desktop background to a solid color (e.g. pitch black) in GNOME 3 I just installed Ubuntu 16.04 with GNOME and I would like to set the background color to black. If I right click in the background I can select a wallpaper or a photo or a color. But there are only a few colors available. How can I open a palette and select the #000000 color ? What are all the correct answers to the Squirrel's questions, and what is the reward when I get them all correct? I encountered The Squirrel at "A tree."              |   |                                                                         |   |                     "   Hello, I'm The                        |             |                        Squirrel. I can                        |             |                      provide you candies,                     |             |                      and lots of things.                                    |                      I know how much you                                    |        _.-'''-,      love candies. But I                                    |      .'        `\     feel alone in this                                    |     /           /          forest.       "                         |        |    /      .--^_^                                                   |        |    |     /  C ,,\                                                           |    |    |   \  _.)                           ___                            |     \   |   /  \                   ____.----'.-'                            |      '-, \./ \)\)               .-' --  __.-'                   |            \        `-/   );/           ___/  - _.-'                        |             \_________''--'-'________.-' --    /                            |              -   --        -  -     -     __.-'                                              -    --    -     --   --  /                                                 _________________________.-'                                 He asks you some questions. What are the correct answers, and what is the reward for getting them correct? static variables in an inlined function I have a function that is declared and defined in a header file. This is a problem all by itself. When that function is not inlined, every translation unit that uses that header gets a copy of the function, and when they are linked together there are duplicated. I "fixed" that by making the function inline, but I'm afraid that this is a fragile solution because as far as I know, the compiler doesn't guarantee inlining, even when you specify the "inline" keyword. If this is not true, please correct me.  Anyways, the real question is, what happens to static variables inside this function? How many copies do I end up with? Linear Discriminant Analysis for $p=1$ I'm studying 'Introduction to Statistical Learning' by James, Witten, Hastie, Tibshirani.   In page 139, of their book, they began by introducing Bayes' Theorem $p_k(X)=P(Y=k|X=x) = \dfrac{\pi_kf_k(x)}{\sum_{l=1}^k \pi_l f_l(x)}$. $\pi$ is not mathematical constant, but denotes the prior probability. Nothing is strange in this equation.   The book claims that it wants to obtain an estimate for $f_k(x)$ that it can plug into the equation given above. To estimate $f_k(x)$, it assumes that is normal. In the one dimensional setting, $f_k(x)=\dfrac{1}{\sqrt{2\pi}\sigma}\exp(-\dfrac{1}{2\sigma^2}(x-\mu_k)^2)$, where $\mu_k$ and $\sigma^2_k$ are the mean and variance for the $k$th class. It is assumed that $\sigma^2_1 = \sigma^2_2 = \cdots = \sigma^2_K$. (I began to get confused from the last statement.)   Plugging $f_k$ into $p_x$, you have this quite messy equation (1) :   $$p_x(k)=\dfrac{\pi_k \frac{1}{\sqrt{2\pi}\sigma}\exp(-\frac{1}{2\sigma^2}(x-\mu_k)^2)}{\sum_{l=1}^K \pi_l \frac{1}{\sqrt{2\pi}\sigma}\exp(-\frac{1}{2\sigma^2}(x-\mu_l)^2)}. $$  Again, no surprises here since it is just substitution.     The Bayes' Classifier involves assigning an observation to the class for which equation (1) is the largest. Taking the log of Equation (1) and rearranging terms, it is not hard to show that this is equivalent to assigning the observation to the class for which the following is the largest:  $$\delta_k(x)=x \cdot \dfrac{\mu_k}{\sigma^2} - \dfrac{\mu_k^2}{2\sigma^2} + \log(\pi_k) $$  Question: I do not understand where this came from, and what it means. I tried doing the log of equation and it doesn't become this. Are we taking the derivative somewhere here, since this is the largest observation? I have video tutorials that I want to show in my presentation with beamer class. I don't want the video files get embedded to the PDF because they will make the PDF size very very huge.  If you know how the videos can be played on the HTML with a reference rather than embedding the video file to the HTML file, I want something like this to be applied to my PDF presentation. I just want to reference the video URL from my PDF presentation.   Shortly speaking, can we use media9 to show a video on a PDF but the video is not embedded to the PDF?  Uploading those videos to a web server might be difficult for me because internet connection is very slow and sometimes not available in the presentation room. :-) I just need to check the reasoning in my proof is correct, I think it is valid although I'm not totally convinced because I can't follow the logic; does proving that $x$ is an integer prove that $ac|bd$?  Theorem: Let $a$, $b$, $c$, $d$ be integers. If $a|b$ and $c|d$, then $ac|bd$.  Proof: $aj=b$ and $ck=d$ for integers $j$, $k$. Then, $ac|bd$ implies $acx=ajck$ and thus $x=jk$ for some $x$. Since the product $jk$ is an integer, $x$ is an integer and thus $acx=ajck$ and thus $ac|bd$. How to completely disable auto-save and versions in Mac OS X Lion? I hate the automatic saving and versioning in Mac OS X Lion.  Is there a way to completely turn it off?  (This has been asked before , but the answer and the linked article are completely wrong, so I thought I'd try again.) I'm sure this is a newbie question, but I can't figure this out. I have tried to follow the advice here:  and here:   But I can not seem to be able to generate any font change. I either get no change or error messages.  Here is the output of one failed attempt to change the font to Times using this command:  \rmfamily \renewcommand{\rmdefault}{ptm}     Apparently I either don't have a correct package installed or...  The output says " Metric (TFM) file not found." but I am not sure where to go from there. If $|G/H|=4$ then $G$ is union of three proper subgroups Let $G$ be a finite group and $N$ a normal subgroup of $G$ of index $4$. Prove that $G$ has a subgroup of index $2$ (hence normal) and if $G/H$ is not cyclic then $G$ is equal to the union of three proper subgroups.   I understand that $G/H$ is isomorphic to $\mathbb{Z}_4$ or $\mathbb{Z}_2\times \mathbb{Z}_2$. Let $K^*$ be a subgroup of $G/H$ of order $2$. Then $K^*\cong K/H$ for some $K$ such that $H$ is normal in $K$ and hence $[G:K]=[G/H:K/H]=4/2=2$.  If $G/H$ is not cyclic then $G/H\cong \mathbb{Z}_2\times \mathbb{Z}_2$. I don't know how to prove $G$ is the union of three subgroups. Could it be true that as $G/H$ is the union of three proper subgroups $K_1^*,K_2^*,K_3^*$ then the corresponding groups $K_1,K_2,K_3$ have union equal to $G$? Would anyone give me a hint to prove this?  Thank you. Over the past few weeks, there have been a number of complaints about users making suggested edits en masse whose quality was at least questionable.  Let an example of a low-quality edit be the addition of the web-frameworks tag to dozens of questions about the PHP web framework Laravel. No one is ever going to use it in a search, but Laravel is a framework, right?  (If you disagree about this being a low-quality edit, please  bear with me anyway - my point here is that the system through which such conflicts could be settled is broken.)   Examples          This is a toxic situation guaranteed to create strife because -   The new user is happy to have found a way to participate and earn some rep; they may be genuinely feeling that they are improving the site. The reviewers greenlighting most of their suggestions confirms them in their belief.   The reviewers usually see only one edit - and it's easy to see how they might go, "meh, this isn't a terribly useful edit, but hey, maybe it helps someone, and it's a new user. No point discouraging them."   The veteran users who check out the editor see dozens of what they perceive as low-quality edits, usually ignoring anything else that should be fixed in the post. To the veterans, the new user is systematically looking for excuses to make their pointless edits, creating a giant mess in order to  gain some rep - a mess they have to clean up, while there are no consequences for the editor, who gets to keep their ill-gotten points. While a bad question or answer can be downvoted - usually leading to a change of behaviour eventually - the edit system looks like it's wide open for gaming.   So tensions are high, and when there's dialog it can be angry. I'm not saying either side is completely right. I'm completely prepared to believe that many of these edits are in good faith, etc. But it's a mess because it's frustrating people. As said, there are no consequences for bad-faith mass editing; apart from commenting on some random post, there is no way to communicate with an editor. The outcome of a moderator flag is very much uncertain.  The absence of a clear set of rules means there's plenty of room for heated arguments.    Something needs to change here.  Either   We need super clear rules on what makes a good tag edit Tag-only edits should be allowed only for 2k+ users, or they should not gain 2 reputation points for &lt;2k users The possible 1000 rep gain for suggested edits needs to be rate-limited (say, 200 per month) (this is my favourite!) The possible 1000 rep gain for suggested edits needs to be lowered, say to 500 or 250 Rollbacks of suggested edits should result in annulment of the 2 points gained (this is terrible) There should be a system to vote on edits (yes, that's been suggested before) There should be a defined and officially sanctioned pathway, and ruleset, for moderator flags cast about these users    ... or something else. But something needs to give. When going to any page of  with a new reputation gain, the achievements dropdown keeps showing a new badge green highlight:    And then trying to dismiss the notification by clicking on it gets rid of the green badge notification, but the +5 remains even after I've clicked away from the dropdown. I am trying to make a map where you have to make a village from scratch, and I need help. I'm trying to make a /clone command happen relative to where a mob that's named house is, and I cant figure it out. Any help? Gravatar profile image not showing sometimes It seems that with some profiles the Gravatar image is broken. I am not sure if this is an issue with SE or Gravatar, or both, so posting here.  As an example,  shows an error on , which shows a HTTP 500 on Gravatar.  Profile image on SO:        Image on Gravatar:        Switching to the MSE profile of the user, the image is working (but has a different hash).  Is this a bug on the SE side? Can anything be done to make Gravatar fix this?    Update 2016-10-04:  It happened to me again two times today. The last user profile was . Calling the service two or three times fixes the issue. Every subsequence of $x_n$ has a further subsequence which converges to $x$. Then the sequence $x_n$ converges to $x$. Table with actions per row How to confirm that mail has been delivered or not? Is there a easy way to test ubuntu on new notebooks before buying it? What class of Devil Fruit does the Gomu Gomu no Mi come under? Considering the three types of Devil Fruits that has been explained are 1. Paramecia Type - where the user can get super human abilities and change their body parts into weapons, etc. 2. Zoan type - where the use can turn into a particular animal and inherit its abilities 3. Logia Type - where the user's body inherits a particular element and the body becomes like air which cannot be touched or damaged by non Haki users.  So what exactly is the type of Gomu Gomu no Mi? It cannot be Zoan or Logia. It's very close to a Paramecia but still doesn't have a logical explanation to be of Paramecia type! So is it some special type of Devil Fruit?