java lang null pointer exception on insert database in javaFX
What is a NullPointerException, and how do I fix it?
Fantasy novel about kid who controls magic through coin changer device I read this book in high school, and I can't remember what it's called. Some kid learns he has magical ability, but only finds out later that he controls it through some kind of coin changer he's been tinkering with the whole book. Why {are you / you are} making noise? Live refresh shows "modified" on tagged questions even when unmodified Is every sub-lattice of $\mathcal P(X)$ isomorphic to a sub-lattice of $\mathcal P(X')$ containing singleton sets? I've bought a  to use with my EOS 200D and while I love the wide aperture, it appears to be quite difficult to achieve sharp focus on people's faces when shooting at f/1.8. I've tried both using Dual Pixel focus in Live View and using the center focusing point in the viewfinder, but it doesn't get me perfect results.  Is this simply a characteristic of cheap wide-aperture lenses? Or is it impossible to get sharp focus with a fully open aperture?  When I'm at at home using a tripod and focusing on a still subject I do get good focus (so it's not a camera or lens issue). But it's hard to do with people who are slightly moving between shots. $(x^3+xy^2-y)dx+(y^3+x^2y+x)dy=0$ I tried to find on Wolfram Alpha but it showed only the solution not in step-by-step, I know that the factor is $\frac{1}{x^2+y^2}$ but how to find it? Showing that $Q_n=D_n+D_{n-1}$ Let $T_n$ be the set of permutations of $\{1,2,\ldots,n\}$ which do not have $i$ immediately followed by $i+1$ for $1\le i\le n-1$; in other words, let \begin{align} T_n=\{\sigma \in S_n: \sigma(i)+1\ne\sigma(i+1) \text{ for all } 1\le i\le n-1\} . \end{align} Let $Q_n$ be the number of elements of $T_n$.    Let $D_n$ be the number of  of $\{1,2,\ldots,n\}$.  It is not hard to show algebraically that $Q_n=D_n+D_{n-1}$, but I am having difficulty coming up with a combinatorial argument to show why this is true.  (I believe there are $D_{n-1}$ elements of $T_n$ that leave $n$ fixed, and $D_n$ elements of $T_n$ that move $n$, but I don't know how to justify this combinatorially.) How can I stop Nautilus from dereferencing symlinks? I use symbolic links to tidy my home folder. This works well in the terminal, since the links create the illusion of normal folders:    In Nautilus, however, the links behave more like , immediately teleporting me to their target:    This is particularly troubling when¹ I later want to navigate "up" to the parent folder, as it strands me somewhere outside of the tree I've carefully tidied.  How can I make Nautilus show symbolic links as normal folders, like the terminal does?  Details   Nautilus did not dereference symlinks in Ubuntu 12.10:   Maybe this new behavior is just a bug? I'm not sure how to tell. Here's what I know:   It's not on the . I've skimmed the  and didn't see anything related. The Nautilus mailing list archive . I received no response from about 120 idlers when posing the question on the GNOME IRC channel. A change was made in Nautilus 3.6 to .  ¹ This is an example. A workaround for this particular scenario does not constitute an answer to my question. Since people seem to be interested in discussing it, though:   Using the Back button is not a suitable workaround; it does not always take me to the parent folder. You can navigate up by pressing Alt+Up. The desired behavior in this example is for "up" to navigate to the parent folder of the symbolic link. The current behavior is to navigate to the parent folder of the target of the symbolic link. What are the differences between a multidimensional array and an array of arrays in C#? What are the differences between multidimensional arrays double[,] and array-of-arrays double[][] in C#?  If there is a difference, what is the best use for each one? Why an abstract class implementing an interface can miss the declaration/implementation of one of the interface's methods? A curious thing happens in Java when you use an abstract class to implement an interface: some of the interface's methods can be completely missing (i.e. neither an abstract declaration or an actual implementation is present), but the compiler does not complain.  For example, given the interface:  public interface IAnything {   void m1();   void m2();   void m3(); }   the following abstract class gets merrily compiled without a warning or an error:  public abstract class AbstractThing implements IAnything {   public void m1() {}   public void m3() {} }   Can you explain why? I have been using the app for 3 days now. I just opened it up again, and it asked me to sign "up" again with either Google or the Trainer server.   So I signed up with the same Google account as when I first started with and the game started again.   Is there Any way I can get my progress back? Can I speed up iCloud photo sync between iPhone and Macbook? I have an iPhone 5 running iOS 9.1 and a Macbook Pro running Yosemite.  Both devices are set up to sync photos to and from iCloud.  When I take a photo on the iPhone (for further processing on the Macbook), it takes an inordinate amount of time until the photo shows up in the Macbook's photos library - sometimes up to 10-20 minutes. Sometimes it seems to work faster if I quit the Photos app on both devices, and start it again.  I often end up sending myself photos through E-Mail because it's quicker. That seems ridiculous!  Is there a way to force a sync on the iPhone, or to speed up the process some other way? How to address a professor in person at US universities? At US universities, how should one address a professor while talking to him or her? In my home country, we usually address the professors as either "sir" or "madam" while talking about our queries in person.   What's the norm at US universities? I have forgotten my keystore password and I want to install my apk on Google Play. What do I do? How can faces be rotated around their individual normals? In edit mode with these settings:   Face selection Pivot point: individual origins Transformation orientation: Normal   The faces don't rotate around the normals, is there another required setting that I overlooked? $|_{x=1}$ notation? I had the equation: $$\frac{1}{(1+x)(1-x)^2}=\frac{A}{(1-x)^2}+\frac{B}{1-x}+\frac{C}{1+x}$$ $$A=\left.\frac{1}{1+x}\right|_{x=1} = \frac{1}{2} \tag2$$ What does $(2)$ mean? Particularly, the notation $|_{x=1}$ How do I dynamically invoke a class method in PHP? How can I dynamically invoke a class method in PHP? The class method is not static. It appears that   call_user_func(...)   only works with static functions?  Thanks. Line numbering paragraph oriented? I'm using the lineno package with the pagewise option but I need a way to get the numbering restart every paragraph break. I need a general solution to pass to the latex command, e.g.:  latex "\AtBeginDocument{\RequirePackage[pagewise]{lineno}\linenumbers}\input{mydocument.tex}"   I read the lineno manual but the package does not provide this feature. Is there any trick to do that? I am trying to follow Blender Guru's beginner tutorial. He went to the Compositor tab and was using it to Denoise an image but when I got there, no nodes show up. Can you guys help? How do we show that equality holds in the triangle inequality $|a+b|=|a|+|b|$ iff both numbers are positive, both are negative or one is zero? I already showed that equality holds when one of the three conditions happens.