Exception in thread "main" java.lang.NullPointerException - JAVA Array Of Record
What is a NullPointerException, and how do I fix it?
What is the difference between # and . when declaring a set of styles for an element and what are the semantics that come into play when deciding which one to use? Tool to manage and/or make available a list of my publications on the web? Meaning of "* */1 * * *" cron entry? Somehow, I am finding it difficult to understand tweaking around * parameters with cron.  I wanted a job to run every hour and I used the below setting:  * */1 * * *   But it does not seem to do the job. Could someone please explain the meaning of above and what is needed for the job? What is the procedure for taking down Titans? SELECT DISTINCT on multiple columns Supposing we have a table with four columns (a,b,c,d) of the same data type.  Is it possible to select all distinct values within the data in the columns and return them as a single column or do I have to create a function to achieve this? How does the Southwest Airlines boarding process work? I'm flying this week on Southwest Airlines for the first time. I paid for "Early Bird" automatic checkin and the FAQ mentions something about "A" boarding passes. I have no idea what that means, and I know that Southwest doesn't have assigned seats.  How does the boarding process work and is there anything I should be aware of? Is static HTML the fastest? I have been researching several different techniques to deliver web content fast, like nginx and node.js.  When it comes down to performance optimization http expires headers and gzip come to mind. After that come common techniques like sprites and CDNs etc.  But I am wondering.  What would be the very fastest technique to load a website?  Is static html the very fastest that can be? Or is there something else even faster? The $n$ complex $n$th roots of a complex number $z$ Removing repeated page numbers from table of contents Hi I'm trying to create a document in LaTeX with a few small subsections on the same page, is there any way to remove the repeated page numbers and keep the numbers when I move onto a new page? I was so excited about the Spring '14  as a way to present data visualizations on a public site, and now it looks like that's not possible.  I created a page that looks basically like the release notes sample:  &lt;apex:page &gt;     &lt;analytics:reportChart reportId="00OW0000000Spru"&gt;&lt;/analytics:reportChart&gt; &lt;/apex:page&gt;   I tested it inside the authenticated environment, where it works fine, then added it to a Site. There, I get the error: To view the report chart, you need both the Run Reports permission and access to the report's folder. But, Run Reports is not a permission I can grant to the Site Guest User.  Anybody have any ideas for a workaround? Or is it not going to be possible to show report charts on a public site? What does `mv ./*` without specifying destination do? I accidentally forgot to specify destination before hitting the Return key. Where does mv ./* without specifying destination move the files and directories under current directory to? When Cantor's Intersection theorem won't work with closed sets Give an example to show that Cantor's Intersection Theorem would not be true if compact sets were replaced by closed sets.    Compact set is closed and bounded, so what I'm going to find is something that is closed but not bounded.  By the Cantor theorem, which says that a decreasing sequence of non-empty compact subset will have a non-empty intersection.  What I was trying to approach is how two sets just "touched" and as if they have not bounded, two sets "touched" nothing. But I cant give an example for that Can't connect to wireless networks on a Dell Latitude D430 As stated above, I can't connect to my home wi-fi with natty but can with Windows 7. The strange thing is I that I have gotten it to connect to other password protected networks with natty, it's just mine that it dosn't like.   I am using a WPA2 pass-code with AES Encryption and all other devises work fine on my network. Laptop used is a Dell Latitude D430. How to display Trash and Home folder icons? I've googled quite a bit but nothing I've found works. I just want to display the Trash, Home folder, Computer etc icons on my Desktop in Ubuntu.  The closest I've come is installing dconf-tools, running it, going to org -&gt; gnome -&gt; desktop -&gt; background and checking show-desktop-icons then org -&gt; gnome -&gt; nautilus -&gt; desktop and checking the icons I want to show.  Nothing happens.  I've also tried looking in compizconfig-settings-manager and gconf-editor but can't find anything there.  Ideas? Searching for words in question titles I'm trying to search for questions that have specific words in their titles using the  search feature, but it seems that it does not return any search results.  Using this feature, I tried to search for questions on Stack Overflow with , but this search query returns no results.  Is it still possible to filter the search results based on words in question titles? Why has my database connection failed? Noether's Theorem: Lie groups vs. Lie algebras; finite vs. infinitesimal symmetries I've had a brief look through similar threads on this topic to see if my question has already been answered, but I didn't find quite what I was looking for, perhaps it is because I'm finding it hard to put words on my question and I hope that you will be able to help me ask it clearly.  I'm trying to link what I know from mathematics to what we are writing in physics for Noether's theorem. If I understand correctly we are looking at the symmetries of the action i.e. under which symmetry groups is it invariant. Noether's theorem allows us to calculate a conserved current in the case of a continuous symmetry (Lie groups), by means of so-called infinitesimal symmetries which I believe to be elements of the Lie algebra (so the tangent space to the neutral element) of the Lie group.  I'm guessing that if the action is invariant under the symmetry then it's "variation" should be 0 when we vary the system (space-time coordinate, or field) using this symmetry; it is exactly this step that I would like to understand better, how can I formalize this step correctly mathematically? How should I understand this variation, and how does it's calculation give rise to the elements of the Lie algebra? I've been trying to understand $\sigma$-algebras and how it encodes information in context of filtration. While certain parts seem clear and logical, I can't say I get the whole picture.  I'll try to explain the counter-intuition I get with the classical example of : the probability space $\Omega = \{ HH, HT, TH, TT \}$ and a r.v. $X(\omega)$ equal to the number of heads.  At times $0$, $1$ and $2$ the available information is represented using $\sigma$-algebras $\mathcal{F}_0=\{\emptyset,\Omega\}$, $\mathcal{F}_1=\{\emptyset, \Omega, \{HH,HT\},\{TH,TT\}\}$ and $\mathcal{F}_2=\{\emptyset, \Omega,\{HH,HT\},\{TH,TT\},\{HH\},\{HT\},\{TH\},\{TT\}\}$.  One can notice that $X(\omega)$ is not measurable with respect to $\mathcal{F}_0$ and $\mathcal{F}_1$, because $X^{-1}((\frac{3}{2}; +\infty))=\{HH\}$. To me it is quite surprising: intuitively $X$ makes perfect sense at all times. In particular it has an expected value at time $0$, which I interpret as that the probability and value of all outcomes $\{\omega\}$ can be computed. How do you think of a non-measurable function?  Here's another way of expressing the same confusion. The most natural choice of $\sigma$-algebra in a finite discrete case is $\mathcal{F}=2^\Omega$, and it is implicitly used in all elementary probability problems. However, this choice of $\mathcal{F}$ does not reflect the fact that some information is known or unknown, conditional probability does. Does it mean that the statement "$\sigma$-algebra is known information" make sense only in conditioning? Why is it convenient then? Force LaTeX image to appear in the section in which it's declared Possible Duplicates:           How can I force an image in a LaTeX documents to appear in the section in which I declared it?  I don't want that an image about "Section A" to appear in "Section F". :(  I actually include an image with  \begin{figure}[ht] \begin{center} \includegraphics[scale=0.7]{./img/RobotManipulator3D_WorkSpace.png} \end{center} \caption{3D View of the robotic workspace (in red).} \label{Img:3DRobotWorkspace} \end{figure} “Screen overlay detected” dialog? Turned off everything, doesn't work I started receiving the “Screen overlay detected” dialog when trying to change apps settings.  Tried to turn off all "draw over other apps" as it says here - , first without system and then with, but it still doesn't work.  Then, I restored apps to original settings and it just made a bigger mess, dialog continue appearing. Any way to go back to previous settings???  Thanks!