Attempt to invoke virtual method 'boolean java.lang.Object.equals(java.lang.Object)' on a null object reference
What is a NullPointerException, and how do I fix it?
How to change background colour in texworks I am using texworks for the first time, I want to change the background of the editor from dark to white, as the code is not visible in dark background. I am using texworks in Manjaro Linux on GNOME desktop environment. Please help me. When are attributive nouns plural? array package: problem with >{declarations} in preamble: Extra alignment tab has been changed to \cr I have a document that uses both the longtable and the array package. At first I ascribed the problem to an interaction of both. After testing, it seems array is the only culprit.  Here's a minimal example.  \documentclass{article} \usepackage{array} \begin{document}  \begin{tabular}{p{0.4\textwidth}&gt;{\raggedright}p{0.4\textwidth}} 1 &amp; a \\ 2 &amp; b \\ 3 &amp; c \\ \end{tabular} \end{document}   It produces the error  ! Extra alignment tab has been changed to \cr. How can I recover data from a 2TB hard drive? I have a Western Digital 2TB External Hard Drive. I basically use it to keep all my movies and videos. Its file system is NTFS, and currently I'm using 1.4TB. One night I turn it on and copied a 4GB file and there was no problem. Then I tried to copy another 6GB file and Ubuntu throw the following error: "Input/output error". I tried to create a new folder with no luck. I still could read the disk an play a file, so I thought restarting the computer would solve the problem, but it didn't. The next time, Ubuntu didn't mount the disk.   After that I tried in another PC with Window 7. It throwed a message telling me: first, that the disk needs to be formatted, and second, a "Local Disk #: Is not accessible. Data error (cyclic redundancy check)". Here is when I started to worry. I tried to fix the disk with CHKDSK (chkdsk \r). After about 5 hours, it crashed with the following error: "An unspecified error occurred".  My guess to all this is that the disk is dying. :'(  Lastly I did one more thing. I installed GSmartControl on Ubuntu to see the SMART info and the attributes tab appears in red with the following line highlited:  ID# ATTRIBUTE_NAME          FLAG     VALUE WORST THRESH TYPE      UPDATED  WHEN_FAILED RAW_VALUE ... 197 Current_Pending_Sector  0x0032   197   197   000    Old_age   Always       -       977 ...   Just to check, I left the disk on for about 2 minutes and then refreshed the page, and the Current_Pending_Sector RAW_VALUE increased from 977 to 979. My guess is that sectors on the disk are dying. Am I right?  If every time I turn on the disk more sectors are going to die, I need to copy the data fast. I don't know if there is a solution on Windows, and I'm worried about the time that it could take to do it with the slowness of Windows. Basically my question is: How can I recover the data? (Or at least some of it). Is there any program on Ubuntu that can help me with this (If I'm still on time)?. My main concern is the size of the disk (2TB), so I think I would need at least another 2TB disk to copy to.  Any help would be appreciated. What does $(command) & do? A customer running Windows 7 Home must have reserved or okayed the Windows 10 upgrade because I am seeing daily messages that the upgrade is failing to install.   This customer is not ready for Windows 10 so it's good that the install is failing. But how to make it stop trying?  Once permission is granted for the upgrade, how do I revoke that permission so it stops attempting to upgrade?  I ran the Windows Update troubleshooter to clear out updates, and I uninstalled and hid KB3035583, but it is still trying to upgrade. In Task Manager, there is no GWX.EXE process.  Event log failure message:  Log Name:      System Source:        Microsoft-Windows-WindowsUpdateClient Date:          8/5/2015 1:28:58 AM Event ID:      20 Task Category: Windows Update Agent Level:         Error Keywords:      Failure,Installation User:          SYSTEM Description:   Installation Failure: Windows failed to install the following update with                 error 0x80240020: Upgrade to Windows 10 Home.   Relevant lines from WindowsUpdate.log:  2015-08-05  01:28:57:885    1068    6698    Agent   ************* 2015-08-05  01:28:57:885    1068    6698    Agent   ** START **  Agent: Installing updates [CallerId = AutomaticUpdates] 2015-08-05  01:28:57:885    1068    6698    Agent   ********* 2015-08-05  01:28:57:885    1068    6698    Agent     * Updates to install = 1 2015-08-05  01:28:57:885    1068    6698    Agent     *   Title = Upgrade to Windows 10 Home 2015-08-05  01:28:57:885    1068    6698    Agent     *   UpdateId = {27E79986-1150-4342-BDD2-76DF82C768D5}.201 2015-08-05  01:28:57:885    1068    6698    Agent     *     Bundles 1 updates: 2015-08-05  01:28:57:885    1068    6698    Agent     *       {FCD6621E-F5D4-4A95-AD43-28F0C58DD2F3}.201 2015-08-05  01:28:58:181    1068    6698    DnldMgr Preparing update for install, updateId = {FCD6621E-F5D4-4A95-AD43-28F0C58DD2F3}.201. 2015-08-05  01:28:58:181    27280   6f84    Misc    ===========  Logging initialized (build: 7.6.7601.18917, tz: -0700)  =========== 2015-08-05  01:28:58:181    27280   6f84    Misc      = Process: C:\Windows\system32\wuauclt.exe 2015-08-05  01:28:58:181    27280   6f84    Misc      = Module: C:\Windows\system32\wuaueng.dll 2015-08-05  01:28:58:181    27280   6f84    Handler ::::::::::::: 2015-08-05  01:28:58:181    27280   6f84    Handler :: START ::  Handler: Windows Setup Install 2015-08-05  01:28:58:181    27280   6f84    Handler ::::::::: 2015-08-05  01:28:58:181    27280   6f84    Handler   : Updates to install = 1 2015-08-05  01:28:58:181    1068    5ecc    AU  &gt;&gt;##  RESUMED  ## AU: Installing update [UpdateId = {27E79986-1150-4342-BDD2-76DF82C768D5}] 2015-08-05  01:28:58:181    1068    5ecc    AU    # WARNING: Install failed, error = 0x80240020 / 0x00000000 2015-08-05  01:28:58:181    27280   6f84    Handler   : WARNING: Exit code = 0x80240020 2015-08-05  01:28:58:181    1068    5ecc    AU  Write OSUpgradeState =14 with OSUpgradephase =2 2015-08-05  01:28:58:181    27280   6f84    Handler ::::::::: 2015-08-05  01:28:58:181    27280   6f84    Handler ::  END  ::  Handler: Windows Setup Install 2015-08-05  01:28:58:181    27280   6f84    Handler ::::::::::::: Is it two-third or two-thirds? Is it two-third or two-thirds? If both are correct, how does their usage differ? What's the fixed size of the suggested edit queue? How do I convert a string to a byte[] in .NET (C#) without manually specifying a specific encoding?  I'm going to encrypt the string. I can encrypt it without converting, but I'd still like to know why encoding comes to play here.  Also, why should encoding even be taken into consideration? Can't I simply get what bytes the string has been stored in? Why is there a dependency on character encodings? How do I prove that $m(TE)=\left|\det(T)\right|m(E)$? Let $m$ be the $n$-dimensional Lebesgue measure and $T$ be a linear operator on $\mathbb{R}^n$. Let $\Sigma$ be the sigma-algebra of Lebesgue measurable sets. How do prove that (1) $\forall E\in\Sigma, T(E)\in \Sigma$ and $m(T(E))=\left|\det(T)\right|m(E)|$? Since the $\sigma$-algebra of Lebesgue measurable sets is strictly larger than the borel algebra, I think it cannot be proven by showing that $T$ is continuous. How do I prove this formally? I have a script from UC Davis and every thing is proven precisely here, except for one lemma which is critical for rest proofs in the script. That is,  Define $\mathbb{B}=\big\{\prod_{i=1}^n [a_i,b_i) : a_i,b_i\in\mathbb{R}\big\}$. Let $T$ be a unitary operator on $\mathbb{R}^n$. Let $A\in \mathbb{B}$ and $\{A_k\}_{1≦k≦m}$ be a finite disjoint sequence such that $\bigcup_{1≦k≦m} A_k \subset T(A)$. Then $\sum_{1≦k≦m} m(A_k) ≦ m(A)$.  It's written in the script: &quot;This result is geometrically obvious, but a formal proof seems to require a fuller discussion of the volume function on elementary geometrical sets, which is included in the theory of valuation in convex geometry. We omit the details&quot; It's okay to me to go through full discussion of volume function if that is precise. If it cannot be proven another easier way(so I can prove it in a day), please recommend me a &quot;convex geometry&quot; text which explains this. Windows 10 on asus x44h touchpad scolling not working I have just updated Windows 7 to Windows 10.  My touchpad scolling (right-side) is not working anymore.    I have no idea how to fix this in Windows 10.  I have hit the start button and typed "synaptic", but have found nothing useful.  I used to have an icon on the taskbar that showed where I was touching the touchpad.  I used to be able to right-click that icon to change settings, but Windows 10 has not brought that icon over.  Also, the asus website has no synaptic touchpad drivers available for Windows 10.  I have tried the enaltech drivers, but upon the installation atempt I am told that my hardware is not correct. How to programmatically send SMS on the iPhone? When ssh'ing, how can I set an environment variable on the server that changes from session to session? If I fall off a cliff - say, 1000 feet - can I wait (readied action?) until I am near enough to the ground (my understanding is you fall 500 ft/round) then  safely to the ground? Or, does the momentum from the fall carry over through the teleport and I still splatter across the rocks? I'm a committer for the .  It went to the private beta phase sometime in the last 12 hours, but yet to have been invited. When I visit  I get the standard "To log in, you must have commited to the Area 51 site proposal and received the invitation email." message.  However, when I navigate to the Pets site via the Android app, I'm able to view the site in it's entirety (questions, answers and comments). When I attempt to post, I get a message saying my user token isn't allowed to take action on this site.  Same behavior is observed when using the iOS app. Intro  I'm working on a lightweight package that allows you to put any content (typically LaTeX code) in an environment, then use that content multiple times, each time scanned separately, so you can use it both as verbatim output and interpreted as LaTeX.  Its main purpose is to typeset LaTeX code and its 'result' side-by-side; useful for documenting TeX packages without having to copy/paste code. But it has other purposes as well.  After experimenting with \scantokens until I gave up in tears, I arrived at the filecontents environment, which almost solved my problem singlehandedly!  The Problem  The problem is, when reintroducing filecontented code through \input, LaTeX adds an implicit newline at the end, which translates to whitespace that I can't seem to get rid of.  I've seen many semi-related questions floating around, with answers employing techniques like:   reading a file line-by-line, using \everyeof in some clever way, playing with \endlinechar or using packages such as catchfile   but none of them provides a clear answer to the following question:  The Question  How can I \input a file without getting the implicit newline?  Minimal Working Example  \documentclass[margin=1mm]{standalone}  \usepackage{filecontents}  \begin{filecontents*}{tmp.tex}     \LaTeX{}\end{filecontents*}  \begin{document}     \fbox{\input{tmp.tex}} \end{document}     Note the extra whitespace to the right of the box.  Note also that I'm definitely not adding any explicit whitespace. Even a manually produced file (so, not using filecontents) with no newlines at all exhibits the same problem. Why did R.A.B. put the locket back in the basin? led me to asking this one. R.A.B. takes the "real" locket out and asks Kreacher to destroy it, then puts the "fake" locket back in the basin. Why would he feel the need to do this? He knows already that Voldemort has used someone else to drink the potion (Kreacher). In fact Kreacher's story to him about his mistreatment on the island seems to push him over the edge to act.   Instead of assuring that someone else (most likely innocent like Kreacher) would have to drink from the basin, why not just leave the note outside the basin for someone to find? If Voldemort finds it then so be it, at least then no presumably innocent person would have to drink again. Let's say I launch a bunch of processes from a ssh session. Is it possible to terminate the ssh session while keeping those processes running on the remote machine? "Open in Terminal" in Ubuntu 18.04 This option seems to have gone away after upgrading from Ubuntu 16.04. I tried installing nautilus-open-terminal but it is unable to locate the package for 18.04. Also trying to install nautilus-actions gives:  Package nautilus-actions is not available, but is referred to by another package. This may mean that the package is missing, has been obsoleted, or is only available from another source     How to fix this? I noticed that $f(x) = x\phi(x)$ seems to be one-to-one, where $\phi(x)$ is Euler's Phi function.  In particular, I'm writing some numerical python code and the line I have looks something like  sorted([n*phi(n) for n in range(1,1000)])   and there are no duplicates in the list.  First, is it one-to-one?  Second, if it is, is there a simple proof sketch?