I am a newbie in objective programming so forgive me if this question is dumb.  I am developing a small to-do program as a exercise. But when I try to load existing txt file &amp; folders for task storage, IDE told me Exception in thread "main" java.lang.NullPointerException. I read the popular one from this site describing this error, I kinda understood why it happened, but I just coudn't find the problem.  Line 17-26 of ListProcess:  public ListItem[] loadList() throws FileNotFoundException {         ListItem[] listitem = new ListItem[200];         int listCount=0;         for (String txts : loadTxtsList()) {             File file = new File(txts);             Scanner scanner = new Scanner("List/"+file);             listitem[listCount].isFolder = false;             listitem[listCount].name = txts.replace(".txt", "");             listitem[listCount].description = scanner.nextLine();             int i = scanner.nextInt();   and yes, I'm using a class called ListItem to store these tasks.  ListItem class:  public class ListItem {     boolean isFolder=false;     String name;     String description;     String[] tags = new String[10];     Status status; }
What are Null Pointer Exceptions (java.lang.NullPointerException) and what causes them?  What methods/tools can be used to determine the cause so that you stop the exception from causing the program to terminate prematurely?
What is the relation between the Higgs field and chirality? Wikipedia  that the spontaneous breaking of chiral symmetry "is responsible for the bulk of the mass (over 99%) of the nucleons".  How do the nucleons gain mass from the spontaneous breaking of chiral symmetry? Why don't leptons gains mass from it? What is the role of the Higgs field in this all? How do I backup ssh keys? I am planning to do a fresh install of ubuntu 11.10 in my system. Before that i have setuped key based ssh authentication in this machine. Is it possible to take backup of those ssh keys, so that i  can use that in my new installation. Or else i must setup keybased ssh authentication again? If i can take backup, what are the files i need to copy? Can someone explain it in detail pls. Thanks in advance. Differentiability implying continuity Theorem: If $f$ is finitely differentiable at $c$, then $f$ is also continuous at $c$.  But according to the definition, for a function to be differentiable at $c$, it need not even be defined at $c$, just that it should have a finite value in the vicinity of $c$.    My question: If function is not defined at $c$, how can it be continuous at $c$?  For example, say we have a straight horizontal line function which is broken at $x=1$, the function is defined at all the points except $x=1$, it has a finite value at all the points except $x=1$, since it is having a value in the nearby region of $x=1$ we say that it is differentiable at $x=1$ but can we say that it is continuous at $x=1$? I just installed Solaris 11.3 on the laptop. This laptop have Broadcom BCM4312 WiFi card.  It looks like the install does not have a driver for this card just like 11.1 version.  I have a Linux installed on this same machine (Gentoo) and this OS does have a driver.  Is it possible to get the driver for this card somewhere? Maybe broadcom.com? Failing that is it possible to use Linux driver inside Solaris?  On the kind of related side - I tried to connect a wire and run Driver Manager, but it does not want to finish. All controls are  still disabled. Any idea?  Thank you for any pointers you can provide. I want to create a   How can I create a formfield with N fields, each 5 mm wide with separations like in the picture?    At the moment I use a workaround with a for loop, but this renders the code hard to maintain. Finally I need a function \formline{N}{cellwidth}{label}{value} to create the complete formfield and fill it with an optional value:   The following code is available on .   \documentclass[a4paper,11pt]{article} \usepackage[utf8]{inputenc} \usepackage{tikz} \usetikzlibrary{shapes}  \thispagestyle{empty} % no pagenumber. The form should be a stand alone macro... later.  \definecolor{SEPAOrange}{RGB}{254,213,161} \definecolor{SEPADOrange}{RGB}{253,185,19} \definecolor{SEPABlindcolor}{RGB}{255,0,0} \begin{document} \begin{tikzpicture}[x=1 mm, y=-1mm] \pgfmathsetmacro{\yh}{4.2333} % y heigth step defined as 1/6 inch =&gt; 1/6 * 25.4 mm = 4.2333 mm \pgfmathsetmacro{\xs}{9} % x start (own definition) \pgfmathsetmacro{\xe}{141.5} % x end (own definition) \pgfmathsetmacro{\widefield}{4.9859} % def: 134.62 mm / 27 \pgfmathsetmacro{\narrowfiels}{3.9594} % def: 134.62 mm/ 34  \filldraw[draw=black,color=SEPAOrange] (7.62, 4.5*\yh) rectangle (149.86-7.62,105.83-1); %orange background  \filldraw[draw=black,color=white] (\xs, 5*\yh) rectangle (\xe, 6.5*\yh -1.5); %Recepient 27 Char \foreach \x in {1,...,26} {  \draw[color=SEPAOrange, line width=0.3mm] (7.62 + \x*\widefield, 5*\yh ) -- (7.62 + \x*\widefield, 6.5*\yh);  \draw[color=SEPAOrange, line width=0.7mm] (7.62 + \x*\widefield, 5.8*\yh ) -- (7.62 + \x*\widefield, 6.5*\yh); }  \filldraw[draw=black,color=white] (\xs, 7*\yh) rectangle (\xe, 8.5*\yh -1.5); %IBAN 34 Char \foreach \x in {1,...,33}  \draw[color=SEPAOrange, line width=0.3mm] (7.62 + \x*4, 7*\yh ) -- (7.62 + \x*4, 8.5*\yh);  \filldraw[draw=black,color=white] (\xs, 9*\yh) rectangle (\xe, 10.5*\yh -1.5); %BIC \filldraw[draw=black,color=white] (\xe-12*5, 11*\yh) rectangle (\xe, 12.5*\yh -1.5); %Value 12 Char  \filldraw[draw=black,color=white] (\xs, 13*\yh) rectangle (\xe, 14.5*\yh -1.5); %Subject1 \filldraw[draw=black,color=white] (\xs, 15*\yh) rectangle (\xe, 16.5*\yh -1.5); %Subject2 \filldraw[draw=black,color=white] (\xs, 17*\yh) rectangle (\xe, 18.5*\yh -1.5); %Subject3  \filldraw[draw=black,color=white] (\xs, 19*\yh) rectangle (\xs+22*5, 20.5*\yh -1.5); % IBAN 22 Char  \filldraw[draw=black,color=white] (149.86-17.59, 19* \yh) rectangle (\xe, 20.5*\yh -1.5); % counter \filldraw[draw=black,color=white] (\xs, 21* \yh) rectangle (42.52, 24.5*\yh); % date \filldraw[draw=black,color=white] (42.52+5, 21*\yh) rectangle (149.86-17.59, 24.5*\yh); % signature  \draw[color=SEPADOrange] (0, 4.5 *\yh) --(149.86, 4.5*\yh); upper dark orange line \draw[color=SEPADOrange] (0, 20.5 *\yh) --(149.86, 20.5*\yh); lower dark orange line \draw[draw=black,color=black, line width=0.3mm] (0,0) rectangle (149.86,105.83); % black border %\draw[align=left] at (\yh,\yh) {SEPA-Überweisung};  \end{tikzpicture} \end{document} Requesting raw data from previously published research Using apt-get how to check have installed latest version ? Hello im just new for Linux   I know that  sudo apt-get   is for installing application   but how I would know that I have installed the latest version of the application   for example apt-get install sun-java6-jdk   is there an option to upgrade or see the latest version   or its ok to install an old version the application and Linux will upgrade it for me ? I've only just begun studying group theory (up to Lagrange) following on from vector spaces and I am still finding them almost frustratingly  arbitrary. I'm not sure what exactly it is about the axioms that motivated them defining groups.  My textbook asks you to list 'common features' of vector spaces and then later defines a set of axioms for vector spaces under addition, scalar multiplication and both, noting that the axioms under addition form an Abelian group. So are groups just a generalisation of vector spaces under any binary operation?  My main problem is that the book notes that 'the axioms may seem rather arbitrary' and links groups with vector spaces but doesn't elaborate.   When introducing groups, you are tasked to complete Cayley tables for the symmetries of an equilateral triangle and square.  Then, similarly to the delivery of vector spaces, notes that the tables have common properties (Closure, Identity, inverse and association) and defines a group as a set of elements under a binary operation that has these features.  So what's so important about these 4 properties? For example, if 1 or 2 the properties were excluded form the  axioms, or we added an extra few properties as axioms how would that cripple the effectiveness of groups?  Are the group axioms ever difficult to work with or do they always work, forgive the crude Littlewood analogy, like a mathematical skeleton key?  What is it about these 4 properties that make groups such a powerful tool in mathematics and physics?  My best guess is that a group is the best way to express our sense of  symmetry and what is symmetric mathematically, but I would prefer some elaboration. What's the past participle form of the word exit? Is it exit (irregular, like set)? exited? exitted? On one page I found exited but if that's the case why isn't it exitted (double t) like with the word emit - emitted? Is there a rule when the consonant at the end is doubled and when not? JComboBox Selection Change Listener? What's difference between shadowing and overriding a method in C#? I'm trying to find the complex roots of $z^3 + \bar{z} = 0$ using De Moivre.  Some suggested multiplying both sides by z first, but that seems wrong to me as it would add a root ( and I wouldn't know which root was the extra ).  I noticed that $z=a+bi$ and there exists $\theta$ such that the trigonometric representation of $z$ is $\left ( \sqrt{a^2+b^2} \right )\left ( \cos \theta + i \sin \theta \right )$ .  It seems that $-\bar{z} = -\left ( \sqrt{a^2+b^2} \right )\left ( \cos (-\theta) + i \sin (-\theta) \right )$  However, my trig is pretty rusty and I'm not quite sure where to go from here. I've lost my portal home, and I am invincible. How can I leave the nether? I have the below list of files  aro_tty-mIF-45875564pmo_opt aro_tty-mIF-45875664pmo_opt aro_tty-mIF-45875964pmo_opt aro_tty-mIF-45875514pmo_opt aro_tty-mIF-45875524pmo_opt   that I need to rename to  aro_tty-mImpFRA-45875564pmo_opt aro_tty-mImpFRA-45875664pmo_opt aro_tty-mImpFRA-45875964pmo_opt aro_tty-mImpFRA-45875514pmo_opt aro_tty-mImpFRA-45875524pmo_opt I'm writing a tool to report information about .NET applications deployed across environments and regions within my client's systems.  I'd like to read the values of assembly attributes in these assemblies.  This can be achieved using Assembly.ReflectionOnlyLoad, however even this approach keeps the assembly loaded.  The issue here is that I cannot load two assemblies that have the same name from different paths, so naturally I can't compare the same application deployed in different systems.  At this point I'm assuming the solution will involve using temporary AppDomains.  Can someone detail how to load an assembly into another AppDomain, read the attributes from it and then unload the AppDomain?  This needs to work for assemblies on the file system as well as those at URL addresses. A white number inside a black circle. How to make a white number inside a black circle (the picture below)? I want to change numbers inside the black circle, of course.  I use Share LaTeX. I have read some articles here but anyone are not what I would like to get. I would like to get this  (the picture below) - the sixth answer.   Thanks for help. What's the difference between importing and extending a class? How can I upload files asynchronously with jQuery? I would like to upload a file asynchronously with jQuery.     $(document).ready(function () {     $("#uploadbutton").click(function () {         var filename = $("#file").val();          $.ajax({             type: "POST",             url: "addFile.do",             enctype: 'multipart/form-data',             data: {                 file: filename             },             success: function () {                 alert("Data Uploaded: ");             }         });     }); }); &lt;script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/2.2.0/jquery.min.js"&gt;&lt;/script&gt; &lt;span&gt;File&lt;/span&gt; &lt;input type="file" id="file" name="file" size="10"/&gt; &lt;input id="uploadbutton" type="button" value="Upload"/&gt;     Instead of the file being uploaded, I am only getting the filename. What can I do to fix this problem? reconfiguration issues with dpkg I ran into some problems installing a package with apt. The terminal hung up during an install and I saw no other choice but to close the terminal. The problem, however, is that I can't seem to solve the issues that this has caused.   As is typical, I get:  E: Could not get lock /var/lib/dpkg/lock - open (11: Resource temporarily unavailable) E: Unable to lock the administration directory (/var/lib/dpkg/), is another process using it?   This gets me nowhere and I'm locked out until I run sudo dpkg --configure -a. Makes sense. However, this process spits the following out and then hangs on the last line:  Setting up virtualbox-dkms (5.2.10-dfsg-6) ... Removing old virtualbox-5.2.10 DKMS files...  -------- Uninstall Beginning -------- Module:  virtualbox Version: 5.2.10 Kernel:  4.15.0-23-generic (x86_64) -------------------------------------  Status: This module version was INACTIVE for this kernel. depmod...  DKMS: uninstall completed.  ------------------------------ Deleting module version: 5.2.10 completely from the DKMS tree. ------------------------------ Done. Loading new virtualbox-5.2.10 DKMS files... Building for 4.15.0-23-generic Building initial module for 4.15.0-23-generic   A typical solution I've read is that you need to fix the broken packages. When I try to fix the broken packages (sudo apt install -f), the system also hangs on the same line, although the output is different:  Reading package lists... Done Building dependency tree        Reading state information... Done 0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded. 3 not fully installed or removed. After this operation, 0 B of additional disk space will be used. Setting up virtualbox-dkms (5.2.10-dfsg-6) ... Removing old virtualbox-5.2.1  0 DKMS files...  ------------------------------ Deleting module version: 5.2.10 completely from the DKMS tree. ------------------------------ Done. Loading new virtualbox-5.2.10 DKMS files... Building for 4.15.0-23-generic Building initial module for 4.15.0-23-generic   I am unable to get out of it unless I kill the process. This I do by checking what is currently running related to apt (ps aux |grep apt), and then I kill the relevant processes with sudo kill -9 process_number_here.  If I try to run things after that, it tells me I still need to reconfigure dpkg.  I tried looking around for more solutions to dpkg and all I really see is the nuclear option:  sudo rm /var/lib/dpkg/lock sudo rm /var/cache/apt/archives/lock sudo rm /var/lib/apt/lists/lock   I also delete the files in /var/lib/dpkg/updates because when I did some digging one of the files inside had the exact same text as the above long output... but I fully admit to being out of my league here and I don't know what to do.   Taking a look at the error messages, I recognize that it hangs on building something related to the kernel. But I have no idea where to even start solving that. Any help is appreciated. My system is ubuntu 18.04 Update Migration Path List for Non-Moderators