Android: progress dialog error java.lang.NullPointerException
What is a NullPointerException, and how do I fix it?
Why is there a file called [ in my /usr/bin directory? Recently back to Linux from another operating system I noticed a file called [ which seems strange to me.  What is it for?  $ ls -l /usr/bin | head -2 -rwxr-xr-x 1 root root       39552 Nov  3 14:44 [   I'm using Ubuntu 15.04 Rstudio is duplicating commands in the command line How to check the maximum number of allowed connections to an Oracle database? Which damage dice exactly does the Great Weapon Fighting fighting style allow you to reroll? I would like to increase the size of pretty much every headlines, so that it is more prominent than the normal text.  I read about the  package, but can't seem to find good example how to use the package.  Using Gonzalo Medina does in fact change the font size, however, it changes the default font as well.  Before:    After: Linear vs nonlinear differential equation How to distinguish linear differential equations from nonlinear ones? I know, that e.g.: $$ y''-2y = \ln(x) $$ is linear, but $$ 3+ yy'= x - y $$ is nonlinear. Why? find all the members of A4/K Let K={(1),(12)(34),(13)(24),(14)(23)} show that K is a normal subgroup of the alternating group of degree A4 and find all the members of A4/K and write down the group table for A4/K.   i know that K is the Klein four group and i have already proven it is a normal subgroup but i need a start on approaching the A4/K part of this question no direct answers are necessary,just ideas thank you! :) Prove by induction that for all $n \geq 3$: $n^{n+1} > (n+1)^n$ Waiting for user input with a timeout I have searched but apparently my google foo is weak. What I need is a way to prompt for user input in the console and have the request time out after a period of time and continue executing the script if no input comes in. As near as I can tell, Read-Host does not provide this functionality. Neither does $host.UI.PromptForChoice() nor does $host.UI.RawUI.ReadKey(). Thanks in advance for any pointers.  EDIT: Much thanks to Lars Truijens for finding the answer. I have taken the code that he pointed out and encapsulated it into a function. Note that the way that I have implemented it means there could be up to one second of delay between when the user hits a key and when script execution continues.  function Pause-Host {     param(             $Delay = 1          )     $counter = 0;     While(!$host.UI.RawUI.KeyAvailable -and ($counter++ -lt $Delay))     {         [Threading.Thread]::Sleep(1000)     } } How do I compare 2 rows from the same table (SQL Server)? I need to create a background job that processes a table looking for rows matching on a particular id with different statuses. It will store the row data in a string to compare the data against a row with a matching id. I know the syntax to get the row data, but I have never tried comparing 2 rows from the same table before. How is it done? Would I need to use variables to store the data from each? Or some other way? (Using SQL Server 2008) What should I do, as my submitted paper is still under review after 1 year? Expected value of a non-negative random variable Newcommand + Stepcounter I'm trying to come up with a command which should increase a counter and return a string including the current value of the counter.  Have a look at the following minimal example:  \documentclass{article}  \newcounter{mycounter} \newcommand{\mystepFAILS}{\stepcounter{mycounter}foo\themycounter} \newcommand{\mystepWORKS}{foo\themycounter}  \begin{document}  \section{\mystepFAILS}  \section{\mystepWORKS}  \end{document}   Why does the command with \mystepFAILS throw an error? What is so special about \stepcounter? Any ideas? Updating a field programmatically, hook_node_update Why are there no discrete zero sets of a polynomial in two complex variables? Why is the zero set in $\mathbb{C}\times\mathbb{C}$ of a polynomial $f(x,y)$ in two complex variables always non-discrete (no zero of $f$ is isolated)? Range of A and null space of the transpose of A So I'm complete stuck with something. I know it the following statements are true (or at least the seem to be from the results that I got from messing around with it a bit on MATLAB), but I don't understand why they are true or how to show so. Let $A$ be and $m$X$n$ matrix. Show that:  a) if $x \in N(A^TA)$ then $Ax$ is in both $R(A)$ and $N(A^T)$.   For this one I messed around with it with my own examples and I got $Ax=0$, therefore satisfing the statement, but I don't understand what's actually going on.   b) $N(A^TA)=N(A)$  again, makes sense when I see the results in MATLAB, but don't undestand why it works.  c) $A$ and $A^TA$ have the same rank  d) If $A$ has linearly independent columns, the $A^TA$ is nonsingular.  For the last two I have no idea on how to even start showing the relationship. I feel like I'm missing some crucial relationship between $A$ and $A^TA$, but I'm just not seeing it.   I would greatly appreciate any help of sugestions on how to show that these statements are true.   Thank you very much. On my fully updated Ubuntu 18.04.3 system, audio doesn't work unless I switch between outputs. When I boot my PC, the right output (stereo speakers) is already selected by default, but there is no audio from Chromium, Firefox, VLC or any other program. However, the GNOME speakers test works. I can hear "front left" and "front right" from there, but no audio from other programs. In order to fix that, I can simply switch to another audio output (e.g. HDMI out) and then switch back to the stereo speakers, and the audio will magically work. Any idea why? It's not a big deal because it takes a couple of seconds to switch between outputs, but it's kind of annoying to do that after every reboot. What licence is subscriber content provided under 4.0, 3.0 or them all? In the footer it says:     site design / logo © 2018 Stack Exchange Inc; user contributions licensed under  with . rev 2018.8.7.31273   However, in the footer under Company > Legal > '6. Content Permissions, Restrictions, and Creative Commons Licensing' it instead doesn't specify which CC BY-SA licence we're releasing our content under. It also links to the CC BY-SA 4.0 license:     The CC-BY-SA Creative Commons license terms are explained in further detail by , but you should be aware that all Public Content you contribute is available for public copy and redistribution, and all such Public Content must have appropriate attribution.   Since  if subscriber content is only provided under 4.0, where the footer says 3.0 it can cause users to break the licences.  The footer under Area 51 also mentions that content is licensed under CC BY-SA 2.5.  Since it's not defined which version of the license the content is provided under, I also interpret it to potentially mean all the versions.    What license is subscriber content licensed under? Alternative to itoa() for converting integer to string C++? I was wondering if there was an alternative to itoa() for converting an integer to a string because when I run it in visual Studio I get warnings, and when I try to build my program under Linux, I get a compilation error. How do I build a SOQL query for records in a list of IDs? Can some one correct my soql? I need to export records in data loader like:  WHERE Id IN ('123123123','123123fsdf')   But this following query does not work for me:  SELECT Id, Syndication_Documents__c FROM ContentVersion  WHERE Syndication_Documents__c in : 'a4fa0000000KzbV','a4fa0000000KzbW'