On clicking the open button, I am trying to fetch the path of the file, including the file name I opened.  Code:  private void jFileChooser1ActionPerformed(java.awt.event.ActionEvent evt) {        JFileChooser chooser=new JFileChooser();     String path=chooser.getSelectedFile().getAbsolutePath();//error     System.out.println(path); }       But I am getting a null pointer exception in the commented (//errror) line.   Where am I going wrong?
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?
Windows 7: Disable Lock Workstation After 10 Minutes Using Group Policy On my Windows 7 PC the system becomes locked after 10 minutes of inactivity. Usually I would find this setting next to the screen-saver configuration. The setting is grayed out, however.  I think this is because of corporate group policy. As I am an administrator on this computer I should be able to reconfigure the group policy setting using gpedit.msc.  What is the group policy setting that I need to change to prevent automatic locking of my workstation?  Edit: I don't have configured a screen-saver. I also want to continue to be able to lock the workstation manually. Reputation does not update after community wiki is removed from a post, and does not match the value displayed in the reputation audit Problem with packages subfiles and import.sty after using TexLive Utility for updating Everything worked fine before using TexLive for updating my packages three days ago. Now it is not possible anymore to use the package subfiles   Here are the MWE  The minimum Preamble.tex file  \documentclass{amsart} \usepackage{subfiles}   The MWE.tex file  \documentclass[MWE.tex]{subfiles} \begin{document} MWE \end{document}   When I compile the MWE file I get on the console  This is pdfTeX, Version 3.14159265-2.6-1.40.20 (TeX Live 2019) (preloaded &gt;format=pdflatex)  restricted \write18 enabled. entering extended mode  (./MWE.tex  LaTeX2e &lt;2020-02-02&gt; patch level 5  L3 programming layer &lt;2020-02-25&gt; (/usr/local/texlive/2019/texmf-dist/tex/latex/subfiles/subfiles.cls  Document Class: subfiles 2020/02/14 v16 Multi-file projects (class)  Preamble taken from file `MWE.tex'  (/usr/local/texlive/2019/texmf-dist/tex/latex/tools/verbatim.sty)  (/usr/local/texlive/2019/texmf-dist/tex/latex/import/import.sty)  ! LaTeX Error: File `import.sty' not found.  Type X to quit or &lt;RETURN&gt; to proceed, or enter new name. (Default extension: sty)  Enter file name:   I checked and the import.sty file is in the right directory, and everything worked fine before. Do you have any idea about what happened (apart from the fact that I should not upgrade stuff before the official releases of TexLive I suppose  ...)? Sex worker student offering her (lawful) services One of my students is an escort/stripper and she has offered me (and other faculty in my department) her "services". I am pretty sure my initial reaction of "thanks for letting me know, now can you answer the question about how to calculate the standard deviation", may not have been the best reaction. The offers have continued. My head of school is aware of the issue, and has asked if I want him to do anything.  Is the student doing anything wrong by offering her services to me? For what it is worth, prostitution is legal in the UK. Is this any different then a student telling me she works in a restaurant?  What is the correct response in a situation like this? "Reality" of length contraction in SR I was in argument with someone who claims that length contraction is not &quot;real&quot; but only &quot;apparent&quot;, that the measurement of a solid rod in its rest reference frame is the &quot;real length&quot; of the rod and all other measurements are somehow just &quot;artificial&quot; and &quot;apparent&quot;. Seemed to me like a bad conversation about poorly defined words and not really relevant to physics, but then some quotes were offered:  ...so that the back appears closer to the front. But of course nothing has happened to the rod itself.  (Rindler)  The effects are apparent (that is, caused by the motion) in the same sense that proper quantities have not changed.  (Resnick &amp; Halliday) At the same time, the  insists that length contraction and time dilation are &quot;real&quot;, with observable consequences:  Time and space dilation are often referred to as ‘perspective effects’ in discussions of STR. Objects and processes are said to ‘look’ shorter or longer when viewed in one inertial frame rather than in another. It is common to regard this effect as a purely ‘conventional’ feature, which merely reflects a conventional choice of reference frame. But this is rather misleading, because time and space dilation are very real physical effects, and they lead to completely different types of physical predictions than classical physics. [...] However, this does not mean that time and space dilation are not real effects. They are displayed in other situations where there is no ambiguity. One example is the twins' paradox, where proper time slows down in an absolute way for a moving twin. And there are equally real physical effects resulting from space dilation. It is just that these effects cannot be used to determine an absolute frame of rest.  I went through a lot of Einstein, Minkowski and Lorentz original material, and didn't find anything about what is &quot;real&quot; and what is not. Finally, I know about muons, where the effects of SR seem to be very real (from , but I had seen it in a physics class before):  When a cosmic ray proton impacts atomic nuclei in the upper atmosphere, pions are created. These decay within a relatively short distance (meters) into muons (their preferred decay product), and muon neutrinos. The muons from these high energy cosmic rays generally continue in about the same direction as the original proton, at a velocity near the speed of light. Although their lifetime without relativistic effects would allow a half-survival distance of only about 456 m (2,197 µs×ln(2) × 0,9997×c) at most (as seen from Earth) the time dilation effect of special relativity (from the viewpoint of the Earth) allows cosmic ray secondary muons to survive the flight to the Earth's surface, since in the Earth frame, the muons have a longer half life due to their velocity. From the viewpoint (inertial frame) of the muon, on the other hand, it is the length contraction effect of special relativity which allows this penetration, since in the muon frame, its lifetime is unaffected, but the length contraction causes distances through the atmosphere and Earth to be far shorter than these distances in the Earth rest-frame. Both effects are equally valid ways of explaining the fast muon's unusual survival over distances.  So which is which? Why do Rindler, Resnick &amp; Halliday use the word &quot;apparent&quot;? Word for "not consciously aware of" What's the word to convey the meaning "not consciously aware of"? Capacity of pen drive shown is less than the actual I have a 8 GB pendrive. I used to write raw data into the pendrive (without creating filesystem) using the dd command.    Today, when I inserted the pen drive, the I am unable to write anything on to it.  When I open gparted it is showing the total space on the pen drive as 500 MB. I am unable to create a new partition table or a partition on the pen drive now.   Here is the fdisk -l output.   Disk /dev/sdb: 0 MB, 512000 bytes 255 heads, 63 sectors/track, 0 cylinders, total 1000 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 4096 bytes I/O size (minimum/optimal): 4096 bytes / 4096 bytes Disk identifier: 0x00095df6   What's wrong with the pen drive? How can I recover the lost space?   Device Boot      Start         End      Blocks   Id  System   When I open gnome-disks, it shows the total space as 8 GB but when I try to create a new partition using it, it shows the following error:  Error creating partition on /dev/sdb: Command-line parted --align optimal --script "/dev/sdb" "mkpart primary ext2 1MiB 7969177599b"' exited with non-zero exit status 1: Error: The location 7969177599b is outside of the device /dev/sdb.  (udisks-error-quark, 0) I have very old Computer  What's the Best Operating System for Old Computer? What should I do if a question has changed since I answered it? The other members vote my answer down because it actually doesn't answer the current question.  This kind of editing sometimes happens with  where the OP keeps adding new questions, making my pre-existing answer now incomplete.  But another pattern is when the OP asks an "XY problem" question, an answer points it out, and he changes the question to react to that.  Those answers now not only aren't answers but can look very tangential to people who don't review the edit history. Password Protect QGIS project On a shared computer, I have a QGIS project which links up to a PostGIS database that contains my data. If a user wants to access layers from the db, they have to enter the db credentials, so that's OK.   However, I have previously logged on and imported layers from my db into QGIS, and manipulated them in QGIS (styling options based on meta-data, etc.)... Anybody who opens my QGIS project can view these layers in QGIS, and can therefore see the data I wish to be protected in my db.  Is there a way to password protect my QGIS project? I've noticed a distressing tendency for questions that seem basic or overly short to be immediately closed and downvoted into oblivion.  Case in point:   Within a minute of being asked, this question received 12 downvotes and was closed as "not a real question".  That particular question is a very real, non-trivial question, but it had somewhat poor grammar and looked a little like a much simpler question.  Can we try to be a little more accepting? What are the differences in targets, and when should I switch to one? So I get the 4 options for target selection are:   Attackers Badges Randoms K.O.s   What I don't understand is the pros/cons for selecting each one, and what situations would make each one useful.  Things like Badges and K.O. makes no sense to start off with because nobody starts off with badges, and nobody is going to start off near death unless they are purposely trying to lose (by hard dropping int he same position). I've tried the strategy then of just sticking with Attackers, but then I all of sudden get wave after wave of garbage late into the game.    So it begs the question -- what are the differences in target choices, and how can I use that to my advantage to become a Tetris 99 champion? I'm looking for a symbol for skeptical consequence so that I can write that something, B, is a skeptical consequence of something else, A.  In a book I read it's written like \(A \vdash B\) or \(A \sststile{}{} B\) but the horizontal line is wavy like \sim, has the same width as the vertical line and does not vary in width. So, what I'm looking for is a binary relation symbol that is similar to the combination of the first two and the last relation in the following image:    That is, something similar to the following mockup but the wavy line should be such that it has a constant width and the same width as the vertical line:    I've tried  without success. Set the location in iPhone Simulator How can I set the location (as it's picked up in CoreLocation services) in the iPhone Simulator? Bug? LaTeX misparses nested optional arguments LaTeX seems to be having problems handling nested optional arguments. I've included a minimal code example that generates the error:  \documentclass[12pt,oneside]{book} \begin{document}  \newcommand{\termbad}[2][]{#2#1} \newcommand{\termgood}[2][]{#2#1}  \newcommand{\up}[1]{#1} \newcommand{\dd}[1][]{#1}  \termgood{\up{Tart}}{Pop} \termbad[\up{Tart}]{Pop}      \termgood{\dd[Tart]}{Pop} \termbad[{\dd[Tart]}]{Pop} %\termbad[\dd[Tart]]{Pop}   \end{document}   If you run this code, it works. If you remove the % in the second to last line, it fails with:  Runaway argument?  Tart{Pop} \par \par \end {document}  !File ended while scanning use of \dd.   After further tinkering, I have discovered the problem: LaTeX is reading the ] for the inner optional argument as the end of the outer optional argument and then passing a malformed argument in. So it is passing in \dd[Tart as the optional argument to \termbad instead of \dd[Tart].  This still feels like a bug to me. Nesting braces in arguments works, brackets should as well. The following are workarounds:   Enclose the inner optional argument in braces (as in the line before %). Redefine your inner function to require its argument instead of using optional arguments. Redefine your outer function to require its argument instead of using optional arguments.   Any one of the three works around the issue.  (Reposted here; question was originally posted to stackexchange and then closed instead of being migrated.) How to fix "W: Duplicate sources.list entry"? I keep getting this warning whenever I try to run sudo apt-get update.  W: Duplicate sources.list entry http://archive.ubuntu.com/ubuntu/ precise-updates/main i386 Packages (/var/lib/apt/lists/archive.ubuntu.com_ubuntu_dists_precise-updates_main_binary-i386_Packages) W: You may want to run apt-get update to correct these problems   Below is the output from /etc/apt/sources.list file:  deb http://archive.ubuntu.com/ubuntu precise main restricted deb-src http://archive.ubuntu.com/ubuntu precise main restricted  deb http://archive.ubuntu.com/ubuntu precise-updates main restricted deb-src http://archive.ubuntu.com/ubuntu precise-updates main restricted  deb http://archive.ubuntu.com/ubuntu precise universe deb-src http://archive.ubuntu.com/ubuntu precise universe deb http://archive.ubuntu.com/ubuntu precise-updates universe deb-src http://archive.ubuntu.com/ubuntu precise-updates universe  deb http://archive.ubuntu.com/ubuntu precise multiverse deb-src http://archive.ubuntu.com/ubuntu precise multiverse deb http://archive.ubuntu.com/ubuntu precise-updates multiverse deb-src http://archive.ubuntu.com/ubuntu precise-updates multiverse  deb http://archive.ubuntu.com/ubuntu precise-security main restricted deb-src http://archive.ubuntu.com/ubuntu precise-security main restricted deb http://archive.ubuntu.com/ubuntu precise-security universe deb-src http://archive.ubuntu.com/ubuntu precise-security universe deb http://archive.ubuntu.com/ubuntu precise-security multiverse deb-src http://archive.ubuntu.com/ubuntu precise-security multiverse   How do I fix it? Singular or plural "set"? Restore deleted photos I accidentally deleted the entire "downloaded" album full of pictures from my Samsung Galaxy S2 (SPH-D710) and am trying to use a  I downloaded.  My phone will not show up as a remove-able storage device on my computer, or on the program. I have tried to change the USB settings on my phone but there is no USB settings when I go to Settings > Wireless and networks as most information instructs.   I found the setting for USB debugging by going to Settings > Developer options and can turn that on and off, but that is the only setting I can find relating to USB storage.   When I connect it to the USB cord it gives me MTP or PTP options but again no USB options.   Any advice??? Thank you! translation invariant of integral on $\mathbb{R}$ Problem 1: Let $f\in L^1(\mathbb{R})$, show $\int_\mathbb{R}f(t)dt=\int_{\mathbb{R}}f(x+t)dt,\forall x\in (-\infty, \infty)$.  Problem 2: Let $f\in L^1(\mathbb{R})$,show $\displaystyle \lim_{t\rightarrow 0}\int_{\mathbb{R}}|f(x+t)-f(x)|dx=0$.  My try for Problem 1:  Consider $\displaystyle \int_{\mathbb{R}}f(t)dt=\lim_{n\rightarrow \infty}\int_{-n}^nf(t)dt=\lim_{n\rightarrow \infty}\int_{\mathbb{R}}f_n(t)dt$, where $f_n(t)=f(t)\chi_{[-n,n]}$.  And since $dt=d(x+t)$, we have $\displaystyle \int_{-n}^nf(x+t)dt=\int_{-n+x}^{n+x}f(t)dt$.  So for each $x\in (-\infty,\infty)$,  $$ \begin{split} \int_{\mathbb{R}}f(t)-f(t+x)dt &amp;=\lim_{n\rightarrow \infty}\int_{\mathbb{R}}f(t)(\chi_{[-n,n]}-\chi_{[-n+x,n+x]})dt\\ &amp;=\lim_{n\rightarrow \infty}\int_{\mathbb{R}}f(t)(\chi_{[-n,-n+x]}-\chi_{[n,n+x]})dt\\ &amp;=\lim_{n\rightarrow \infty}\lim_{k\rightarrow \infty}\int_\mathbb{R}\varphi_k(t)(\chi_{[-n,-n+x]}-\chi_{[n,n+x]})dt\\ &amp;=\lim_{k\rightarrow \infty}\lim_{n\rightarrow \infty}\int_\mathbb{R}\varphi_k(t)(\chi_{[-n,-n+x]}-\chi_{[n,n+x]})dt \end{split} $$ where $\varphi_k(t)$ is simple function pointwise converges to $f(t)$, simple function vanish out of set of finite measure, so $\varphi_k(t)(\chi_{[-n,-n+x]}-\chi_{[n,n+x]})$ vanishes when $n$ big enough(is this right?)    Another try:  Since $f\in L^1$, $f$ is bounder a.e. so can be approximated by simple functions, and $\chi_{A+t}(x)=\chi_A(x-t)$,thus $$\int f(t)=\lim_n\int\varphi_n=\lim_n \sum_{i=1}^nc_i\mu(E_i)=\lim_n \sum_{i=1}^nc_i\mu(E_i-x)=\int f(t+x)$$  For problem 2, I guess they share the same method.   Any help or correction about these two problems? Thanks. I want to get the following:    I tried the following  \[    a(i,k) \leftarrow     \min\Big\{0, r(k,k) + \sum_{i^{'} | i^{'}\notin \{i,k\}}\max\{0, r(i{'},k)\}\Big\} \]   and got    How can I make the part under the summation extend to left and right without making a space between plus and max as in the first figure?