I have a JTable, which was built in Netbeans, with a column that is set to Boolean value. To obtain the rows that were checked, the user has to click the 'Reorder' button which checks the table to see which rows were selected.  The code that is supposed to find the stock id based on if the JCheckBox is checked is as follows:     for(int i=0; i&lt;jTable2.getModel().getRowCount(); i++){       boolean check = (Boolean) jTable2.getModel().getValueAt(i, 4);       if(check){             Object o = (Object)model2.getValueAt(i, 0);             int stockID = Integer.parseInt(o.toString());             System.out.println(stockID);         }     }       Note that model2 is jTable2.getModel(). The above code throws the NullPointerException. If I print out    jTable2.getModel().getRowCount()   I will get the accurate row count. If I print out   boolean check = (Boolean) jTable2.getModel().getValueAt(2, 4)   I will get the accurate boolean value. But it throws the exception when I use the code in a for loop.
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?
is keyword in Python Let $G$ be a group of order $150$.  I must show that it has a normal subgroup of order $25$.  The hint says to show that is has a normal subgroup of order $5$ or $25$.  Now from Sylow, I know that the number $n_5$ of Sylow-$5$ subgroups (which each have $25$ elements) must be either $1$ or $6$, since $n_5$ must also divide $6$.  Now clearly if $n_5=1$ we are done, so I can assume that $n_5=6$.  My problem is I haven't figured out how to use this information (I am going for a contradiction, just based on what the problem asks me to prove).  I know by Cauchy's theorem I can get a subgroup of order $5$, but I don't see immediately if it must be normal.   Any direction I should try to be moving? Multiple WHERE clause in Linq Just noticed the "meta user" link under the picture and reputation on the Stack Exchange user's page. It doesn't seem to work for all users. Error is "Page Not Found".   Not working:  /  Working:  /    My guess is this is because they've never logged into the meta site. Possible Duplicate:          Most commands I use in linux behave exactly the same whether I include the trailing slash / character on the end of a directory name or not.  For example:  ls /home/cklein ls /home/cklein/  cp foo bar cp foo/ bar/   When does this trailing slash matter?  What is the semantic meaning of the trailing slash? What does kill 0 do actually? In the man page, it says:  kill [ -s signal | -p ] [ -a ] [ -- ] pid ...  pid... Specify the list of processes that kill should signal.  Each pid can be one of five things:           0      All processes in the current process group are signaled   And I tried like this in bash:  $ man kill &amp; [1] 15247 $ [1]+  Stopped                 man kill $ kill 0 $ ps 15247 pts/41   00:00:00 man   Here 0 is used as pid. As I understood, kill 0 will kill all processes in the current process, which includes pid15247. However, it didn't do anything in this example. Does anyone have ideas about how to use it? Show $\frac{a_{1}+...+a_{n}}{b_{1}+...+b_{n}}$ is between the smallest and largest fraction $\frac{a_{i}}{b_{i}}$, where $b_{i}&gt;0$.  Attempt  Assume the largest is $\frac{a_{n}}{b_{n}}\Rightarrow$  $\frac{a_{n}}{b_{n}}-\frac{a_{1}+...+a_{n}}{b_{1}+...+b_{n}}\Rightarrow $  $\frac{b_{1}+...+b_{n-1}}{{b_{1}+...+b_{n}}}[\frac{a_{n}}{b_{n}}-\frac{a_{1}}{b_{1}+...+b_{n-1}}-...-\frac{a_{n-1}}{b_{1}+...+b_{n-1}}]\Rightarrow $  if $a_{1}&lt;0$, $w=\frac{a_{n}}{b_{n}}-\frac{a_{1}}{b_{1}+...+b_{n-1}}-...-\frac{a_{n-1}}{b_{1}+...+b_{n-1}}&gt;\frac{a_{n}}{b_{n}}-\frac{a_{2}}{b_{1}+...+b_{n-1}}-...-\frac{a_{n-1}}{b_{1}+...+b_{n-1}}$  any hints or solutions? The question is to calculate the radius of convergence of $\sum\limits_{n=0}^\infty n!x^{n^2}$.  I dont know how to calculate R.O.C for such type of questions involving $n^2$ as power of x. How do we do this? Any help appreciated. How to disable Import option in LibreOffice Calc while pasting text in a cell? I'm making a table in which I have to copy few lines from pdf to a table. I'm using LibreOffice calc for table making purpose. Problem is that even though I am copying simple text from the pdf, when I paste it to LibreOffice, Import Option keeps on poping up(randomly-sometimes it pop up sometime it does't). And due to this pasted text's font size also very small. Desired result is that when I paste the text in the cell, it just got pasted in the cell, without any time wasting popup which also disturbs the font size. Same question is asked here but no solution. Reputation and inbox notification shows up again after refresh Does installing many programs really slow down Windows? Using Joint Distributions and conditional probabilities This exercise is particularly confusing me because I do not understand the distribution of 'X-Y' or how to calculate the probabilities Move EFI System Partition to another drive Sometimes I want to learn about a new programming related issue—topics such as DB ORM, search indexer, identity providers, logging, etc.  When I don't know anything about a subject, I ask for benchmarks or comparisons. I got some serious answers like links to tests, pros/cons, and Gartner's reviews. I found these very constructive and helpful. But then the question was blocked or deleted. Sometimes this happens even before I get an answer.  So where would it be more appropriate to ask questions about third party products and/or open source frameworks with which I am completely unfamiliar? What could cause a microcontroller to unexpectedly reset? One particularly irritating variety of bug in a microprocessor-controlled system is for the microprocessor to unexpectedly reset. An important tool for debugging this kind of problem is a list of possible causes. What could cause a microcontroller to unexpectedly reset? How are release codenames chosen? So I was configuring VS code on my Notebook when suddenly I noticed that my interface font got really small on my desktop, terminal and files. I use Gnome Tweaks Tool to increase my scaling factor to 1,15 , but, even though it was active, the font stayed tiny. The solution I found was moving my scaling factor, which instantly fixed my font issue, however, every time I restart my Notebook the font gets tiny again and I have to repeat the process. I tried reseting my font configuration using this command, but had no success. gsettings reset org.gnome.desktop.interface text-scaling-factor  I also tried using the command dconf reset -f /  Finally, I tried using dconf-editor, but still had no success altering the font rendering DPI or changing the scaling factor. All of the steps I mentioned fixed my fonts temporarily, but the issue still persists when I restart my Notebook I am out of ideas and even considered getting a fresh Ubuntu install by now... My video card: NVIDIA GeForce GTX 1050 GPU Gray cone obscuring/clipping the 3D Viewport What is the radius of convergence of $\sum z^{n!}$? How to find the radius of convergence of $\sum z^{n!}$?   I'm used to applying the ratio test to power series of the form $\sum a_{n}z^{n}$, but for a different power of $z$, I am a bit stumped. What about $\sum z^{2n+a}$ for another example? Where $a\in \mathbb{R}$. Custom Button on Lightning Experience I created a custom button Send Email in Lightning Experience. The problem is that button in visible in feed section layout, but I want to put it in the upper right corner of page layouts near Edit, Clone, Delete ecc....  How Can I do that? Thanks  I add an image that explain the situation.    EDIT: I would like to explain you better my problem.  I have created three custom quick action:   I have added them to the case page Layout as you can see    I would like to understand the reason why I don’t see these three custom action in the Page Layout in the section in the top right