exception in thread "main" java.lang.NullPointerException at javax.swing.ImageIcon. at labelframe at LabelTest
What is a NullPointerException, and how do I fix it?
Random integer in VB.NET I need to generate a random integer between 1 and n (where n is a positive whole number) to use for a unit test. I don't need something overly complicated to ensure true randomness - just an old-fashioned random number.  How would I do that? I have two files in a directory. One has correct permissions and the other has not. Is there a way I can "copy" the set of permissions from one file to another? Vertical uniform circular motion.. can it really be uniform? This is the picture in my mind:    For centripetal force, I learned that: $T-mg\cos\theta= \frac{mv^2}{r}$  In vertical circular motion, the velocity is naturally going to decrease as kinetic energy is converted to potential energy as the particle moves up the circle- and thus resulting into a non-uniform circular motion.  However, I was told that if tension changes accordingly, the velocity will remain constant(as from the equation). What I do not get about this part of the explanation is that which force will balance mgsinθ (tangential force in the diagram  )? When is "Y" a vowel? In school we are taught the vowels: A, E, I, O, U, and sometimes Y.    got me thinking about when the letter Y is considered to be a vowel.  I understand (perhaps incorrectly) that in words like bicycle and why it is a vowel. What about the word voyeur (as mentioned in the XKCD alt-text)?   If I've got this backwards, and Y is almost always a vowel, how can I tell when it is a consonant? Thinking back, I don't think my education ever covered the difference between them, we just memorized which letters were which. How to change the language for the front-end only? A non-blocking read on a subprocess.PIPE in Python I'm using the  to start a subprocess and connect to its output stream (standard output). I want to be able to execute non-blocking reads on its standard output. Is there a way to make .readline non-blocking or to check if there is data on the stream before I invoke .readline? I'd like this to be portable or at least work under Windows and Linux. Here is how I do it for now (it's blocking on the .readline if no data is available): p = subprocess.Popen('myprogram.exe', stdout = subprocess.PIPE) output_str = p.stdout.readline() Let V denote the Klein 4-group. Show that $\text{Aut} (V)$ is isomorphic to $S_3$ After a week in my Abstract Algebra class, the professor proposed this as a problem. I'm not entirely sure where to begin. $ V = \{ e, \tau, \tau_1, \tau_2 \}$, so I'm not sure exactly what is meant by $\text{Aut} (V)$. Is it simply saying that the only way to have an automorphism on $V$ is to rearrange the order of the elements of $V$ and therefore $\text{Aut} (V) \cong S_3$? Do I make money in the stock market from other people losing money? i want to create new event in SharePoint calendar list in which I have some custom columns,i tried below code but it is not working      function bookingRoomForMeeting() {         var ctx = new SP.ClientContext(appWebUrl);//Get the SharePoint Context object based upon the URL           var list = ctx.get_web().get_lists().getByTitle("MyCalendarList"); //Get the List based upon the Title         var listCreationInformation = new SP.ListItemCreationInformation(); //Object for creating Item in the List         listItem = list.addItem(listCreationInformation);         listItem.set_item('Title', $("#txt_Title").val());         var date = $("#txt_startTime").val();         var dateTime = moment(date, 'DD/MM/YYYY HH:mm a').format("MM/DD/YYYY HH:mm a");         listItem.set_item('EventDate', dateTime);         var enddate = $("#txt_endTime").val();         var enddateTime = moment(enddate, 'DD/MM/YYYY HH:mm a').format("MM/DD/YYYY HH:mm a");         listItem.set_item('EndDate', enddateTime);         listItem.set_item('EmailId1', $("#txt_EmailId1").val());         listItem.set_item('EmailId2', $("#txt_EmailId2").val());         listItem.update();         ctx.load(listItem);         ctx.executeQueryAsync(             Function.createDelegate(this, success),             Function.createDelegate(this, fail)            );     } function success() {     alert("Completed"); } function fail() {     alert("operation failed"); }   list am using is SharePoint hosted app list,can any one tell me where am going wrong? "detached entity passed to persist error" with JPA/EJB code Event button as a module or as user program? Algorithm to find the irreducible polynomial What algorithm can be used find an irreducible polynomial of degree $n$ over the field $GF(p)$ for prime $p$. The reason I ask is I want to make a program for finite field arithmetic, but creating a field $GF(p^k)$ requires finding a irreducible polynomial. (I'm mostly interested in $GF(2^k)$.) Can every even integer be expressed as the difference of two primes? I hear so many terms involving the word "linear". Linear function, linear equation, linear system, linear operator, linear transformation, linear mapping, linear space, linear algebra, linear electrical circuits, linear filters, linear electrical elements, linear approximation, linear optimization.  I'm getting crazy trying to understand the application of the "linear concept" to all this aspects (function, equation, mapping, system, operator, transformation, algebra, etc.) and I wish to know the one essence that is to be linear. What something has to be to be linear? If I say something is linear, what do I know for sure about that something (no matter what the something is)?       I heard a definition of linearity is by homogeinity (scaling the input results in a scaled output) and addition (summing the inputs results in summing the outputs). Can I apply this simple definition to all the branches (operator, mapping, system, transformation, algebra, ...) I mentioned ? Do they all behave like a line ?  y = ax + b, for example, is a line but doesn't behave like a line because y is not linear. Inspired exercise Sheet from Indesign I would like to create this sheet which was made it by adobe indesign   Could someone create it with latex ?     Here's my code:  \documentclass[12pt,a4paper,twocolumn]{report} \usepackage[margin=0.5in]{geometry} \usepackage[french]{babel} \usepackage{fontspec} \usepackage{graphicx} \usepackage{amsthm,amssymb,amsfonts,mathtools} \usepackage[utf8]{inputenc} \usepackage{multicol} \usepackage{multirow} \usepackage{amssymb} \usepackage{array} \usepackage{graphicx} \setlength{\columnseprule}{0.5pt} \thispagestyle{empty} %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% \begin{document} %%%%%%%%%%head%%%%%%%%%%%%%%%%%%%%%%% \twocolumn[    \begin{@twocolumnfalse}  \begin{center}  \fbox{\Large Exercise Sheets} \end{center}     \hrulefill \end{@twocolumnfalse}   ]  %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%  \fbox{ Exercise $1$:}\\  Compute the following limits \begin{multicols}{2} \begin{enumerate} \item $\lim_{x\to 2}\dfrac{4x^{3}-5x-22}{x^{2}-x-2}$ \item $\lim_{x\to 0^{+}}\dfrac{x-\sqrt{x}}{x+\sqrt{x}}$ \item $\lim_{x\to 1}\dfrac{\sqrt{x+3}+\sqrt{x}-3}{x-1}$ \item $\lim_{x\to 2}\dfrac{x^{2}\sqrt{x+2}-8}{4-x^{2}}$ \end{enumerate} \end{multicols}  %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% \fbox{ Exercise $2$:}\\ Let $n\in\mathbb{N}^{*}$ \begin{enumerate}     \item calculate : ${\displaystyle \lim_{x\to 0}\dfrac{1-\cos(x)\cos(2x)\ldots+\cos(nx)}{x^2} }$     \item b     \item c     \item d     \item e     \item f \end{enumerate} %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% \end{document} Is there a way to output for Print. I want to save in a higher DPI than the default 72dpi say 300dpi that's a good quality for printed pieces. I tried downloading an add-on but don't know if I am installing it correctly it isn't showing up but the bar in python is green. I'm using the 2.69 version of Blender. If no such feature exists what size have any of you found best for print quality. Thank you Storage order vs Result order This is a spin-off question from .   says this on the subject of storage order (clustered index) and the output order     A lot of people believe that a clustered index guarantees a sort order on output. But that's not what it does; it guarantees a storage order on disk.   See, for example, .   I've read the blog post by Hugo Kornelis and understands that an index doesn't guarantee that the sql server reads the records in a specific order. Yet I have a hard time accepting that I can't assume this for my scenario?  CREATE TABLE [dbo].[SensorValues](   [DeviceId] [int] NOT NULL,   [SensorId] [int] NOT NULL,   [SensorValue] [int] NOT NULL,   [Date] [int] NOT NULL, CONSTRAINT [PK_SensorValues] PRIMARY KEY CLUSTERED  (   [DeviceId] ASC,   [SensorId] ASC,   [Date] DESC ) WITH (     FILLFACTOR=75,     DATA_COMPRESSION = PAGE,     PAD_INDEX = OFF,     STATISTICS_NORECOMPUTE = OFF,     SORT_IN_TEMPDB = OFF,     IGNORE_DUP_KEY = OFF,     ONLINE = OFF,     ALLOW_ROW_LOCKS = ON,     ALLOW_PAGE_LOCKS = ON)   ON [MyPartitioningScheme]([Date])   My original query was this:  SELECT TOP 1 SensorValue   FROM SensorValues   WHERE SensorId = 53     AND DeviceId = 3819     AND Date &lt; 1339225010   ORDER BY Date DESC   But I suggest that I could as well use this one (read below for my explanation):  SELECT TOP 1 SensorValue   FROM SensorValues   WHERE SensorId = 53     AND DeviceId = 3819     AND Date &lt; 1339225010   As you can see, my table rows are small (16bytes) and I've got only one index, a clustered. In my scenario, the table consists of 100.000.000 records at this moment (and this will most likely increase tenfold).  When the database server queries this table it has two ways of finding my rows, either it seeks the primary key and thereby reading and returning my values in desc. order of Date, or it has to do a full table scan. My conclusion is that a full table scan on all those records will be way too slow and the database server will therefore always seek the table via its primary key and thereby returning the values sorted by Date DESC I am writing an article in English, with some pages in Russian.  \documentclass[12pt]{article}  \usepackage[T1,T2A]{fontenc}  \usepackage[utf8]{inputenc}  \usepackage[russian,english]{babel}  \usepackage{newtxmath} \usepackage{newtxtext} \begin{document}  hello \textbf{hello}  \selectlanguage{russian} привет \textbf{привет}  \end{document}   Output:  hello hello привет привет  I am using \selectlanguage{} to switch between languages when needed.  However, I noticed that when I try to use \textbf{} when in Russian language mode, it does not work because of newtxtext, which I am using for math formulas.  Does anyone know how to solve this problem?  Thank you. If $\gcd(a,b)=1$, how can I find the values that $\gcd(a+b,a^2+b^2)$ can possibly take? I can't find a way to use any of the elemental divisibility and gcd theorems to find them. Change Error Message on FBA Login page On the default FBA Login Page, when a user enters wrong username/password an error message gets displayed:      "The server could not sign you in. Make sure your Username and Password are correct, and then try again.".    I want to change this error message to simple text      "Invalid Username and Password".    How can I achieve this?