Please help to escape NullPointExeption error in the String.split() method in Java. String got from the user entering. It can't compile. In the case of hard code of the variable all is fine.   Class Calculator:  public class Calculator {     private String mathExpression;      public void setMathExpression(String mathExpression) {         this.mathExpression = mathExpression;     }      private String[] parts = mathExpression.split(" ");      private String firstNumber1 = parts[0];     //add other elements to the array...     public void calculatorRun() {         //using all the variables     } }   Class CalculatorTest:  public class CalculatorTest {     public static void main(String[] args) {         Scanner scanner = new Scanner(System.in);         String userAnswer = "y";         Calculator calculator = new Calculator();          while (userAnswer.equals("y")) {             System.out.print("Please put the math expression: ");             calculator.setMathExpression(scanner.nextLine());             calculator.calculatorRun();         }     } }
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 the difference is here? Are you seeing ? VS Do you see? Are you seening family members arriving at the hospital to find some of the miners? ( exact quote from BBC presenter asking someone over the phone )  Do you see .......  Difference in meaning not grammar. Login as other user setting for other profile except System Adminsitrator If a user is setup as System Administrator profile, the user can login as other user. However, is there any option that I can enable this function for other profile except System Administrator because I don't want to give them other System Administrator permission access?  In the past as I remember in summer 12, there's an option called "managing user permission" which allow me to disable or enable the profile to login as other user. But I don't see this anymore. When should I use "a" vs "an"? In the following example, is it appropriate to use a or an as the indefinite article, and why?     He ate __ green apple.   I know that in the case of just "apple", it would be "an apple," but I've heard conflicting answers for "green apple," where the noun is separated from the article by an adjective.  Also, which is more appropriate in this case:     He ate  __ enormous Pop-Tart. Unable to upgrade pip Does the hom-tensor adjunction hold for $O_X$ modules also? With sheaf hom and sheaf tensor product, the statement would consist of a natural transformation $Hom_O (M \otimes_O N, K)\cong_{nat} Hom_O(M, Hom_O(N, K))$, $O = O_X$ is the structure sheaf and $M,N,K$ are sheaves of $O_X$ modules.  If true I think I can check this by hand, by describing sheaves in terms of compatible germs, defining this adjunction on the germs and checking that they glue together. It is easier in the quasi-coherent sheaves on a scheme case because then one can just work in an affine cover and the distinguished base.  I am little bit concerned that one might need a finite presentation hypothesis somewhere, in order for $Hom$ to localize well. ($Hom_{R[S^{-1}]}(M[S^{-1}], N[S^{-1}]) \cong Hom_R(M,N)[S^{-1}]$ needs $M$ finitely presented.) Connecting subplots Is there a way to draw a sort of connection between subplots in TiKz/pgfplot, like in this ? I'm looking to achieve something like this:    But I would need to draw the "x 2000" line between the plots.  EDIT: So right now I have something like this:    Coming from my main.tex:  \input{aipcheck}  \documentclass[final]{aipproc}  \layoutstyle{8x11single} \usepackage[utf8]{inputenc} \usepackage{algorithm2e} \usepackage{color} \usepackage[usenames,dvipsnames]{xcolor} \usepackage{cleveref} \usepackage{pgfplots}  \pgfplotsset{ tick label style={font=\tiny}, %axis numbers label style={font=\small}, %axis labels legend style={font=\tiny} }  \begin{document}  (...)  \begin{figure}     \centering     \newlength\figureheight      \newlength\figurewidth      \setlength\figureheight{5cm}      \setlength\figurewidth{5cm}     \input{figs/_ddmp2d.tikz} \label{fig2D} \end{figure}   with _ddmp2d.tikz, originally created from matlab2tikz, but already modified, containing:  % This file was created by matlab2tikz v0.3.3. % Copyright (c) 2008--2013, Nico Schlömer &lt;nico.schloemer@gmail.com&gt; % All rights reserved. %  % The latest updates can be retrieved from %   http://www.mathworks.com/matlabcentral/fileexchange/22022-matlab2tikz % where you can also make suggestions and rate matlab2tikz. %  %  %   \begin{tikzpicture}  \begin{axis}[% width=\figurewidth, height=\figureheight, scale only axis, xmin=0, xmax=15, xlabel={Number of iterations}, ymin=0, ymax=16000000000000, name=plot1, after end axis/.append code={\coordinate (a) at (axis description cs:1,0);}]  \addplot [ thick, color=red, dash pattern=on 1pt off 3pt on 3pt off 3pt, forget plot ] table[row sep=crcr]{ 1 15841000000000\\ (...) 15 25160000000\\ }; \addplot [ thick, color=black, dashed, forget plot ] table[row sep=crcr]{ 1 15841000000000\\ (...) 15 52501000000\\ }; \addplot [ thick, color=blue, dotted, forget plot ] table[row sep=crcr]{ 1 15841000000000\\ (...) 15 5324200000\\ }; \addplot [ thick, color=green, solid, forget plot ] table[row sep=crcr]{ 1 15841000000000\\ (...) 15 551920000\\ }; \addplot [ thick, color=green, solid, forget plot ] table[row sep=crcr]{ 3 0\\ 3 16000000000000\\ };  \addplot [ thick, color=blue, dotted, forget plot ] table[row sep=crcr]{ 4 0\\ 4 16000000000000\\ }; \addplot [ thick, color=black, dashed, forget plot ] table[row sep=crcr]{ 5 0\\ 5 16000000000000\\ }; \addplot [ thick, color=red, dash pattern=on 1pt off 3pt on 3pt off 3pt, forget plot ] table[row sep=crcr]{ 8 0\\ 8 16000000000000\\ }; \end{axis}  \begin{scope}[xshift=5cm] \begin{axis}[% width=0.35\figurewidth, height=\figureheight, scale only axis, xmin=995, xmax=1000, xtick={997,998,999,1000}, xticklabels={$997$,$998$,$999$,$1000$}, ymin=0, ymax=8000000000, at=(plot1.right of south east), anchor=left of south west, yticklabel pos=right, axis x discontinuity=crunch, after end axis/.append code={\coordinate (b) at (axis description cs:0,1);} ] \addplot [ thick, color=red, dash pattern=on 1pt off 3pt on 3pt off 3pt ] table[row sep=crcr]{ 995 6093100000\\ 996 6093100000\\ 997 6093100000\\ 998 6093100000\\ 999 6093100000\\ 1000 6093100000\\ };  \addplot [ thick, color=black, dashed ] table[row sep=crcr]{ 995 1577100000\\ 996 1598000000\\ 997 1598500000\\ 998 1628600000\\ 999 1631000000\\ 1000 1595900000\\ };  \addplot [ thick, color=blue, dotted ] table[row sep=crcr]{ 995 2592000000\\ 996 2591900000\\ 997 2591700000\\ 998 2591600000\\ 999 2591500000\\ 1000 2591400000\\ };  \addplot [ thick, color=green, solid ] table[row sep=crcr]{ 995 391810000\\ 996 391810000\\ 997 391810000\\ 998 391810000\\ 999 391810000\\ 1000 391810000\\ };  \end{axis} \draw[gray] (a) -- (b) node[pos=0.5,sloped,fill=white] {$\times$2000}; \end{scope}  \end{tikzpicture}% Omission of 'for' with various quantified time intervals: influence of verb Just freeze an application (suspend the CPU, save its state to disk) and 'defrost' it when I want to use it 4 weeks later. I have two partitions, one of them has a file system and the other is unallocated.  How to merge two partitions? Assume $f:A\to A'$ is a function, $B\subset A'$, $C\subset A'$, and $f^{-1}(B\cap C)=\emptyset$  How can we see that $f^{-1}(B)\cap f^{-1}(C)=\emptyset$? What to do when visa admission expires during lockdown? I was admitted to the US as a visitor for a period which expires soon.  Until tonight, I had solid plans to return to Europe soon, prior to the expiration of the visa entry, but that is no longer an option.  I do not wish to overstay or do anything that would cause problems with future admissions or visa applications.  However, I can't go back to Europe because of new travel restrictions put in place by the US government (/resulting flight cancellations).    My passport still has years of validity left.  What is the best course of action? Is there any official guidance on this subject?  I am a little concerned that contacting officials to explain the situation would just lead me to be flagged for prompt enforcement action, but I don't want future problems.    Related:  and .    Update: OP now planning an escape to Canada.  The question still stands, though. I've been trying to install 12.04 for a while now, I'm running on Windows 7 and I already made the partition (it's dynamic). I've tried booting from a disc and also the Windows installer. I haven't tried used any repair-boot programs or anything. Every time I tried to load from either, I get an error:  command=C:\windows\sysnative\bcdedit.exe /set {03f9077f-661f-11e1-845a-d08b36406c3d} device partition=U;  retval=1  stderr=An error has occured setting the element data. The request isn't supported  stdout=   Then after that, it makes a log file with information that I don't understand.  If it is simply due to the fact of it being a dynamic partition, someone please help. If it is more extensive, anyone with details on possible solutions or definite ones please express them. I'm trying to prove that ${n \choose r}$ is equal to ${{n-1} \choose {r-1}}+{{n-1} \choose r}$ when $1\leq r\leq n$.  I suppose I could use the counting rules in probability, perhaps combination= ${{n} \choose {r}}=\frac{n!}{r!(n-r!)}$.  I want to see an actual proof behind this equation.  Does anyone have any ideas? Can Cycles physically mix colours? Was there any reason why Dr Soong chose for Data's eyes to be yellow?  I can understand that he wasn't going for a completely human-looking android based on his skin color, but why yellow eyes? `/usr/bin/cd` is not working in mac terminal Let L1 be the line passing through the point $P_1=(−11, 10, −1)$ with direction vector $\vec d_1=\begin{bmatrix}−2\\ 3\\ −1\end{bmatrix}t$, and let $L_2$ be the line passing through the point $P_2=(−8, 9, 10)$ with direction vector $\vec d_2=\begin{bmatrix}−1\\ 3\\1\end{bmatrix}t$. Find the shortest distance, $d$, between these two lines, and find a point $Q_1$ on $L_1$ and a point $Q_2$ on $L_2$ so that $d(Q_1,Q_2) = d$.   I dont really understand how to properly approach this question, how do i start? Are there any synonyms for the noun 'crush'? I must clarify, when I say 'crush', I mean the subject of an unrealistic, one-sided infatuation. For example, it can be used in this sentence: 'My celebrity crush is David Beckham.'  Could that word be interchanged for another? Preferably, can it be a word which is not necessarily too formal/complex? I've searched online for a while but can't find any synonyms for this form of 'crush.'  I want the word for a novel which is set in an old-ish fantasy period so I don't think 'crush' would feel in-place.  The main character is a lower-class worker. Back when the first discussion about deleted questions came up, I  building an official unofficial read-only archive for good deleted SE content.  I had a plan to build something like this:    Each link would point to a 1:1 scraped StackOverflow (or other SE network) deleted question (of course with a big fat disclaimer to the top, historical data, legal stuff, yada yada yada - and of course after asking Stack Exchange for permission, seeing as this would go far beyond what the CC license allows.)   I also registered a domain name that would (IMO) suit nicely, overflown.org.  However, when thinking about it, I realized doing this properly is a lot of work. You would have to:   build a scraper that can use a 10k+er's OpenID to fetch the deleted question (using the API or the data dump is for wusses. If we go through all this trouble, we want a historical document of what the site looked like "back then", right?) edit the page's DOM to remove dynamic elements, remove the "deleted" CSS classes, remove all the voting abilities from the buttons, and add the "this is historical data" disclaimer fetch - this is the biggest part and applies even if you use the API or data dump - all linked image resources (even those from imgur - even images used only in deleted questions could be purged one day), store them, and link them fetch all associated CSS style sheets and store them intelligently - preferably in a way that you don't fetch a copy of each file for each page (as normal page scrapers do), but also in a way that doesn't break if SE update their style sheets   long story short, I won't be in a position to build this any time in the foreseeable future - with old work, new work, and studying, I really have enough on my plate already.  Of course, if somebody else in the community feels like giving this a try, cool! But what I was really thinking is - maybe this is something Stack Exchange should build after all?   I know Jeff's  on these questions is used to be     @system I did think about a sweet place for them, in the bitbucket. – Jeff Atwood♦ Dec 29 '10 at 1:54   but come on. Think about it:     Future deletion discussions and changes in on-topicness policy would become way more relaxed because the popular and loved stuff has a place to go. A site for "overflown" questions could be curated by selected community members, who decide whether a contribution deserves to be archived or not.  A separate domain name (I'm happy to donate overflown.org for the purpose if desired) and the separate site design would create enough distance to the Stack Exchange network: it would be crystal clear that this read-only archive is for historical purposes only, and the existence of a question there does not mean you can ask something similar on one of the live sites. The pages would be 1:1 scrapes of what the site looked like at the time of the scraping, making it a general historical archive as well. These questions traditionally drive a lot of traffic. The possibility of continuing to show ads in the usual places would allow Stack Exchange to take advantage of that traffic without endangering content quality on the SE network. Hosting an archive like this is a job for a business, not us regular joes. A private project hosted by some community member can go down once they forget to pay a bill, or decide they want to password protect their private blog or photo album. The ideal place to host a site like this is at a company with professional admins that intends to stay online for a long time.    How about it? proving logical equivalence $(P \leftrightarrow Q) \equiv (P \wedge Q) \vee (\neg P \wedge \neg Q)$