I get a nullPointerException calling a function from some methods and not from others
What is a NullPointerException, and how do I fix it?
Why does energy have to be emitted in quanta? I was reading some popular science book and there was this sentence. It says that energy has to be emitted in discrete portions called quanta. Otherwise the whole energy in the universe would be converted into  high frequency waves.  I'm not a physicist, so this conclusion seems to me like a huge leap.  First, we assume that energy is emitted in a continuous way (not in quanta).  And how do we get to the statement "the whole energy in the universe would be converted into  high frequency waves"? Big floor symbols When I write  \lfloor\dfrac{1}{2}\rfloor   the floors come out too short to cover the fraction. How can I lengthen the floor symbols? How to detect, from browser, if user is running in Remote Desktop session? What are Guinan's powers from Star Trek: TNG? In Star Trek: The Next Generation episode "" (Season 2, Episode 16) Q seems disturbed by the presence of Guinan to the point of raising his hands as if to use his powers on her. Guinan responds by raising her hands as if to cast a "magic" spell of her own.   Is it ever established what powers she or her race may possess? If $Y$ is connected, why is $A\cup Y$ connected in this case? Toast message with Chinese characters, is it a virus? I recently received some updates today from the Play Store. Every so often a pop notification, one of those bubble ones at the bottom of the screen with Chinese characters.  The most recent update I've noticed is the ES File Explorer. I wouldn't mind, but my device is rooted and so I am at risk. I have a screenshot of the notification.  My device is the Samsung Galaxy Tab A 9.7 and I have stock ROM installed.    What my question(s) are: Do I have a virus (it's not being picked up by Avast) and if I do, how do I remove it? What can I do if a repository/PPA does not have a Release file? When updating, I get the following error message:   W: The repository 'http://ppa.launchpad.net/mc3man/trusty-media/ubuntu xenial Release' does not have a Release file.   Here, I find another statement on this error:   This recommends removing certain PPAs; and, I'm not sure if I should do that since it might mean not getting the updates that I need.    Is this what I should do? Entire function with vanishing derivatives? Let $f:\mathbb{C}\rightarrow\mathbb{C}$ be an entire function. And assume that at each point, one of it's derivatives vanishes.  What can you say about $f$?  A hint suggests that $f$ must be a polynomial. Is there a way to choose a beginning and ending edge and auto select all the edges in between? I have been using Blender for quite a long time and I just want to make sure that there isn't a better way of selecting edges, that I might not be aware of. It is so cumbersome to have to click every single edge when I don't want to select an entire edge loop but a portion of one instead. I was wondering if there is some way in to specify a start edge and an end edge and then be able to auto select every edge in between? Im asked to prove that a polynomial of an odd degree has a root. Im going to use IVT to prove this, but I'm wondering if I can use the assumption that an odd degree polynomial has either two cases:  $$ \lim_{x\to\infty}h(x)=+\infty \\ \lim_{x\to-\infty}h(x)=-\infty \\ $$ $$and$$ $$ \lim_{x\to\infty}h(x)=-\infty \\ \lim_{x\to-\infty}h(x)=+\infty \\ $$ Then by this there exists numbers $a,b$ such that $$ h(a)&lt;0&lt;h(b) $$ $$or$$ $$ h(b)&lt;0&lt;h(a) $$ Which I think would prove that odd degreed $h(x)$ has at least a root. Or is there a more convincing way to show that there are numbers in $h(X)$ greater than zero and less than zero?  edit: (sorry about the bad limit notation) Contour graphing algorithm I am not sure if this belongs on Mathematics Stack Exchange, but it is somewhat relevant here.       The Problem If you've installed any graphing/plotting apps on your smartphone, you will notice that the app will only take the equation in form of a single variable for 2D (e.g  $y=f(x)$) or in 2 variables for a 3D plot (e.g $z=f(x,y)$). This is problematic as many equations are tough to reduce to the form of $y=f(x)$ or $z=f(x,y)$. The plotters like this because this is the only way they can plot it in form of lines connecting multiple points. These plotters compute the $y$ value at fixed intervals of $x$ and join the point to the previous one. The brute force approach to counter this is to check if the function satisfies it at each point on the image. The problem is that this not only takes more time, but gives discontinuous graph for the function as the image cannot have infinite resolution.         The Question The only way to fix this is to identify which point comes after the next in the plot and join them together by a line. That is where I am stuck. How do you identify which point is sequentially the next one for a given function? Keep in mind that for a human, this might be very easy to do. But, for a computer, this requires a general algorithm. Any ideas? What is the term for replacing a name or brand with a funny pejorative / sardonicism? What is the term for when one replaces a well-known name [(Proper) noun, company, brand, etc.] with one that tries to be funny yet pejoratively descriptive, different but similar enough that one's audience can likely understand the replacement?  For example: Whole Foods ===> Whole Paycheck; Comcast ==> Scumcast; Starbucks ==> Charbucks; Kinko's == Stinko's; eBay ==> Evil Bay  I tend to use sobriquet don't believe this explicitly implies funny as well as insulting. Moniker again is close but not specific to the above description.  There is a similar question which proposes tortonym and malapropsim, but it does not seem to settle the argument definitively:   Another answer here proposes dysphemism, but to me it isn't a full fit:  because it doesn't cover the humor aspect. What are weapon damage dice? Following discussion , what constitutes a weapon damage die?  Is it any damage die dealt by the weapon? For example, consider a  longsword.     While the sword is ablaze, it deals an extra 2d6 fire damage to any target it hits.   What are the weapon damage dice? Just the 1d8 from the longsword? Or do the 2d6 Fire damage also count? I saw a dog.       I have seen a dog.   What are the differences between them? Did these events happen on the same day? Why $x^{p^n}-x+1$ is irreducible in ${\mathbb{F}_p}$ only when $n=1$ or $n=p=2$ I have a question, I think it concerns with field theory.     Why the polynomial $$x^{p^n}-x+1$$ is irreducible in ${\mathbb{F}_p}$ only when $n=1$ or $n=p=2$?   Thanks in advance. It bothers me for several days. Can I adjust starting point when using ListPlot? How to disable gedit side panel? How do i disable this stupid side panel of gedit, that somehow appeared? There is nothing in the settings or plugins. Tried rm -r -f ~/.config/gedit as well, with no success. I don't have big screen and i find it totally useless and eating up what little free space for editing documents i have. See Screenshot I want to know if there is another way to solve the equation:  $$(x+1)^y-x^z=1$$  for positive integers $x,y,z$ greater than $1$ without using the Catalan identity. Does exist? By now I only know that $x\mid y$. Finding the Eclipse Version Number Sorry for the bad English. I'm trying to use the tikz-cd package to make commutative diagrams. My code  \documentclass{article} \usepackage[brazil]{babel} \usepackage{tikz-cd} \begin{document} \begin{tikzcd} A \ar[r, "x"] &amp; B \end{tikzcd} \end{document}    The problem occurs when putting a name under the arrow, the syntax "x" is incompatible with the brazil option of the babel package. When exchanging brazil for english it works normally. I already tried using  \usepackage[main=brazil, english]{babel}, \usepackage[brazil, english]{babel} e  \usepackage[brazil, main=english]{babel}   But it did not work. I also tried to use  \usepackage[english, brazil]{babel} \usepackage{polyglossia} \setmainlanguage{brazil} \setotherlanguages{english}   And finally  \selectlanguage{english}   However, it only works if I remove the option brazil