FirebaseRecyclerAdapter throws a null object
What is a NullPointerException, and how do I fix it?
Rows to column conversion of file Suppose I have a file:  File1:   PAPER  TEAM  MANISH NISHA GARIMA JYOUTI ........etc    File2 I want:  PAPER     TEAM MANISH NISHA GARIMA     JYOUTI   Rows to column conversion of File1. Basically this suggestion for the Android app:   Many times I'll see that a post has been edited on the Android app. I'll want to see exactly what was edited, and the Android app doesn't show this. Can the revision history be added to the Android app? I'm looking for a closed-form expression (in terms of $n$), that will give the sequence  $$ (s_n) = \left( \frac{3}{10}, \, \frac{3}{10} + \frac{33}{100}, \, \frac{3}{10} + \frac{33}{100} + \frac{333}{1000}, \dots \right). $$  Can anyone think of one? I made a related post to this question several minutes ago but I realized I was interpreting the sequence wrong. Basically I would like to use on website a "Norasi" font, that was bundled with Ubuntu, but I cannot find any license. Am I allowed to distribute that font through website? What is its license? Wrong (hyper-)references after resetting chapter counter The following MWE produces a PDF whose TOC has two entries: “Foo” and “Bar” with correct page numbers. So far, so good. However, upon clicking on the link to “Bar”, I am taken to the page for “Foo” instead.  \documentclass{report} \usepackage{hyperref} \newcommand*\backmatter{\setcounter{chapter}{0}}  \begin{document} \tableofcontents \chapter{Foo} \backmatter \chapter{Bar} \end{document}   (Produced with pdflatex, run twice.)  This MWE is whittled down from a (much!) more complex document but the above does seem to reproduce the error reliably.  Re-setting the chapter count seems to confuse hyperref, even though the page references are still accurate. Notice that in my real document, \backmatter does other things, including setting the numbering style to alphabetical so there’s no chance of confusion even though both chapters are ostensibly labelled as “Chapter 1”.  How do I fix this? Is this a bug? Are there workarounds? A very basic ring theory question, which I am not able to solve. How does one show that    $\mathbb{Z}[i]/(3-i) \cong \mathbb{Z}/10\mathbb{Z}$. Extending the result: $\mathbb{Z}[i]/(a-ib) \cong \mathbb{Z}/(a^{2}+b^{2})\mathbb{Z}$, if $a,b$ are relatively prime.   My attempt was to define a map, $\varphi:\mathbb{Z}[i] \to \mathbb{Z}/10\mathbb{Z}$ and show that the kernel is the ideal generated by $\langle{3-i\rangle}$. But I couldn't think of such a map. Anyhow, any ideas would be helpful. Determine which circuits are parallel and which are in series I need to find the Equivalent Resistance across A and B. The problem is, I don't know which one's are in series and which ones are in parallel. How do I identify which ones are parallel or series? Is there any difference between Present Perfect and Present Perfect Continuous? I have studied "present perfect" and "present perfect continuous" for a week. I know forms, verb and helping verb I should use when I write them.  For me, they have nearly same definition because I can use them interchangeably in Thai language. (My native language)  For example, the sentences        I have learned English language in the past few weeks.    I have been learning English language in the past few weeks.       have no difference in meaning to me. They both mean "I began learning the English language in the past and I am still learning it"  Can I use them interchangeably in English? Or is there any difference between them? For example, when should I use present perfect but not present perfect continuous? How to get a set $E$ such that $0<\mu(E\cap I)<\mu(E)$ for all interval $I$? How did R.A.B get to know about Voldemort's Horcruxes? Difference between differentiation and derivatives What is the difference between differentiation  and derivatives of a function ? Did other meta-humans enter a coma? In the first episode of The Flash (2014), Barry's struck by lightning, some chemicals fall on him, and he enters a coma for 9 months.  This happens when the S.T.A.R. Labs particle accelerator is turned on for the first time.  9 months later, he wakes up and has powers.  He then starts fighting crime, especially other meta-humans who were created by the same particle accelerator accident.  However, this is all 9 months after the accident, where were the other meta-humans during those 9 months?  The S.T.A.R. Labs people make it sound like they hadn't seen any meta-humans active during the 9 months Barry was out.  Did all people granted powers by the particle accelerator accident also fall into comas?  Why weren't they active heroes/villains during the 9 month gap? Can you dispel a magic effect you can't perceive? Discussions about Dispel Magic seem to imply that as long as you can perceive a magic effect in range of the spell, you can try and dispel it.   See  and  from @Miniman:      knowing where it is means that you know where it is. This allows you to use spells like Dispel Magic to remove its invisibility.   But what if you can't perceive it?  Two scenarios come in mind:   In combat, an evil wizard casts Invisibility on himself, walks away from the fray and uses the hide action on his next turn. Since PCs know/assume/deduce he's invisible and certainly in range of the spell, can one use Dispel Magic to end the spell? PCs enter a 80'&times;80' room. Can one declare: "I dispel any Invisibility spell in range", thus revealing one (the closest?) invisible enemy in the room?   What's enough to enable a caster to cast Dispel Magic on a magic effect:    perceiving (seeing, hearing, smelling, etc.) it? knowing/assuming/deducing it's there? or merely suspect/predict it? So I have seen the similar question and answers on here for $x^4 +1$, but I am having trouble extending anything there to this polynomial... I understand it is fairly trivial with Galois theory, but my class has just barely covered Field Extensions, so suffice it to say we have no Galois theory to play with.  I managed to prove it for the primes such that $p \equiv 1, 7 \pmod 8$, by noting that $2$ is a square modulo those primes and thus $x^4 - 2x^2 +1 = (x^2 -1 + 2qx)(x^2 - 1 - 2qx)$ for those $\mathbb{Z}_p$... however, trying to get a similar result for $3 \pmod 8$ and $5 \pmod 8$ has been stumping me for a long time, I am having a hard time making $q^2 = -1$ and $q^2 = -2$ give me something factorable...  I guess the worst part of all of this is that I don't think this solution is even particularly enlightening, in terms of abstract algebra. It's really just some number theory trickery. I don't think my course has prepared me theoretically for this problem, does anyone have an elementary approach to it? Using more than one set of Locators in a Manipulate Point Renderings Slightly Off in Mathematica Ubuntu kernel not upgrading with upgrade to 15.10 check if "it's a number" function in Oracle Render every Nth frame of an animation I want to render every Nth frame of an animation, in this case every 12th frame. This way I can play back the animation at 2fps and see if everything is going correctly.  I'm a real novice with Blender Python and cobbled this together:  import bpy  for f in range(startframe,endframe,NthFrame):     bpy.context.scene.frame_current = f     bpy.ops.render.render()     bpy.data.images['Render Result'].save_render(filepath="" + str(f) + '.png')    This kind of works, the right images are rendered and saved. However it completely freezes up Blender, and after about an hour it crashes on windows due to being unresponsive I guess. How can I fix this? Preferably I'd like it to work like rendering an animation normally works, i.e. being able to still use Blender and seeing the progress of each rendered frame. I've seen a lot of people talking about FPGA's before and I know that it stands for field-programmable gate array but how does it work and what is the purpose of using an FPGA?