Java lang Null Pointer Exception, onCreate
What is a NullPointerException, and how do I fix it?
When is the present perfect tense used instead of the past tense? When is the present perfect tense used instead of the past tense?    I know that the present perfect tense is used when some adverbs (e.g., never, ever) are present in the sentence; the same is true for sentences like the following one.     When you returned, I have been at home since 3:00 PM.   In which other cases should I use the present perfect? Do the following sentences require it?     I have walked downtown everyday for a year.        I have been at home since 3:00 PM. Autokey (autokey-qt) freezes and won't insert text How to modify a specified commit? Is there a single word for “one who explains his point of view very clearly”? In case of a syntax error, pdflatex usually (in \errorstopmode) gets interactive and asks you what to do. I know I can press:   X to terminate S to enter \scrollmode (continue processing without stopping if further syntax errors arise, but stop for other errors) R to enter \nonstopmode (continue processing without stopping if further errors arise) Q to enter \batchmode (continue processing without stopping if further errors arise and suppress further output to the terminal)   Apparently, only the latter three (SRQ) can be provided implicitly by the respecive \...mode commands or the -interaction=...mode command line option. However, what I need is a mode that mimics the implicit pressing of X, that is, to make the pdflatex process terminate after the first error. How to add keyboard shortcuts? I want Ctrl+Alt+B bring up a browser.  Ctrl+Alt+Delete is handy.  Can I set up Ctrl+Alt+B to bring up a browser (either default or specific)? Run command on another(new) terminal window How to make the BibTeX reference list visible in a LaTeX document Im very new at LaTeX and I would appreciate some help solving this problem. I have created a BibTeX file containing all references to a document. In this text file BibTeX items are inserted and no other text are written, for instance @article{...}. When I call for this bib file from the main.tex file I use the commands:  \bibliographystyle{plain} \bibliography{thebibliography}   Now to my question. All i get when I compile this main.tex is the title (bibliography) for this chapter, otherwise the textfield is blank. Is this error occurring because I should write anything in the bib file or have I missed any lines in the main.tex file. Why does boiling water in the microwave make a cup of tea go weird? When I boil water in the kettle, it makes a nice cup of tea.  Sometimes I need to use a microwave because a kettle isn't available.  I boil the water in the mug and it looks pretty normal, but when I drop in the teabag the water froths up and looks foamy.  I don't see what the chemical difference is here, so I assume it must be some physical difference.  I have noticed this with multiple types of tea and multiple microwaves, the results being consistent so it's not just a weird microwave or something like that.    What is the reaction here and how/why does it occur?  Here is a photo of the 'fizzy' looking tea just after dunking in the teabag. Does an increasing sequence of reals converge if the difference of consecutive terms approaches zero? Is the trio's Polyjuice escapade in Chamber of Secrets ever discovered? Negative energy levels in the diagram for a hydrogen atom The higher the number of the shell (n), the higher is the energy level of the electron. However, why was it necessary to have negative values. So for example, when $n=1$, the energy could be $5 eV$ and for $n=2$, $6 eV$... having positive values could also have supported the idea that as $n$ increases, energy of electron increases. What is the point of having negative numbers, does it somehow aid calculations? I don't know how many of you have experienced the  principle when posting questions on SO, but I know I have on a few occasions. And then I just discard my question. So here's the question:  Should we go ahead and post the question?  Of course if it's something stupid like forgetting a semicolon, etc., I would say no... but there are several occasions, like if a data structure doesn't make sense, that at least someone would eventually benefit from the question/answers.  And if you should ask the question, how would you recommend choosing an answer for it? Define $\sigma(m) = \sum$ d : d|n.  Prove that $p^j$$q^i$ cannot be a perfect number for $p, q$ odd, distinct primes.  Attempt at Solution: I have shown that $p^k$ can never be a perfect number, and im trying to use the multiplicative property of $\sigma$ to generalize to $p^j$$q^i$ I started reading "The Mathematics of nonlinear Programming - AL peressini" recently.  Theorem : Suppose that $f(x) , f'(x) ,f''(x)$ exist on the closed interval $[a,b]$. If $x^* ,x $ are two different points of $[a,b]$ , then there exists a point $z$ strictly between $x^*$ and $x$ such that   $$f(x)=f(x^*)+f'(x^*)(x-x^*)+\frac{f''(z)}{2}(x-x^*)^2$$  I tried to prove this theorem using The Fundamental theorem of calculus. But I can not stop it at the second derivative . Do I have to use mean value theorem ? or is there a simple proof for this ? Mirror cells so that a change in either cell updates the other I have 2 cells containing the same picklist values on separate sheets. I want the cells to mirror each other so that whenever I choose a new value in either sheet 1 or sheet 2, the value on the other sheet is updated to match the newly selected value. Is this possible?  UPDATE   Worksheet 1:   Worksheet Name: 'Live Forecast Tool' Cell containing picklist: C3:D3 (merged) Picklist values within range: ='SF MRF'!H5:Y5  Worksheet 2:   Worksheet Name: 'AH' Cell containing picklist: C3:D3 (merged) Picklist values within range: ='SF MRF'!H5:Y5    Cell C3:D3 needs to update to show the value that has been changed on the other sheet. Batch file to create Folder based on Date and Copy Files from One Location to Another Location? Updates for a private plugin? If I write a private plugin, is there any way to use the WordPress auto-update mechanism to update it?  I want to encapsulate the functionality, but it's specific to my own 5 or so blogs, so it's not a good candidate for the public plugins resource. But I love the easy-updating mechanism.  Is there a way to do this? Examples of a non-commutative division ring Difference between "theoretical computer science" and (beta) "computer science" Possible Duplicate:          Title says it all. From what I can see, "theoretical computer science" questions seem to be slightly more isolated to discussing algorithms, whereas "computer science" seems to have questions that are slightly broader and higher-level. Is there any place on the Stack Exchange sites where they give a longer description?  I'm just curious as to what niche the beta "computer science" site is meant to fill, as I see many topics in both forums that overlap.