Attempt to invoke virtual method on a null object reference issue
What is a NullPointerException, and how do I fix it?
How to reduce the fan noise and how to increase battery life? I have a brand new Sony Vaio S series laptop.() It came factory installed with Windows 7 professional Edition 64bit. Runs Intel core i5, 500 GB HDD , 4GB Ram. First I installed ubuntu 11.10 64 bit along side Windows to dual boot. Later,since the problem did not solve, I installed ubuntu 12.04 64bit along side Windows to dual boot. However the problem keeps annoying me.  Problem: When running ubuntu 11.10/12.04, the battery lasts only about 1.5 hours. The Fan runs loud and continuously. And there is a lot of heat generated. System monitor shows less than 5% CPU used. My laptop enjoys hybrid graphic and I tried turning off ADM graphic card and keep Intel graphic card on. However I can not get the Fan noise or heat to go away and consequently the battery drain continues. BTW, in windows, the laptop gives 4-5 hours of battery power, Fan is silent and there is no heat problem. Any ideas on how to reduce the fan noise and how to increase battery life in ubuntu 11.10/12.04? I am generating one report where I need to use background image. But I found that image always starts leaving some margin space to left side.    \documentclass{article} \usepackage{wallpaper} \usepackage{mdframed} \usepackage[top=2cm, bottom=2cm, outer=0cm, inner=0cm]{geometry} \begin{document}  Some content \ThisLRCornerWallPaper{1.0}{image.jpg} \end{document}    How can I use background image covering whole page? "Distribution worker" vs. "distributed worker" I cannot differentiate the meanings of the two words. Could you please clarify?   In general, when should I use a noun (distribution) or an adjective (distributed) for verbs similar to distribute, like organize, create? Rule of thumb for choosing an implementation of a Java Collection? Anyone have a good rule of thumb for choosing between different implementations of Java Collection interfaces like List, Map, or Set?  For example, generally why or in what cases would I prefer to use a Vector or an ArrayList, a Hashtable or a HashMap? Is it possible to delete multiple elements from a list at the same time? If I want to delete elements at index 0 and 2, and try something like del somelist[0], followed by del somelist[2], the second statement will actually delete somelist[3].  I suppose I could always delete the higher numbered elements first but I'm hoping there is a better way. I am including pages using Ajax but I also need to include their respective javascript files, which requires removing the previous javascript files from memory at the same time.  How can I unload the currently-loaded javascript files (as well as their code in memory) so that I can load the new page's files? They will more than likely conflict, so having multiple independent files' javascript files loaded. Before I start, YES, I have done my own research - I know how annoying a repeat question is. Yet each answer is so specific to others...  When I tried the beta 2.8 64 bit, it says "Blender requires a driver with at least OpenGL 3.3 support. The program will now close."    The question: I know that it is true that 2.8 requires OpenGL 3.3. But does my PC not have it, doesn't support it, or do I have it and blender won't detect it? I'm not sure what info to include or what to look for, so here's my PC's specs:  Windows 10 (64 bit) Core -        Intel Core i5-2400 CPU @ 3.10GHz RAM -         8GB (7.89GB usable) System type - 64-bit Operating System, x64-based processor  Thanks!  EDIT: Graphics properties: Where did the world go? I was playing on my main world when my laptop ran out of power.  I found a charger and woke it up, but Minecraft had crashed.  Now, it doesn't appear in the world selection screen!  I have verified that it still exists in the Minecraft folder, and the directory contents look to be in order.  Does Minecraft save an internal flag somewhere when it crashes hard?  If so, how do I reset it? What should I do when Ubuntu freezes? All operating systems freeze sometimes, and Ubuntu is no exception. What should I do to regain control when...   just one program stops responding? nothing at all responds to mouse clicks or key presses? the mouse stops moving entirely? I have an    In what order should I try various solutions before deciding to pull the power plug?  What should I do when starting up Ubuntu fails?  Is there a diagnostic procedure I can follow? How to add a script to Startup Applications from the command line? I have a shell script. I want to configure my script to run automatically during startup. I know how to do this from GUI. But I wanted to do this from terminal. How can I do this?  On a primary research I found that the file needs to be moved to /etc/int.d/ directory. But this operation needs sudo permission. I wanted to do this without super user permissions.   I also found that there are files under ~/.config/autostart/ which are having some settings regarding the startup applications. But I don't know how to edit them to achieve this.   Can someone tell me the exact procedure to achieve this? How do I add VBA in MS Office? Prove that the function $f(x)=\frac{x}{x^2+1}$ is continuous at $x=-1$. Prove  that the function $\displaystyle f(x)=\frac{x}{x^2+1}$ is continuous at $x=-1$. You should give a proof that is directly based on the  definition of continuity.   I saw many similar questions on this website, but none of them gave me a satisfactory answer. I more or less understand how epsilon-delta proofs work but my problem lies more in the algebraic manipulations probably. So here's my "attempt".  Definition of continuity; for $f:A \to \mathbb{R}$     $$\forall \varepsilon &gt;0 \ \exists\delta&gt;0\ \forall x \forall x_0 \in A:|x-x_0|&lt;\delta \Rightarrow |f(x)-f(x_0)|&lt;\varepsilon$$   So from what I understand, the procedure for epsilon-delta proofs are as follows: 1. Plug the point of interest $x_0$ into $|f(x)-f(x_0)|&lt;\varepsilon$ 2. Write $x$ in terms of $\varepsilon$ 3. Then plug $x$ into $|x-x_0|&lt;\delta$ 4. Find $\delta$ in terms of $\varepsilon$. Done    At step 1, we have $\left|\dfrac{x}{x^2+1}+\dfrac{1}{2}\right|&lt;\varepsilon$. Step 2 is where I'm stuck because of the 2nd degree polynomial in the denominator. First, I did this: $\left|\dfrac{x}{x^2+1}\right|&lt;\left|\dfrac{x}{x^2+1}+\dfrac{1}{2}\right|&lt;\varepsilon$. Then, I wasn't too sure about what to do, I thought about getting rid of the "$1$", but that would screw up my inequality. I thought about factoring $x^2+1$, but it doesn't have any real roots. I tried inverting the fraction, but that led me to nowhere. And I've already exhausted the tools I have. How do I proceed?  Apparently, epsilon-delta proofs are the most basic building blocks of analysis. And I'm already failing, this is both embarrassing and depressing... My understanding is that in machine learning it can be a problem if your dataset has highly correlated features, as they effectively encode the same information.  Recently someone pointed out that when you do one-hot encoding on a categorical variable you end up with correlated features, so you should drop one of them as a "reference".  For example, encoding gender as two variables, is_male and is_female, produces two features which are perfectly negatively correlated, so they suggested just using one of them, effectively setting the baseline to say male, and then seeing if the is_female column is important in the predictive algorithm.  That made sense to me but I haven't found anything online to suggest this may be the case, so is this wrong or am I missing something?  Possible (unanswered) duplicate: Signed to unsigned conversion in C - is it always safe? When is double-quoting necessary? The old advice used to be to double-quote any expression involving a $VARIABLE, at least if one wanted it to be interpreted by the shell as one single item, otherwise, any spaces in the content of $VARIABLE would throw off the shell.  I understand, however, that in more recent versions of shells, double-quoting is no longer always needed (at least for the purpose described above).  For instance, in bash:  % FOO='bar baz' % [ $FOO = 'bar baz' ] &amp;&amp; echo OK bash: [: too many arguments % [[ $FOO = 'bar baz' ]] &amp;&amp; echo OK OK % touch 'bar baz' % ls $FOO ls: cannot access bar: No such file or directory ls: cannot access baz: No such file or directory   In zsh, on the other hand, the same three commands succeed.  Therefore, based on this experiment, it seems that, in bash, one can omit the double quotes inside [[ ... ]], but not inside [ ... ] nor in command-line arguments, whereas, in zsh, the double quotes may be omitted in all these cases.  But inferring general rules from anecdotal examples like the above is a chancy proposition.  It would be nice to see a summary of when double-quoting is necessary.  I'm primarily interested in zsh, bash, and /bin/sh. How to remove the top horizontal bar in fancyhdr? When using fancyhdr, how do you remove the top horizontal rule?  I do not want a header at all, just a footer.  This is what I do now:  \documentclass{article} \usepackage{fancyhdr} \pagestyle{fancy}  \lfoot{text} \cfoot{text 2} \rfoot{text 3}  \begin{document} Foo Bar \end{document} How to integrate a paper where I am third author, but did a lot of work, into my master's thesis? I am writing my thesis currently and I want to include papers that I am included on as an author.  I will have a couple papers where I am 1st author, but there is one where I am third but did a lot of the work.  How do I go about integrating it into my thesis?  Can I copy/paste most of the text still or do I need to rewrite it?  I don't want to plagiarize but don't want to rewrite it if I don't have to. Height of colorbox Hide and seek game $A$ and $B$ go to the Senate to play a game of Hide-and-Seek. There are $100$ rooms in the Senate, and $B$ picks one of them and hides there till the game ends.  $A$, at the beginning of every turn, picks one room and searches in it. Since he is human and thus fallible, he only has a $60\%$ chance of finding $B$ if she is in fact hiding in the room. If he fails to find her in the room, $B$'s score increases by one, and the next turn starts, whereupon $A$ must pick another room to check (he can also check the same room again). $B$ remains in the room she initially chose.  Given that $A$ and $B$ play with perfect strategies, what is the expected value of $B$'s score at the end of the game?  I tried with $1$ room. There is only one hiding place for $B$. So the expected score of $$B = \sum_{n=1}^{\infty}0.4^{n-1}0.6(n-1)=\frac{2}{3}.$$ Test whether a glob has any matches in bash