I have a boolean which checks if an action is to be performed or not, the boolean is being being accessed through setters and getters, I have other booleans am accessing in a similar way and they are not giving me any errors except this one, at first I was checking it in a piece of code within a seperate thread and that part was not working without producing an exception so I put it in a toggleButton just to do a simple read and write on it, then the nullPointerException came up, here is my code I have commented it  toggleButton.setOnMousePressed(new EventHandler&lt;MouseEvent&gt;() {         @Override public void handle(MouseEvent event) {          //this part is executing perfectly          //meaning my toggleButton is ok          System.out.println("Toggle Button Clicked");           //this is where I am getting the NullPointerException          if(!getblackAndWhite()){              setblackAndWhite(true);           }else{                setblackAndWhite(false);            }         }});   private void setblackAndWhite(Boolean blackAndWhite)  {     this.blackAndWhite = blackAndWhite; }  private Boolean getblackAndWhite() {     return this.blackAndWhite; }
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?
Short story as a letter to original colonisers of earth What is the source for defaulting to plain English readings of non-game terms? Accessing the iPhone's Call log with the iPhone SDK I did an upgrade today to the latest version of ubuntu. Everything looked good and fine only for me to discover that I cannot find my applications after clicking the 'Show Applications' icon. The same applies when I search for an application in the search bar, I do not see it. It shows me an endless search.  These are the screenshot images of the problem:      In the meantime, I access my applications from the menu at the top bar and also use the terminal to run applications with CLI. How to sum up values of each two rows across their line in linux This is a pretty simple question, at least it seems like it should be, about sudo permissions in Linux.  There are a lot of times when I just want to append something to /etc/hosts or a similar file but end up not being able to because both &gt; and &gt;&gt; are not allowed, even with root.  Is there someway to make this work without having to su or sudo su into root? Given the differential equation $$\dot x = -2x + u$$ determine the optimal control law $u = - kx$ that minimizes the performance index $$J = \int_0^{\infty} x^2 \, \mathrm d t$$  My approach was to find the state feedback $k$. But since the value of $R$ (positive semidefinite Hermitian) is not given, that means $R=0$. How do I determine the optimal control for this system where $R=0$? Is smell a bad way of determining whether meat is still good? I have always relied on my sense of smell to determine whether meat (most often chicken) is bad and I thought it was reliable. However, I have just heard that [1] smell is not always reliable, since some of the toxins produced by bacteria won't cause any smell whatsoever and you won't be able to notice that the meat is off until after you've eaten it.   Is this true? If yes, is this true for all meat or only for some? Is there a more reliable way of determining whether meat is still good.  [1] "Heard that" isn't very reliable; so that's why I'm asking the question here. :) The the title is self explanatory, I guess.  Why can two (or more) electric  never cross? What are the drawbacks with using UUID or GUID as a primary key? I would like to build a distributed system. I need to store data in databases and it would be helpful to use an  or a  as a primary key on some tables. I assume it's a drawbacks with this design since the UUID/GUID is quite large and they are almost random. The alternative is to use an auto-incremented INT or LONG.  What are the drawbacks with using UUID or GUID as a primary key for my tables?  I will probably use Derby/JavaDB (on the clients) and PostgreSQL (on the server) as DBMS. How to find $\lim\limits_{x\to0}\frac{e^x-1-x}{x^2}$ without using l'Hopital's rule nor any series expansion? How to move 100 files from a folder containing thousands? I have a directory with thousands of files. How can I move 100 of the files (any files will do) to another location. I am writing a few rather large pseudocode functions using algorithm and algorithmic, i.e. my code looks something like:  \begin{algorithm}                      \caption{Coolest Algorithm ever}           \label{findme}                           \begin{algorithmic} [1]                   % enter the algorithmic environment \REQUIRE    Here are a few variables \\             variable 2 \\             variable 3  \ENSURE     this is the output \\             output 2  \STATE $some cool code here$ \STATE $some cool code here$ \STATE $some cool code here$ \STATE $some cool code here$ \end{algorithmic} \end{algorithm}   Unfortunately this code does not fit on one page and I am definitely not able to split it into some subfunctions or so (I already did that as far as possible).  So now I need to split up the algorithm into two pages, but I have no idea how.  The easiest way I can imagine is just to start a new algorithm on the new page, but this time letting the line counter start at line 35 or so instead of 1. But how can I do that?  Please not that there is already a similar question here on this site, but it deals with the package algorithmicx. What are the tools to help import my data into Salesforce I am switching from old CRM and looking for easy to use tools to import my data Sobolev inequality If $f\in H^2(\mathbb R^2)$, I want to show that    $||f||_{L^\infty}\le c||f||_{H^2}$ $||f||_{L^\infty}\le c||f||_{H^1} [1+\ln(1+||f||_{H^2})]$   For 1, I use $||f||_{L^\infty}\le \sup_{x\in \mathbb R^2} |f|\le\int_{\mathbb R^2} |\hat f(\xi)|d\xi = \int(1+|\xi|^2)^{-1}(1+|\xi|^2)|\hat f(\xi)|d\xi \le (\int (1+|\xi|^2)^{-2}d\xi)^2(\text {which is integrable in this case})||f||_{H^2}\to \text{is this correct?}$   But for 2, I am stucked. How can I get the "ln"? and how can I make it into a product of $H^1$ and $H^2$ norm? continuous functions on $\mathbb R$ such that $g(x+y)=g(x)g(y)$ Let $g$ be a function on $\mathbb R$ to $\mathbb R$ which is not identically zero and which satisfies the equation $g(x+y)=g(x)g(y)$ for $x$,$y$ in $\mathbb R$.   $g(0)=1$. If $a=g(1)$,then $a&gt;0$ and $g(r)&gt;a^r$ for all $r$ in $\mathbb Q$.   Show that the function is strictly increasing if $g(1)$ is greater than $1$, constant if $g(1)$ is equal to $1$ or strictly decreasing if $g(1)$ is between zero and one, when $g$ is continuous. Changes to parameter not showing on Report Server after deployment Can't pair apple wireless keyboard Keyboard: Apple Wireless Keyboard (model number MC184LL/B)  System: Macbook Pro Early 2011 running OS X 10.8  The keyboard gets detected and when I try to pair it, the system asks to enter some numbers through the keyboard.   However when I press the key (on the wireless keyboard) nothing happens, the only key that seems to work (i.e. to move to the next key in the code) is 0. I can also press enter to confirm but it always fails (since the only code I can enter is 0000...0).   I've also tried pairing from the bluetooth preference and changing the passcode option. However this won't work either.   Any ideas? The keyboard was paired with another MacBook Pro (I don't have access to it anymore). Is there any method to 'reset' the keyboard to factory settings? What form of the verb is used with compound subjects containing "or"? How do I diff the outputs of two commands? How can I use the diff command to compare 2 commands' outputs?  Does something like this exist?   diff  ($cat /etc/passwd) ($cut -f2/etc/passwd)