Card karte; Stack &lt;Card&gt; kartenstapel;   public Standard52() {       /** this works*/      this.karte = new Card(Suit.HEARTS,13);                              /** this throws a 0-pointer exception when I try to initial*/       this.kartenstapel.addElement(new Card(Suit.HEARTS, 13));      this.kartenstapel.addElement(new Card(Suit.HEARTS, 13));      this.kartenstapel.addElement(new Card(Suit.HEARTS, 13));      this.kartenstapel.addElement(new Card(Suit.HEARTS, 13));  }   Why i get a null pointer exception when i try to inital it.  Its more theorie then practice but i do not undersstand my failure maybe some of you can explain me where my mistake is.
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?
Does the Black Panther suit give extra speed? So in Civil War, the Black Panther suit seems to give the suit holder some extra speed, because the guy was running as fast as Bucky and Captain America.  So does it give extra speed? If so, how does that work? Does it make any difference to SEO ratings what-so-ever if your url has a trailing slash:  http://www.example.com/some/slug/paths/   as opposed to one that does not:  http://www.example.com/some/slug/paths PhD Student : Publish Paper with Wife? "I saw him crossing" vs. "I saw him cross" I saw him crossing the road.   I saw him cross the road.   Which one is correct and why? It's not like there's anything else to do.   Shouldn't the speaker say: "There's something else to do." ? so what's the meaning of the sentence and what's the difference between the two of them? Thank you, Picturing the how the covariant derivative acts on vector fields I am currently working through the problems in , with the goal of hopefully understanding how magnets work. At the moment I am a little stuck on one of the early problems in the first chapter. And I would like a Hint about how to proceed. The problem is to solve the time derivative of the expectation value of momentum of a particle. ie: $$ \frac{d\left&lt;p\right&gt;}{dt}. $$ My working so far Just prior to that question the text gives an expression for momentum, $$\int\limits_{-\infty}^{+\infty}{\Psi^*\left[-i\hbar \frac{\partial}{\partial x}\right]\Psi}dx, $$ (Where $\Psi$ is a function satisfying Schrödinger's equation, $i$ is the square root of negative 1, and $\hbar$ is Planck's constant divided by $2\pi$.) So my initial approach was to try and differentiate this with respect to $t$. $$ \frac{d}{dt}\int\limits_{-\infty}^{+\infty}{\Psi^*\left[-i\hbar \frac{\partial}{\partial x}\right]\Psi}dx. $$ However I didn't know how to do that, so I asked around in the maths chatroom, and got a lot of help. Specifically  from @RobJohn: $$ \begin{align} \int vv'\,\mathrm{d}x &amp;=vv-\int vv'\,\mathrm{d}x\\ &amp;=\frac12vv+C \end{align} $$ So I suppose it would follow that, $$ \begin{align} \int\limits_{-\infty}^{+\infty}{         \left(             \Psi^*                 \left[                     \frac{\partial}{\partial x}                 \right]             \Psi         \right)         }\,\mathrm{d}x &amp;=  \left[\Psi^* \cdot \Psi\right]_{-\infty}^{+\infty} - \int\limits_{-\infty}^{+\infty} {\Psi\frac{\partial \Psi^*}{\partial x} }\,\mathrm{d}x\\ &amp;= \frac{1}{2}|\Psi|^2 \Big|_{-\infty}^{+\infty}, \end{align} $$ And then, $$ \begin{align} &amp;\frac{d}{dt}\int\limits_{-\infty}^{+\infty}{\Psi^*\left[-i\hbar \frac{\partial}{\partial x}\right]\Psi}dx \\&amp;=-i\hbar \frac{d}{dt}\left( \frac{1}{2}|\Psi|^2 \Big|_{-\infty}^{+\infty} \right). \end{align} $$ But this feels wrong. I'm not sure exactly why. (Maybe it's just because it is the limits of my maths)  For reference, regarding what I understand, my maths is pretty low-level, I took a course in undergrad calculus over 10 years ago and only just passed that at the time, and my physics knowledge is not much further than that of an enthusiastic lay person. What is the !! (not not) operator in JavaScript? Sending file of custom python script with all parameters for popup interface already defined? I have a python script in ArcGIS 10 that when clicked, has a popup for a user to choose parameters. I would like to send this file to someone else. While I could send them the python code and have them setup the parameters - this method repeats work I have already done.   I would like to send someone one file that contains all of this information so they can just recieve my file, add it to a toolbox, and then have it all work. I am wondering where the file resides that has both the python code and parameters / what is the export process/ file type I should be looking at? (All the searches I do for "export script" seem to refer to exporting a model to python code...) I'm bugged by the following that's summarized on p. 109 of .     False theorem: All horses are the same color.      Proof by induction:      $\fbox{$P(n)$ is the statement: In every set of horses of size $n$, all $n$ horses are the same color.}$   $\fbox{Base Case or $P(1)$:}$ One horse is the same color as itself. This is true by inspection.   $\fbox{Induction Step:}$ Assume $P(k)$ for some $k \geq 1$.   $\fbox{Proof of $P(k + 1) :$}$   Since $\{H_1, H_2, ... , H_n\}$ is a set of $n$ horses, the induction hypothesis applies to this set. Thus, all the horses in this set are the same color.   Since $\{H_2, H_3, ... , H_{n+1}\}$ is also a set of $n$ horses, the induction step likewise holds for this set. Thus, all the horses in this set are the same color too.         Therefore, all $n +1$ horses in $\{H_1, H_2, H_3, ... , H_n , H_{n+1}\}$ are the same color. QED.   The issue the instructor was trying to point out is clearly valid. For the case $n = 1$, there is only ${H_1}$. So this case says nothing about possible overlapping elements of each set of $(n + 1)$, for instance $H_2$ in the above proof.    But it was proposed in the class discussion that this was the only problem. Had you been able to prove $P(2)$ true, then a proof of the above format would have been fine.    My interpretation is that yes, you could prove all horses are the same color, if you can prove that any set of two horses will be the same color. But this format would not work.  Why not? The problem I see is that the above proof is for the existence of at least one particular pair of sets of horses of sizes $n$ and $n + 1$, such that in each set, all horses are the same color.  Particularly when the set of size $n$ is a subset of the set of size $n + 1$.  In order to prove the induction step, don't you need to prove that sets of sizes $n$ and $n + 1$, do not necessarily contain the same, overlapping elements?  You could prove that any horse can be added to a set of 2 horses.  Take the last two, and they must be the same color, and so on.  Wwhatever color the first two happen to be, all other horses must thus be the same color.    Am I misinterpreting the example, or am I making a logical error? Thanks in advance. How do I filter out addresses using HTTPS for a D-Link router? I recently got a new router, a DRL-600L Router from D-Link, and was setting up some filters to block out certain websites.  One problem I am having is blocking out addresses that use https instead of http.  For example, I'm trying to block out Facebook, because Facebook.   So far, the filter filters http://www.facebook.com perfectly fine, but for the url https://www.facebook.com, it won't block that.  How can I block those kinds of websites? How can one expand the function $f_1(x) = x$ on $(−π, π)$in terms of the functions $\cos nx, n = 0, 1, 2, ...$ and $\sin nx, n = 1, 2, ...,$ in a way so that $$f_2(x) = a_0 + \sum_{n=1}^{\infty}(a_n \cos nx + b_n \sin nx)$$ is the expansion of the $f_1$, how is that? I have asked  related to the same issue but didn't get full answer, I have been told that this is a standard application of Fourier series, $f_1$ and $f_2$ are equivalent in the sense that $f_1(x)=f_2(x)$ for all $x∈(−π,π)$. For any $x$ in this interval, the Fourier series will converge to $f(x)$, but I didn't get any rigorous proof  with elaborate explanation. So, plz provide rigorous proof of $f_1=f_2$ with elaborate explanation as I am new to the subject. Thanks You. I have attached the excerpt below - Functional Analysis. Continuous extensions of linear functionals. I would like to show that a continuous functional on a subspace $W$ of a normed space $(V,\|\cdot \|)$ has a unique continuous extension to $V$ iff $W$ is dense in $V$.  I have proved $(\Leftarrow$). But the converse is currently eluding me! Help would be much appreciated! I have a dedicated server with 2 TB storage.   My problem is that the whole storage is allotted to the root partition.   Whenever I try to resize it using lvresize, the root partition gets corrupted and then I have to reprovision the server.   Is there any option to resize the root partition without unmounting in lvm?  I am trying to reduce the root partition to 100GB.  Vgs  root@s93079:/home/customer# vgs   VG        #PV #LV #SN Attr   VSize VFree   s93079-vg   1   2   0 wz--n- 1.82t    0   Lvs  LV     VG        Attr       LSize  Pool Origin Data%  Meta %  Move Log Cpy%Sync Convert   root   s93079-vg -wi-ao----  1.79t    swap_1 s93079-vg -wi-ao---- 32.00g   Fdisk - l  Device     Boot  Start        End    Sectors  Size Id Type /dev/sda1  *      2048     499711     497664  243M 83 Linux /dev/sda2       501758 3907028991 3906527234  1.8T  5 Extend /dev/sda5       501760 3907028991 3906527232  1.8T 8e Linux  Disk /dev/mapper/s93079--vg-root: 1.8 TiB, 1965782204416 byt es, 3839418368 sectors Units: sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk /dev/mapper/s93079--vg-swap_1: 32 GiB, 34355544064 byte s, 67100672 sectors Units: sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes   Vgdisplay   --- Volume group ---   VG Name               s93079-vg   System ID   Format                lvm2   Metadata Areas        1   Metadata Sequence No  3   VG Access             read/write   VG Status             resizable   MAX LV                0   Cur LV                2   Open LV               2   Max PV                0   Cur PV                1   Act PV                1   VG Size               1.82 TiB   PE Size               4.00 MiB   Total PE              476870   Alloc PE / Size       476870 / 1.82 TiB   Free  PE / Size       0 / 0   VG UUID               dPrEwA-77pM-pGai-9jZB-ldMZ-iL20-HAe9 Dj   lvdisplay /dev/s93079-vg/root   --- Logical volume ---   LV Path                /dev/s93079-vg/root   LV Name                root   VG Name                s93079-vg   LV UUID                bpGNau-XirV-P7PA-8d6k-OCOy-TAwN-HXl FVI   LV Write Access        read/write   LV Creation host, time s93079, 2016-08-27 09:22:05 -0500   LV Status              available   # open                 1   LV Size                1.79 TiB   Current LE             468679   Segments               1   Allocation             inherit   Read ahead sectors     auto   - currently set to     256   Block device           254:0   Lvdisplay /dev/s93079-vg/swap_1  --- Logical volume ---  LV Path                /dev/s93079-vg/swap_1  LV Name                swap_1  VG Name                s93079-vg  LV UUID                j74PLZ-E9gK-9Bbb-EkKq-xRJv-TuU4-FgH gm  LV Write Access        read/write  LV Creation host, time s93079, 2016-08-27 09:22:05 -0500  LV Status              available  # open                 2  LV Size                32.00 GiB  Current LE             8191  Segments               1  Allocation             inherit  Read ahead sectors     auto  - currently set to     256  Block device           254:1   Df - h  /dev/dm-0       1.8T  923M  1.7T   1% / udev             10M     0   10M   0% /dev tmpfs           3.2G  8.5M  3.2G   1% /run tmpfs           7.9G     0  7.9G   0% /dev/shm tmpfs           5.0M     0  5.0M   0% /run/lock tmpfs           7.9G     0  7.9G   0% /sys/fs/cgroup /dev/sda1       236M   33M  191M  15% /boot What is the datatype of facebook userid How to change an application Icon What are these fuse-looking cartridge case components on small, battery operated RF tranceivers? I have recently opened up 3 dead, battery-operated RF transceivers lying around, both wearable and key-chains. I've noticed that all three had components that looked like fuses (cartridge case), soldered down, that are quite large compared to the size of the circuit. See the pictures below. I'm not posting full circuit pictures because I don't know if I should, I can update if they are necessary.  Device 1:    Device 2:    Device 3:    I can't see why such a device will require a fuse, and I couldn't find any other common components manufactured in cartridge cases, maybe I'm not using the correct name. I don't see them on any applications notes or reference designs for the ICs used either.  I've tried to figure out how they are connected to the circuit, I don't have schematics and PCBs are more than 2 layers so they may not be complete, but see the schematics I've figured below.  Device 1:    Device 2:    Device 3:    Also, when I do a continuity test between the terminals of the components with a multimeter, resistance starts in ~50 Ohms range and goes down to short as I keep the probes on its terminals so my best guess is something for ESD protection, maybe Varistors or Thermistors?   Does anyone know what these components are and why they are there? Is it a good practice to ask before exiting an application (with nothing to save)? Every now and then, I come across applications that, when clicking on the main window's "X", ask me whether I'm sure that I want to quit the application.    I'm not talking about asking me to save unsaved documents, but about applications that aren't document related at all.  This always bothers me, since I feel totally interrupted in my workflow. I was already thinking two steps ahead of what I want to do next, and this message box abruptly pulls 100% of my attention.  My question:  Are there any valid use cases where a non-document-centric application should ask me whether I'm sure that I want to exit the application? At the end of . the author states that  Suppose we have $n \times n$ matrix $A$ having only positive elements and satisfying the property $a_{ij}=1/a_{ji}$ (a matrix satisfying this property is called a reciprocal matrix).  If its largest eigenvalue $\lambda_{max}$ is equal to $n$, then the matrix $A$ satisfies the property (consistency property) $a_{ij} a_{jk} = a_{ik}$ where $i,j,k=1,2,...,n$.  I'm not convinced this theorem is true. Could anyone help? What are the assumptions for applying a quantile regression model? The question has been asked (one time) on CV before, but the answer is really imprecise and does not really answer the question in my opinion.  So: What are the assumptions for estimating a linear regression model via quantile regression?  To my understanding (and as several CV users have mentioned), quantile regression does not assume any specific distribution of the error terms - does that mean that, in a time series model, autocorrelation and heteroscedasticity do not have to be accounted for?  What about the other Gauss-Markov assumptions? I would assume that the assumption of no perfect multicollinearity has to be met when applying quantile regression, but do the parameters have to be linear? The linearity assumption only has to hold for the specific quantile I would assume.  Anyways - I do not find any backup for any of my thoughts in the scientific literature and I would appreciate a comprehensive answer. Thank you!