java.lang.NullPointerException: Cannot invoke "java.sql.Connection.prepareStatement(String)" return value null
What is a NullPointerException, and how do I fix it?
Do we keep hats from year to year? This is the first year that I pay attention to hats (I love hats!) and I wonder if I will keep my hats for next year?  Or will I start over with zero hats next year? How does the secondary effect of the Heat Metal spell work? The  spell description states:  If a creature is holding or wearing the object and takes the damage from it, the creature must succeed on a Constitution saving throw or drop the object if it can. If it doesn't drop the object, it has disadvantage on attack rolls and ability checks until the start of your next turn...  I am unsure how this disadvantage mechanic functions as a whole. When do you suffer from it and in what ways (if any) can you end it? For example: What happens if you fail the save but cannot drop the object? Does dropping the object later, on your turn, do anything? What happens if you succeed on the save?  Does dropping the object later, on your turn, do anything? I would like it to be assumed that ; however, heat metal can still force you to drop the weapon. I would also like it to be assumed that . How can I find my hardware details? Is there any built-in software or terminal method allowing me to view the hardware profiles on my system? Windows equivalent of such a feature would be Device Manager. Can I manually put an external hard disk to sleep? When using unicode-math, how do I get the original calligraphic alphabet back? I am happy with the great majority of what unicode-math does. But at times I find that I prefer a symbol the way it was before. With \varnothing and \complement, for example. In those cases I was able to save them under a different name before loading unicode-math, but this doesn't always work.  Right now I'm trying to access the \mathcal alphabet from plain LaTeX. How might I accomplish this?    Additional Question  I've been looking through unicode-math, trying to figure out where exactly the original \mathcal alphabet gets discarded, but I eventually gave up.  It would be interesting if someone could explain:   how/where the original \mathcal font is defined anyway, and what kind of 'switch' is thrown by unicode-math that makes it unavailable. ggplot2: facet_wrap strip color based on variable in data set What do spacelike, timelike and lightlike spacetime interval really mean? Suppose we have two events $(x_1,y_1,z_1,t_1)$ and $(x_2,y_2,z_2,t_2)$. Then we can define $$\Delta s^2 = -(c\Delta t)^2 + \Delta x^2 + \Delta y^2 + \Delta z^2,$$ which is called the spacetime interval. The first event occurs at the point with coordinates $(x_1,y_1,z_1)$ and the second at the point with coordinates $(x_2,y_2,z_2)$ which implies that the quantity $$r^2 = \Delta x^2+\Delta y^2+\Delta z^2$$ is the square of the separation between the points where the events occur. In that case the spacetime interval becomes $\Delta s^2 = r^2 - c^2\Delta t^2$. The first event occurs at time $t_1$ and the second at time $t_2$ so that $c\Delta t$ is the distance light travels on that interval of time. In that case, $\Delta s^2$ seems to be comparing the distance light travels between the occurrence of the events with their spatial separation. We now have the following definitions:  If $\Delta s^2 &lt;0$, then $r^2 &lt; c^2\Delta t^2$ and the spatial separation is less than the distance light travels and the interval is called timelike.  If $\Delta s^2 = 0$, then $r^2 = c^2\Delta t^2$ and the spatial separation is equal to the distance light travels and the interval is called lightlike.  If $\Delta s^2 &gt;0$, then $r^2 &gt; c^2\Delta t^2$ and the spatial separation is greater than the distance light travels and the interval is called spacelike.   These are just mathematical definitions. What, however, is the physical intuition behind them? What does an interval being timelike, lightlike or spacelike mean? How do I stop Outlook Out-Of-Office from replying to certain addresses? When I am out of the office, if I turn Out-of-Office on, it auto-replies to the automated emails I get from our Bug Tracking system, which leads to our Bug Tracking system getting full of message about my holiday.  With Outlook Out-of-Office, how do I set it to not respond to certain 'From' addresses? I see its something to do with the optional Rules in the O-o-O dialog, but its not that clear how to stop it from replying using the rules.  I'm on Outlook 2003 and Exchange 2003 but advice for any version will probably be useful to people. How can I find the points at which two circles intersect? Given the radius and $x,y$ coordinates of the center point of two circles how can I calculate their points of intersection if they have any? Level 10 vim adventures beers on the wall complete solution I saw this question  but it doesn't have a full solution. What is the full solution to the 99 bottles of beer on the wall for Vim adventures?  Context: for the sake of being a good SO member I will give more details but a full solution will answer my question. It seems from reading the other post that my register is incorrect for some reason. I can't get the &lt;NL&gt;. I think that's the issue since pasting won't work... Does order matter when casting a cantrip with a casting time of a bonus action and another spell? When casting a spell as a bonus action, you can't cast another spell on the same turn except a 1-action cantrip - can the order be "reversed"? Can you cast a cantrip first as a bonus action, then any other spell? If not, would it be broken to allow it?  I'm thinking a Sorcerer casting a Quickened true strike, then casting a leveled spell requiring a touch attack. Seems like a great use of the cantrip + Metamagic feature, but it seems like it is not allowed. How do I run .sh scripts? Proving that any permutation in $S_n$ can be written as a product of disjoint cycles I have attempted a proof of this, but upon looking at my notes, I feel it might be incorrect: it is noticeably simpler than the one in my notes.  Proposition: any permutation in $S_n$ can be written as a product of disjoint cycles.  Proof (attempt): $s\in S_n$. Let $\langle s\rangle$ act on $X=\{1,\cdots,n\}$. Define $x\sim x'\iff x'\in\text{Orb}(x)$ for $x,x'\in X:$ this is clearly an equivalent relation, hence the orbits partition $X$. Each orbit corresponds a cycle in $s$, so we are done.  Does this hold, or have I missed something vital? Is the sign of principal components meaningless? Does the sign of the vectors returned by PCA have any significance after I center my variables? Ubuntu system is broken after accidentally uninstalling many packages I accidentally removed all the packages starting with the name jpeg with:  sudo apt-get remove jpeg*   This screwed up a lot of things, removed Unity, Firefox, Flash player etc.  I somehow managed to recover the desktop and unity but then a lot of things are still buggy. For example .rpm files and .tag.gz just won't open up at all.  What I want is a way to fix everything that's amiss. Something that is the equivalent of a 'repair installation' with a windows disc.  Any tips, anyone? I'm using pdflatex, and use \includegraphics to include content of figures from PDF. PDF are exported from InkScape.  \begin{figure} [!h]     \centering     \includegraphics[height=3cm]{fig/SUSAN.pdf} \end{figure}   Included PDF or source SVG has same colors. Green has always RGB value (0, 255, 0). Problem occurs when I include this files from LaTeX. In output PDF on some pages colorspace is darker. Even same image on other page has different colourity.  My PDF  . As you can see on page 7 (11 in PDF) USAN areas are bright green, but then on page 5 (9 in PDF) are green points on corners more darker. is it problematic to cluster across two datacenters w/aag? In general is it problematic to cluster across two datacenters that are up to 15-miles apart?  For this one particular project the approach is the following?   2-Node Failover Cluster across two datacenters, one node per datacenter local SAN disks, no shared disks 'Node and FileShare Majority' at third location on-campus employ AAG, failover will be manual; asynchronous mode   Is anyone implementing something like this with success??!?  Thanks so much for the help!! macOS Catalina File Structure: Cannot remove &gt; sudo rmdir /sw rmdir: /sw: Read-only file system  &gt; mount | grep read /dev/disk1s5 on / (apfs, local, read-only, journaled)  &gt; sudo mount -o rw / &gt; mount /dev/disk1s5 on / (apfs, local, journaled) &gt; sudo rmdir /sw rmdir: /sw: Operation not permitted     root /&gt;$ mkdir a root /&gt;$ rmdir a root /&gt;$ rmdir sw &lt;b&gt;rmdir: sw: Operation not permitted&lt;/b&gt; root /&gt;$ rmdir opt &lt;b&gt;rmdir: opt: Operation not permitted&lt;/b&gt; root /&gt;$ rmdir mnt &lt;b&gt;rmdir: mnt: Operation not permitted&lt;/b&gt; root /&gt;$ rmdir home &lt;b&gt;rmdir: home: Operation not permitted&lt;/b&gt;   What exactly is preventing me from removing these directories even with SIP disabled? Is normal extension of normal extension always normal? Finding Elevation Change, any method So, I think it'd be cool - for goal setting for example - if I could keep track of my elevation change.  The problem is, the local cyclocomputers I looked at seem to use barometric pressure to determine the change.  This is fine, unless some weather is moving in, which happens not infrequently in the Midwestern United States.  Or do some of them try to use an inclinometer, your speed, and some math you learn in Calculus II to keep track of your change?  That would seem more accurate!  I could try to use a GPS meter, but those things are expensive -  and based on back when I had service to my smart phone, not guaranteed to match my car's odometer for distance even - I've read from some other riders that the distance varies at least slightly from local measurement on a bike as well.   Alternatively, let's say that I ride along a known route.  Is there any good way of plotting that route for elevation change?  Thanks!