NullPointerException Error on simple program
What is a NullPointerException, and how do I fix it?
is a simple way to script small GUIs.  Can anyone give a nice example with a button and a text widget. When the button is pressed should a shell command be executed and the output piped to the text widget.  If you have other nice and clean examples for useful tasks, please add them too. Inferring father/son relationships from Senior (Sr.) / Junior (Jr.) naming? As in my other questions, I am investigating the spread of the Blackstone family name in early America. I came across the following tidbits and I would like to know if my interpretation is (likely to be) correct.  In the "All Kent County, Delaware Probate Records, 1680-1800" collection on ancestry.com, we have the following items.   In 1792, there was a will executed by Eben Blackiston, Sr. In 1794, there was a will executed by Ebenezer Blackiston, Jr. (and Abraham Redgrave).   My question is simple.  Is this enough evidence to reasonably conclude that there was a father/son combo of Ebenezer Blackistons living in Kent County, Delaware during the 1790s?  This would be an interesting result for me as my current research only has two people by this name in the state at the time, and none of them were part of a Jr./Sr. combination.  If this is not enough evidence, what are some other possibilities I need to consider? Validate/verify PDF files integrity Is there any tool which I can run on the PDFs archives (all directories) and finally it lists/identifies the corrupt/invalid PDFs? I have hundreds of PDF files (related to documentation etc.) on my computer (Windows machine), and very often I receive/have to send dozens of PDFs via email. It is now a normal routine that the PDF I receive or send is corrupted. This creates serious trouble sometimes, when the source file (e.g. Word file or the Tex file) is missing/not available instantly. Checking these thousands of PDFs is not possible in finite time, so I have searched for a tool which I can run once and it would scan all PDFs (in directories and sub-directories), and finally I would get a list of files which I should re-create. Up to now, it seems there is no such tool. My kids are playing Minecraft on 2 PCs, creative mode.  They are connected by the way of one of them starts a single player game on the other one than joins that game over the LAN.  Can I, using Minecraft PE on my iPad, join their game as well? Backup of clients' directory to Windows Server 2008 Finding an expression for $\tan (a+ b + y)$ which involves only $\tan a, \tan b,$ and $\tan y$. How to find this ?   I'm stuck at $1$ and how to $1$ to change the tangent associated with a,b or c.  I meant this ,everybody.  $\frac{tan(a)+tan(b)+tan(y)−tan(a)tan(b)tan(y)}{1−tan(a)tan(b)−tan(a)tan(y)−tan(b)tan(y)}$ The final state of 1000 light bulbs switched on/off by 1000 people passing by There are  1000  light bulbs and 1000 tutors. All light bulbs are off. Tutor 1 goes flipping light bulb 1,2,3,4... tutor 2 then flips 2,4,6,8... tutor 3 then 3,6,9...etc until all 1000 tutors have done this.  What is the status of light bulb 25? 93? 576?  Is there a general solution to find out the status of any light bulb?  How many light bulbs are on after all 1000 tutors have gone by?  Not homework but a UK university interview question. Please help. After Upgrade to Ubuntu 20.04: "Oh no! Something went wrong" Full file date (without GNU utilities) I am trying to obtain the full date (created or modified) of a particular file for passing to another program. I have tried variations of options with the ls command but none provide a full date for files less than 6 months old and I have limit usage of the options. When I try certain options I have seen trying to research this I get the following message:  usage: ls [-1ACFHLNRabcdefgilmnopqrstuxEUX] [File...]   None of which seems to provide what I needs as far as I can tell so I tried to use the stat command but it is not available to me.  I am using the Korn shell on AIX 5.3 which has limited commands available, can anyone suggest another way that I might be able to obtain a file's created or modified date as a full date (either dd/mm/yyyy or yyyy/mm/dd). How to Micro Manage Manipulator What desktop environments can group window icons in the taskbar like Windows 7? I find it much faster to identify a window in the taskbar (window list) by its icon,    rather than by its text:    The problem with most graphical interfaces I've  is that they don't group windows, and if you have more terminals or file managers, they'll just clutter the taskbar and you won't know which is which. Windows 7 offers a relatively elegant solution to this by grouping similar window icons together.  Question: What Linux  have this functionality? If addons exist that provide it, that's alright.  For reference, a Cinnamon applet that sort of does this is . Why Lasso or ElasticNet perform better than Ridge when the features are correlated I have a set of 150 features, and many of them are highly correlated with each other. My goal is to predict the value of a discrete variable, whose range is 1-8. My sample size is 550, and I am using 10-fold cross-validation.   AFAIK, among the regularization methods (Lasso, ElasticNet, and Ridge), Ridge is more rigorous to correlation among the features.  That is why I expected that with Ridge, I should obtain a more accurate prediction.  However, my results show that the mean absolute error of Lasso or Elastic is around 0.61 whereas this score is 0.97 for the ridge regression. I wonder what would be an explanation for this.  Is this because I have many features, and Lasso performs better because it makes a sort of feature selection, getting rid of the redundant features? showing a collection of sets contain all closed sets Let $X$ be infinite set and $a \in X $. Let $$\mathscr{F} = \{ A \subset X: |A| \; \; finite \; \;, a \notin A \}$$  Then $\mathscr{F}$ is the set all of all closed sets for some topology $\mathcal{T} $ on $X$. Also, any two continuous maps $f,g: (X, \mathscr{T}) \to Y$ ( $Y$ is metric space) have the property that if $f(b) = g(b)$ for all $b \neq a $, then $f(a) = g(a)$.  In my notes my professor posted this theorem without proof, so I was wondering what is best way to proof this theorem. Since there are gravitational lenses, are there gravitational mirrors? Gravitational lensing is an observed phenomenon. Can one have a gravitational mirror?   A slightly unrelated question: Can gravitational waves be reflected? On iPhone it's very easy to clone an app (running multiple copies of the app on the same device); e.g.:    Is it possible to do this on Android? Often floats may land quite a bit later in the document than the point they are created, sometimes after a section break.  Is there a way to force a new section to start on a new page, after any unplaced floats? Does anyone know of a script that can select all text references to URLs and automatically replace them with anchor tags pointing to those locations?  For example:  http://www.google.com   would automatically turn into  &lt;a href="http://www.google.com"&gt;http://www.google.com&lt;/a&gt;   Note: I am wanting this because I don't want to go through all my content and wrap them with anchor tags. How strong is Superman on Krypton? When Superman goes back to visit his home planet (using his ability to travel through time, I guess), is he:    an exceptionally strong and athletic Kryptonian? just an average Kryptonian male? a weakling on account of spending a lifetime in the comparative microgravity of Earth?   A possibly related question: why is Superman so muscular? What kind of weights does he lift to stay in shape?  The answers to  are all about Superman's superpowers on Earth compared with other visitors from Krypton; I'm asking about Kal El without his superpowers.  Clarification: I'm asking about the "classic"  Superman, say late Golden to early Silver Age, roughly 1945-1960. (Yes, I know the concept evolved during those years.) I'm not sure what that would be in terms of "numbered Earths", those came along after my time. I'm pretty sure the Kryptonians of that era had no superpowers in their native milieu, nor would Kal El if he were deported in space-time to his native world. Can you catch a native exception in C# code? In C# code can you catch a native exception thrown from deep in some unmanaged library? If so do you need to do anything differently to catch it or does a standard try...catch get it? Interaction term positive while components are negative? I am confused about the interpretation of my interaction term , I have been through similar questions but I am still not sure about the interpretation that I should give to my output .  So this is my model , Y  stands for earnings management , X1 = CSR , X2=CEO duality , as you can see both of the coefficients are negative CSR reduces earnings management manipulation and Duality in my sample reduces em as well  which is in line with the literature and confirm my hypothesis , but to my surprise my interaction term is positive and significant does that mean that CSR combined with duality increase EM ? Or that CEO duality moderates the effect of CSR on EM knowing that in papers that I've read, they only use&quot; moderate &quot;when the interaction term and the components are all negative . Could you please help me ? I am supposed to comment my results but I don&quot;t understand this . Thank you