How to avoid the Null Pointer Exception from crashing my app?
What is a NullPointerException, and how do I fix it?
Profitable strategy in coin tossing? There is a coin with a probability $p$ of heads, and $1-p$ of tails. Tosses are independent of each other. When you bet an amount of money $x$, you receive $2x$ if it lands heads, and you lose what you bet if it lands tails.  We are going to use the following strategy:  You start betting an initial amount $x_0$. Every time you lose, you bet twice what you bet in the previous throw. You keep doing this, until you win, at which point you retire, or start again, betting $x_0$.  The interesting case of course is when $p &lt; 0.5$.  The question is: How profitable is this strategy? Intuitively I feel that eventually I can always win an arbitrarily large amount of money. But that can't be entirely right ("the house always wins!"). So what am I missing here? What's the expected win in each run?  Also, does this sort of strategy have a name in the literature?  P.S.: Found this later, Will self-citation be viewed as self-promotion in academia? As we know, citation counts are important to judge one's research activity. Is it good to cite one's previous works? Will it be viewed as an act of advertisement or self-promotion? How to find out what's accessing a particular hard drive on Windows? Possible Duplicate:          My HDD on a dock just started making noises like it's being accessed but I don't see any program accessing it.  Is there a program that shows which HDD is accessed by which program in percentages similar to how the task manager shows which programs use the most CPU? UEFI machine doesn't boot Ubuntu through NVRAM bootcatalog. How to fix? What is the current state of apple device (iPhone, iPod, etc.) support? What ubuntu applications provide support? (guides, how to's, status) Also, specifically, details on support for syncing music to iPhone's and iPod's with the latest OS version:   Can you sync music to apple devices using >iOS4? (iPhone &amp; iPod) What applications allow you to do this and how? (guides, how to's, status)    What has already been established is:   Apple does not support Linux and has no plans to.  provides some support, however it currently does not support music/video synchronization with devices &gt;iOS4. Go to  and scroll to the section titled "" to see if your device version is supported. I know blender can display both orthographic and perspective projection. But, when we look at a cube in blender's viewport, I'm unable to distinguish by eye, if the projection in the viewport is a one-point, a two-point or a three-point perspective. What does blender use, and is this something changeable? What is the purpose of a Windows Workgroup? In Microsoft Windows, what is the purpose of a Workgroup? I understand that a Domain allows the administration of security (user names, passwords, file access, etc.) to be centralized. But what does a Workgroup give you? This is the error I get when I open the software center. I've tried rebooting and running sudo apt-get update but I see no improvement. It worked earlier but I don't know what went wrong since then. I'm using Ubuntu 16.04 final release on a Dell Inspiron 15R. Any advice will be appreciated. Thanks in advance.  EDIT: The problem magically solved itself without me doing anything special (or maybe inadvertently doing something, I don't know). So I'd still like to get to the root of this. I have a really simple Java class that effectively decorates a Map with input validation, with the obvious void set() and String get() methods.  I'd like to be able to effectively call those methods and handle return values and exceptions from outside the JVM, but still on the same machine Update: the caller I have in mind is not another JVM; thanks @Dave Ray  My implementation considerations are typical    performance ease of implementation and maintenance (simplicity?) reliability flexibility (i.e. can I call from a remote machine, etc.)   Is there a 'right way?' If not, what are my options, and what are the pro/cons for each?  (Stuff people have actually done and can provide real-life feedback on would be great!) I'm trying to convert Shapefiles from the  website into a GeoJSON file for use with Google Maps API. I'm using QGIS to facilitate but I can't get the projection/coordinates right. So far I've tried Google Mercator (EPSG:900913) and WGS 84 (EPSG:4326) with no luck. I'm using the OpenLayers to verify results and it keeps placing Texas near the  Gulf of Guinea (0 lat, 0 lng). Does "a couple" always mean two? Wireframe iOS design apps for iPad? Is there an app for iPad to assist in wireframe design for iPad and iPhone apps?  I don't mean actual development, just placing standard widgets and the things you usually do with photoshop and associated kits. Can you cast a spell learned from the Magic Initiate feat using spell slots? Say I play a wizard who learns cure wounds by taking the Magic Initiate feat. Could I cast that spell using the Wizard's spell slots? How do rich people guarantee the safety of their money, when savings exceed the FDIC limit? I am curious how a millionaire would guarantee the safety of his money, given that the FDIC only insures up to $250K of an individual's deposits at a bank.  If someone had $3 million that they wanted to put into the bank, would they have to open up 12 different bank accounts and deposit $250K into each one, so that all of his money is insured by the FDIC?  Or is there an easier way to guarantee the safety of all his money? Why does Ubuntu only support versions for a limited time (and what does it mean)? Unable to install "": snap "" has "install-snap" change in progress Should I use exit() or just return statements in main()? Personally I favor the return statements because I feel it's like reading any other function and the flow control when I'm reading the code is smooth (in my opinion). And even if I want to refactor the main() function, having return seems like a better choice than exit().  Does exit() do anything special that return doesn't? If diary Tom Riddle had succeeded, would there have been two Voldemorts? How to control fan speed? This seems to be one of those tricky examples. I only know one proof which is quite complicated and follows by localizing $\mathbb{Z}[\sqrt[3]{2}]$ at different primes and then showing it's a DVR. Does anyone know any simple quick proof?