Throws nullPointerException and app crashes
What is a NullPointerException, and how do I fix it?
Why can this product of rectangular matrices not be the identity matrix? I install virtualBox on Ubuntu 16.04, but after install and create new virtual Host shows this error:     Kernel driver not installed (rc=-1908)      The VirtualBox Linux kernel driver (vboxdrv) is either not loaded or there is a permission problem with /dev/vboxdrv. Please install virtualbox-dkms package and load the kernel module by executing  modprobe vboxdrv       as root. If it is available in your distribution, you should install the     DKMS package first. This package keeps track of Linux kernel changes and   recompiles the vboxdrv kernel module if necessary.  where: suplibOsInit what: 3 VERR_VM_DRIVER_NOT_INSTALLED (-1908) - The support driver is not installed. On linux, open returned ENOENT.     How to address this modprobe vboxdrv error? Database design help. many-to-many relationship How to choose the right bean scope? Add manually installed application to 'Show Applications' grid in Ubuntu 18.04 I have been stuck in a problem, that has thrown my brain out of the coding. This problem is at very high priority and I need the solution as early as possible. Problem is as :  There are exactly N advertising boards on the highway. Now a company want to advertise on some of these advertising boards(each advertising board costs some money) .  Company strategy is that, they want at least 'K' advertisement should be there among M consecutive advertising boards. But at the same time Company want to pay minimum for its advertisement .  Now, what is the total number of ways, different ways Company can advertise meeting its minimum cost strategy.  As for Example: N= 3, M = 2, K=1 ==> there is only one way for minimum cost, ie. 0C0 , where '0' denotes No company advertisement, and 'C' denotes company advertisement board.  Similarly, for N =4, M =2, K =1 ==> there is 3 possible ways, ie. C0C0, 0C0C, 0CC0.  Hope to get a reply from someone soon. Thanks. Converting Older United States Dollar Bills I received from my Dad 150 American Dollars about 12 years ago. I never have thought to change this money but a few days I tried change it in a currency exchange in Sydney and the guy didn't change it because the series are old.     What do I have to do to change this money? How can I get free or trial ExactTarget instance How can I get free or trial ExactTarget instance. I need to do ExactTarget SAML2.0 Single Sign-On connector development, integration and testing. Is there any step by step documentation available so that I can work on ExactTarget SAML2.0 Single Sign-On ? $ \tan 1^\circ \cdot \tan 2^\circ \cdot \tan 3^\circ \cdots \tan 89^\circ$ How can I find the following product using elementary trigonometry?     $$ \tan 1^\circ \cdot \tan 2^\circ \cdot \tan 3^\circ \cdots \tan 89^\circ.$$   I have tried using a substitution, but nothing has worked. What is the point of Refresh if Dynamic has an UpdateInterval option? Why is $\mathbb{R}^2$ not a subspace of $\mathbb{R}^3$? I've been told that I should use simple past in reported speech when the direct speech is in simple present such as I **am** the best   ~>   He said he **was** the best  but what happens for imperative mood direct speech     "Mom said dont trust strangers"   Or     "Mom said didn't trust strangers"   I think I should maintain the first form. But I'm not sure. And I'm not even sure this relates to the sentence mood. I need the best choice and a further explaination for this :) How Can I prove (a+b) mod m = (a mod m) + (b mod m)) mod m? modular arithmetic  How Can I prove (a+b) mod m = (a mod m) + (b mod m)) mod m ? Confusing [...] List in Python: What is it? So I was writing up a simple binary tree in Python and came across [...]  I don't believe this to be related to the Ellipsis object, more it seems to have something to do with an infinity loop (due to Python's shallow copy?). The source of this infinity loop and why it doesn't get expanded while expanding when accessed is something I'm completely lost to, however   &gt;&gt;&gt; a [[[[[], [], 8, 3], [[], [], 3, 2], 6, 3], [], 1, 4], [[], [], -4, 2], 0, 0] &gt;&gt;&gt; Keys(a)#With a+b [0, 1, 6, 8, 3, -4] &gt;&gt;&gt; Keys(a)#With [a,b] [8, [...], [...], 3, [...], [...], 6, [...], [...], 1, [...], [...], -4, [...], [...], 0, [...], [...]] &gt;&gt;&gt; Keys(a)[1]#?? [8, [...], [...], 3, [...], [...], 6, [...], [...], 1, [...], [...], -4, [...], [...], 0, [...], [...], 8, [...], [...], 3, [...], [...], 6, [...], [...], 1, [...], [...], -4, [...], [...], 0, [...], [...]]     Version using a+b  def Keys(x,y=[]):     if len(x):y+=[x[2]]+Keys(x[0],y)+Keys(x[1],y)#Though it seems I was using y=y[:]+, this actually outputs an ugly mess     return y   version using [a,b]  def Keys(x,y=[]):     if len(x):y+=[x[2],Keys(x[0],y),Keys(x[1],y)]     return y   So what exactly is [...]? What's the meaning of "be blowed"? I would like to know what's the meaning of "be blowed" in the following text:     'I'm going to smoke' Jenkins said; 'be blowed to Bertie dear.' (Mrs. Smythe had once addressed her husband in the office as 'Bertie dear', and thereforth that had been his name among the staff.) Richard made no answer. When a minute later Jenkins, discreetly directing his puffs to the open window, asked him for the titles of one or two of Zola's novels in English, and their price, he gave the required information without turning round and in a preoccupied tone.   , Arnold Bennett, 1911. Winter is Coming It's my understanding that the phrase "Winter is Coming" is the motto of the Stark house, when the story first reaches the wall it's implied that the winter is not a periodic season like it is in our world.  Does the winter refer to a particularly severe season or does a winter only occur every few years? -ing vs -in' ending I wonder if the &quot;g&quot; in the -ing forms is pronounced. When I hear it it seems as if it's not pronounced sometimes or just slightly, though sometimes I've been told that I should pronounce &quot;g&quot; for example in &quot;meeting&quot; just to avoid saying &quot;mitten&quot;. So how should I pronounce &quot;-ing&quot;? Sometimes -ing is written in an informal way as -in' such as:  taking takin'  Is the letter &quot;g&quot; in each case pronounced differently? Can I run CAT5/6 cables parallel to electrical cables? I am building a new house and am planning to hardwire network cables into each room.   Can I run CAT5/6 cables parallel to electrical wires without introducing any general safety issues or losing much in connection quality?  Wiring runs for up to 25 metres from patch panel and distribution board in garage to rooms.   My research indicates that is should be fine if they are in separate conduits or if the CAT cables are shielded. Seeking Symbology for Interactive Mapping? When a user clicks on a map what should they expect to see?   I would say a symbol for where they clicked.  A pushpin seems to be the most accepted icon for generic data. Google has pushed the upside down tear drop.   What are other ideas/options and is there a place for finding professional gis oriented icon packs?  I ended up creating this,     This just popped up from the guys at map box. Clean I made changes to iptables config file in /etc/iptables/filter in Ubuntu and want to reload them. I read the man page and also googled but couldn't find the information. Any help will be appreciated.