Button array causes app to crash I have multiple buttons in my app and I want to set the same text for every button using a loop. So I declared an array and filled it with the buttons in this manner:  public class MainActivity extends AppCompatActivity {     Button b1,b2,b3;      @Override     protected void onCreate(Bundle savedInstanceState) {         super.onCreate(savedInstanceState);         setContentView(R.layout.activity_main);         b1=(Button)findViewById(R.id.button);         b2=(Button)findViewById(R.id.button2);         b3=(Button)findViewById(R.id.button3);     }      Button[] buArray ={b1,b2,b3};      void b1clicked(View view) {         for (int i =0;i&lt;3;i++) {             buArray[i].setText("it works");         }     } }   But when i try to set text for a button from the array like this   buArray[0].setText("some text");   This causes my app to crash and force closes  And gives me an error like this in the the log  "NullPointerException
What is a NullPointerException, and how do I fix it? 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?
My MATLAB launcher doesn't work I've installed MATLAB R2011a on Ubuntu 11.10 today following . I've also followed the steps to create the launcher. It appeared, but when I click on it nothing happens. Does anyone knows what can I do to fix it? Additional info I can run it perfectly through terminal. My only problem is getting the launcher to work. To create the launcher I used :   Get an icon:  sudo wget http://upload.wikimedia.org/wikipedia/commons/2/21/Matlab_Logo.png -O /usr/share/icons/matlab.png   Get the launcher file:  sudo wget 'https://help.ubuntu.com/community/MATLAB?action=AttachFile&amp;do=get&amp;target=matlab-r2011a.desktop' -O /usr/share/applications/matlab.desktop Is there a program that can make live USBs for any distro, iso, you get the point. I can only find ones that make live USBs for other linux distributions and none for anything else. I had internet connection, but when I upgraded my VGA and restarted my PC then everything for eth0 has gone.     When I used ifdown:     ifdown: interface eth0 not configured   Is there something I could do?    EDIT: Content of /etc/network/interfaces    auto lo iface lo inet loopback   When I ifconfig I don't have these lines:    inet addr:192.168.1.5  Bcast:192.168.1.255  Mask:255.255.255.0 inet6 addr: fe80::219:5bff:fe5e:a5e/64 Scope:Link   In the Terminal typed:  sudo gedit /etc/network/interfaces   and then added these lines in the bottom:  auto eth0 iface eth0 inet dhcp   then I typed:    sudo ifdown eth0 sudo ifup eth0   when I send the second command I received the below message:    No DHCPOFFERS received No working leases in persistent database - sleeping   Any help? Using custom tables in nft I have a Fedora 31 system on which I am using iptables-nft. I need this because there is still a bunch of software that expects the legacy iptables command line tools.  This means that my nftables configuration has the corresponding set of tables to match the legacy configuration:  table ip filter table ip nat table ip6 filter table ip mangle table ip6 nat table ip6 mangle   I use a containerized VPN service that, prior to nftables, would enable masquerading on my primary ethernet interface by running something like this when the vpn comes up:  iptables -t nat -A POSTROUTING -s 172.16.254.0/24 -o eth0 -j MASQUERADE   Since upgrading to Fedora 31 and iptables-nft, this no longer works. The container (running alpine) does not have the iptables-nft compatability wrapper, but it does have the nft command itself.  I can't use the nft cli to add rules to the existing tables, because this will break iptables-nft. But I can create new tables. I was hoping I could just apply a configuration like this:  table ip vpn {     chain postrouting {         type nat hook postrouting priority filter; policy accept;         ip saddr 172.16.254.0/24 oifname "eth0" counter masquerade     }      chain forward {         type filter hook forward priority filter; policy accept;         ip saddr 172.16.254.0/24 counter accept     } }   ...but this doesn't appear to have any impact. By setting the chains in this table to priority 0 I was hoping they would match before the legacy nat table, but that doesn't appear to be the case.  Is there a way to make this work? When should I use Inline vs. External Javascript? I would like to know when I should include external scripts or write them inline with the html code, in terms of performance and ease of maintenance.  What is the general practice for this?  Real-world-scenario - I have several html pages that need client-side form validation. For this I use a jQuery plugin that I include on all these pages. But the question is, do I:   write the bits of code that configure this script inline? include all bits in one file that's share among all these html pages? include each bit in a separate external file, one for each html page?   Thanks. How do I get Gmail to ask me to be a mailto handler again? TikZ is undergoing lots of development with new features being added, but the versions distributed with standard TeX releases are often a little old. How do I get the latest version? If I want to be sure that I get the latest stable version, how do I do that?    Note: I'm not asking this question for myself, but because a question like this seems to be useful for pointing to it when a new feature of TikZ is mentioned in an answer to some other question. Feel free to post answers for any operating system/TeX distribution combination. I'm still new to ZFS. I've been using Nexenta but I'm thinking of switching to OpenIndiana or Solaris 11 Express. Right now, I'm at a point of considering virtualizing the ZFS server as a guest within either ESXi, Hyper-V or XenServer (I haven't decided which one yet - I'm leaning towards ESXi for VMDirectPath and FreeBSD support).   The primary reason being that it seems like I have enough resources to go around that I could easily have 1-3 other VMs running concurrently. Mostly Windows Server. Maybe a Linux/BSD VM as well. I'd like the virtualized ZFS server to host all the data for the other VMs so their data could be kept on a physically separate disks from the ZFS disks (mount as iscsi or nfs).  The server currently has an AMD Phenom II with 6 total cores (2 unlocked), 16GB RAM (maxed out) and an LSI SAS 1068E HBA with (7) 1TB SATA II disks attached (planning on RAIDZ2 with hot spare). I also have (4) 32GB SATA II SSDs attached to the motherboard. I'm hoping to mirror two of the SSDs to a boot mirror (for the virtual host), and leave the other two SSDs for ZIL and L2ARC (for the ZFS VM guest). I'm willing to add two more disks to store the VM guests and allocate all seven of the current disks as ZFS storage. Note: The motherboard does not have IOMMU support as the 880G doesn't support it, but I do have an 890FX board which does have IOMMU if it makes a huge difference.  My questions are:  1) Is it wise to do this? I don't see any obviously downside (which makes me wonder why no one else has mentioned it). I feel like I could be making a huge oversight and I'd hate to commit to this, move over all my data only to go fubar from some minute detail I missed.  2) ZFS virtual guest performance? I'm willing to take a small performance hit but I'd think if the VM guest has full disk access to the disks that at the very least, disk I/O performance will be negligible (in comparison to running ZFS non-virtualized). Can anyone speak to this from experience hosting a ZFS server as a VM guest? count lines in a file I'm sure there are many ways to do this: how can I count the number of lines in a text file?  $ &lt;cmd&gt; file.txt 1020 lines Young adult book about a boy(?) who gets sent through a portal to another world which is really the distant future Is there a way to determine what version (distribution &amp; kernel version, I suppose) of Linux is running (from the command-line), that works on any Linux system? The muffins were rock hard, what did I do wrong? Here is the recipe I used, I did not mix it for long, as that make the muffins very hard.   The muffins were very hard, and had a bad after taste and smell. I missed adding some oil, but what else could be the reason ?   Red Millet Flour, 50 g Whole Wheat flour, 50 g Toasted Oat Bran, 40g Whole Green Mung Beans - Sprouted, 100 g Domino - Light Brown Sugar 50g Baking Soda, 2 tsp Salt, 1 Tablespoon Liquid Egg White, 4 eggs 100% Whey (Vanilla), 75g Chobani - Greek Yogurt - 0% Vanilla, 5.3 oz (small packet) Carrots - Raw, 1 cup, grated Bananas - Raw, 1 cup, mashed White, all-purpose, enriched, bleached, 40 g   Also I wanted to try yeast instead of baking soda, but due to eggs and other veggies I cannot let is rise overnight (any ideas ?). I was trying to make good protein muffins which are an ideal breakfast, grab one with a glass of milk and done!   They run approximately 160 calories per muffin 25g carbs, 1g fat, 12g protein. Is there an easy way to tell if a graph can be embedded on a Möbius strip (with no edges crossing)?  A specific version of this: if a simple graph with an odd number of vertices has all vertices of degree 4, can it be embedded on a Möbius strip?    Answer summary:   There are  for the Möbius strip that are   and drawn on . There are  for the Möbius strip, they are , and even better there are only .   I have not yet answered the second question, but Jim Belk's excellent explanation has given me good ideas. How to avoid the wrinkle at the poles of the UV sphere? How can we prove that a binomial coefficient $n\choose m$is divisible by the ratio of $n$ and $\gcd(n,m)$? Prove that for every $n\geq m \geq1$ natural numbers, the following number is an integer:  $${\gcd(n,m)\over n}\cdot{n\choose m}$$  Where $\gcd$ is the greatest common divisor.  I tried to make it simpler by cancelling the $n$ from the left side, and making it $(n-1)!$ on the right: $\gcd(n, m) \cdot \frac{(n-1)!}{m!(n-m)!}$, but can't really go further.   This was problem B-2 on the . Comparing complex numbers If $a+ib$, $c+id$, $e+if$ are three complex numbers, than can we tell which one is greater or smaller between them? If yes, then how and if no then why not?   Can somebody give explanation on this.... I will be grateful to him. On a plane, there are two congruent circles, $O_1, O_2$. One line intersects $O _1$ and A and B and $O_2$ at C and D such that AB=BC=CD=14. Another line intersects $O _1$ and E and F and $O_2$ at G and H such that EF=FG=GH=6. What is the radius of the circle.   The configuration was hard to draw. . You can reflect the lines over the centers, but it is still the same. Cleary, $\widehat{AB}=\widehat{CD}$ and $\widehat{EF}=\widehat{GH}$. I have no idea how to proceed. Prove that there exists at least one $x_0\in\mathbb{R}$, such that $f(x_0)+f''(x_0)=0$ Let $f:\mathbb{R}\to\mathbb{R}$ be a function, two times   differentiable with $\left|f(x)\right|\leq1,\forall x\in\mathbb{R}$   and $f^2(0)+\left(f'(0)\right)^2=4$. Prove that there exists at least   one $x_0\in\mathbb{R}$, such that $f(x_0)+f''(x_0)=0$.   I have tried the usual Rolle method by $e^x$, but didn't go far... Any help available? Is product of two closed sets closed? If $A$ is closed in $X$ and $B$ is closed in $Y$,   does it follow that $A \times B$ is closed in $X \times Y$ ? Some publications capitalize He, Him, etc., when referring to a god.    What is this practice called? 'Proper noun' is rather generic.