I would like to access my array of objects from another method in my class. My code is as follows. I get a NullPointerException error.  The nameArray is simply reading a text file, and data is being stored in it.  public class menu {      static Scanner askInfo = new Scanner(System.in);     public static Student ArrObj[] = new Student[15]; //instantiates an array of student objects       public static void main(String args[]) throws IOException {         for (int i = 0; i &lt; 15; i++) {             ArrObj[i] = new Student(); //creates an array of student objects             System.out.println("Here is the list of all children.");             System.out.println("Which child's information do you want to enter?");             int InName = askInfo.nextInt();             switch (InName) {                 case 1:                     ArrObj[i].setName(Read.nameArray[0].substring(3));                     break;                 case 2:                     ArrObj[i].setName(Read.nameArray[1].substring(3));                     break;                 case 3:                     ArrObj[i].setName(Read.nameArray[2].substring(3));                     break;                 case 4:                     ArrObj[i].setName(Read.nameArray[3].substring(3));                     break;             }         }         for (int i = 0; i &lt; 15; i++) {             System.out.println(ArrObj[i].getName());         }     }  }   The (important parts of) Student class:  public class Student {     private String name;      //name of student          public void setName(String name) {             this.name = name;     }      public String getName(){         return name;     } }   The Read class:  import java.io.*; import java.util.*;  public class Read {      static String nameArray[] = new String[100]; //to be safe, declare plenty      public static void ReadNames() throws IOException //method to read names     {         Scanner read = new Scanner(new File("C:\\IA\\names.txt")); //this will read the names of students         int counter = -1; //-1 so that when incremented, the first index is 0          while (read.hasNext()) {             counter++;             nameArray[counter] = read.nextLine();         }     } }
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?
I'm studying for qualifying exams and ran into this problem.  Show that if $\{a_n\}$ is a nonincreasing sequence of positive real numbers such that $\sum_n a_n$ converges, then $\lim_{n \rightarrow \infty} n a_n = 0$.  Using the definition of the limit, this is equivalent to showing \begin{equation} \forall \varepsilon &gt; 0 \; \exists n_0 \text{ such that } |n a_n| &lt; \varepsilon \; \forall n &gt; n_0 \end{equation} or \begin{equation} \forall \varepsilon &gt; 0 \; \exists n_0 \text{ such that } a_n &lt; \frac{\varepsilon}{n} \; \forall n &gt; n_0 \end{equation} Basically, the terms must be bounded by the harmonic series. Thanks, I'm really stuck on this seemingly simple problem! Uninstalling Ubuntu from Windows Dual Boot if I don't have Windows recovery CD I installed Ubuntu (I had already had Windows 8.1) from USB (I still have live Ubuntu on it). Is there a way I can uninstall Ubuntu in a way that my Windows will remain bootable? All the tutorials I have seen say that uninstalling ubuntu will delete GRUB also so I will need a Windows recovery CD to boot into it, but I don't have one. Is there a solution? $n$-th digit in the sequence of natural numbers What's the $n$-th digit in the sequence $S$ of numbers formed by the natural numbers, i.e.,  $n$-th digit in the sequence 1 2 3 4 5 6 7 8 9 10 11 12... ? For example 11th digit in the sequence is 0. How do I properly access Windows software RAID 0? I am a new Ubuntu user with a fresh installation, and am eager to get started with it. However, all of my important data is on Windows software RAID 0 array, and I need it to stay there as I'm also dual booting Windows. I need access to this data on Ubuntu, and can't really get anything real done until I have access.  I have already researched this subject as best as I could, and I managed to find a very helpful post:      The post describes how to get Ubuntu to see a Windows RAID 0 array that is made up of two drives. The main command used is sudo mdadm --build /dev/md0 --chunk=64 --level=0 --raid-devices=2 /dev/sdd2 /dev/sdc2. According to that user, and the other posters in the thread, it actually does work. That's great.  I have not tried following these instructions yet. Why? The post includes a warning about how you must not write to it if you enter the wrong chunk size; it's understandable how that could cause problems. My concern is that my setup is different to their example, and I am not sure that the commands should be entered exactly the same for my setup. I am afraid to break it by doing it wrong, and therefore wish to get the advice of somebody more experienced.  This is how my setup differs from their example:   I have three 1 TB drives, not two drives (of whatever size they used). I have two RAID 0 partitions spread across those three drives: one 500 GB and 2.3 TB. This means that I need to NOT use the full disks when creating the RAID array, but instead use just part of them. I used a non-default block size for at least one of my RAID 0 partitions when I set them up years ago. I have no idea if this block size is the same as the chunk size that they mention. My 500 GB partition has a block size of 4 kb (4096 bytes per cluster), and my 2.3 TB partition has a block size of 64 kb (65536 bytes per cluster).   The relevant output from sudo lsblk -o NAME,FSTYPE,SIZE,MOUNTPOINT,LABEL (for just those three RAID0 drives) is:  NAME   FSTYPE   SIZE MOUNTPOINT            LABEL sdb           931.5G             ├─sdb1            1M             ├─sdb2          127M             └─sdb3        931.4G             sdc           931.5G             ├─sdc1            1M             ├─sdc2          127M             └─sdc3        931.4G             sdd           931.5G             ├─sdd1        166.7G             └─sdd2        764.7G    The relevant output from cat /proc/partitions (for just those three RAID0 drives) is:  8       16  976762584 sdb 8       17       1024 sdb1 8       18     130048 sdb2 8       19  976631478 sdb3 8       32  976762584 sdc 8       33       1024 sdc1 8       34     130048 sdc2 8       35  976631478 sdc3 8       48  976762584 sdd 8       49  174763008 sdd1 8       50  801865728 sdd2   The "Disks" program in Ubuntu displays the following partitions for my drives:  /dev/sdb:   GUID Partition Table . /dev/sdb1:  1.0 MB, Microsoft LDM metadata. /dev/sdb2:  133 MB, Microsoft Reserved. /dev/sdb3:  1.0 TB, Microsoft LDM data. /dev/sdc:   GUID Partition Table partitioning. /dev/sdc1:  1.0 MB, Microsoft LDM metadata. /dev/sdc2:  133 MB, Microsoft Reserved. /dev/sdc3:  1.0 TB, Microsoft LDM data. /dev/sdd:   Master Boot Record partitioning. /dev/sdd1:  179 GB, Unknown. /dev/sdd2:  821 GB, Unknown. /dev/sdd:   136 MB, Unallocated space.   I hope I've provided enough information here. So now, my question is this: what is the proper command for me to enter with my setup, so that I can access both of my Windows RAID 0 partitions from Ubuntu?  Thank you very much in advance. This is a follow-up question to the discussion about the finite axiom of choice .  Suppose we have a countable collection of non-empty sets $\{A_1, A_2, A_3,\cdots\}$ Reasoning as indicated in that discussion, we can prove the existence of a choice function $c_n$ such that $c_n(i)$ belongs to $A_i$ for $i = 1,\cdots,n$  Again reasoning as suggested and using induction, we can prove the existence of a function $C$ defined over $\{1, 2, \cdots\}$ such that $C(n)$ is a choice function defined for $i=1,\cdots,n$ with $C(n)(i)$ an element of A_i. We can require in addition that $C(n)(i)$ and $C(n-1)(i)$ are equal for $i=1,\cdots,n-1$.  Now it would it seem that we can prove the countable axiom of choice by taking the union of $C(1)$, $C(2)$, $\cdots$  The question is as follows: why is that proof wrong? I suspect the answer may have something to do with the axiom of union. How to remove the association between two Gmail accounts? I want to remove that other account. Both of them are Gmail accounts. How could I do? What the pointer size in 64 bits computer in C++? Weird Integer boxing in Java Title of short story: God granting immortality to others to find a way to kill himself Export all symbols when creating a DLL With VS2005, I want to create a DLL and automatically export all symbols without adding __declspec(dllexport) everywhere and without hand-creating .def files. Is threre a way to do this? How to use GROUP BY to concatenate strings in MySQL? Basically the question is how to get from this:   foo_id   foo_name 1        A 1        B 2        C   to this:   foo_id   foo_name 1        A B 2        C Get width of a given text as length Ubuntu 16.10 Wifi Trouble - RT2561/RT61 I've used Ubuntu before, but I'm still very new. I just installed 16.10 on a new computer yesterday, and the Wi-Fi has been considerably slower than my Windows laptop. I put the computer together mainly to play Dota 2, and I experience decent ping but constant 5%-10% packet loss while playing. Occasionally, after the computer has been left on for a while, the Wi-Fi connection will drop completely- I can still see networks in the drop down menu, including my home network, but my computer will not reconnect without a reboot. I've looked all over for a solution, but my inexperience has prevented me from getting anything to work. My Wi-Fi card is a Ralink RT2561/RT61, here's some info  The output of sudo lshw -C network   *-network                          description: Wireless interface         product: RT2561/RT61 802.11g PCI         vendor: Ralink corp.         physical id: 6         bus info: pci@0000:01:06.0         logical name: wlp1s6         version: 00         serial: 00:0e:2e:de:df:c0         width: 32 bits         clock: 33MHz         capabilities: pm bus_master cap_list ethernet physical wireless         configuration: broadcast=yes driver=rt61pci driverversion=4.8.0-22-generic firmware=0.8 ip=192.168.1.107  latency=64 link=yes multicast=yes wireless=IEEE 802.11         resources: irq:17 memory:dfef8000-dfefffff   Here is the output of sudo iwconfig:   *-network                          description: Wireless interface         product: RT2561/RT61 802.11g PCI         vendor: Ralink corp.         physical id: 6         bus info: pci@0000:01:06.0         logical name: wlp1s6         version: 00         serial: 00:0e:2e:de:df:c0         width: 32 bits         clock: 33MHz         capabilities: pm bus_master cap_list ethernet physical wireless         configuration: broadcast=yes driver=rt61pci driverversion=4.8.0-22-generic firmware=0.8 ip=192.168.1.107  latency=64 link=yes multicast=yes wireless=IEEE 802.11         resources: irq:17 memory:dfef8000-dfefffff   I'm at a loss, I'm very bad at this. If any additional info is needed I can provide it My understanding is that heat is essentially atomic vibrations. If there are almost no atoms, how can there be residual heat?  Also, as I understand in space there is no heat transfer via convection and it is mainly through EM radiation. In this case, why is it that if i were to go into space with no suit and just an airtight helmet through which I could breathe, I would still freeze to death very quickly? Is it Possible to Disable Feed and Topics for an Object Completely at Profile Level / Page LayOuts In Pokémon Sun and Moon, when you've finished the game you can switch day and night by going though the wormhole at the altar where you've caught the box legendary. Are there any more differences when going through the wormhole, excluding the day or night difference? For example, the altar of the sunne and altar of the moone switch when going through the portal. How can I install the Google Apps Package (Play Store, ...) on my Android device? Prove $2^n-1$ is divisible by $(2^m-1)^2$ iff... Prove that for any $m,n\in\mathbb{Z}^+$, the number $2^n-1$ is divisible by $(2^m-1)^2$ iff the number $n$ is divisible by $m(2^m-1)$.  My work so far:  It's an if and only if statement, so the common approach is to split the proof into two "if then" proofs ($A\rightarrow B \text{ and } B\rightarrow A$).  Starting with $A\rightarrow B$, for a direct proof, I would assume $A$ and prove $B$. I can use the definition of divisibility:  Assume $n=m(2^m-1)k$ for some integer $k$  Then I need to prove that $2^n-1=(2^m-1)^2h$ for some integer $h$  So I'm thinking I need to start with the expression $2^n-1$ and transform it to $(2^m-1)^2h$, or vice versa, and I need to use the assumption $n=m(2^m-1)k$ somehow.  I notice that the LS of the equality contains the variable $n$ while the RS contains $m$, and the assumption relates $n$ to $m$, so that could be a way forward. For example, simple substitution gives $2^{m(2^m-1)k}-1$, but I'm not sure what I could do from here. Perhaps there's a divisibility theorem that could help?  Other things I notice: $2^n-1$ and $(2^m-1)^2$ are always odd. Also, the divisors in both cases are multiples of $2^m-1$.  Any help/hints appreciated. Is the Dungeon Magazine 4e Adventure List spreadsheet still available? used to go to a spreadsheet with all the 4E adventures published in Dungeon Magazine (and possibly some others, IIRC) during that edition's duration. I remember it listed out each adventure by name, start/end level, adventure path, and maybe even a little summary blurb.  However, the spreadsheet behind that link seems to have disappeared into the digital ether, and I can't find a copy of it in my own google drive (implying I never made a copy of it).  Does anyone happen to have a copy of that spreadsheet that they could share, and/or other resources that would let me sort through the many adventures from 4E Dungeon Magazine? Server only reachable over VPN I have an Apache server running on a Raspberry P and it works just fine in the local network. And after forwarding port 80 and trying to connect using the public IP, Chrome says ERR_CONNECTION_REFUSED. But the strange thing is that I CAN reach the server when using VPN and using the same IP. What can I do?     -telnet 80.***.***.78 80      Trying 80.***.***.78...     telnet: connect to address 80.***.***.78: Connection refused     telnet: Unable to connect to remote host     -route -n      Destination     Gateway         Genmask         Flags Metric Ref    Use Iface     0.0.0.0         192.168.0.1     0.0.0.0         UG    0      0        0 eth0     192.168.0.0     0.0.0.0         255.255.255.0   U     0      0        0 eth0      -sudo netstat -lapute:              Active Internet connections (servers and established)     Proto Recv-Q Send-Q Local Address           Foreign Address         State       User       Inode       PID/Program name     tcp        0      0 *:http                  *:*                     LISTEN      root       6137        2051/apache2     tcp        0      0 *:ssh                   *:*                     LISTEN      root       6367        2249/sshd     tcp        0      0 pi.local:ssh            nmb.local:65535         ESTABLISHED root       8669        2565/sshd: pi [priv     udp        0      0 *:9949                  *:*                                 root       5918        1809/dhclient     udp        0      0 *:mdns                  *:*                                 avahi      6293        2184/avahi-daemon:     udp        0      0 *:54070                 *:*                                 avahi      6295        2184/avahi-daemon:     udp        0      0 *:bootpc                *:*                                 root       5946        1809/dhclient     udp        0      0 pi.local:ntp            *:*                                 root       6310        2200/ntpd     udp        0      0 localhost:ntp           *:*                                 root       6309        2200/ntpd     udp        0      0 *:ntp                   *:*                                 root       6304        2200/ntpd