This problem came up in a practice test:  create a new string array, initialize it to null, then initializing the first element and printing it.  Why does this result in a null pointer exception?  Why doesn't it print "one"?   Is it something to do with string immutability?     public static void main(String args[]) {         try {             String arr[] = new String[10];             arr = null;             arr[0] = "one";             System.out.print(arr[0]);         } catch(NullPointerException nex) {              System.out.print("null pointer exception");          } catch(Exception ex) {             System.out.print("exception");         }     }   Thanks!
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?
Story about a deadly alien creature on another planet that has some chemical in its body that makes it faster Minecraft pocket edition restoring skin problem I updated Minecraft PE so I can have custom skins. I clicked on 'restore skins' without selecting any particular skin, It is now stuck with a  message saying 'we're restoring your skins!' but it has been like that for 20 minutes. Is there a reason why it is like this? Counting integer partitions of n into exactly k distinct parts size at most M How can I find the number of partitions of $n$ into exactly $k$ distinct parts, where each part is at most $M$?  The number of partitions $p_k(\leq M,n)$ of $n$ into at most $k$ parts, each of size at most $M$, is given by the generating function: $$  \binom{M+k}{k}_{x} = \prod_{j=1}^{k}\frac{1-x^{M+k-j+1}}{1-x^j}= \sum_{n=0}^{kM} p_{k}(\leq M,n) x^n $$  For the number of the partitions $p_k(\mathcal{D},n)$ of $n$ into at most $k$ parts there is the recurrence relationship: $$   p_{k}(\mathcal{D},n) = p_{k}(\mathcal{D},n-k) + p_{k-1}(\mathcal{D},n) $$  But what, if I want to count only the partitions with distinct parts and restricted number of parts and restricted part size?  Update: Now I know the generating function for the number of distinct restricted partitions $p_k(\leq M, \mathcal{D},n)$ of $n$ into exactly $k$ distinct parts, all at most $M$ is $$    \prod_{j=1}^{M} (1+xq^{j}) = \sum_{k,n=0}^{\infty}p_k(\leq M, \mathcal{D},n)x^{k}q^{n} $$ and there is also a recurrence relation $$    p_k(\leq M, \mathcal{D},n) =         p_{k-1}(\leq M-1, \mathcal{D},n-k) +         p_k(\leq M-1, \mathcal{D},n-k) $$ How can I prove this? Could you recommend a book, where I could read about this? How to show $a,b$ coprime to $n\Rightarrow ab$ coprime to $n$? Let $a,b,n$ be integers such that  $\gcd(a,n)=\gcd(b,n)=1$. How to show that $\gcd(ab,n)=1$?   In other words, how to show that if two integers $a$ and $b$ each have no non-trivial common divisor with and integer $n$, then their product does no have a non-trivial common divisor with $n$ either.     This is a problem that is an exercise in my course.   Intuitively it seems plausible and it is easy to check in specific cases but how to  give an actual proof is not obvious. Where can I find the location of folders for installed programs? Chat Feature-Request: Thumbs-Up Add an additional form of "I agree" besides starring or pinning (since pinning is restricted to a smaller subset to begin with) or something that we can use to not clog up the right hand star bar.  This is because sometimes you want to say "I agree" but you don't want to star it because ... let's face it, that's not star-worthy, and you don't want to clutter the stream with fifty thousand "like totes for sure, hella right!" because then it becomes one big back-patting party and you lose all semblance of conversation.  So I would propose a fourth "flag" for chat, that allows us to say "I {agree with|like|am of the same opinion as} this comment" and that it would only be useful in the live-chat (and maybe but not really in the transcript) and that it have no other useful semantics (no badges, no list of's [unless the list is of comments you've upthumbed]). Get month name from Date How do I address unchecked cast warnings? How does RNA polymerase II CTD bind to the RNA modification proteins if the tail is flexible? The tail of RNA polymerase II is flexible, not folded into a fixed structure , but does each repeat have more &quot;rigid&quot; structure (i.e. fold into a structure that has less rotation freedom inside a repeat)? If not, then how can the proteins bind some repeat with high specificity? (you can't make lock and key with soft material) Strange artifacts along window borders after waking computer from sleep mode What happens if my flight out of the Schengen area is cancelled on the last day of my visa? If/Else with Selenium IDE - when confirmation message comes up I have a scenario, in case of the user registration successful, it will display a success message on the next page otherwise an error message shows on the same page. How to automate the test case to return as passed if it is success and failure in case of error message comes up.  Please help me out here. I've been reading the  and it mentions about virtual terminals which, if I understood it correctly, it is a Linux-specific feature (not in Unix) to allow multiple login consoles in a non X11 system. You create virtual terminals by pressing ALT-F2. I'm running Linux Mint and in my /dev folder though I see many tty devices and I don't know what they are for. Here is the grepped output:  crw-rw-rw-  1 root tty       5,   0 Jan  2 19:45 tty crw--w----  1 root tty       4,   0 Jan  2 19:10 tty0 crw-rw----  1 root tty       4,   1 Jan  2 19:10 tty1 crw--w----  1 root tty       4,  10 Jan  2 19:10 tty10 crw--w----  1 root tty       4,  11 Jan  2 19:10 tty11 crw--w----  1 root tty       4,  12 Jan  2 19:10 tty12 crw--w----  1 root tty       4,  13 Jan  2 19:10 tty13 crw--w----  1 root tty       4,  14 Jan  2 19:10 tty14 crw--w----  1 root tty       4,  15 Jan  2 19:10 tty15 crw--w----  1 root tty       4,  16 Jan  2 19:10 tty16 crw--w----  1 root tty       4,  17 Jan  2 19:10 tty17 crw--w----  1 root tty       4,  18 Jan  2 19:10 tty18 crw--w----  1 root tty       4,  19 Jan  2 19:10 tty19 crw-rw----  1 root tty       4,   2 Jan  2 19:10 tty2 crw--w----  1 root tty       4,  20 Jan  2 19:10 tty20 crw--w----  1 root tty       4,  21 Jan  2 19:10 tty21 crw--w----  1 root tty       4,  22 Jan  2 19:10 tty22 crw--w----  1 root tty       4,  23 Jan  2 19:10 tty23 crw--w----  1 root tty       4,  24 Jan  2 19:10 tty24 crw--w----  1 root tty       4,  25 Jan  2 19:10 tty25 crw--w----  1 root tty       4,  26 Jan  2 19:10 tty26 crw--w----  1 root tty       4,  27 Jan  2 19:10 tty27 crw--w----  1 root tty       4,  28 Jan  2 19:10 tty28 crw--w----  1 root tty       4,  29 Jan  2 19:10 tty29 crw-rw----  1 root tty       4,   3 Jan  2 19:10 tty3 crw--w----  1 root tty       4,  30 Jan  2 19:10 tty30 crw--w----  1 root tty       4,  31 Jan  2 19:10 tty31 crw--w----  1 root tty       4,  32 Jan  2 19:10 tty32 crw--w----  1 root tty       4,  33 Jan  2 19:10 tty33 crw--w----  1 root tty       4,  34 Jan  2 19:10 tty34 crw--w----  1 root tty       4,  35 Jan  2 19:10 tty35 crw--w----  1 root tty       4,  36 Jan  2 19:10 tty36 crw--w----  1 root tty       4,  37 Jan  2 19:10 tty37 crw--w----  1 root tty       4,  38 Jan  2 19:10 tty38 crw--w----  1 root tty       4,  39 Jan  2 19:10 tty39 crw-rw----  1 root tty       4,   4 Jan  2 19:10 tty4 crw--w----  1 root tty       4,  40 Jan  2 19:10 tty40 crw--w----  1 root tty       4,  41 Jan  2 19:10 tty41 crw--w----  1 root tty       4,  42 Jan  2 19:10 tty42 crw--w----  1 root tty       4,  43 Jan  2 19:10 tty43 crw--w----  1 root tty       4,  44 Jan  2 19:10 tty44 crw--w----  1 root tty       4,  45 Jan  2 19:10 tty45 crw--w----  1 root tty       4,  46 Jan  2 19:10 tty46 crw--w----  1 root tty       4,  47 Jan  2 19:10 tty47 crw--w----  1 root tty       4,  48 Jan  2 19:10 tty48 crw--w----  1 root tty       4,  49 Jan  2 19:10 tty49 crw-rw----  1 root tty       4,   5 Jan  2 19:10 tty5 crw--w----  1 root tty       4,  50 Jan  2 19:10 tty50 crw--w----  1 root tty       4,  51 Jan  2 19:10 tty51 crw--w----  1 root tty       4,  52 Jan  2 19:10 tty52 crw--w----  1 root tty       4,  53 Jan  2 19:10 tty53 crw--w----  1 root tty       4,  54 Jan  2 19:10 tty54 crw--w----  1 root tty       4,  55 Jan  2 19:10 tty55 crw--w----  1 root tty       4,  56 Jan  2 19:10 tty56 crw--w----  1 root tty       4,  57 Jan  2 19:10 tty57 crw--w----  1 root tty       4,  58 Jan  2 19:10 tty58 crw--w----  1 root tty       4,  59 Jan  2 19:10 tty59 crw-rw----  1 root tty       4,   6 Jan  2 19:10 tty6 crw--w----  1 root tty       4,  60 Jan  2 19:10 tty60 crw--w----  1 root tty       4,  61 Jan  2 19:10 tty61 crw--w----  1 root tty       4,  62 Jan  2 19:10 tty62 crw--w----  1 root tty       4,  63 Jan  2 19:10 tty63 crw--w----  1 root tty       4,   7 Jan  2 19:10 tty7 crw--w----  1 root tty       4,   8 Jan  2 19:10 tty8 crw--w----  1 root tty       4,   9 Jan  2 19:10 tty9 In Adobe Photoshop I am able to select multiple layers at once with Shift+Click.  How can I do that in GIMP? Attempting to create a tag wiki when a user has hit the suggested edit limit should alert the user that no more edits can be suggested at this time I ran into an issue on Gaming.SE where I attempted to create a tag wiki and wiki excerpt for a tag which did not have one already while I already have the maximum of five suggested edits in the queue.  Navigating to the tag page for the  provides a link to  for this tag. This link redirects to the  for this tag, without telling me that I can't submit an edit because I've reached the maximum number of suggested edits. Instead of silently redirecting, the page should alert me that I can't suggest any more edits until my suggestions are reviewed. Add leading zeroes to number in Java? Why didn't the basilisk bite in Chamber of Secrets destroy the Horcrux? As the title asks, why didn't the basilisk bite received in the Chamber of Secrets destroy the Horcrux inside the bitten person?   Yes, I know Fawkes quite quickly healed the bite wound with his phoenix tears, but when Harry used the basilisk fang to destroy Tom Riddle's diary the destruction of that Horcrux was immediate. When Ron hit the locket with the Sword of Gryffindor, it was destroyed immediately. Although the destruction of the ring occurred off-page, Dumbledore used the Sword of Gryffindor to destroy it, so presumably, like the locket, it was gone right away. Nagini died straightaway when Neville decapitated her. The destruction of the Hufflepuff cup happens off-page. The diadem seems to have been destroyed by Fiendfyre immediately as well, as when Harry examined it outside the Room of Requirement it was already leaking a blood-like substance, and then it cracked in half. When Voldemort hit Harry with Avada Kedavra in the forest, Harry woke up in limbo with the last fragment of Voldemort's soul - that awful flayed baby-like being - separated from him immediately.   Is there a logical/canon-based explanation for why the fragment of Voldemort's soul residing in Harry wasn't destroyed upon Harry being bitten by the basilisk?  NOTE: I've read the HP Wiki's entry on Horcruxes; however, I find the HP Wiki to be inconsistent in its accuracy, so I'm hesitant to accept the Wiki's explanation on the matter. I'd prefer an explanation constructed from information in the books or a statement by JKR, or the like. Why does the Cauchy distribution have no mean? From the distribution density function we could identify a mean (=0) for Cauchy distribution just like the graph below shows. But why do we say Cauchy distribution has no mean? What happens to Red Skull after Thanos gets the Soul Stone? Why must $a$ and $b$ both be coprime when proving that the square root of two is irrational? Suppose we wish to prove that the square root of two is irrational. We begin by assuming that it is rational.  Namely, where both $a$ and $b$ are integers $$\frac{a}{b} = \sqrt 2  % MathType!MTEF!2!1!+- % faaagCart1ev2aaaKnaaaaWenf2ys9wBH5garuavP1wzZbqedmvETj % 2BSbqefm0B1jxALjharqqtubsr4rNCHbGeaGqiVu0Je9sqqrpepC0x % bbL8FesqqrFfpeea0xe9Lq-Jc9vqaqpepm0xbba9pwe9Q8fs0-yqaq % pepae9pg0FirpepeKkFr0xfr-xfr-xb9Gqpi0dc9adbaqaaeGaciGa % aiaabeqaamaabaabaaGcbaWaaSaaaeaacaWGHbaabaGaamOyaaaacq % GH9aqpdaGcaaqaaiaaikdaaSqabaaaaa!31D3! $$  Why is it so important that both $a$ and $b$ be coprime and the fraction be irreducible?  That is, if $a$ and $b$ are not coprime and the fraction is indeed reducible, then$$\frac{a}{b} \ne \sqrt 2  % MathType!MTEF!2!1!+- % faaagCart1ev2aaaKnaaaaWenf2ys9wBH5garuavP1wzZbqedmvETj % 2BSbqefm0B1jxALjharqqtubsr4rNCHbGeaGqiVu0Je9sqqrpepC0x % bbL8FesqqrFfpeea0xe9Lq-Jc9vqaqpepm0xbba9pwe9Q8fs0-yqaq % pepae9pg0FirpepeKkFr0xfr-xfr-xb9Gqpi0dc9adbaqaaeGaciGa % aiaabeqaamaabaabaaGcbaWaaSaaaeaacaWGHbaabaGaamOyaaaacq % GHGjsUdaGcaaqaaiaaikdaaSqabaaaaa!3294! $$