I would like to return the Host thats have the same domain as the Host in the List. But it gives me and error: "This method have to return a type of Host".  How I have to return the object Host?  public class Manager {  private List&lt;Host&gt; hosts = new ArrayList&lt;Host&gt;();  public Host getHost (String domain) {        for(int i = 0; i &lt; hosts.size(); i++) {           if(domain == hosts.get(i).getDomain()) {               return hosts.get(i);           }}         }     Thanks.
I've been using the == operator in my program to compare all my strings so far. However, I ran into a bug, changed one of them into .equals() instead, and it fixed the bug.  Is == bad? When should it and should it not be used? What's the difference?
Let $G$ be a non-empty finite set with an associative binary operation so that cancellation law holds, i.e. $ab=ac$ or $ba=ca$ implies $b=c$, for any choices of $a,b,c$ in $G$. Assume that there is an identity element $e$ in $G$. Show that $G$ is a group.  Proof: To show $G$ is a group, conditions must hold. Suppose that $ab=ac$, then $b=eb=(a^{-1}a)b =a^{-1}(ab)=a^{-1}(ac) =(a^{-1}a)c=ec=c$. So left cancellation holds in $G$.  2) Suppose $ba=ca$, then $b=be=b(aa^{-1}) =(ba)a^{-1}=(ca)a^{-1} =c(aa^{-1})=ce=c$. So right cancellation holds in $G$.  3) If $a$ exists in $G$ then $aa^{-1}=a^{-1}a=e$, where $a$ is an inverse of $a^{-1}$. Since inverses are unique, $(a^{-1})^{-1}=a$.  4) Let $x$ be the inverse of $ab$. Then $(ab)x=e$. By associativity we have $a(bx)=aa^{-1}$. Through left cancellation we have  $bx=a^{-1}bx=ea^{-1}=b(b^{-1}a^{-1})$ and $x=b^{-1}a^{-1}$.  Thus $(ab)^{-1}=b^{-1}a^{-1}$. So all conditions hold, $G$ is a group.  Is this proof correct? I know to show $G$ is a group these conditions have to be met. This is all I have to show right? How can I explain how to play D&D to new players without them falling asleep from boredom? Some of my friends just started playing Dungeons &amp; Dragons [5e] for the first time and don't know anything about how to play. I have tried explaining to them the things that are completely necessary and teach them the rest while playing but I could not get them to understand. None of them have a players handbook and they can't afford one and they really want to play. I really want a simple way to explain the basics and since I have a habit of explaining things in ways that are much too complicated. I have already told them the basic rules so all I need to know is a simple way to explain how to play. Can I attack a specific player? I was in a clan and someone kicked me from it.   I think I'm stronger than him. Is there any way I can attack him? The only method I see to attack is random players. Can I attack a specific player? Fixed point, union of $\aleph_0, \aleph_{\aleph_0},\aleph_{\aleph_{\aleph_0}}\dots$ [see Noah's comment on notation] How to put a full-width table at the top or bottom of the same two-column page as the reference text? Integrate $\int_0^{\pi/2} \frac{1}{1+\tan^\alpha{x}}\,\mathrm{d}x$ Evaluate the integral $$\int_0^{\pi/2} \frac{1}{1+\tan^\alpha{x}}\,\mathrm{d}x$$ NS list does not match list from parent zone I'm attempting to figure out an error message that I got from dnsstuff.com when examining my DNS records.  The error reads as follows.     NS list does not match list from parent zone. This should be addressed because queries for this domain may require an extra lookup (and more overhead) because there is no direct relationship between the NS records at the parent and the NS records at the authoritative servers. This can cause delays. The mismatched NS list is:      nameserver ns1.domain.co. | xxx.xx.xxx.xxx is missing NS2.domain.co. | yy.yyy.yy.yyy   There are a couple questions I have regarding this.   What is the difference between a parent and authoritative zone?  In other forum posts I've seen, the seem to be used interchangeably (although that could be my misperception). What does it mean for the NS list not to match the list from the parent zone?  What is "the list from the parent zone" to which they refer? How might you recommend that I resolve this?   In case this affects any answers, I'm running Virtualmin on Ubuntu 12.04.  Any help is appreciated.  Many thanks in advance! Reading a 5 Band resistor with Gold as a middle band? Can anyone read the resistor that the arrow is pointing to?  From what I know you can not have a gold band as a number and if I am reading it correctly it has a tolerance of 0 which does not seem right. $a,b,c$ are distinct real numbers that $$(a^2)(1-b+c)+(b^2)(1-c+a)+(c^2)(1-a+b)=ab+bc+ca.$$ Prove $$\frac{1}{(a-b)^2}+\frac{1}{(b-c)^2}+\frac{1}{(c-a)^2}=1.$$ I have tried two different approaches to this problem but am stuck.  First I started by expanding the bottom of each fraction. $\frac{1}{(a^2)-2ab+(b^2)}+\frac{1}{(b^2)-2bc+(c^2)}+\frac{1}{(c^2)-2ac+(a^2)}=1$  I also tried to expand $(a^2)(1-b+c)+(b^2)(1-c-a)+(c^2)(1-a+b)=ab+bc+ca$   $(a^2)-(a^2)b+(a^2)c+(b^2)-(b^2)c-(b^2)a+(c^2)-(c^2)a+(c^2)b=ab+bc+ca$ $(a^2)-(a^2)b+(a^2)c+(b^2)-(b^2)c-(b^2)a+(c^2)-(c^2)a+(c^2)b-ab-bc-ca=0$ Then I added one to both sides $(a^2)-(a^2)b+(a^2)c+(b^2)-(b^2)c-(b^2)a+(c^2)-(c^2)a+(c^2)b-ab-bc-ca+1=0+1$ Help will be appreciated. Powershell Rename Multiple Files with LastWriteTime Prefix I am trying to put together a Powershell script that will:  -Search recursively from a root directory -Exclude files with existing "yyyyMMdd " file name prefix -Rename the files not excluded above with ""yyyyMMdd " file name prefix based on their specific LastWriteTime  Note: ideally, this script should include all file type extensions  I have tried myself, but it would seem to be above my head, as my attempts are not going well.  Thanks, in advance.    #StampMe.ps1 param( [string] $fileName)  # Check the file exists if (-not(Test-Path $fileName)) {break}  # Display the original name "Original filename: $fileName"  $fileObj = get-item $fileName  # Get the date $DateStamp = get-date -uformat "%Y-%m-%d@%H-%M-%S"  $extOnly = $fileObj.extension  if ($extOnly.length -eq 0) {    $nameOnly = $fileObj.Name    rename-item "$fileObj" "$nameOnly-$DateStamp"    } else {    $nameOnly = $fileObj.Name.Replace( $fileObj.Extension,'')    rename-item "$fileName" "$nameOnly-$DateStamp$extOnly"    }  # Display the new name "New filename: $nameOnly-$DateStamp$extOnly"   I am hoping to change the line:  $DateStamp = get-date -uformat "%Y-%m-%d@%H-%M-%S"   To be LastWriteTime instead of get-date, but I have no idea how to make this happen.  This code (from another Super User question):  Get-ChildItem "Test.pdf" | Rename-Item -newname {$_.LastWriteTime.toString("yyyyMMdd") + " Test.pdf"}   ...successfully renames a single file, but I can't seem to integrate this into the larger script.    With regards to running the above recursively, I have tried this (also from ):  foreach ($file in get-ChildItem *.* -recurse) { ./StampMe.ps1 $file.name }   Which succeeds to apply the PS script to files in the root directory, but fails to apply to any files in the sub-folder tree that propagates from the root directory. What counter balances gravity here? Lets consider a stone tied to one end of a massless and unstretchable string... Now if i'll start rotating, it will form a conical pendulum &amp; then the equilibrium is achived when the pendulum attains horizontal circular motion.... Now to maintain that state we give a constant force to string.... Here, which force counterbalances gravity? Is it the torque due to applied force cancels out the torque due to gravity?  The angle θ changes from 0 to 90° A question here on meta for instance may stick around for quite a while. A feature-request  maybe even for months. Then the status (tags) gets changed to  or  or whatever and the OP does not get notified.  On a normal post-edit we get a notification but retagging does not count for that. Please add retagging to the edit notifications. How does a magnet work? Let $A$ be a real square matrix en let $I$ be the identity matrix with the same size. Let $n&gt;0$ be the smallest natural number for which there exist  $a_0,a_1,...a_{n-1} \in {R}$ such that $A^n+a_{n-1}A^{n-1}+....+a_1A+a_0I=O$.  Show that A is invertible if and only if $a_0\neq0 $.  So i need to proof    $A$ invertible $\rightarrow$$a_0 \neq 0$ $a_0 \neq0 \rightarrow$ $A$ invertible    I don't really know where to start with 1, and with 2 I tried to prove it with a contradiction but I don't think it's right either. Removing intercept from GLM for multiple factorial predictors only works for first factor in model I am running a binomial logistic regression with a logit link function in R. My response is factorial [0/1] and I have two multilevel factorial predictors - let's call them $a$ and $b$ where $a$ has 4 factor levels  $(a_1,a_2,a_3,a_4)$ and $b$ has 9 factor levels $(b_1,b_2,\dotsc,b_9)$. Therefore:  mod &lt;- glm(y ~ a + b, family = binomial(logit), data=pretend) summary(mod)   The model output would then show all the information about the model as well as the coefficients.  There is a factor level for both a and b missing (a1 and b1) from the summary output. I understand that it is constrained in the "intercept" of the model. I have read that if I want to remove the intercept term and see the estimates for those factor levels I can just add -1 to the model formula, i.e.:  mod2 &lt;- glm(y ~ a + b - 1, family=binomial(logit), data=pretend) summary(mod2)   In the new model (mod2) the intercept term is then gone and variable a's factor-level a1 is given amongst the list of coefficients. But, variable b's factor-level b1 is still missing and given that there is no intercept term anymore, how can I interpret the odds-ratio for that factor level then?  Could someone please explain to me how to get the coefficient for b1 too and why this is happening? How to prevent RGB composite flatten to 1 band after raster calculation I have a series of landsat wanting to process in raster calculator, but after doing the tool it happened these output images only contain one single band. They used to be RGB 3-band images.  It is on arcmap 10.3. I was using raster calculator to remove a certain value in my 3-band landsat image. After I type in the conditional statement to remove all 0 value from the inpur RGB image, it only returns an image of 1band, black and white. How can I preserve the RGB value in output. There's something funky about some titles in revision histories here on Meta Stack Exchange How to draw a return arrow from node-3 to node-1 This is a  about  Related:      I have a question regarding capacity planning. Can the Server Fault community please help with the following:   What kind of server do I need to handle some number of users? How many users can a server with some specifications handle? Will some server configuration be fast enough for my use case? I'm building a social networking site: what kind of hardware do I need? How much bandwidth do I need for some project? How much bandwidth will some number of users use in some application? 1970s: Student creates complex program, forgets about it, and it becomes intelligent and finds him years later