@override hashcode() in HashMap
What issues should be considered when overriding equals and hashCode in Java?
How do I install the latest version of node.js? How do I install the latest  on Ubuntu? I've been looking around, and I can't find anything. Is there a Ubuntu package for node.js, or do I have to compile it myself? Determining application path in a Python EXE generated by pyInstaller I'm writing a mildly dystopian scenario where competition is taken to vicious extremes, and I was wondering if there was a word that I could use (specifically a noun that was a synonym of "competition") to describe the sort of vicious, cutthroat ... _________ (the word that I want) that was going on.  I'm specifically looking for a word that doesn't refer to a one-off event (like "contest" or "tug-of-war"), but rather is more about the state of things. Moving set of polygons in ArcGIS Pro? Divisibility, LCM and GCD for fractions (rationals) how do i find lcm of two fractions?  For example:  $\frac{2}{3}$ and $\frac{5}{8}$ I keep getting an error in line 38 saying "Extra alignment tab has been changed to \cr." \documentclass [12pt]{article} \oddsidemargin=0pt \topmargin=0pt \textwidth=6.5in \textheight=8.5in \begin{document} \begin{center} {\large\bf\LaTeX\ Example 6} \end{center} We can typeset array structures \begin{equation} \mathbf{A}\times \mathbf{B}=\left| \begin{array}{ccc} \mathbf{i} &amp; \mathbf{j}  &amp; \mathbf{k} \\      a_1  &amp;      a_2        &amp; a_3 \\       b_1  &amp;      b_2        &amp; b_3  \end{array}  \right| \end{equation} \begin{quote} \begin{verbatim} \begin{equation} \mathbf{A}\times \mathbf{B}=\left| \begin{array}{ccc} \mathbf{i} &amp; \mathbf{j}  &amp; \mathbf{k} \\  a_1  &amp;  a_2   &amp; a_3 \\  b_1  &amp;  b_2   &amp; b_3 \end{array} \right| \end{equation} \end{verbatim} \end{quote} Or \begin{equation} \mathbf{A}=\left( \begin{array}{ccc} a_{11} &amp; a_{12} &amp; \cdots &amp; a_{1n} \\ a_{21} &amp; a_{22} &amp; \cdots &amp;  a_{2n} \\ \vdots &amp; \vdots &amp; \ddots &amp; \vdots \\ a_{n1} &amp; a_{n2} &amp; \cdots &amp; a_{nn} \end{array} \right) \end{equation} \end{document} A guide to moderating chat Chat is an offshoot of the main site, and using it is  during their time here.  Chat is our place for:        Real-time collaboration   Meeting fellow members of the community   Less structured, casual (but still roughly on-topic) conversation      Our chat system exists to serve the main site; users of each site can gather and commune with each other.  When in chat, we expect all users to abide by our  policy, which means that we expect community members to treat each other with respect.    While it is a place where the community can go to interact on a more casual level, chat still needs to be moderated by the community and there are tools in place to help with the moderation. This raises a few questions, that are addressed here: How do you reopen a closed question? To reopen a closed question,  must agree that the question is suitable for the site and cast votes to reopen the question. But:  How does one actually vote to reopen? Is there a reputation level that you must have before you can see this function? Or do I just leave a comment along the lines of, &quot;I vote to reopen&quot;? What happens if someone with less than 3000 reputation leaves a comment that they wish to vote to reopen? How can one draw attention to their closed questions? Is it done via a posting new question? Or do you edit the closed question?   Related:  For more information, see &quot;&quot; in the . I am writing a novel and fairly new to using LaTeX.  Please bare with me if this is a silly question.  I am working off of the novel demo LaTeX file using the TexWorks software.  I have inserted my words into the file.  When I run the LaTeX code, I get the error message saying "! LaTeX Error: File `novel.cls' not found."  Do I need to download this file from somewhere?  If so, where can I get it? Let $G = (\mathbb{C} - \{0\}, \cdot)$, a subgroup $U = \{x+yi \mid x^2 + y^2 = 1\}$. Use the Fundamental Theorem to show that $G/(\mathbb{R}_{&gt; 0},\cdot)$ is isomorphic to $U$ where $\mathbb{R}_{&gt; 0}$ denotes the positive reals.  I am struggling to find the correct mapping from $G$ to $U$ that results in the the kernel being the nonnegative reals under multiplication. I'm hoping to get help with this mapping then I can show it is a homomorphism and onto and can use the Fundamental Theorem. Update from 14.04 to 16.04 failed with GPG error I am a new Ubuntu user running Ubuntu 13.04.  I've been trying to install and use a DeDRM tool, but I've been having problems doing so. I was following some directions that said I needed a version of Python 2.7, but not anything Python 3.0 or later (because 3.0 versions are missing some necessary libraries?). I tried to install Python 2.7.5.6, but it didn't work. I thought it was probably because I had the later version of Python, so I went through terminal and removed Python 3.3, so I could install the earlier version of Python.  Now that I've uninstalled Python 3.3, a lot of applications no longer work, including the terminal and the Ubuntu Software Center. I have no idea how to fix this problem now. I have basic programming skills (I program simple vba python and lisp scripts and had gone through a java course a long time ago), but it seems to me (judging by ESRI publications) that there is no escaping the need to learn .NET for future relevance in the GIS job market (even as an analyst). I've gone through a basic c# course and can program (regrettably) quite poor programs, but I have no idea how to link the c# knowledge to actually programming for ArcGIS in order to progress.  I know the differences aren't big, but does ArcGIS use .NET or C#?  I know the best way to further my experience in .NET is to program more and more but are there any good .NET programming books or courses I can learn techniques from?  In your opinion, what is the best way to learn to program in .NET for ArcGIS? Are there any useful books or websites?   I seek your comments regarding ArcGIS 10 (and will be saving them for later) but also for ArcGIS 9.3.1. How can I access Apache (on VirtualBox guest) from host? I installed Apache on an Ubuntu VM. When I go into the guest and load up Firefox I can see that Apache is working fine when I browse to localhost.  I would like to access this same page through the host. I've tried using the IP address of the guest but nothing comes up. Ideally I would love to set up my Windows 7 (host) to request http://guestserver.com of the Apache server on the guest. How can I do this? In sampling without replacement the probability of any fixed element in the population to be included in a random sample of size $r$ is $\frac{r}{n}$. In sampling with replacement the corresponding probability is $\left[1- \left(\frac{1}{1-n}\right)^r\right]$.  Please help me show how this is proved. How should I parse user input in a text adventure game? Parsing user commands in a text adventure is a spectrum from 's simple "go north" to some mind-bogglingly clever ones in .  I seem to remember reading nice how-tos in computer magazines back in the 80s, but now I find almost nothing on the 'net except a .  How would you do it?    Update: I went with the simplest approach possible in . The problem: The links at the bottom of the Stack&nbsp;Exchange newsletter link to a YouTube video instead of the right place on the website. I´m not sure if this is an oversight or a clever hack.  Screenshot: How is Gauss' Law (integral form) arrived at from Coulomb's Law, and how is the differential form arrived at from that? Benefit of date in URL segments I was curious about the date in URL segments, is there any SEO point of benefit? For example the following URLs:  http://techcrunch.com/2013/06/18/netflix-will-launch-in-the-netherlands-later-this-year-as-its-international-expansion-slows/ http://tips-for-new-bloggers.blogspot.in/2007/02/adding-favicon-icon-to-blogger-url.html  https://community.jivesoftware.com/blogs/jivespace/2013/05/15/eol-of-the-html5-ipad-web-app   In all the above URLs there is date segment. The information of those blogs can be fetched via blog stub like "netflix-will-launch-in-the-netherlands-later-this-year-as-its-international-expansion-slows" so why to use that date part? Failed to download repository information due to missing CDROM When updating I got this error message:  W:Failed to fetch cdrom://Ubuntu 11.10 _Oneiric Ocelot_ - Release amd64 (20111012)/dists/oneiric/main/binary-i386/Packages  Please use apt-cdrom to make this CD-ROM recognized by APT. apt-get update cannot be used to add new CD-ROMs W:Failed to fetch http://ppa.launchpad.net/synce/ubuntu/dists/your_ubuntu_version/main/source/Sources  404  Not Found   What to do?