Java Inheritance: Question regarding the parent reference variable.  I am learning Java and going through the inheritance problems in Java, have one question here.  public class Shape {     private String shapeName;     private String area;     //normal getters and setters }  public class Triangle extends Shape {     private String typeOfTriangle;     //normal getter and setter. }  public class ShaperRunner {     public static void main(String[] args) {         Shape shape = new Triangle();         // Here the shape reference variable referencing to Triangle object is allowed, however using this shape object. I cannot call         shape.setTypeOfTriangle("Scalence")         System.out.println("The shape of the triangle is " + shape.getTypeOfTriangle());     } }   My Question is if shape reference variable can be used to call only the getters and setters confined to what is defined in it, then why do we even consider using shape object to reference Triangle object. I have seen such code in few places but could not understand what is the advantange of doing it.
I have seen this mentioned a few times and I am not clear on what it means. When and why would you do this?   I know what interfaces do, but the fact I am not clear on this makes me think I am missing out on using them correctly.   Is it just so if you were to do:  IInterface classRef = new ObjectWhatever()   You could use any class that implements IInterface? When would you need to do that? The only thing I can think of is if you have a method and you are unsure of what object will be passed except for it implementing IInterface. I cannot think how often you would need to do that.   Also, how could you write a method that takes in an object that implements an interface? Is that possible?
How to pick the title of a remote webpage How can I watch Amazon Prime videos using Firefox on Ubuntu 16.04? How can I watch Amazon Prime videos using Firefox on Ubuntu 16.04? Currently Firefox version is 48.0. When I attempt to watch a video, I get the following Digital Rights Error message:  Your web browser is missing a digital rights component. In your web browser’s address bar, type about:addons, press Enter, and then on the left, click Plugins. For the Widevine Content Decryption Module, select Always Activate, and then refresh the video’s page and try watching the video. If the video doesn’t play, go back to Plugins, click the gear icon at the top of the page, and then click Check for Updates. When the plugins have updated, refresh the video’s page, and then try watching the video.  I didn't find Widevine Content Decryption Module. I searched for a solution, but it didn't work... One solution I found was to sudo apt-get install flashplugin-installer and then do the following: sudo apt-add-repository ppa:flexiondotorg/hal-flash sudo apt-get update &amp;&amp; sudo apt-get install libhal1-flash  However, it didn't work and I still got the same Digital Rights Error message. I am able to watch Amazon Prime videos using Google Chrome, but not with Firefox. I want to know if it's possible on Firefox on Ubuntu 16.04. I have this table definition as part of a invoice  \begin{tabularx}{\textwidth}[ht]{lXrr}%   It worked fine for years until I have a very short word in the X column for the first time. Now my table is very small in width and centered horizontally on the page.  In my expectation the X column should fill up all space until the width of the table reaches the width of the page except the margins.  I have read about workarounds specifying something like 1.2\textwidth, but I don't like that, because the table is a template included via \include, so it would affect all my invoices.  I also tried \linewidth, \hsize and \columnwidth, but everything results in the same layout.  Is there a way to make the only X column expand so that it uses all available space?    Complete included table definition (Rechnungstabelle.tex):  \newcommand{\Rechnungstabelle}[4]{% vielen Dank für Ihren Auftrag. \noindent \begin{tabularx}{\textwidth}[ht]{lXrr}% \toprule% \bf{Anzahl} &amp; \bf{Bezeichnung} &amp; \bf{Einzelpreis} &amp; \bf{Gesamtpreis} \\% \midrule% #1% \bottomrule% &amp; \bf{Rechnungsbetrag}  &amp; &amp; \bf{\EUR{#2}} \\% \ifthenelse{\equal{#3}{}}{}{&amp; Enthaltene MwSt. 19\% &amp; &amp; \EUR{#3} \\}% \ifthenelse{\equal{#4}{}}{}{&amp; * Enthaltene MwSt. 7\% &amp; &amp; \EUR{#4} \\}% \end{tabularx}% }   Changing the table header row to  \bf{Anzahl} &amp; \bf{Bezeichnung} \hspace{\textwidth} &amp; \bf{Einzelpreis} &amp; \bf{Gesamtpreis} \\%   is a workaround, but I don't think that would be good TeX style.  Minimum example for reproducing:  \documentclass[ fontsize=12pt,                  paper=a4,                 foldmarks=TBMPL,                 fromalign=center,                 ngerman                 ]{scrlttr2} \usepackage{babel} \usepackage[utf8]{inputenx} \usepackage[right]{eurosym} \usepackage{tabularx} \usepackage{ltablex} \usepackage{booktabs} \usepackage{ifthen}  \input{Rechnungstabelle} \begin{document} \begin{letter}  \Rechnungstabelle{     1,0 h &amp; Do something &amp; \EUR{99,00} &amp; \EUR{99,00} \\      }     {99,00}     {}{} \end{letter} \end{document} I need to be able to compare some month names I have in an array.  It would be nice if there were some direct way like:  Month.toInt("January") &gt; Month.toInt("May")   My Google searching seems to suggest the only way is to write your own method, but this seems like a common enough problem that I would think it would have been already implemented in .Net, anyone done this before? Calculate the area of an irregular cyclic convex polygon Is there a faster way to open a process as Administrator (With UAC enabled)? Currently (In Windows 10) - if I want to open a CMD prompt, I'll hit the Windows key, type CMD and hit Enter. If I want it open as an administrator, I have to right click the item and click Run As administrator. Is there a way I can do this without using the mouse? Let $s_n$ be a sequence defined as given below for $n \geq 1$. Then find out $\lim\limits_{n \to \infty} s_n$.   \begin{align}   s_n = \int\limits_0^1 \frac{nx^{n-1}}{1+x} dx  \end{align}  I have written a solution of my own, but I would like to know it is completely correct, and also I would like if people post more alternative solutions. Degrees of freedom in theoretical sample variance (for use in F-distribution) My question is essentially simple: suppose we have a sequence of heads and tails with an apparent chance of getting heads $\hat{p} = 0.5$.      h h t h t t t h t t h ...   How do we tell if this sample was drawn from a binomial distribution with this $\hat{p}$ or if it comes from a combination of different distributions which produces the same average? (e.g. $p = 0.25$ or $p = 0.75$)  Here's what I was thinking of doing:   We chop the sequence into subsections of length $n$, for example $n=5$, and calculate $\hat{p}$ in every such window: {h h t h t}, {t t h t t}, {h ...}0.6, 0.2, ... We then calculate the standard deviation in these $\hat{p}$ values: $\sigma_{ex}=\sqrt{\frac{\sum_{i=1}^M{(\hat{p}_i - \hat{\mu})^2}}{M}}$, where $\hat{\mu}$ is the average $\hat{p}$ and $M$ is the total number of windows of size $n$ we can make.  We calculate the standard deviation in $\hat{p}$ based on a binomial distribution, $\sigma_{th}=\sqrt{\frac{\hat{p}(1-\hat{p})}{n}}$.   Now comes the problem: how to determine if these two values are the same? After a lot of research, I decided to try using an F-ratio test and plugging the result into an f-distribution.  F-ratio: $F = \frac{\sigma_{ex}^2}{\sigma_{th}^2}$ (only valid for normal-distributions :S)  And then an f-distribution to get to a p-value we can check against. However, for the f-distribution I need to know the degrees of freedom in the nominator and denominator. And therein lies my problem: what are the degrees of freedom for the variance calculated from theory? (In the experimental case I think it is M)  If you have this answer or any suggestions on how to solve this problem differently, I would love to hear about it! How to unit test an object with database queries I've heard that unit testing is "totally awesome", "really cool" and "all manner of good things" but 70% or more of my files involve database access (some read and some write) and I'm not sure how to write a unit test for these files.  I'm using PHP and Python but I think it's a question that applies to most/all languages that use database access. Least-action classical electrodynamics without potentials Is it possible to formulate classical electrodynamics (in the sense of deriving Maxwell's equations) from a least-action principle, without the use of potentials? That is, is there a lagrangian which depends only on the electric and magnetic fields and which will have Maxwell's equations as its Euler-Lagrange equations? Does a filament of lamp still have resistance when no current flows, and if yes, why? Does a filament lamp still have resistance when no current flows? Best way to randomize an array with .NET Related to : The question specifies morphs, but I wondered if this was true for Manifest as well? As Manifest is not an ability on the card, does  prevent it from being turned face up for its mana cost? Package babel Error: Unknown option `francais' How to find and delete files older than specific days in unix? Spontaneous electroweak symmetry breaking (i.e. $SU(2)\times U(1)\to U(1)_{em}$ ) is at scale about 100 Gev. So, for , gauge bosons $Z$ &amp; $W$ have masses about 100 GeV. But before this spontaneous symmetry breaking ( i.e. Energy > 100 GeV) the symmetry $SU(2)\times U(1)$ is not broken, and therefore gauge bosons are massless.  The same thing happens when we go around energy about $10^{16}$ GeV, where we have the Grand Unification between electroweak and strong interactions, in some bigger group ($SU(5)$, $SO(10)$ or others). So theoretically we should find gauge bosons $X$ and $Y$ with masses about $10^{16}$ GeV after GUT symmetry breaks into the Standard Model gauge group $SU(3)\times SU(2)\times U(1)$, and we should find massless X and Y bosons at bigger energies (where GUT isn't broken).  So this is what happened in the early universe: when temperature decreased, spontaneous symmetry breaking happened and firstly $X$ &amp; $Y$ gauge bosons obtained mass and finally $Z$ &amp; $W$ bosons obtained mass.   Now, I ask: have I understood this correctly? In other words, if we make experiments at energy above the electroweak scale (100 GeV) we are where $SU(2)\times U(1)$ isn't broken and then we should (experimentally) find $SU(2)$ and $U(1)$ massless gauge bosons, i.e. $W^1$, $W^2$, $W^3$ and $B$ with zero mass? But this is strange, because if I remember well in LHC we have just make experiments at energy about 1 TeV, but we haven't discovered any massless gauge bosons. Let $f(x)$ and $g(x)$ be two continuous functions on $[0,1]$ and  $$\int_{0}^{1}f(x) dx= \int_{0}^{1}g(x)dx = 1$$   Show that there exist  $[a,b]\subset [0,1]$, such that  $$\int_{a}^{b}f(x) dx= \int_{a}^{b}g(x)dx = \frac{1}{2} $$  The question can be solved by considering the fundamental group of $S^1$, now I am wondering if we can solve it by real-analysis.  Here is the topological solution:  Assume that for any $[a,b]\subset[0,1]$, we always have  $$(\int_{a}^{b}f(x) dx\neq \frac{1}{2}) \quad \vee \quad(\int_{a}^{b}g(x)dx \neq \frac{1}{2}) $$ Consider mapping $$\phi:D\rightarrow\mathbb{E}^2\backslash\{(\frac{1}{2},\frac{1}{2})\},\,\,(x,y)\mapsto(\int_{y}^{x}f(t) dt,\int_{y}^{x}g(t) dt)$$ where $D=\{(x,y)|0\leq x\leq y\leq 1\}$.  Let $a$ be path from $(0,0)$ to $(0,1) $in $D$ and $b$ be path from $(0,1)$ to $(1,1) $in $D$, then $ab$ is a path from $(0,0)$ to $(1,1) $in $D$ and $$\phi\circ (ab):[0,1]\rightarrow\mathbb{E}^2\backslash\{(\frac{1}{2},\frac{1}{2})\} $$ Notice that $$(\phi\circ (ab))(0)=(\phi\circ (ab))(1)=(0,0)$$  so $\phi\circ (ab)$ is a loop based on $(0,0)$ in $\mathbb{E}^2\backslash\{(\frac{1}{2},\frac{1}{2})\}$.  For any $t\in [0,\frac{1}{2}]$, it's not hard to get that $$(\phi\circ (ab))(t+\frac{1}{2})=(1,1)-(\phi\circ (ab))(t)$$ is equivalent to $$(\phi\circ (ab))(t+\frac{1}{2})-(\frac{1}{2},\frac{1}{2})=-((\phi\circ (ab))(t)-(\frac{1}{2},\frac{1}{2}))$$  Define retraction  $$r:\mathbb{E}^2\backslash\{(\frac{1}{2},\frac{1}{2})\}\rightarrow S^1,\quad (x,y)\rightarrow\ \frac{(x,y)-(\frac{1}{2},\frac{1}{2})}{||(x,y)-(\frac{1}{2},\frac{1}{2})||}$$  Then $r\circ \phi\circ (ab)$ is a loop on $S^1$, such that $$(r\circ \phi\circ (ab))(t+\frac{1}{2})=-(r\circ \phi\circ (ab))(t),\quad\forall t\in [0,\frac{1}{2}]$$  So $&lt;r\circ \phi\circ (ab)&gt;$ is not trivial in $\pi_1(S^1)$.   However, $ab$ is path homotopic to $c$ in $D$, where $c$ is the path between $(0,0)$ and $(1,1)$ in $D$. In this case, $r\circ \phi\circ (ab)$ is a point-path in $S^1$ by $$(\phi\circ c)(t)=\phi(t,t)\equiv (0,0)$$  which leads to contradiction. 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