i'm new to java and it's my second quarter class.  however I don't understand how to fix this null exception.  I can finish my program but it's just bugging me why i can't compile it  enter code here      Character letter = null;     String[] boy_Names = null;     String randName = null;     Character[] strConvert2Char = null;     String names = boyNames(boy_Names, randName);     String[] name = null;     Character[] charChar = convertString2Char(names, strConvert2Char);     char cC = Character.toLowerCase(checkChar[j]);      String emptyUnderscores = null;     int underscoreLength = boyNames(name, emptyUnderscores).length();     Character[] checkChar = new Character[underscoreLength];      System.out.println("Character[underscoreLength]" + underscoreLength);       System.out.println("\n\nPlease Guess a Letter: ");     String[][] hangmanMenu = null;     Scanner inputStream = new Scanner(System.in);     for (int i = 0; i &lt; 25; ++i) {         for (int j = 0; j &lt; 25;) {             System.out.println("checkChar" + checkChar[j]);             Character nextChar = inputStream.next().charAt(i);             char nC = Character.toLowerCase(nextChar);              char cC = Character.toLowerCase(checkChar[j]);              if (nC == cC == true) {                 System.out.println("TRUE" + "j: " + j);                  j = j + 1;             } else {                 if (Character.toLowerCase(nextChar) == Character.toLowerCase(checkChar[j]) == false)                     j = j + 0;                 System.out.println("FALSE" + "j: " + j);              }           }     }   i seem to be running null exceptions at the checkChar[j];    any help or info on this would help!  i've debugged it and i seem to be running null and if someone could help be run a better syntax on comparing two characters to equal false or true through a for loop, that would help me a lot!
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 am trying to find and replace the * (star, or shift+8) character in a bunch of formulas in Excel 2007.  * of course matches the ENTIRE contents of the cell, which is not what I want.  How do I disable this behavior? Task manager for Ubuntu uname -r and available linux-headers- packages do not match How can I see the history of stories I've read on Apple News? Sometimes I'll be interrupted in the middle of reading a story on Apple News and later when I open the app, it didn't save the story I was previously reading. I want to be able to resume reading the article, how can I find it again? How to configure an app to run correctly on a machine with a high DPI setting (e.g. 150%)? I need to prove that $H$ is a maximal normal subgroup of $G$ if and only if $G/H$ is simple.  My proof to the $(\Rightarrow)$ direction seems too much trivial:  Let us assume there exist $A$ so that $A/H\lhd G/H$. Then by definion, $H$ must be normal in $A$. Because $H$ is maximal, we get $H=A$ and therefore $A/H={1}$  Is it correct?  Update:  Now I see that I need to prove that not only $A\lhd H$ but also $A\lhd G$. Assumig I have proven that, is the proof correct? Distribution of a ratio of uniforms: What is wrong? Suppose that  $X$ and $Y$ are two i.i.d. uniform random variables on the interval $[0,1]$  Let $Z=X/Y$, I am finding the cdf of $Z$, i.e. $ \Pr(Z\leq z) $.  Now, I came up with two ways of doing this. One produces a correct answer consistent with the pdf here: , the other does not. Why is the second method wrong?  First Method  $\newcommand{\rd}{\mathrm{d}} \Pr(Z\leq z) = \Pr(X/Y\leq z) = \Pr(X\leq zY) = \int^{1}_{0}\int^{\min(1,zy)}_{0} \rd x \rd y = \int^{1}_{0}\min(1,zy)\ \rd y$ $  = \left\{      \begin{array}{lr}        \int^{1/z}_{0}zy\ \rd y + \int^{1}_{1/z} \rd y&amp; : z &gt; 1\\        \int^{1}_{0}zy\ \rd y &amp; : z \leq 1      \end{array}    \right. $ $  = \left\{      \begin{array}{lr}        1 - \frac{1}{2z} &amp; : z &gt; 1\\        \frac{z}{2} &amp; : z \leq 1      \end{array}    \right. $  This appears correct.  Second Method  $\Pr(X/Y\leq z) = \Pr(X \leq zY\ |\ zY \geq 1)\Pr(zY \geq 1) + \Pr(X \leq zY\ |\ zY &lt; 1)\Pr(zY &lt; 1) $ by total probability  $ = \Pr(X \leq zY\ |\ zY \geq 1)\Pr(Y \geq 1/z) + \Pr(X \leq zY\ |\ zY &lt; 1)\Pr(Y &lt; 1/z)$  Taking $z&gt;1$ yields $ (1)(1-\frac{1}{z}) + (\int^{1/z}_{0}\int^{zy}_{0} \rd x \rd y)(\frac{1}{z}) = 1-\frac{1}{z} + (\int^{1/z}_{0}zy\ \rd y)(\frac{1}{z}) = 1-\frac{1}{z} + \frac{1}{2z^{2}}$  This is already different. Why is this wrong?  Thanks! How can I get the HTML source of a given web address in C#? Proof that if $p\equiv3\,\left(\mbox{mod 4}\right)$ then $p$ can't be written as a sum of two squares I'd appreciate your help showing that if $p\equiv3\,\left(\mbox{mod 4}\right)$   then p can't be written as a sum of two squares.  Thanks! Simple request, really.  Can we add a detection for the     Please avoid extended discussions in   comments. Would you like to   automatically move this discussion to   chat?   prompt, so that if one of the users in the "extended discussion" has under 20 rep it doesn't appear?  I think a lot of the users this apply to will have low rep and it may take some back and forth to get good info out of them.  New suggestion: how about if a sufficiently high-rep user is clicking on the link, the low-rep user gets a field promotion sufficient to chat? Low-rep users are particularly prone to post questions to lead in this direction of needing to move to chat. Why does Venus spin in the opposite direction? Given: Law of Conservation of Angular Momentum.   Reverse spinning with dense atmosphere (92 times > Earth &amp; CO2 dominant sulphur based). Surface same degree of aging all over. Hypothetical large impact is not a sufficient answer.   Assuming any object large enough to alter a planets rotation or even orbit would likely destroy most of its shape, yet Venus has retained a spherical property with a seemingly flat, even terrain indicating no volcanoes,and few if any visible meteor impacts. It would be fragmented and dispersed for billions of years.  Even the question of what meteor, comet, asteroid composition could survive traveling that close to the sun's temperature, radiation, electromagnetic energy, solar flares, or gravity to equal a mass reactionary change as to alter it's spin. Force drop db while others may be connected Which English dialects have 2nd person plural? "Y'all" is the famous southern US form of the 2nd person plural.  The Brooklyn / Italian-American "youse" might be another.  While the existence and usage of "y'all" has been addressed somewhat thoroughly here:  , I've found nothing else on EL&amp;U regarding 2nd person plural forms in other English dialects.  I know there was a dual form in Old English () does that survive in any of the dialects in the Danelaw?  Do Scots / Gaelic / Welsh / Australian / other dialects retain any type of 2nd person plural / dual in modern usage? How to extract the n-th elements from a list of tuples? The pdf of $\frac{X_1-\bar{X}}{S}$ Suppose $X_1, X_2,...,X_n$ be i.i.d from $N(\mu,\sigma^2)$ with unknown $\mu \in \mathcal R$ and $\sigma^2&gt;0$  Let $Z=\frac{X_1-\bar{X}}{S},$ S is the standard deviation here.  It is can be shown that  $Z$ has the Lebesgue p.d.f.  $$f(z)=\frac{\sqrt{n} \Gamma\left(\frac{n-1}{2}\right)}{\sqrt{\pi}(n-1)\Gamma\left(\frac{n-2}{2}\right)}\left[1-\frac{nz^2}{(n-1)^2}\right]^{n/2-2}I_{(0,(n-1)/\sqrt{n})}(|Z|)$$  My question is then how to get this pdf?  The question is from  in example 3.3.4  to find the UMVUE of $P(X_1 \le c)$. I can understand the logic and procedures to find the UMVUE but don't know how to get the pdf.  I think this question also relate to this    Thank you very much for help or point to any related references will be also appropriated. One of the first things ever taught in a differential calculus class:   The derivative of $\sin x$ is $\cos x$. The derivative of $\cos x$ is $-\sin x$.   This leads to a rather neat (and convenient?) chain of derivatives:   sin(x) cos(x) -sin(x) -cos(x) sin(x) ...   An analysis of the shape of their graphs confirms some points; for example, when $\sin x$ is at a maximum, $\cos x$ is zero and moving downwards; when $\cos x$  is at a maximum, $\sin x$ is zero and moving upwards.  But these "matching points" only work for multiples of $\pi/4$.  Let us move back towards the original definition(s) of sine and cosine:  At the most basic level, $\sin x$ is defined as -- for a right triangle with internal angle $x$ -- the length of the side opposite of the angle divided by the hypotenuse of the triangle.  To generalize this to the domain of all real numbers, $\sin x$ was then defined as the Y-coordinate of a point on the unit circle that is an angle $x$ from the positive X-axis.  The definition of $\cos x$ was then made the same way, but with adj/hyp and the X-coordinate, as we all know.  Is there anything about this basic definition that allows someone to look at these definitions, alone, and think, "Hey, the derivative of the sine function with respect to angle is the cosine function!"  That is, from the unit circle definition alone.  Or, even more amazingly, the right triangle definition alone.  Ignoring graphical analysis of their plot.  In essence, I am asking, essentially, "Intuitively why is the derivative of the sine the cosine?" What does why would I do it mean in this context? I've often heard people saying this. And even I say it when someone accuses me of doing something that I didn't do.  I'd say:  Why would I do that?  But what's the grammar behind it?  Is it future from the past tense or something or what? It's obviously not a conditional construction 😒  Context from SE01 EP02 Austin &amp; Ally  Austin: what does the jacket have to do with the music video?  Trish: It's a line in Ally's song, "my jacket's in the lost and found."  Ally: "my jacket"? It says "I like it." The line is "I like it when you hang around."  Dez: "hang around"? I thought it said "kangaroo." ♪ I like it when you kangaroo. ♪.  Ally: Why would I write "I like it when you kangaroo"? Default currency symbol I'm looking for a way to get the Default currency symbol (in a none-multi-currency org) of the salesforce org locale (to have it displayed on a visualforce page in a field that can't be &lt;apex:inputField&gt; or &lt;apex:outputField&gt;) preferably query-able from apex (via the database, a describe or whatever) and then again the actual symbol, meaning € for Euro, $ for dollar, and so on...  There must surely be some sort of mapping hidden in the code somewhere salesforce does this via the input/outputfields if bound to an sobject of type currency  Can anyone point me in the right direction? I am a computer scientist, and one of my professors today used the symbol $\propto$. I tried to search that using google, but it returns no results, and I do not even know its name.  So, I would like to ask, what does the operator $\propto$ mean? What is its name, and how is it used? How do I install drivers for Realtek RTL8812BU? So I've been experimenting with Ubuntu on and off for a while, but I honestly have no idea what the hell I'm doing. So I have a realtek RTL8812bu WiFi dongle that I'm hoping to get working. I did some research, and came across  that a couple people across two threads said worked for them:  At the bottom it said there is a new version . So somewhere it said it was confirmed to work on kernels up to 4.16, so I checked and I'm on 4.15.0. But the problem I'm having, is what am I supposed to do? There is some installation guide at the bottom that is about as clear as mud to me since I don't know much.