I want to fill a table with in 1st row the index and in 2nd row an element generated on a uniform law. To follow the steps of my work I did a non-executable file: import java.util.Random;  public class CSignal {     private int N, V;     private double[][] tabSig;     public double k;      public CSignal() {         V = 4;         N = 10;          Remplit();     }      public void Remplit() {         for (int i = 0; i &lt; N; i++) {             tabSig[0][i] = i;             Random e = new Random();             k = e.nextDouble();             tabSig = new double[2][2];             this.tabSig[1][i] = k * V;         }     }      public int get_N() {         return N;     }      public int get_V() {         return V;     }      public double[][] get_tab() {         return tabSig;     }      public void Affiche() {         System.out.println(tabSig);     }  }   and then the executable: public class TP {      public static void main(String[] args) {         // TODO Auto-generated method stub         CSignal signal;         signal = new CSignal();         signal.Affiche();     } }    When i try this prog I got the following error: Exception in thread &quot;main&quot; java.lang.NullPointerException: Cannot load from object array because &quot;this.tabSig&quot; is null
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?
How do I animate time? Can we access class properties dynamically with Object class? Is it possible to access Apex class properties dynamically? While we can create Object's, and assign any other class to an Object, I'm not sure how I can access the properties of these Object's. Can anyone provide some documentation or references to code which would allow me to do this?   Example:  public class XYZ {    public string s1 { get; set; }    public string s2 { get; set; } }  XYZ testXyzObj = new XYZ(); Object obj = testXyzObj;  // Method does not exist or incorrect signature: [Object].get(String) String s1 = obj.get('s1'); TTY doesn't wait for password In many scientific papers, the article before the word "Equation" is omitted. Is there any grammar statement behind this? For instance:     "Equation (8) contains various approximations, and we have to check their consistency." Trying to remap my left SUPER key (also called WINDOWS key) to left or right CONTROL key, with xkg How many times can I repeat a keyword without looking spammy to Google? I have an eCommerce based on Opencart, but I have some doubts about how many times I can repeat the same word.  For example, the keyword is present in the title, description, h1, h2 and is repeated several times in the text:   Page Title: Shop Iphone other keyword Page description: Shop Iphone other keyword   (and they continue appearing below)   H1: Shop Iphone other keyword H2: Shop Iphone other keyword 10 more times in the text: Shop iPhone   I mean, if Googlebot sees the same WORD 30 times, can it be considered SPAM? Can I lose something or can I use keywords a lot?  In WOORANK I saw my review and I noticed that I need to improve my keywords, and a lot. I have some keywords like: payment, description, promotion, sales... keywords really "empty"  [ UPDATE ]  Can repeating keywords make them lose importance? How can I verify a Google authentication API access token? How can I verify a Google authentication access token?  I need to somehow query Google and ask: Is [given access token] valid for the [example@example.com] Google account?  Short version: It's clear how an access token supplied through the  can be used to then request data from a range of Google services. It is not clear how to check if a given access token is valid for a given Google account. I'd like to know how.  Long version: I'm developing an API that uses token-based authentication. A token will be returned upon provision of a valid username+password or upon provision of a third-party token from any one of N verifiable services.  One of the third-party services will be Google, allowing a user to authenticate against my service using their Google account. This will later be extended to include Yahoo accounts, trusted OpenID providers and so on.  Schematic example of Google-based access:    The 'API' entity is under my full control. The 'public interface' entity is any web- or desktop-based app. Some public interfaces are under my control, others will not be and others still I may never even know about.  Therefore I cannot trust the token supplied to the API in step 3. This will be supplied along with the corresponding Google account email address.  I need to somehow query Google and ask: Is this access token valid for example@example.com?  In this case, example@example.com is the Google account unique identifier - the email address someone uses to log in to their Google account. This cannot be assumed to be a Gmail address - someone can have a Google account without having a Gmail account.  The Google documentation clearly states how, with an access token, data can be retrieved from a number of Google services. Nothing seems to state how you can check if a given access token is valid in the first place.  Update The token is valid for N Google services. I can't try a token against a Google service as means of verifying it as I won't know which subset of all Google's services a given user actually uses.  Furthermore, I'll never be using the Google authentication access token to access any Google services, merely as a means of verifying a supposed Google user actually is who they say they are. If there is another way of doing this I'm happy to try. How long does it take for police 'presence' to clear when they are alerted? I engaged with some enemy NPCs, and accidentally shot a civilian in the head (though not sure it would've mattered if I hit them somewhere else or not) as they ran across my screen. As a result of this, I was alerted by the game that the NCPD (the police) were automatically en route to 'investigate', and that I could avoid them by leaving the area and &quot;lying low for a while&quot;. How long does it take for the police to stop searching for me, and is there any kind of visual information on the HUD that alerts me to when NCPD is or is no longer looking for me? How to search by key=>value in a multidimensional array in PHP Why is the sample distribution the Exponential distribution Gamma distributed? Studying for CISSP these choices seemed limited:     What is the advantage of digital signatures over message authentication codes?         Digital Signature provides integrity verification while message authentication code does not   Digital Signature provides confidentiality while message authentication code does not   Digital Signatures provide authenticity while message authentication code does not   Digital Signatures works faster than message authentication codes      Using the following chart as a reference, I'm leaning towards #2, but none of the choices really fit properly…  Cryptographic primitive | Hash |    MAC    | Digital Security Goal           |      |           | signature ------------------------+------+-----------+------------- Integrity               |  Yes |    Yes    |   Yes Authentication          |  No  |    Yes    |   Yes Non-repudiation         |  No  |    No     |   Yes ------------------------+------+-----------+------------- Kind of keys            | none | symmetric | asymmetric                         |      |    keys   |    keys   Hopefully an expert here can clarify. Capturing image from webcam in java? How can I continuously capture images from a webcam?  I want to experiment with object recognition (by maybe using java media framework).   I was thinking of creating two threads  one thread:   Node 1: capture live image Node 2: save image as "1.jpg" Node 3: wait 5 seconds Node 4: repeat...   other thread:   Node 1: wait until image is captured Node 2: using the "1.jpg" get colors from every pixle Node 3: save data in arrays Node 4: repeat... I would like to typeset the top part of Pascal's triangle. To get the triangle with the names of the binomial coefficients, i.e., {n \choose k}, I used the following code  \begin{tikzpicture} \foreach \n in {0,...,4} {   \foreach \k in {0,...,\n} {     \node at (\k-\n/2,-\n) {${\n \choose \k}$};   } } \end{tikzpicture}   The result is this   Now I want to be equally lazy and do something like this for the values of the binomial coefficients, i.e., replace {\n \choose \k} in the node label with \CalculateBinomialCoefficient{\n}{\k} where \CalculateBinomialCoefficient is a hypothetical macro that calculates the binomial coefficient. Has anyone done something like that?  The result should look like this: Evaluate $\lim_{n\rightarrow\infty} \int_0^1 f(x^n) dx$ Let $f$ be a real, continuous function defined for all $0\leq x\leq 1$ such that $f(0)=1$, $f(1/2)=2$, and $f(1)=3$. Show that  $$\lim_{n\rightarrow\infty} \int_0^1 f(x^n) dx$$  exists and compute the limit.  Attempt:   Since $f$ is real-valued continuous on $0\leq x\leq 1$ and the boundaries $f(0)=1$ and $f(1)=3$, $f$ is bounded on the interval  and the integral $\displaystyle\int_0^1 f(x^n)dx$ exists for any positive $n$. Thus, we can interchange the limit and the integral and compose the limit, \begin{align*} \lim_{n\rightarrow\infty} \int_0^1 f(x^n)dx&amp;=\int_0^1\lim_{n\rightarrow\infty}f(x^n)dx\\ &amp;=\int_0^1 f\left(\lim_{n\rightarrow\infty} x^n \right)dx\\ &amp;=\int_0^1 f(0)dx=1. \end{align*}  Questions: So, my first question concerns whether interchanging the limit and the integral is correct. It seems it would be justified by the dominated convergence theorem, where $f(x^n)$ is dominated by a function $g(x)=\displaystyle\sup_{0\leq x\leq 1} f(x^n)$ and $f_n(x^n)$, on $0\leq x\leq 1$, converges pointwise to a function $f$ that takes value 1 for $x\neq 1$ and 3 for $x=1$.  My next question is whether the interchange between the limit and composition of the function is allowed. Since the function is continuous and the limit exists at that point, it seems the interchange would be justified. Automorphism group of direct product of groups I was working on a problem in group theory, which asks about the automorphism group of a direct product of groups.  Okay, so I know that if $G,H$ are two groups whose orders are relatively prime, then $\operatorname{Aut}(G\times H)\cong\operatorname{Aut}(G)\times \operatorname{Aut}(H)$.  I also know that if $G,H$ are abelian and simple and isomorphic, then $\operatorname{Aut}(G\times H)\cong \operatorname{GL}_2(\mathbf{Z}_p)$ where $p$ is the order of $G$.  What I don't know is the following: what if $G,H$ are simple, yet not abelian? Let us for now focus on a more restricted case where $G\cong H$, in particular, $G=H$. What can we say about the group $\operatorname{Aut}(G\times H)$? (I heard something about this group being related to what is called "wreath product", which I do not know...)  Thanks bunch in advance! Putting a table next to a figure What is the difference between ++i and i++? In Star Wars: "The Force Awakens," how could this lightsaber have turned up where it did? In The Force Awakens:      Maz Kanata tells Rey that the lightsaber she just picked up and had visions from belonged to Anakin and Luke and now it's hers.   The lightsaber that Luke got from Obi-Wan Kenobi in A New Hope was lost/destroyed when Luke fought Darth Vader in Star Wars: The Empire Strikes Back.  In Return of the Jedi Darth Vader compliments Luke on building a new lightsaber and tells Luke that his skills are now complete.   How could that possibly be the lightsaber that Anakin used originally, and that was then passed on to Luke, when that lightsaber no longer exists?  Writers notes, director's notes, interviews, cast interviews, etc. are welcome. Thanks. Windows 7 "Waiting for background program to close" I am using Windows 7 Home Premium. When I shut down my computer why does the screen show this:    Before shutting down I'm close all programs. I have 2 hard disks, on first I have installed win xp. I boot into xp and run setup of win7 and installed it on second hard disk. Now the problem is that win7 bootloader is installed on first harddisk, so if I remove the first harddisk, I cannot boot into win7.   How I can move / install bootloader of win7 on second hard disk?