Given below code is giving null pointer exception at  public class Testing {     public static final String HD_DATA = "STOCK,D1,D2,D3,D4,D5,D6,D7,D8,D9,D10";     public static final String HD_DATA_1 = "1,10,20,30,40,50,60,70,80,90,100";     public static final String HD_DATA_2 = "2,11,22,33,44,55,66,77,88,99,111";     public static void main(String[] args) {         String[] hdDataArray = HD_DATA.split(",");         String[] hdDataArray1 = HD_DATA_1.split(",");         String[] hdDataArray2 = HD_DATA_2.split(",");         String[][] pram = new String[3][];   //[null, null, null]          for(int i=0;i&lt;3;i++) {             for(int j=0;j&lt;hdDataArray.length;j++) {                 if(i ==0) {                     pram[i][j] = hdDataArray[j]; // Exception in thread "main" java.lang.NullPointerException                 }                 else if (i ==1){                     pram[i][j] = hdDataArray1[j];                 } else if(i == 2) {                     pram[i][j] = hdDataArray2[j];                 }             }         }            System.out.println(pram);     } }   Null pointer exception generate while trying to give but i would like to insert the data at the run time is there any way to we can insert data in array of arrays at runtime identify the size of arrays of array like jagged array
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?
Why is this simple Excel calculation not netting Zero? $(n^2 - 1)!$ is a multiple of $(n!)^n$ Question: Find all positive integers $n$ such that $(n^2 - 1)!$ is a   multiple of $(n!)^n$.   I can show that the required condition fails if $n$ is a prime, and by direct computation, it also fails for $n=4$. After doing a few small examples by hand, I believe that the required answer is 1 and all composites greater than 4. However, I cannot seem to prove this.  For each prime $p&lt;n$, I tried to count the number of appearances of $p$ on both sides, but I get that I am supposed to compare $n(\lfloor{\frac{n}{p}} \rfloor + \lfloor{\frac{n}{p^2}} \rfloor +\dots)$ against $\lfloor{\frac{n^2-1}{p}} \rfloor + \lfloor{\frac{n^2-1}{p^2}} \rfloor + \dots$, which is not obvious to compare.  Any help will be gretaly appreciated. Omitting the Milliseconds in a Date problems installing mathtools Title pretty much sums it up.  The external style sheet has the following code:  td.EvenRow a {   display: none !important; }   I have tried using:  element.style.display = "inline";   and  element.style.display = "inline !important";   but neither works. Is it possible to override an !important style using javascript.  This is for a greasemonkey extension, if that makes a difference. How do I prove $\sqrt{x + y} \le \sqrt{x} + \sqrt{y}$? for $x, y$ positive?  This should be easy, but I'm not seeing how.  A hint would be appreciated. How can I reduce the file size of a scanned PDF file? I have a 72.9MB PDF file that I need to shrink into under 500KB.  The file was a JPEG image that I had scanned, and then converted to pdf. Are there examples of third-(or higher)-order linear differential equations in physics or applied mathematics? The classical second-order linear ordinary differential equation is that named after Sturm and Liouville: formally, \begin{equation} (pu')'=ru. \end{equation} It arises naturally in many physical situations, for example through radial considerations of Schrödinger's equation. A higher-order "analogue" of it is the Orr$-$Sommerfeld equation, which, after relabelling the coefficients, may be written as \begin{equation} (\phi u'')''=\psi u. \end{equation} It also arises naturally, namely from certain simplifications applied to Navier$-$Stokes' (in)famous equation, and describes to great accuracy the cross-stream behaviour of channel fluid flow.  I have been thinking long and hard about whether there are additional higher-order linear differential equations that emerge naturally from our mathematical models of the world. It even seems pretty much all of the linear partial differential equations (heat, wave, Schrödinger, etc.) are of second order. Does anybody know of higher-order examples? How do I bake multiple texture maps into 1 UV, In Blender Cycles? In general, what is meant by saying that the fraction $x$ of the variance in an analysis like PCA is explained by the first principal component? Can someone explain this intuitively but also give a precise mathematical definition of what "variance explained" means in terms of principal component analysis (PCA)?  For simple linear regression, the r-squared of best fit line is always described as the proportion of the variance explained, but I am not sure what to make of that either. Is proportion of variance here just the extend of deviation of points from the best fit line? I am trying to prove a result, for which I have got one part, but I am not able to get the converse part.  Theorem. Let $R$ be a commutative ring with $1$. Then $f(X)=a_{0}+a_{1}X+a_{2}X^{2} + \cdots + a_{n}X^{n}$ is a unit in $R[X]$ if and only if $a_{0}$ is a unit in $R$ and $a_{1},a_{2},\dots,a_{n}$ are all nilpotent in $R$.  Proof. Suppose $f(X)=a_{0}+a_{1}X+\cdots +a_{n}X^{n}$ is such that $a_{0}$ is a unit in $R$ and $a_{1},a_{2}, \dots,a_{r}$ are all nilpotent in $R$. Since $R$ is commutative, we get that $a_{1}X,a_{2}X^{2},\cdots,a_{n}X^{n}$ are all nilpotent and hence also their sum is nilpotent. Let $z = \sum a_{i}X^{i}$ then $a_{0}^{-1}z$ is nilpotent and so $1+a_{0}^{-1}z$ is a unit. Thus $f(X)=a_{0}+z=a_{0} \cdot (1+a_{0}^{-1}z)$ is a unit since product of two units in $R[X]$ is a unit.   I have not been able to get the converse part and would like to see the proof for the converse part. I realize this is probably going to come off as a bit silly, but in Iron Man II how could James Rhodes easily don the Mark II armor that was designed to fit Tony Stark?  As you can see in this image (which isn't an "in universe" shot) Tony and Rhodey are roughly the same height, but it appears that Rhodey has a smaller frame than Tony, which would seem to make for an ill fit of the armor, especially for flight.  This issue could of course have been addressed by the Air Force during the retrofit with Justin Hammer. After installing Ubuntu Studio 12.04, I have found that it uses a low latency kernel.   I searched for an explanation and how to change back it to a real-time or generic one. However, it looks like this part of Linux hasn't been covered to explain the details.   Q: Why choose a low latency kernel over a generic or real-time one?  PS: I have already read the answers from  question and  post. Possible Duplicate:          I got two answers for the same question from different users and both of them correct and working perfectly, but I am unable to accept both of them. Why? There may be some questions that can be answered in several ways, but I can't here in Stack Overflow. Why? Why is defragmentation unnecessary? How and why do accelerating charges radiate electromagnetic radiation? Let's consider it case by case:  Case 1: Charged particle is at rest. It has an electric field around it. No problem. That is its property.  Case 2: Charged particle started moving (it's accelerating). We were told that it starts radiating EM radiation. Why? What happened to it? What made it do this?  Follow up question: Suppose a charged particle is placed in uniform electric field. It accelerates because of electric force it experiences. Then work done by the electric field should not be equal to change in its kinetic energy, right? It should be equal to change in K.E + energy it has radiated in the form of EM Waves. But then, why don't we take energy radiated into consideration when solving problems? (I'm tutoring grade 12 students. I never encountered a problem in which energy radiated is considered.) Beamer: Vertical alignment of multi-column ToC Time Dilation When In Orbit Allow me to add my own "top questions" too! I know, I know, the site should be more heavily weighted to answering, but sometimes, how and what people ask is important too! For example I recently asked  which I think is a fairly good question. Clearly I'm going to avoid questions where I've asked something very simple, but I know of a user or two who are implementing their own C standard libraries and the depth of those questions is important/ought to be on show.  Of course, the argument I can just look at their profile holds, but that awesome q/a might have been from a year or so ago in which case finding it is difficult. "He saw it stop and his son get out" I have been reading Men With Brooms for a few days. I read a sentence which did not make any sense to me, so I landed here to get some help on it. I have pasted the sentence from the novel. Please go through it and let me know your valuable feedback on it.  An excerpt from the novel (Men With Brooms: A Sweeping Epic, paperback 2002, a novelization by Diane Baker Mason):     Gordon was about to walk away from the Impala when he saw it stop and his son get out. So it was real the boy had come.   As per my opinion it should have been:     Gordon was about to walk away from the Impala when he saw it stopped and his son got out. So it was real the boy had come.   I have two questions here:   Why did the writer use stop and get instead of stopped and got? As she is telling us a story which happened in the past. Let's say the writer is telling us her mind's situation and she used the present tense for it but why did she use stop and get instead of stops and gets?