I'm getting a NullPointerException in java (at this line :FileReader fstream = new FileReader(fileName)) when I try to read a text file line by line and store them in an arraylist with this code :   public ArrayList&lt;String&gt; StoreLineByLine(String fileName) throws IOException {     String str;      ArrayList&lt;String&gt; Line = new ArrayList&lt;String&gt;();     FileReader fstream = new FileReader(fileName);     BufferedReader myFileReader = new BufferedReader(fstream);      while ((str = myFileReader.readLine()) != null) {         Line.add(str);     }     myFileReader.close();     return Line; }   Could anyone help me understand the problem ? Thanks 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?
Not a problem, but have been seeing questions recently of people not being offered upgrade from 18.04 to 20.04.  I thought these upgrades were offered back in June.  I upgraded to 20.04 from 19.10 and this was offered back in May.  Imagine that different versions paths have different schedules, but google does not help explaining(that I found).  Does someone know the schedules? How can I stop iPhone prompting me to setup Apple Pay in Settings? I'm looking for a command (or command line program) to toggle (disable/enable) internet access to the outside world in Windows XP machines. It should temporarily block internet access but leave the LAN working.   I looked for ways to change the DNS, but browsers like Chrome keep their own cache. The machines are configured via DHCP. Is it possible to convert virtual machines to physical environments? Removing all fraction symbols like “¼” and “½” from a string Explicit construction of a finite field with $p^n$ elements At the end of Billions, Season 3, Episode 9, Grigor Andolov (John Malkovich) tells a story to Bobby Axelrod (Damian Lewis) about the Christmas market in Moscow. He asks a question about what happened to a boy:  Andolov: Many years ago, I was walking along the Moskva Christmas market. You ever seen Moskva Christmas market? Always a sense of good cheer, even during the lean years. I think it was the wine. They serve warm wine with the spices in it... cinnamon and... I was waiting on the line — everyone was always waiting on the line — and finally I got my cup, I turn, and there was this little boy. Runny nose. He looking at me so desirous of my cup of this warm, warm wine that I give him a sip. He stares at me with such a gratitude. And then I notice his mother. Plump breasts. She must have known someone. So I give him my cup of wine. And I take his mother away from the square. Behind the soldiers. And after, I leave her for the soldiers. And I walked back, and this little boy is staring at me with his greedy drunken eyes. Do you know what happened to him? Axelrod: No. Andolov: I always ask. No one ever knows.  What is the real meaning of this story? And how is it connected to the Axelrod – Andolov relationship? I'd like to use JavaScript to calculate the width of a string. Is this possible without having to use a monospace typeface?  If it's not built-in, my only idea is to create a table of widths for each character, but this is pretty unreasonable especially supporting  and different type sizes (and all browsers for that matter). what is the general definition for some partial differential equation being called elliptic, parabolic or hyperbolic - in particular, if the PDE is nonlinear and above second-order.  So far, I have not found any precise definition in literature. $f^2$ and $f^3$ are holomorphic implies $f$ is holomorphic. Identifying genes from a list of genes Calculating roundness/compactness of polygon? I am trying to find ways to quantitatively describe the shapes of various polygons. For my project, these polygons represent lakes, rivers, lagoons, and parks. So they can be almost any shape. One easy metric is to calculate perimeter vs. area, which is at best an only slightly useful metric. But I would also very much like to be able to say something about the 'roundness' of a polygon. Or how 'compact' the shape is on a map.  The only way I can think of doing this easily is to calculate the area of each polygon in relation to a bounding box for that polygon (which I already have). But this seems like a poor solution.  So now I am thinking of something more like this - take the centroid of the polygon, add on a series of buffers of increasing areas (say 50%, 100%, 150%), then compare how much overlap there is between each buffer and the original polygon. A perfect circle will have perfect overlap at 100%, and I can use the 50% and 150% buffers to judge how much and in what way each polygon differs.  But even that feels cumbersome, and like a poor workaround for what somebody else has probably already figured out far better.  For reference, at a minimum I will need to be able to look at the resulting indices for the shape of various polygons, and be able to make an educated guess as to their source (River? Reservoir with dendritic shape? Lake/Lagoon? Park?) Help ID this plant, quite possibly a weed I found this plant near my South Indian home in , India. Most probably it could be some sort of weed. Anyhoo, is this plant of any medical or commercial value? Is it a remedy for something?   It has a white tap root with little veins off the main root It has a really small yellow flower It's leaves are similar to that of a clover, except for that it has three to five leaves        Merci d'avance!  (P.S. Forgive me if this is some very common plant that I should know about, I'm in 7th grade.) I'm trying to prove that the rationals are not the countable intersection of open sets, but I still can't understand why   $$\bigcap_{n \in \mathbf{N}} \left\{\left(q - \frac 1n, q + \frac 1n\right) : q \in \mathbf{Q}\right\}$$   isn't a counter-example. Any ideas? Thanks! Do save bonuses stack from multiple magic items in AL? I play in Adventurers League and have a character that has a +1 Ring of Protection, which gives +1 to AC and saves. I also have a Stone of Good Luck which gives a +1 to saves and ability checks.  If I equip both items and my base Dex save is +4, would it become +6 due to receiving both bonuses, or +5 with just one? I can't find much in the PHB or Google to answer this. How can I reuse existing materials, objects, etc from an existing .blend? missing $ inserted error for equation I get the missing $ inserted error for the following code:  \begin{equation}  C = $ \frac{2}{\omega^2N^2\mu\pia} $  \end{equation}   I have tried out different changes based on Googling for this error, but nothing seems to help. Any suggestions would be appreciated. How do I allow long URLs to have line breaks at any point. This is in the bibliography not the main text. I am trying to save space so don't want extra spaces to be added to make it only break at slashes, for example, as it does by default.  I am using biblatex+biber. Google AJAX API - How do I get more than 4 Results? Show that a continuous function has a fixed point Question: Let $a, b \in \mathbb{R}$ with $a &lt; b$ and let $f: [a,b] \rightarrow [a,b]$ continuous. Show: $f$ has a fixed point, that is, there is an $x \in [a,b]$ with $f(x)=x$.  I suppose this has to do with the basic definition of continuity. The definition I am using is that $f$ is continuous at $a$ if $\displaystyle \lim_{x \to a} f(x)$ exists and if $\displaystyle \lim_{x \to a} f(x) = f(a)$. I must not be understanding it, since I am not sure how to begin showing this... Should I be trying to show that $x$ is both greater than or equal to and less than or equal to $\displaystyle \lim_{x \to a} f(x)$ ?