Java- Default constructor with one initialized variable of type array and calling it in main I have this program which has a class Ant where:  The default constructor initialises the instance variables queens to only 1 queen named “Beth” and colonySize to 100,000.  The defined constructor takes in two parameters and initialises the corresponding instance variables.  The method display, shows the information about an ant in the format below:  This ant colony has the following queens: Queen 1: Beth The colour of the ants: black The approximate colony size: 100000   Here is what I have done:  public class Ant {  private String[] queens; private String colour= "black"; private int colonySize;   public Ant(){     queens[0]= "Beth";     colonySize= 100000; }  public Ant(String[] queens, int colonySize){     this.queens[0]= queens[0];     this.colonySize= colonySize; }  public void display(){     System.out.println("Queen 1: "+ this.queens[0]);     System.out.println("Colour of the ants: "+colour);     System.out.println("The size of the colony: "+ this.colonySize);    } }   The prob is arising when I am calling it in the main.  Main Class  public class MainAnts {      public static void main(String[] args) {         // TODO Auto-generated method stub         Ant obj= new Ant();        obj.display();      }  }   I am getting a Null Pointer Exception (because I suppose that's not the right way to call the display method in the main since it has an array variable).
What is a NullPointerException, and how do I fix it? 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?
Grammatical number agreement in a complex phrase using singular "they" Negative quotients and their remainders Since $16 \div{-3} = -5.\overline{3}$, I thought I could also express this as $16 \div{-3} = -5\:R\:1$ or in other words $16\mod{-3} = 1$. My calculator tells my it is in fact $-2$.  Along the same lines, I see that $-16\mod{3} = 2$. So, while the true answer evaluates to $-5.\overline{3}$ again, the "remained notation" is $-6\:R\:2$ here, and $-6\:R\:-2$ in the first example.  Why do we go "past" $15$ to $18$ (or in the second example, past $-15$ to $-18$) and calculate the remainder from there?  Further warping my brain, $-16\mod{-3} = -1$, so it looks like we "stop" at $-15$ in this example. How can I speed up D&D 3.5e combat? Algorithms for computing multiplicative order modulo $n$ Prove that $L(V,W)$ forms a vector space Let $V$ and $W$ be vector spaces over a field $F$. Let $L(V,W) = \{T:V\to W : T \text{ is linear} \}$, that is, $L(V,W)$ is the collection of all linear functions from $V$ to $W$. For $S,T \in L(V,W)$ and $a \in F$, define new functions $(S+T):V \to W$ and $ aT :V \to W$ by $(S+T)(x) = S(x)+T(x)$ ; $(aT)(x) = a(T(x))$.   Prove that $S+T$ belongs to $L(V,W)$ and $aT$ belongs to $L(V,W)$. Why is Facebook PHP SDK getUser always returning 0? About $\lim \left(1+\frac {x}{n}\right)^n$ I was wondering if it is possible to get a link to a rigorous proof that  $$\displaystyle \lim_{n\to\infty} \left(1+\frac {x}{n}\right)^n=\exp x$$ Hi Blender coders and artists.  I am updating one of my add-ons for Blender 2.8 and have run into some  issues finding the appropriate way to hide a collection that is added to my scene.  I want to deselect the eyeball on the toolbar with a python command in a script but I don't want to disable the collection in the view-port entirely as it is used as a collection in a particle system.   I just want to deselect the eyeball circled in green below.  Anyone know the python API for this? SEDE should pick up on changes to community metadata It appears that site meta data isn't updated in SEDE. As an example, Moderators.SE was  to  in December 2014. It is still listed in SEDE as Moderators.SE, as of July 2015.  To search for Community Building data, we need to search the "Moderators" community:    It is not listed as Community Building: Access to original contents of mount point I know this sounds kind of ridiculous, but someone stole my mouse from my cubicle.. I came to work in the morning and was about to give my mouse a little shove to wake up the monitor, but it wasn't there!  I'm trying to figure out when this happened. I'm running Windows 7 and it's a USB mouse. I checked the event logs, but there doesn't seem to be any logs that might tell me what I'm looking for.  Is there any place where USB unplug events are logged? How to typeset a primed vector I write a vector with an arrow above the letter using \vec{p} and sometimes the vector needs to be primed using ' (or ^{\prime}, equivalently).  However, neither  \vec{p}'     nor  \vec{p'}     looks satisfactory (first option: prime dash overlaps with vector arrow, second option: arrow looks misplaced).  How would one write a primed vector? Solving the diophantine equation $y^{2}=x^{3}-2$ It is known that the diophantine equation $y^{2}=x^{3}-2$ has only one positive integer solution $(x,y)=(3,5)$. The proof of it can be read from the book "About Indeterminate Equation" (in Chinese, by Ke Zhao and Sun Qi). But the method I have known of solving this problem is algebraic number theory.  My question:      Does there exists an elementary method for solving the diophantine equation $y^{2}=x^{3}-2$?   I have gotten an elementary method by the assumption that "$x$" is a prime. That is, we can get a conclusion from the equation that $3\mid x$. Since $x$ is a prime we get the only solution $(x,y)=(3,5)$. But if $x$ is not a prime, the answer seems to be difficult.  Thank you for your help. External program from our Java program How can I write a program in Java that will execute another program? Also, the input of that program should be given from our program and the output of that program should be written into a file.  This is my small set of code to get its output:  Process p = Runtime.getRuntime().exec("C:\\j2sdk1.4.0\bin\\helloworld.java"); BufferedReader input =         new BufferedReader(new InputStreamReader(p.getInputStream())); while ((line = input.readLine()) != null)    System.out.println(line);  input.close();   This was my set of code but this throws an IOException. Proof that the One-Dimensional Simple Harmonic Oscillator is Non-Degenerate? Practical way to implement prevention of IP Spoofing I am an undergraduate Computer Science student and was hoping to gain some knowledge of ways to help prevent IP spoofing but all the resources I have tried out elaborate this concept in a theoretical way. I want to try out my hands at one of the techniques like:      How do I simulate this whole situation in my own system were I myself am the attacker and I myself have to defend it? And once I have gained an understanding of it, then how do I start translating that into programming terms? Stack Exchange iOS app nearing beta We're getting very close to releasing our iOS app on the App Store.  Since the , we have taken on hundreds of users, fixed a lot of bugs, and we have approached feature completion for v1.0.  We're still working on finishing touches and fixing crashes - but there aren't too many of those these days.  We believe we'll have this out in .    Current Alpha Testers:  We want to extend to you a huge thank you for using our app and giving us feedback.  We've made a ton of improvements that filtered through  here on meta.  We're pretty greedy, though, and we want more of your feedback as we get close to beta.  If you've been using the app, please leave an answer to tell us how you think we've done so far.  Don't go easy on us - we want to get this as right as we can before hitting the App Store.  You might even consider telling us how many stars you would give us if we were in the store.  Also, we created a room called  for more casual discussion about the app.  Everyone Else:  The alpha will continue in the interim, and we still .  The invitations are sent out once a week (usually), so if you don't get an invite right away, don't panic.  We'll get to you.  Bugs or feature requests should be reported here on meta and tagged .  Update, 5/1/2014    As of today, the app is submitted for review.  A great big thanks to all our alpha testers!  Your feedback has been invaluable and has truly helped us make the app much better than it would have been without you.  So what now?  Well, we intend to keep the alpha test group around, except now we're considering it the "beta channel".  It's still important to us, particularly since the update cycle through the AppStore is slow.  We'll still roll out updates in the same way that we have been.  We will also from time ask for targeted feedback on specific features.  And, lastly, if you're just now getting here and wished you had signed up for the alpha, feel free to sign up now anyway.  The form is still there, and we may still let in additional users to the beta channel depending on what our "active users" count looks like. Cannot find Background Images feature in Blender 2.8 Cannot find Background Images feature to add in a photo in Blender 2.8  Where is it? I'm creating side skirts for a truck and I am duplicating the frames I want. The problem is it's making the duplicated object into another object. How do I put it into the same one? Compound possessives and yours