Handler Class Crashing after removing object That was probably a very confusing title, but I'm pretty confused. I am making a game, and there are explosions. I just ran into this one stupid problem. Here's my code for the explosions (without the package and imports):  public class LBExplosion extends GameObject{ private int tick; private int startSize,endSize,size; Handler handler; public LBExplosion(float x, float y, ID id, int startSize, int endSize, Handler handler) {     super(x, y, id);     // TODO Auto-generated constructor stub     this.startSize = startSize;     this.endSize = endSize;     size = startSize; }  @Override public void tick() {     // TODO Auto-generated method stub     tick++;     size++;     if (size &gt;= endSize) {         this.handler.removeObject(this); //here     } }  @Override public void render(Graphics g) {     // TODO Auto-generated method stub     if (tick % 2 == 0) {         g.setColor(Color.white);     } else if (tick % 2 == 1) {         g.setColor(Color.red);     }     g.fillRect((int) x - size/2, (int) y - size/2, size, size); }  @Override public Rectangle getBounds() {     // TODO Auto-generated method stub     return null; }   }  And it errors when I try to remove it (at line 25).  Here's the code for the handler class (without the package and imports):  public class Handler { LinkedList &lt;GameObject&gt; objList = new LinkedList &lt;GameObject&gt;();  public void tick() {     for (int i = 0; i &lt; objList.size(); i++) {         GameObject tempObject = objList.get(i);         tempObject.tick();     } } public void render(Graphics g) {     for (int i = 0; i &lt; objList.size(); i++) {         GameObject tempObject = objList.get(i);         tempObject.render(g);     } }  public void addObject(GameObject object) {     objList.add(object); } public void removeObject(GameObject object) {     objList.remove(object); } public void removeAllEnemies() {     for (int i = 0; i &lt; objList.size(); i++) {      } }   } And here's the constructor for the game class (where it's spawned):  public Game() {     handler = new Handler();     hud = new HUD();     spawner = new Spawner(handler);      this.addKeyListener(new KeyInput(handler));     new Window(WIDTH,HEIGHT,"Game", this);      handler.addObject(new Player (16, 16, ID.Player,hud,handler));     handler.addObject(new LBExplosion (300, 316, ID.LBExplosion,0,64,handler));  }   It gives me this error:  Exception in thread "Thread-2" java.lang.NullPointerException at com.wave.noah.two.p.a.c.k.a.g.e.something.main.LBExplosion.tick(LBExplosion.java:26) at com.wave.noah.two.p.a.c.k.a.g.e.something.main.Handler.tick(Handler.java:12) at com.wave.noah.two.p.a.c.k.a.g.e.something.main.Game.tick(Game.java:80) at com.wave.noah.two.p.a.c.k.a.g.e.something.main.Game.run(Game.java:62) at java.lang.Thread.run(Unknown Source)   Don't mind the long package name.  How do I fix this unexpected error?
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?
List of apps ever downloaded Dedicated mouse and keyboard for a virtual machine, is it possible? I have a repeated composition of functions ${T_n}(z) = {\tau _0} \circ {\tau _1} \circ {\tau _2} \circ  \cdots  \circ {\tau _n}(z)$  By analogy with $\sum\limits_{i = 1}^n {} ,\prod\limits_{i = 1}^n {} ,\bigcup\limits_{i = 1}^n {} ,\bigcap\limits_{i = 1}^n {} ,$ I want to write ${T_n}(z) = \left( {\mathop  \circ \limits_{i = 0}^n {\tau _i}} \right)(z)$ or even ${T_n}(z) = {\mathop  \circ \limits_{i = 0}^n {\tau _i}} (z)$. Can I do this? With biblatex, alphabetic style, I have     &lt;author&gt;. &lt;title&gt;   But I want to have a colon ":" instead of the period "." after the author:     &lt;author&gt;: &lt;title&gt;   What do I have to change? I want to add a comma in the thousands place for a number.     String.Format()? What is causing disabled options when adding a mesh/curve object to the scene? Orthogonal basis for infinite-dimensional vector spaces Automatically hide old comments Comments are useful. Many, many posts need some small amount of meta discussion, and comments fulfill this need.   Comments are also noisy and distracting. Occasionally, someone will post an insightful and informative comment that complements the post its attached to... But more often, they're tangential, quickly irrelevant and in the way: stale comments show up first, making newer comments less visible.  The guidance here for a long time has been that comments are transient, . And yet, some do hang around for months or years because .   So let's fix that.   I propose that all comments older than 7 days be hidden by default unless the comment has been up-voted in the past 30 days. Hidden comments should be indicated by a note below the post ("add / show 3 more comments") and made visible to anyone who cares to click it.   This doesn't destroy anything, but it would get it out of the way of most readers - and hopefully encourage folks to edit it into the actual answers as a result.  Note: I previously suggested this . Other  have been . However, I'm not suggesting that comments be automatically deleted, and they should be hidden based purely on the age / activity of the comment itself, not of the post to which they're attached. How do you disable browser autocomplete on web form field / input tags? How do I resolve "WILL_NOT_PERFORM" MS AD reply when trying to change password in scala w/ the unboundid LDAP SDK? Change all file type associations from one program to another The list has several empty strings in it for me right now: Problem with defining shortcuts for TikZ matrices For  I wanted to define a shortcut for creating a matrix inside a tikzpicture. As a minimal example, consider  \newcommand\mymatrix[1]{     \begin{tikzpicture}         \matrix[matrix of math nodes] {#1};     \end{tikzpicture}% }   which would then be used as  \mymatrix{     a &amp; b \\     e &amp; f \\ }   But LaTeX complains about Package pgfbasematrix Error: Single ampersand used with wrong catcode at the line with the closing brace of \amatrix{}. Why does it do that and how can I avoid it? What is the best collation to use for MySQL with PHP? I'm wondering if there is a "best" choice for collation in MySQL for a general website where you aren't 100% sure of what will be entered? I understand that all the encodings should be the same, such as MySQL, Apache, the HTML and anything inside PHP.  In the past I have set PHP to output in "UTF-8", but which collation does this match in MySQL? I'm thinking it's one of the UTF-8 ones, but I have used utf8_unicode_ci, utf8_general_ci, and utf8_bin before. I read it as a paperback book somewhere in the mid-90s, I think. The protagonist lived in an apartment building. He's out on the balcony when a birdlike (but humanoid) alien swooped down and attacked him. The presence of the aliens was commonly known and was a known danger. He kills it with his watering can and is rewarded by either the aliens or the humans for it with money. Other than that, all I remember was that the chapters were started with an internet-like news report which I think chronicled things getting worse and more violent. One of the updates involved the bombing of a bridge with the casualties raised by having two slow-moving trucks moving side by side obstructing traffic and ensuring a full bridge.  The internet system was pretty ubiquitous as I recall. I think that he looked up his watering can shortly after the incident with the aliens, but decided to keep this one, even if it leaks a bit. I want to say that it was by Piers Anthony, but none of the book titles look familiar. I think the cover I had showed the man being attacked by the bird-man, which looked kind of like the illustrations on the cover of The Stand. Clamp velocity along local axis In the attached , I have a representation of a airplane/jet fighter (cube scaled at one end to indicate direction of flight). I am using torque to steer, and adding Linear Velocity along a local axis for thrust/brakes. What I want to know is how to clamp the velocity along the plane's local axis so when the plane steers, it does not simply keep flying in the direction that is was before it turned. I would prefer a solution with logic bricks, but if that is not possible, python would be acceptable. (it just needs to keep a speed relative to how long the thrust/breaks have been held no mater which direction it is pointing.) A problem with my reasoning in a problem about combinations I am trying to compute this integral/limit, I don't feel like I have any good insight...   $$\lim_{n \to \infty} \int_0^{n^2} e^{-x^2}n\sin\frac{x}{n} \, dx.$$  I have tried to make a change of variable to get rid of the $n^2$, I changed to $X=\frac{x}{n^2}$ but got something even worse, I've tried to reach a situation where I could use a convergence theorem for Lebesgue Integrals,... I'm not sure I'm even on the right track!  Could you give me a hint on how to start this?  Thank you very much! Assessing approximate distribution of data based on a histogram Can't read code blocks from the Stack Exchange android app