im trying to create my own BinaryTree class and i also got a JUnit-Class which outputs the tests for the non added value and the first added value as a Nullpointer..  The Nullpointer occurs in my BinaryTree class at the while-loop, which doesnt make sense to me, as i've got the following lines of code to check it:   if(key.compareTo(current.key) == 0) {            return current.value;       }       return null;   }   The first added value should be checked first (at least i think)  Here is my code:  public class BinaryTree&lt;K extends Comparable&lt;K&gt;, V&gt;{      int count = 0;   //Please don't add any further attributes.   private K key;   private V value;   private BinaryTree&lt;K,V&gt; left, right;   private BinaryTree&lt;K,V&gt; root;   /**    * Constructor creates new BinaryTree instance, initially without child nodes.    */   // Done!!   public BinaryTree(K key, V value){       this.value = value;       this.key = key;       left = null;       right = null;   }    /**    * Stores a key-value pair in the tree.    * If the key has already been stored, then the current value for this key    * is replaced by the new value.    */   public void put(K key, V value) {       BinaryTree&lt;K,V&gt; newNode = new BinaryTree&lt;K,V&gt;(key, value);         if (root == null) {           root = newNode;           root.value = value;           root.key = key;           count += 1;           return;         }         BinaryTree&lt;K,V&gt; current = root;         BinaryTree&lt;K,V&gt; parent;           while (true) {             parent = current;             if (key.compareTo(current.key) == -1) {               current = current.left;               if (current == null) {                 parent.left = newNode;                 count += 1;                 return;               }             } else {               current = current.right;               if (current == null) {                 parent.right = newNode;                 count += 1;                 return;               }             }           }       }     /**    * Returns the value object stored with the given key.    * Returns null if the key is unknown.    */   public V get(K key) {       BinaryTree&lt;K,V&gt; current = root;        while(key.compareTo(current.key) != 0) {            if(key.compareTo(current.key) &lt; 0) {             current = current.left;             } else if(key.compareTo(current.key) &gt; 0) {             current = current.right;                      }        }       if(key.compareTo(current.key) == 0) {            return current.value;       }       return 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?
I have a computer with a video card that has no Linux support.  I discovered this issue while trying to use a persistent usb to boot from.   I found that I can boot like that if I change options and edit so as to add nomodeset there (see ).  Also, editing the syslinux.cfg file from my live persistent USB and adding nomodeset in a line there made this setting automatic for booting from the persistent USB.  Can I make a similar edit for proper install from the same live USB?  Is it possible to edit something on the live USB in order to install the SO from it,  -- that is: having automatically the nomodeset setting already there when the installation starts?  My problem is that in order to install I think I already have to have added nomodeset or I'll see nothing on my display. I need a way to be sure that nomodeset it's permanent from the start. How to check who owns the Slack's workspace? I'd like to check who owns (or at least some kind of public profile page) some workspace based on its subdomain (e.g. xyz.slack.com).  Is it possible? How will people upgrade from 12.10 to later releases after 13.04 is EOL? A teacher wants to randomly form two teams of 5 students from a group of 5 girls and 5 boys for a sports activity. A teacher wants to randomly form two teams of 5 students from a group   of 5 girls and 5 boys for a sports activity. Two of the girls, Ann and   Alice, are selected as team leaders. Find the probability that one   team has exactly 3 girls.   If i do this way $$\dfrac{{3 \choose 2}{5\choose 2}{1\choose 1}{3\choose 3} \times 2!}{{8 \choose 4}{4 \choose 4}} = \dfrac{6}{7}$$  Which turns out to tally with the answer. But i got one big question, is my way correct. Do i really need to times $2$ here? Please see my link below to my previous question cause the previous question make me doubt if i should times $2$. Can a 20V 4.51A power supply be used with a computer that requires a 19V 3.42A power supply? What does !$ mean? I'm following through a tutorial and it mentions to run this command:  sudo chmod 700 !$   I'm not familiar with !$. What does it mean? Disable RAM stick in Windows 7 I have 2 8gb RAM sticks on my motherboard. One is faulty on some bytes and is giving me BSOD once in a while.  Is it possible to disable one of them without removing it physically? I want to keep it inside the motherboard as I dual boot with Xubuntu and I can block the fauly bits there, and as far as I know, it is impossible to block them in Windows. What is the most efficient way to deep clone an object in JavaScript? I have to move a MongoDB Collection (Size: 1TB+) from Sharded MongoDB Cluster to another[5 shards on both clusters]. During this operation, it is assumed that the accompanying program will be offline, so no need to worry about inconsistent data, but I need to minimize the downtime.  I've tried testing it with mongodump and mongorestore, but looks like that is taking ages to finish.  Please share your experiences for such kind of scenarios.  Note: Cluster has only one collection, so I am open at cluster level sync as well. I'm trying to install wifi drivers for a particular mini wifi card i bought. The output of lsusb is:  0bda:f179 Realtek Semiconductor Corp   I've searched everywhere for drivers, but could not find anything. Any help?  Thanks In $\mathbb{R}$ with standard topology the closure of the above set $M$ is $M \cup 0$. I fail showing this by purely topological means. I.e. not using the fact that this holds in the reals as a metric space and deduce it for the induced topology.  I assumed that there exist a closed subset $A$ containing $M$ but not 0. Hence, the complement of $A$ is an open subset containing 0. Does this already yield a contradiction or do I need a different approach?  Could you help me on this? How can I reuse existing materials, objects, etc from an existing .blend? Get three highest values from the array Formula for the $n$th term of $1, 2, 2, 3, 3, 3, 4, 4 ,4, 4, 5, ...$ Warning: Total photoshop newb!  I recently got a cool image of my fiancee and I holding hands and showing off her engagment ring. The backdrop is the beach:    I tried to trace an image using a combo of the laso and magic wand tools to select my target. Then I used that to pull out the target as another layer.  I then pasted in a background gradient.     Ended up with a really lame photoshoped looking picture. Notice the white lines where I didn't get the arms close enough and the choppy spots where I got too close.    So what's my main problem here?   Is their a way to bet a better cutout? Is their a blending tool that will make the background look more natural? both   I tried a dozen or so tutorials I found in google searches but they just don't blend these types of images together in any of them. Thanks in advance. If I inherit from a base class and want to pass something from the constructor of the inherited class to the constructor of the base class, how do I do that?  For example, if I inherit from the Exception class I want to do something like this:  class MyExceptionClass : Exception {      public MyExceptionClass(string message, string extraInfo)      {          //This is where it's all falling apart          base(message);      } }   Basically what I want is to be able to pass the string message to the base Exception class. How to "unpivot" or "reverse pivot" in Excel? Windows 10 stuck in install loop I was having a time getting my bootable USB 3, 32GB W10 install USB to be recognized. It recognized one time but I had to restart for something and it never came up again. I eventually removed all other boot up options to make it easier and faster to try again (no F12 needed).  Finally I gave up and tried another drive (16GB this time FWIW) and then it worked.  HOWEVER, it's stuck on a reboot loop now. I can choose to install, then to select the right disk, then it says it's loading file and then next thing I know it's saying do you want to install or upgrade. In follow up to , it appears that some numbers cannot be represented by floating point at all, and instead are approximated.  How are floating point numbers stored?  Is there a common standard for the different sizes?  What kind of gotchas do I need to watch out for if I use floating point?  Are they cross-language compatible (ie, what conversions do I need to deal with to send a floating point number from a python program to a C program over TCP/IP)? Copy material to another object? I saw a video where the person copied a material from one object to another (Cycles).  How can I accomplish this?