Not quite sure why i'm getting a NullPointerException, new to Java so any help would be greatly appreciated!  public class MainActivity extends AppCompatActivity {       private TextView httpstuff;      @Override     protected void onCreate(Bundle savedInstanceState) {         super.onCreate(savedInstanceState);         setContentView(R.layout.activity_main);         TextView httpstuff = (TextView)findViewById(R.id.tvHttp);         Button button = (Button) findViewById(R.id.button);         button.setOnClickListener(             new Button.OnClickListener(){                 public void onClick(View v){                     new JSONTask().onPostExecute("http://samples.openweathermap.org/data/2.5/weather?q=Chicago&amp;appid=93eea9a9277a0520d2f444c3ff8c62da");                 }             }     );  }     class JSONTask extends AsyncTask&lt;String,String,String&gt; {         @Override         protected String doInBackground(String... urls) {         HttpsURLConnection connection = null;         BufferedReader reader = null;         try {             URL url = new URL("https://samples.openweathermap.org/data/2.5/weather?q=Chicago&amp;appid=93eea9a9277a0520d2f444c3ff8c62da");             connection = (HttpsURLConnection) url.openConnection();             connection.connect();              InputStream stream = connection.getInputStream();             reader = new BufferedReader(new InputStreamReader(stream));             StringBuffer buffer = new StringBuffer();             String line;             while ((line = reader.readLine()) != null) {                 buffer.append(line);             }             return buffer.toString();          } catch(MalformedURLException e) {             e.printStackTrace();         } catch(IOException e) {             e.printStackTrace();         }                      finally {             if(connection != null){                 connection.disconnect();             }             try{                 if(reader != null){                     reader.close();                 }             }catch(IOException e) {                 e.printStackTrace();             }          }             return null;     }    @Override    protected void onPostExecute (String result){        super.onPostExecute(result);        httpstuff.setText(result);         }     } }   Android Studio Logs says that the NullPointerException error is occurring at  httpstuff.setText(result);   And at  new JSONTask().onPostExecute("http://samples.openweathermap.org/data/2.5/weather?q=Chicago&amp;appid=93eea9a9277a0520d2f444c3ff8c62da");   private TextView httpstuff is a designated as a field but says that it is not initialized, but I use it in class JSONTask? Any ideas on why the exception is occurring? Thanks alot in advance!
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?
What are good learning resources for a LaTeX beginner? This is a "catch-all" question designed to serve as an answer for all questions about choosing web hosting.  Pro Webmasters no longer accepts new questions about how to choose hosting.  All future questions pertaining to finding web hosting should be closed as a duplicate of this question. For more information about this policy please see .    How to find web hosting that meets my requirements?  What we're looking for in answers to this question are the basics about web hosting:   What is web hosting? What is the difference between shared, VPS, and dedicated hosting? How does a content delivery network relate to web hosting? Anything else you feel is helpful in finding a web host.   What we do not want is:   Endorsements or recommendations for specific web hosts We do not want your experience or other subjective information (just the facts please) LCM is associative: $\ \text{lcm}(\text{lcm}(a,b),c)=\text{lcm}(a,\text{lcm}(b,c))$ Definition: The least common multiple of $a.b\in\Bbb{Z}$ is the smallest  $k\in\Bbb{N}$ that is divisible by both a and b.         Proposition: $\text{lcm}(\text{lcm}(a,b),c)=\text{lcm}(a,\text{lcm}(b,c))\tag{2}$    Proof: We want to show $\text{lcm}(\text{lcm}(a,b),c)\mid\text{lcm}(a,\text{lcm}(b,c))$ and $\text{lcm}(a,\text{lcm}(b,c))\mid \text{lcm}(\text{lcm}(a,b),c)$ such that $\text{lcm}(\text{lcm}(a,b),c)=\text{lcm}(a,\text{lcm}(b,c))$.  Let $k=\text{lcm}(\text{lcm}(a,b),c)$, then $c\mid k$ and $\text{lcm}(a,b)\mid k$, but if we let $l=\text{lcm}(a,b)$, then $a\mid l\,\,\text{and}\,\, b\mid l$. Therefore $c\mid k\,\,,a\mid k\,\,\text{and}\,\, b\mid k$, but then $\text{lcm}(b,c)\mid k$. Thus $\text{lcm}(a,\text{lcm}(b,c))\mid k$      Question: Does this makes sense, ifso can I do the same for $\text{lcm}(\text{lcm}(a,b),c)\mid \text{lcm}(a,\text{lcm}(b,c))$? The simplistic undergrad explanation aside, I've never really understood what energy really is. I've been told that it's something when converted from one kind of something to another kind, or does some "work", as defined by us, but what is that something?  Moreover, if the total amount of energy in the universe is finite and we cannot create energy. Then, where did it come from? I've learned from thermodynamics where it goes, but where does it come from?  I know this sounds like something trivially simple, but there is so much going on in the physical universe and I just can't grasp what it is. Maybe it is because I lack the mathematical understanding that I can't grasp the subtle things the universe is doing. Still, I want to understand what it is doing.  How do I get to the point of understanding what it's doing?  (Note: What prompted me to ask this was . I'm afraid that it just puzzled me further and I sat there staring at the screen for a good 10 minutes.) Run faster than outer turret attacks As the title says, is there any way to run faster than the turret attack (the missile like thing) so that you can arrive spawn before the attack reaches you, and therefore can't kill you? You know, when you have low health, and you are targeted by the turret? Is there any item sets or things like that? Is there any built-in way to get the length of an iterable in python? For example, files, in Python, are iterable - they iterate over the lines in the file. I want to count the number of lines.   One quick way is to do this:  lines = len(list(open(fname)))   However, this loads the whole file into memory (at once). This rather defeats the purpose of an iterator (which only needs to keep the current line in memory).  This doesn't work:  lines = len(line for line in open(fname))   as generators don't have a length.  Is there any way to do this short of defining a count function?  def count(i):     c = 0     for el in i: c += 1     return c   To clarify, I understand that the whole file will have to be read! I just don't want it in memory all at once 3-regular graphs with no bridges Problem. Use Tutte's 1-factor theorem to prove that every 3-regular graph with no bridges has a 1-factor.  I honestly have no idea how to approach this problem. I have drawn a couple of graphs to gain some insight to no avail. Any hints or tips will be greatly appreciated. Proving $\lim_{n\to\infty} a^{\frac{1}{n}}=1$ by definition of limit Okay so I remember almost nothing of this show. The only thing I know is that I used to watch this show on Cartoon Network and it had a hero who used a sword to fight monsters and a girl who used bow and arrows. Also, the monsters kind of looked like computer generated and there was a book and stones which were somewhat related to the story? Hosting multiple distinct folders for distinct domains Which way should arrows point in a collapsible accordion? Left/down … down/up? How exactly do DLL files work? There seems to be an awful lot of them, but I don't know what they are or how they work.  So, what's the deal with them? Excuse my lack of knowledge and expertise in math,but to me it would came naturally that the cubic root of $-8$ would be $-2$ since $(-2)^3 = -8$.  But when I checked Wolfram Alpha for , real it tells me it doesn't exist.  I came to trust Wolfram Alpha so I thought I'd ask you guys, to explain the sense of that to me. How do you concatenate matrices? And how do you make block matrices? Another (perhaps humorous) term for "The Gold Standard" Gold Standard as in:     an example against which others of the same type are compared   -    Any other humorous ways to refer to this?  Something like "the holy mother"... Where are all the major log files located? Keep iphone active while running program how to set iPhone device to stay active ( to not lock ) while my app is running ? Any idea I'm having a difficult time understanding this statement. Can someone please explain with a concrete example? I am looping through a text file, using 'while read'. I read three variables from each line - two filenames and a decimal number. I know that this works in a vanilla setup (loop, read line, echo line, extract variables, nothing else), because I have tested it on my input file.  I am getting an odd result, though, once I add in the meat of my routine - which is a call to ffmpeg to merge the audio and video streams represented by the filenames. Successive 'read' operations omit leading characters from the line. I read  that calls for 'read' input within a 'while read' loop can cause problems, and wonder if the ffmpeg call is doing something that confuses bash, but this seems unlikely and bizarre! NB: I don't really understand the ffmpeg call - I got it from an answer to another question.  Any help would be appreciated!  The first 'read' works as expected (and the ffmpeg command completes):  LINE  1 vidsNeedingSound/448£generic@06_10_16-09_30_47.mp4 soundToAdd/448£generic@06_10_16-12_11_54.wav 6.988354 V: vidsNeedingSound/448£generic@06_10_16-09_30_47.mp4   A: soundToAdd/448£generic@06_10_16-12_11_54.wav   D: 6.988354   The second 'read' loses 36 characters from the beginning of the line (and the ffmpeg command fails because the file represented by the variable V which takes the first item of the line doesn't point at a file):  LINE  2 6-09_30_47.mp4 soundToAdd/452£generic@06_10_16-12_11_54.wav 9.64663 V: 6-09_30_47.mp4   A: soundToAdd/452...   The third 'read' works as expected (and the ffmpeg command completes):  LINE  3 vidsNeedingSound/452£left@06_10_16-09_30_47.mp4 soundToAdd/452£left@06_10_16-12_11_54.wav 9.862118 V: vidsNeedingSound/452£left@06_10_16-09_30_47.mp4   A: soundToAdd/452...   The fourth 'read' loses 37 character (one more than the last fail) from the beginning of the line (and the ffmpeg command fails):  LINE  4 09_30_47.mp4 soundToAdd/452£right@06_10_16-12_11_54.wav 9.431392 V: 09_30_47.mp4   A: soundToAdd/452....   That's the pattern. When not preceded by a successful call to ffmpeg, the 'read' works as expected. After each successive successful ffmpeg call, characters are omitted from the beginning of the line: 36 characters to begin with, then 37, 38, 39...  The clincher is that when ffmpeg fails after a 'successful' read (due to another problem), the following 'read' works as expected.  CONCLUSION: a successful ffmpeg call results in a read fail on the next iteration through the loop.  Why does this happen, and how can I stop it?  Here's my code: ...  # Loop through lines in the merge file IT_COUNT=1 while read MERGE_LINE                do              echo "LINE " $IT_COUNT     ((IT_COUNT+=1))     echo $MERGE_LINE   # testing use     read VID_FILE AUD_FILE DURATION &lt;&lt;&lt; "$MERGE_LINE" # Get the data from each line     echo "V: $VID_FILE   A: $AUD_FILE   D: $DURATION"         # testing use ....     # add audio to video     ffmpeg -i $VID_FILE -i $AUD_FILE -filter_complex "aevalsrc=0:d=$AUD_SHIFT[s1];[s1][1:a]concat=n=2:v=0:a=1[aout]" -c:v copy -map 0:v -map [aout] $FILE_OUT -hide_banner  done &lt;$MERGE_FILE     Thanks for looking! What can I expect from a Skype interview for PhD admissions?