This is my error:  java.lang.NullPointerException: Attempt to invoke virtual method 'void   android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference   This is part of my code:  public static final String PLACEHOLDER_LIST_FILE = "placeholder_file"; public static final String STORY_NUMBER_FILE = "story_number_file";   Button button3; Story story; EditText placeholderField; TextView wordsLeftText; Set&lt;String&gt; placeholderList; int storyIndex; int placeholderCount;  @Override protected void onCreate(Bundle savedInstanceState) {     super.onCreate(savedInstanceState);     setContentView(R.layout.display);      // Restore preferences     SharedPreferences placeholderSettings = getSharedPreferences(PLACEHOLDER_LIST_FILE, 0);     placeholderList = placeholderSettings.getStringSet("placeholders", null);     if (placeholderList == null) {         placeholderList = new HashSet&lt;&gt;();     }      SharedPreferences storyNumberSettings = getSharedPreferences(STORY_NUMBER_FILE, 0);     storyIndex = storyNumberSettings.getInt("story_number", 404);     storyIndex = 404; // Used to test spinner      if (storyIndex == 404) {         storyIndex = getIntent().getIntExtra("selected_story", 404);     }      InputStream is;     is = this.getResources().openRawResource(getStoryNumber(storyIndex));     story = new Story(is);      for (String currentPlaceholder : placeholderList) {         story.fillInPlaceholder(currentPlaceholder);     }      @Override protected void onStop() {     super.onStop();      SharedPreferences placeholderSettings = getSharedPreferences(PLACEHOLDER_LIST_FILE, 0);     SharedPreferences.Editor editor1 = placeholderSettings.edit();     editor1.putStringSet("placeholders", placeholderList);     editor1.apply();      SharedPreferences storyNumberSettings = getSharedPreferences(STORY_NUMBER_FILE, 0);     SharedPreferences.Editor editor2 = storyNumberSettings.edit();     editor2.putInt("story_number", storyIndex);     editor2.apply(); }   What I want to fix:  When I press the button in the second activity to continue to the 'input'activity. Without getting a crash and the nullpointer error.   What have I done to try and fix it:  Look at people who also had the problem, but their fixes don't apply to my code.  I have also no idea why I can't declare it to null.   Any help would be appreciated.  p.s. If you guys see any error in my code please tell me
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?
Proper display of fractions The  recommends that images have Copy-On-Write disabled on the directory when using btfs.  I do see that it would be a good idea if you had a lot of file read/writes.   question explores this idea.  I know that VMWare will grow into different files and will write snapshots out which could be problematic when using Copy-On-Write.  For QEMU the file is left open for the VMs existance so there is a potential problem in the write after the VM is shutdown, but I would see slow I/O after a VM is shutdown not being an issue.  What pitfalls would I be avoiding by performing this step for QEMU.    Additionally: I have assumed that the image is raw for this question.  Is there a possible stability issue as qcow2 already has copy-on write. Showing that $f$ is identically $0$ on $\mathbb{D}$ Here is the question: Let $f:\mathbb{D}\rightarrow\mathbb{C}$ be an analytic function.  Suppose that there exists $\epsilon&gt;0$ such that for every $\theta$, $|\theta|&lt;\epsilon$, and $\lim_{z\rightarrow e^{i\theta}}f(z)=0$.  Prove that $f$ is identically $0$ on $\mathbb{D}$. My thoughts:  Well, honestly, I am quite stumped here.  I was thinking I could let $f$ be analytic in some other region (can I even do this?), say the lower half plane and suppose $\lim_{z\rightarrow x}f(z)=0$ whenever $-1\leq x\leq1$, by assumption.  Maybe then I could show that $f$ is identically $0$ on the bigger region, and then consider $f$ on the intersection of those two regions, and then ultimately making my way towards using the uniqueness theorem to show what I want... but I am quite stuck on how to do that... any thoughts, suggestions, etc. are greatly appreciated!  Thank you. How do I combine two lists into a dictionary in Python? Ubuntu 20.04 interface font too small after restart, even with high scaling factor Can I watch the progress of a `sync` operation? 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Cook's blog: )  Why doesn't it take, say, four uniforms? Or five? Or...? When I try to connect to servers or join up on lan worlds in Minecraft it says "Failed to Login : Invalid session (Try restarting your game)". Multiplayer used to work fine but now keeps coming up with this error. Can anybody help? What should be in the sources.list for Kali Rolling Linux? This is exact content from my sources.list:  #  # deb cdrom:[Debian GNU/Linux 2016.1 _Kali-rolling_ - Official Snapshot amd64 LIVE/INSTALL Binary 20160830-11:29]/ kali-rolling contrib main non-free #deb cdrom:[Debian GNU/Linux 2016.1 _Kali-rolling_ - Official Snapshot amd64 LIVE/INSTALL Binary 20160830-11:29]/ kali-rolling contrib main non-free   I couldn't install the Synaptic package manager and was told to modify sources.list.  I googled a lot and added some repos into it and ran update and upgrade command only to see Kali crash... I had to recover it.  Please mention the exact content that should be there to ensure that Kali Linux works. How to hide a folder in sdcard in android Movie where a guy is sent to a sandy planet where time moves really fast but slow to the outside observer All I remember is the guy was sent to a planet to test something or he did something illegal, and time moved really fast on the planet but slow to the outside world. He had to fix something to leave the planet I think. His dad was also dying and he checked how many days he had left every day, but in the end his dad didn't actually die as time was fast. It took place on a sandy planet. Change Proxy Settings In Ubuntu I want to use the Ubuntu Software Center to install software, but I cannot download them.  How can I give my proxy settings in Ubuntu terminal (just like we use cmd in Windows to choose IE proxy settings)? Parse error in sudoers file Let $m \in \mathbb{Z^+} , n \in \mathbb{Z^+}$ and let $d=\gcd(m,n)$. 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