I am a new developer in java, and i am making a small app i am getting error about null object reference Here Is My Logcat File: E/AndroidRuntime: FATAL EXCEPTION: main Process: com.example.torque, PID: 24687 java.lang.IllegalStateException: Could not execute method for android:onClick at androidx.appcompat.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:414) at android.view.View.performClick(View.java:5610) at android.view.View$PerformClick.run(View.java:22265) at android.os.Handler.handleCallback(Handler.java:751) at android.os.Handler.dispatchMessage(Handler.java:95) at android.os.Looper.loop(Looper.java:154) at android.app.ActivityThread.main(ActivityThread.java:6077) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:866) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:756) Caused by: java.lang.reflect.InvocationTargetException at java.lang.reflect.Method.invoke(Native Method) at androidx.appcompat.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:409) at android.view.View.performClick(View.java:5610)  at android.view.View$PerformClick.run(View.java:22265)  at android.os.Handler.handleCallback(Handler.java:751)  at android.os.Handler.dispatchMessage(Handler.java:95)  at android.os.Looper.loop(Looper.java:154)  at android.app.ActivityThread.main(ActivityThread.java:6077)  at java.lang.reflect.Method.invoke(Native Method)  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:866)  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:756)  Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void androidx.drawerlayout.widget.DrawerLayout.openDrawer(int)' on a null object reference at com.example.torque.NavDrawermenu.openDrawers(NavDrawermenu.java:48) at com.example.torque.ProfileActivity.ClickMenu(ProfileActivity.java:19) its showing errors in my two files Profileactivity and nav drawer activity Here is Navdrawer.java Code I Think the error is in the openDrawer function: public void ClickMenu(View view) {     openDrawer(drawerLayout); }  public static void openDrawer( DrawerLayout drawerLayout) { drawerLayout.openDrawer(GravityCompat.START); }
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?
Users below 15 reputation can't effectively vote. It says:     Votes cast by those with less than 15 reputation are recorded, but do not change the publicly displayed post score   Does it mean that they will take effect after I reach 15 reputation or because they were cast before, they're recorded but ignored? Trigger Setup Wizard at next boot using command-line I am looking for a way to use ADB to trigger Setup Wizard at next boot. I know I can run the following command and get it to pop up. However, I can't figure out what triggers it to start at boot.  adb shell am start -a android.intent.action.MAIN -n com.google.android.setupwizard/.SetupWizardTestActivity   The phone I am currently using is stock and I would like to keep it that way.   I've read the  question: How can I ensure my Samsung Series 7 is actually using the Radeon switchable graphics? I have a Samsung Series 7 with the Radeon 6750M switchable graphics. The ATI software lets you force programs to use the dedicated card. However, I'm not convinced it is actually ever using it, as the frame rates on some non-taxing games (Portal, TF2) are merely OK. To make matters worse, it looks like the ATI Catalyst Control has vanished from my laptop. To make it even worse, you can't download the driver and ATI CCC from ATI's site, you need to download it from Samsung, and the ZIP they provide is corrupted.   How can I ensure my Samsung Series 7 is actually using the Radeon switchable graphics? Insert list of figures in the table of contents Is it possible to create a list of all the figures at the end of a document (this I can do) and make it appear in the table of contents?  So in the the table of content there will be a line saying List of figures ... 19 for example? How do I hide an element when printing a web page? I have a link on my webpage to print the webpage. However, the link is also visible in the printout itself.  Is there javascript or HTML code which would hide the link button when I click the print link?  Example:   "Good Evening"  Print (click Here To Print)   I want to hide this "Print" label when it prints the text "Good Evening". The "Print" label should not show on the printout itself. How to proof that $\forall n \ge 1: \sum_{i=1}^n (i(i+1))^{-1} = n(n+1)^{-1}$ using mathematical induction So for a better presentation:   I need to prove this using mathematical induction, so i started with a base of $n=1$  Since $i$ starts at $i = 1$ I got this:  $$\frac{1}{i(i+1)} = \frac{n}{n+1}$$ $$\frac{1}{2} = \frac{1}{2}$$  So since this was true I went to the induction part: I chose $n = k$ and assumed this was true:  $$\frac{1}{i(i+1)} = \frac{n}{n+1}$$ $$\frac{1}{i(i+1)} = \frac{k}{k+1}$$  but I got stuck here since I didn't know if I needed to increment $i$ or not and because I didn't know if I needed to add the summation symbol or not and needed to do a few things with it. Word for someone that always has to be right Is there a word for someone that always has to be right? The person gets angry if they are not. How to make the taskbar blink my application like Messenger does when a new message arrive? Is there an API call in .NET or a native DLL that I can use to create similar behaviour as Windows Live Messenger when a response comes from someone I chat with? Show group of order $4n + 2$ has a subgroup of index 2. Let $n$ be a positive integer. Show that any group of order $4n + 2$ has a subgroup of index 2. (Hint: Use left regular representation and Cauchy's Theorem to get an odd permutation.)  I can easily observe that $\vert G \vert = 2(2n + 1)$ so $2 \mid \vert G \vert$ and 2 is prime. We have satisfied the hypothesis of Cauchy's Theorem so we can say $G$ contains an element of order 2.  This is where I am stuck  I am confused about how the left regular representation relates to the group. So my understanding at this point is that every group is isomorphic to a subgroup of some symmetric group. My question: is the left regular representation $\varphi : G \to S_G$ an isomorphism? where $G \cong S_G$ or is $S_G$ the same thing as $S_{\vert G \vert}$ and $\varphi$ is only an injection? I'm using Dummit and Foote for definitions.  I saw an argument online that said that since we have an element of order 2, there is a $\sigma \in S_G$ of order 2, but it is a product of $2n + 1$ disjoint 2-cycles. I don't understand how they could claim this and tried working it out on my own but didn't get there. -- They then went on to use the parity mapping $\varepsilon : S_G \to \{\pm1\}$ and since we have an odd permutation $\sigma$, we have $[S_G:\text{ker }\varepsilon] = 2$. I understood their computation but not how that directly shows that $G$ has a subgroup of order 2? unless $G \cong S_G$ because of how left regular representation is defined. (but again, I'm not understanding that concept very well yet.)  So, to be clear about my questions:   What is meant by left regular representation, is it an isomorphism or just an injection? and how would it be used here. If it is an isomorphism, the argument online starts to make more sense, but how can they say that since $\sigma$ is even, it is made up of $2n + 1$ disjoint transpositions? If you have a full, proof, I'd appreciate it, but good hints are just as good!   Thanks you! Sphere rolling up a ramp In this question, I did energy conservation, with the states being the initial one and the one where it is at the top , and I got $$ .5 I w^2 + .5 mv^2 = mgh$$ However, in  the answer key they have done, $$ .5 mv^2 + .5 Iw^2 = .5 Iw^2 + mgh$$ Now why would the k.e be turned to p.e but not the rolling energy?? How can I efficiently recover a permanently deleted folder at once? I played 1st and 2nd edition AD&amp;D a lot back in the day. But when 3rd edition came out, I dropped out of the hobby. Partly I just couldn't be bothered to re-learn the rules. The conversion systems, previews and material for 3rd edition I was seeing in Dragon and Dungeon magazines made it look like a very major change.  I recently picked up the new 5th edition starter set on a whim. Obviously the starter set rules are very stripped down in comparison to the full rules, but nevertheless, I was amazed by how comfortable and familiar the system felt. The only thing that felt like a truly radical change was the way things like thief skills and the like were now handled with a d20 instead of a percentage system.  There's plenty of information online (and here) comparing editions of the game in an incremental manner. But I'd be interested in a breakdown of how 2nd and 5th edition compare directly, specifically looking at whether there are broad areas of similarity. How to sort strings in JavaScript I have a list of objects I wish to sort based on a field attr of type string. I tried using -  list.sort(function (a, b) {     return a.attr - b.attr })   but found that - doesn't appear to work with strings in JavaScript. How can I sort a list of objects based on an attribute with type string? How can I do a full shutdown of windows 10 without logging in? I have a computer with both Windows 10 and Ubuntu 17.04 installed on it. I can't log in to Windows, and think it's a problem with the registry. Luckily, there is a way to restore the registry from backup from Ubuntu, but you have to be able to modify files on the Windows partition. Right now, I can't write to the NTFS partition because Windows didn't do a full shutdown.  How can I force windows 10 to do a full shutdown without being able to log in? Can a particle be physically observed inside a quantum barrier? I understand that if a particle approaches a finite potential barrier of height $V_0$ with energy $E &lt; V_0$, there is still a finite probability of finding the particle on the other side of the barrier due to quantum tunneling.  My question is, since the wavefunction is nonzero inside the barrier region, is it possible to actually make a position measurement and locate a particle inside the barrier?  I mean, if we can say that "there is a nonzero probability that the particle is inside the barrier", surely this would suggest we can do so?  If not, why not? Am I understanding the whole wavefunction/probability distribution thing right? Can I use Minecraft PC textures and worlds in Pocket Edition? Now that I've discovered that I can host a , I'd like to know if is it possible to use the textures and maps of the PC version for the pocket version.  I'm planning to visit Peru and Machu Picchu. It would be really cool to entice them for the voyage by letting them play a  in their favourite video game. Unfortunately, this God of Deceit world looks really sophisticated. I don't believe the Pocket Edition would be able to play it. Function whose inverse is also its derivative? Cannot change backlight brightness Ubuntu 14.04 This morning I found that I cannot change the brightness of my Dell XPs 13 laptop's display anymore. I tried the following to change the brightness   Use keyboard brightness keys Run the commands shown below Boot with kernel option acpi_backlight=vendor. This resulted in a dell_something folder being present in the /sys/class/backlight folder. Changing the brightness file in that folder does not help. Add 'intel_backlight' to xorg.conf Set "load legacy option ROM" BIOS option to enabled and "secure boot" to disabled Boot with kernel option i915.disable-pch_pwm=0 Boot from a fresh Ubuntu 12.04 USB stick installation. I can still not control the brightness. This is strange as the laptop came preinstalled with 12.04. Maybe this a hardware problem? Install latest intel video driver   Any ideas why this broke suddendly? I've upgraded from 12.04 to 14.04 in April and till yesterday the brightness keys were working fine.  Thanks!  echo 100 &gt; /sys/class/backlight/intel_backlight/brightness echo 100 &gt; /sys/class/backlight/acpi_video0/brightness Why is it wrong to serial voteup someone you like his answers?  Sometimes I just came to stackoverflow to read certain people answers(there are 4 guys currently) I have their profile bookmarked in my browser and in my free time at office I go to their profile and read their answers and learn a lot from them, but because I'm afraid to be a serial voter, I dont voteup them.   I think there is nothing wrong with that, if there is, please let me know. how to show image in table cell through json parsing