I want to display data on the profile page stored in firebase, but when I try to display text with only numbers, and run the application and then go to the profile page for the user, it gives an error like this:  E/AndroidRuntime: FATAL EXCEPTION: main Process: com.example.drheartbeatmonitor, PID: 3415 java.lang.RuntimeException: Unable to start activity  ComponentInfo{com.example.drheartbeatmonitor/com.example.drheartbeatmonitor.Profile}:  java.lang.NullPointerException: Attempt to invoke virtual method 'void  android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3449)     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3601)     at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:85)     at  android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)     at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2066)     at android.os.Handler.dispatchMessage(Handler.java:106)     at android.os.Looper.loop(Looper.java:223)     at android.app.ActivityThread.main(ActivityThread.java:7656)     at java.lang.reflect.Method.invoke(Native Method)     at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592)     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:947)  Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void  android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference     at com.example.drheartbeatmonitor.Profile.onCreate(Profile.java:67)     at android.app.Activity.performCreate(Activity.java:8000)     at android.app.Activity.performCreate(Activity.java:7984)     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1309)     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3422)     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3601)      at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:85)      at  android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)      at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)      at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2066)      at android.os.Handler.dispatchMessage(Handler.java:106)      at android.os.Looper.loop(Looper.java:223)      at android.app.ActivityThread.main(ActivityThread.java:7656)      at java.lang.reflect.Method.invoke(Native Method)      at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592)      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:947)    This is my code : 1.login page: String ID_Device = snapshot.child(Username).child(&quot;ID_Device&quot;).getValue().toString(); String HealthInsure = snapshot.child(Username).child(&quot;Health Insure&quot;).getValue().toString(); intent.putExtra(&quot;ID_Device&quot;, ID_Device); intent.putExtra(&quot;Health Insure&quot;, HealthInsure);  2. profile page String ID_Device = Patient.ID_Device; String HealthInsure = Patient.HealthInsure; health_insure.setText(HealthInsure); ID_Dev.setText(ID_Device);
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?
When are attributive nouns plural? Sorry for the title, it is not very evident and intuitive but I really do not how to tell it better...  Well, you know, several times, or better, many times, we use this form:  If I want to say:      "development of special weapons was   the first point in Hitler's   program..."   I will say this (a better form):      "special weapon development was..."   OK...  is it      "special weapon development"   or      "special weapons development" (note   the plural...)   what's the grammar rule in order to understand how to use this very used form? Dirac Delta or Dirac delta function? Why isn't $V= V_1 + V_2$? $V=V_a - V_c = V_a - V_b + V_b - V_c$, $V_a - V_b= V_1$ and $V_b - V_c = V_2$ Doesn't that prove that $V = V_1 + V_2$? Regardless of $V_3$, If i'm wrong , is there a way to obtain $V$ in terms of $V_1$, $V_2$ and $V_3$ How can I mine redstone ore? I found redstone ore in Survival Mode (Minecraft Pocket Edition) and tried to use all five tools to collect it. It took about a minute or two to break, but I couldn't collect anything from it once broken.  How do I mine redstone ore? This question isn't so much about how to achieve the effect of making a scene look like it's modelled in miniature, but why tilting the focal plane creates the effect. What is it about photographing miniatures that makes them look like miniatures, and how is this replicated by tilting the focal plane?  I can understand how when photographing a model of a scene, you have a much higher magnification, which leads to a shallower depth of field compared to when capturing the real-sized scene, but how does tilting the focal plane help? Is it just that you have the focal plane tilted relative to the plane that most of your subject is on, so that you can achieve a narrower depth of field for the focal length and aperture, or is there more to it than that? Nonzero $f \in C([0, 1])$ for which $\int_0^1 f(x)x^n dx = 0$ for all $n$ Possible Duplicate:           What book would you recommend for an undergraduate wanting to learn the basics of topology? I've come across several books that claim to give an introduction to the subject, but I wasn't sure which one(s) to pick.  Here are some of the books I came across:   Introduction to Topology - Bert Mendelson Basic Topology - M.A. Armstrong First Concepts of Topology - William G. Chinn Topology Without Tears - Sidney A. Morris Topology - James Munkres   They don't go over the exact same topics, some are more in-depth than others, some seem to target slightly different audiences etc. What would be right for me (not necessarily from that list)? To give some more background, I want to learn topology because I feel it will be somewhat helpful in the field of Computer Vision. Solving "MySQL server has gone away", mysql error 2006 I was thinking of the noted 1980 paper by Sidney Coleman and Frank de Luccia--"Gravitational effects of and on vacuum decay"-- about metastable vacuum states that could tunnel to a lower energy "true vacuum" with catastrophic results. I suspect the answer is that if our vacuum is a false one, we wouldn't "see" the true one til it hit us. Electric charge is lorentz invariant I know that electric charge is lorentz invariant quantity and I can easily think of experiment to check that. Is a though experiment that can prove that also? A fleet of nine taxis is dispatched to three airports, in such a way that three go to airport A, five go to airport B and one goes to airport C.  If exactly three taxis are in need of repair. What is the probability that every airport receives one of the taxis requiring repairs.  My method was total number of ways is (9!)/(3!*5!*1!)= 504 (this is correct)  Now you have three groups and of every group one position is already filled. So: ....R, ..R, R So the numbers of ways to distribute the rest is: (6!)/(2!*4!)=15  But according to answer model of my professor, it should be 90. So I assume he says the number of ways of distrubiting these 3 broken cabs over the 3 spots is 3*2*1. But to me this seems wrong? The broken taxis don't differ so R(1)R(2)R(3) is same as R(2)R(1)R(3). If you standing at the airport A, it doesn't matter which of the broken cabs stands there? Change Gmail account to make in-app purchase? how to disable system apps without root? I'm pretty sure the answer to this should be obvious - even to me ...  It's been a while I've been reading and attempting to construct simple electronic circuits. The supply almost always is either through a battery/cell, or AC duly rectified to DC.   I have the impression electronic circuits rarely ever work off an AC supply.    Is this impression correct? If yes, why is an electronic circuit rarely (if ever) powered/biased using straight AC? Let $\Omega$ be an open subset in $\mathbb{C}$. Let $\{f_n\}$ be a sequence of holomorphic functions on $\Omega$ such that $f_n\to f$ pointwise and converges uniformly on any compact subset $K\subseteq \Omega$. Then by Cauchy Theorem and Morera Theorem, $f$ is holomorphic. Let $f_n$ and $f'$ be the derivatives of $f_n$ and $f$ respectively. Prove that $f_n'\to f'$ uniformly on any compact subset $K\subseteq \Omega$.   How to prove? I'm trying to create a signature and date line in a document.  I need the date line to always be in the same spot on the page no matter what name is under the signature line, such as:  ----------------------   ---------------------- Representative           Date  ----------------------   ---------------------- Program Manager          Date   Here is the code I currently have:  \makebox[2.5in]{\hrulefill} \hspace {1.0in}\makebox[2.5in]{\hrulefill} \\ User Representative \makebox[2.5in][r]{Date} \\  \vspace{.2in} \makebox[2.5in]{\hrulefill} \hspace {1.0in}\makebox[2.5in]{\hrulefill} \\ Program Manager \makebox[2.5in][r]{Date} \   I want to be able to change the names, such as change Program Manager to Joe Foo and have the word 'Date' stay in the exact place.  Any help would be greatly appreciated.  I'm still a newbie at TeX so please forgive my ignorance. How to encrypt a file or directory in Linux? What's the most popular command to do such things as encrypting a file or directory in terminal in Linux? Python interpreter error, x takes no arguments (1 given) I'm writing my final report in LaTeX for my bachelor's degree. I'm aiming at having a document similar to the .doc template used normally.   I want to have my customs headers and footers applied on pages when I'm starting a new chapter.  I'm using documentclass report with fancyhdr and lastpage packages.  My headers are defined like this:  \lhead{\myTitle} \rhead{\today} \cfoot{\thepage\ of \pageref{LastPage}}   My chapters are created using standard \chapter{title} macro.  On pages with new chapters, the only headers/footers I see is the standard page number at the bottom.  What should I do?  EDIT: I've finally gone with Peter Breitfeld's solution. I'Ve gone a step further and created my own chapter command:  \newcommand{\myChapter}[1]{     \chapter{#1}     \thispagestyle{fancy} }   Thanks for the help! Is 'hair' singular or plural? When one says I was washing my hair, is it singular or plural? What is the singular for hair?