nullpointerexception

问题 Android Studio 3.6 in app/build.gradle: android { viewBinding.enabled = true Here my xml: <?xml version="1.0" encoding="utf-8"?> <androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:app="http://schemas.android.com/apk/res-auto" android:layout_width="match_parent" android:layout_height="match_parent"> <androidx.constraintlayout.widget.ConstraintLayout android:id="@+id/bluetoothBottonMainContainer" android:layout_width="0dp" android

问题 This question's answers are a community effort . Edit existing answers to improve this post. It is not currently accepting new answers or interactions. 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? 回答1: When you declare a reference variable (i.e. an object) you are really creating a pointer to an object. Consider

问题 This question already has answers here : What is a NullPointerException, and how do I fix it? (12 answers) Closed 2 years ago . I got a problem while trying to search a specific Java object in a list. Actually i got the search function i want working for another Java class. Now i tried it for a different one but instead of returning a list of results i get a NullPointerException. This is how my function looks: public static List<Customer> searchByEverything(String keyword){ List<Customer>

问题 I have the following scala code which half machine-generated and half modified by hand. I am getting a null pointer exception, I think I do not override a method and it causes the error. The code is kind of large so I can't post the whole code here but I put the repo URL at the bottom. I know the question is too general but all I am looking for is being able to run the code with minimal modification. Thank you. object tiny_circular_simple_implicit { val tiny_circular_simple_loaded = true;;

问题 I have the following scala code which half machine-generated and half modified by hand. I am getting a null pointer exception, I think I do not override a method and it causes the error. The code is kind of large so I can't post the whole code here but I put the repo URL at the bottom. I know the question is too general but all I am looking for is being able to run the code with minimal modification. Thank you. object tiny_circular_simple_implicit { val tiny_circular_simple_loaded = true;;

问题 I have a service class that is being proxied by Spring, like so: @Service @Transactional open class MyService { ... } If I remove the open modifier, Spring complains that it needs to proxy the class to apply the @Transactional annotation tweaks. However, this is causing issues when calling a function on the proxied service, which attempts to access a variable: @Service @Transactional open class MyService { protected val internalVariable = ... fun doWork() { internalVariable.execute() //

问题 I have a service class that is being proxied by Spring, like so: @Service @Transactional open class MyService { ... } If I remove the open modifier, Spring complains that it needs to proxy the class to apply the @Transactional annotation tweaks. However, this is causing issues when calling a function on the proxied service, which attempts to access a variable: @Service @Transactional open class MyService { protected val internalVariable = ... fun doWork() { internalVariable.execute() //

问题 Whenever I assign an android:onClick attribute to an AutoCompleteTextView, my application immediately crashes upon loading the activity. I've tested AutoCompleteTextView without assigning an onClick method and it seems to work fine, as does assigning onClick to other views (including EditText, Spinners, TextViews, Buttons and ImageButtons). I've managed to narrow down the error to specifically to line 24 (setContentView(R.layout.activity_main)). Can anyone shed some light on this?

问题 I am creating an Android app and I am trying to use a SettingsManager class to read and write preferences. To use this, I have to pass context to this SettingsManager in order to use the SharedPreferences API. However, my code keeps giving me a NullPointerException . Can anyone tell me why? Main.java @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_status); mNavigationDrawerFragment = (NavigationDrawerFragment)

问题 I'm getting Exception in thread "main" java.lang.NullPointerException at java.io.FileOutputStream.<init>(FileOutputStream.java:201) at java.io.FileOutputStream.<init>(FileOutputStream.java:99) at lib.Entry.serialize(Entry.java:17) at main.Main.main(Main.java:8) Where Entry.java:17 is stream.writeObject(this); (see below) Entry.java package lib; import java.io.*; public class Entry { // Superclass. String filename; // Set below. String name; // Set by the subclass. public void main() { this