nullpointerexception

问题 I'm new here. I followed a tutorial to create a card list using RecyclerView. The app crashes at launch and the log says: java.lang.RuntimeException: Unable to start activity ComponentInfo{com.wc.gap.worldcupfixture/com.wc.gap.worldcupfixture.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.widget.RecyclerView.setHasFixedSize(boolean)' on a null object reference Caused by: java.lang.NullPointerException: Attempt to invoke virtual method

问题 I just added Google Play Service Library to my project and when I am making a modification in one of my project files I am keep getting an error dialog from eclipse: 'Running Android Lint' has encountered a problem. Failed. So, I enabled Error Log (Window -> Show View -> Error Log) tab and I found a warning and an error line: Error: Failed: com.android.ide.eclipse.adt java.lang.NullPointerException at com.android.tools.lint.checks.ApiDetector$ApiVisitor.checkField(ApiDetector.java:1416) at

问题 I have an address object that I want to create an equals method for. I could have made this quite simple by doing something like the following (shortened a bit): public boolean equals(Object obj) { if (this == obj) return true; if (obj == null) return false; if (getClass() != obj.getClass()) return false; Address other = (Address) obj; return this.getStreet().equals(other.getStreet()) && this.getStreetNumber().equals(other.getStreetNumber()) && this.getStreetLetter().equals(other

问题 I have been searching for 3 or 4 days about a solution on this. I have tried: Null Pointer exception in using support library share action provider or why MenuItemCompat.getActionProvider returns null? and some others but still I get null on ShareActionProvider. I am pretty new on developing android apps so I really need some help. My xml menu file is: <menu xmlns:android="http://schemas.android.com/apk/res/android" xmlns:app="http://schemas.android.com/apk/res-auto"> <item android:id="@+id

问题 I have been searching for 3 or 4 days about a solution on this. I have tried: Null Pointer exception in using support library share action provider or why MenuItemCompat.getActionProvider returns null? and some others but still I get null on ShareActionProvider. I am pretty new on developing android apps so I really need some help. My xml menu file is: <menu xmlns:android="http://schemas.android.com/apk/res/android" xmlns:app="http://schemas.android.com/apk/res-auto"> <item android:id="@+id

问题 Every JavaFX application I've run throws two NullPointerExceptions. They don't prevent or even affect the execution of the projects, and I can only see them if I run my applications in debug mode. I'm even having this issue with the HelloWorld sample from Oracle and this minimal program: public class JavaFXTSample extends Application { @Override public void start(Stage primaryStage) throws Exception { StackPane iAmRoot = new StackPane(); Scene scene = new Scene(iAmRoot, 300, 250);

问题 I just downloaded the GlassFish 5.0 archive - Full Platform, unzipped it, I run it through the command line. asadmin start-domain problem: Exception in thread "main" java.lang.NullPointerException at com.sun.enterprise.module.common_impl.AbstractModulesRegistryImpl.initializeServiceLocator(AbstractModulesRegistryImpl.java:152) at com.sun.enterprise.module.common_impl.AbstractModulesRegistryImpl.newServiceLocator(AbstractModulesRegistryImpl.java:144) at com.sun.enterprise.module.common_impl

问题 Im getting null pointer exception in unbindDrawables where im Removing callbacks on all the background drawables. protected void onDestroy() { super.onDestroy(); unbindDrawables(findViewById(R.id.top_layout)); Runtime.getRuntime().gc(); } private void unbindDrawables(View view) { if (view.getBackground() != null) { view.getBackground().setCallback(null); } if (view instanceof ViewGroup) { for (int i = 0; i < ((ViewGroup) view).getChildCount(); i++) { unbindDrawables(((ViewGroup) view)

问题 I have this code: package tests; import java.util.Hashtable; public class Tests { public static void main(String[] args) { Hashtable<String, Boolean> modifiedItems = new Hashtable<String, Boolean>(); System.out.println("TEST 1"); System.out.println(modifiedItems.get("item1")); // Prints null System.out.println("TEST 2"); System.out.println(modifiedItems.get("item1") == null); // Prints true System.out.println("TEST 3"); System.out.println(Boolean.valueOf(null)); // Prints false System.out

问题 This question already has answers here : What is a NullPointerException, and how do I fix it? (12 answers) Closed 6 years ago . I'm currently attempting to create a tic-tac-toe game in java as a college project. So far all I've done is created the skeleton code of a gameBoard method. I'm already running into an error saying : java.lang.NullPointerException at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) at sun