nullpointerexception

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

问题 A) Class Parent4{ private I18nUtils i18n; //-----------Here Nullpointerexception occur---------------- public Parent4(){ SetText(i18n.getText("HELLO"); } } B) Class Parent3 extends Parent4{ private I18nUtils i18n; } C) Class ParentParent2 extends Parent3{ private I18nUtils i18n; } D) Class Parent extends ParentParent2{ private I18nUtils i18n; } E) Class Child extends Parent{ protected method_name(){ //.......DO Something...... } } My Test Class: public testclass{ Class cls = Class.forName(

问题 I have a problem with an example. I get this error when I am listing Elements in an action, but I don't know why. I think that the bean wasn't created, because the error occurs when execute() action is called. Struts Problem Report: Struts has detected an unhandled exception: Messages: File: actions/ListingAction.java Line number: 26 Stacktraces: java.lang.NullPointerException actions.ListingAction.execute(ListingAction.java:26) sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) sun

问题 import java.util.function.Function; public class Playground { public static void main (String[] args) { Object o = null; System.out.println(o); Function<Object, String> toStringFunc = Object::toString; String s = toStringFunc.apply(o); System.out.println(s); } } This code will result in a NullPointerException being thrown, reported at the line containing toStringFunc.apply(o) . This is a trivial example, so it's easy to see that o == null , but how in general can we understand why this line

问题 This question already has answers here : What is a NullPointerException, and how do I fix it? (12 answers) Closed 16 days ago . Unable to fetch data from my database all permissions are public and dependencies included. I am trying to print data to logcat, receiving NullPointerException MainActivity.java import android.support.annotation.NonNull; import android.support.v7.app.AppCompatActivity; import android.os.Bundle; import android.util.Log; import com.google.firebase.database.DataSnapshot

问题 I've been struggling for no reason and i don't see why. Here is my java code : public class SousRubrique extends RelativeLayout { private View sousRubriqueView; private TextView titleTextView; public SousRubrique(Context context, AttributeSet attrs, int defStyle) { super(context); init(context); } public SousRubrique(Context context, AttributeSet attrs) { super(context); init(context); } public SousRubrique(Context context) { super(context); init(context); } // Initialization methods public

问题 I want to separate my code in to smaller functions. But had an issue as driver was not available to all functions. So i declared it as a constant (or is there a better way of doing this ?) but in 3rd function it is failing on line : Select dropdown_finance_product = new Select(driver.findElement(By.xpath("//select[@id='ResultsNumber']"))); Here is the console message : Exception in thread "main" java.lang.NullPointerException at Scraping.scrapeit.fetch_urls(scrapeit.java:49) at Scraping

问题 I'm pretty new to Android and I'm trying to create an application that will score matches of the Vex Robotics Competition. I have a ViewPager with fragments for each team and i have a lot of buttons that increase and decrease numbers in EditTexts . I created an OnClickListener for each one. This code was working before I introduced SharedPreferences to carry values to the activity that calculates the score. Fragment Code (sorry, there's a lot of it): package com.bearsandthings

问题 I'm pretty new to Android and I'm trying to create an application that will score matches of the Vex Robotics Competition. I have a ViewPager with fragments for each team and i have a lot of buttons that increase and decrease numbers in EditTexts . I created an OnClickListener for each one. This code was working before I introduced SharedPreferences to carry values to the activity that calculates the score. Fragment Code (sorry, there's a lot of it): package com.bearsandthings

问题 I'm trying to understand DI, but my spring bean is not injected or created when I use the autowire and component annotations. Instead I get a nullpointer exception because my bean is null. Should I created it manually and in that case where? Where do you specify the order in which the beans are created, when several beans depend on each other? Here is my code: App.java package se.springtest; import se.springtest.Person; import org.springframework.core.io.ClassPathResource; import org