nullpointerexception

问题 I'm developing an app using Primefaces tag library. So far I've copied some examples from their official website and all seems to work except for anything that uses the RequestContext.getCurrentInstance() method. It either returns null every time, causing Tomcat to throw a NullPointer exception or hangs forever, never returning anything. Here's my code (the case where it hangs): GlobalCounterBean.java package org.primefaces.examples.view; import java.io.Serializable; import org.primefaces

问题 It seems like it is not a good idea to catch a nullpointerexception. If that's the case, why is it thrown by methods? Should it just be caught with Exception? Also, if I encounter a parameter which is null (can either be primitive type like string or a class with fields), how should I handle it? (assumingly not throw npe)? Thanks 回答1: A nullpointerexception usually indicates a programmer error. You won't catch a null pointer exception if you don't expect such a programmer error. For instance,

问题 all. I've searched, but can't find anything that helps me fix this problem. My app quits almost immediately on launch due to a NullPointerException. I suspect maybe the problem is that I'm using a drawable image (ImageView) rather than a button (View) as the thing you click on. Thanks for any help. This has been driving me bonkers for hours! Code is as follows: package com.example.imageswitchermk2; import android.app.Activity; import android.os.Bundle; import android.view.View; import android

问题 This question already has answers here : What is a NullPointerException, and how do I fix it? (12 answers) Closed 8 months ago . I'm having problems with a NullPointerException. I was doing the debugging and the element is not null, I have the problem in the first IF and I can not see what the problem is. I thought that happened when the state of the element was null, but I tried to fix it and it did not work // Update: The problem is when I Check the status for (Items item : master.getItems(

问题 This question already has answers here : What is a NullPointerException, and how do I fix it? (12 answers) Closed last year . I am having a following error: Can anyone solve this Debugger: AdroidRuntime: FATAL EXCEPTION: main Process: com.example.avishek.wifidirect, PID: 8053 java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.avishek.wifidirect/com.example.avishek.wifidirect.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android

问题 I've been getting an NPE whenever i try to access my array. Even calling for the .length attribute gives me an NPE. Any help would be appreciated. Here is my constructor and the method that keeps failing. public SkierList() { Skier[] skiers= new Skier[INITIAL_CAP]; for (int i = 0; i < skiers.length;i++){ skiers[i] = new Skier(""); } int count = 0; } public void add(Skier newSkier) { if (this.size() < skiers.length) { skiers[count] = new Skier(newSkier.getName(), newSkier.getLevel()); count++;

问题 I have an abstract class that declares a number of object references, specifically a JLabel. I have two classes that both extend that class. One of the children instantiates the JLabel and calls a couple of its methods. That classes sibling attempts to call the setText method on the JLabel and I get a NullPointerException(The sibling that instantiates it is called before the other.) I had thought that all children refer to the same object in memory and would thus modify the same object but

问题 I'm making a layout with a LinearLayout. This layout will have another layout inflated inside. Currently, I'm getting problems (nullexceptions) with that. My inflating code is the next: private void addLayoutInvoices() { LinearLayout ll_invoices = new LinearLayout(getActivity()); ll_invoices.setGravity(Gravity.CENTER); ll_invoices.setOrientation(LinearLayout.VERTICAL); LinearLayout.LayoutParams llp = new LinearLayout.LayoutParams(LinearLayout.LayoutParams.MATCH_PARENT, LinearLayout

问题 This question already has answers here : What is a NullPointerException, and how do I fix it? (12 answers) Closed 3 years ago . I have 3 activity that display listview and it has an image to display icon and textview to display data. I want to make an adapter that can use general for my listview on these activity. But when I run my app, the logcat show me null pointer exception. 08-25 22:43:04.090 28942-28942/com.example.xiaoking.dilibus A/art: art/runtime/thread.cc:1113] Throwing new

问题 This question already has answers here : What is a NullPointerException, and how do I fix it? (12 answers) Closed last year . I'm trying to use SharedPreferences in a non activity class from onResume() in an activity but I'm getting a NullPointerException on the context . For some reason I cannot get the context in onResume() . Not sure if I'm missing something, but any help would be appreciated. onResume() Method in my activity @Override protected void onResume() { super.onResume(); // The