nullpointerexception

问题 A web service returns a huge XML and I need to access deeply nested fields of it. For example: return wsObject.getFoo().getBar().getBaz().getInt() The problem is that getFoo() , getBar() , getBaz() may all return null . However, if I check for null in all cases, the code becomes very verbose and hard to read. Moreover, I may miss the checks for some of the fields. if (wsObject.getFoo() == null) return -1; if (wsObject.getFoo().getBar() == null) return -1; // maybe also do something with

问题 This question already has answers here : What is a NullPointerException, and how do I fix it? (12 answers) Closed 3 years ago . The question is simple. I have created a class named "handler" and within its constructor it contains a parameter for "c", a JComponent. When this constructor is called on a certain JComponent, preferably a JPanel, an oval is drawn at the mouse's current coordinates. This is the source code: import javax.swing.*; import java.awt.*; import java.awt.event.MouseEvent;

问题 This question already has answers here : System.out is declared as static final and initialized with null? (2 answers) Closed 2 years ago . In the documentation code of java "out" is an object of PrintStream class which is initialized in the System class of package lang.This object "out" is initialized to null.So why does'nt the code throws a null pointer exception whenever the line System.out.println(...); is used 回答1: It is the field declaration. Look at the initializeSystemClass() static

问题 I I have created an app that was working perfectly before I introduces ViewFlipper into it. I really need to use this, but now I'm stuck or this exception. frag_home.java public class Frag_home extends Fragment { private String mParam1; private String mParam2; Animation fade_in, fade_out; ViewFlipper viewFlipper; private OnFragmentInteractionListener mListener; public Frag_home() { // Required empty public constructor } // TODO: Rename and change types and number of parameters public static

问题 I want to call an activity from Dialogfragment, I have attached the code and logcat below for your reference on what I have tried.Kindly provide me your knowledge on it. Thank you. Intent intent = new Intent(getActivity(), LinkActivity.class); getActivity().startActivityForResult(intent, 0); Logcat: 02-12 13:47:17.345: E/AndroidRuntime(670): FATAL EXCEPTION: main 02-12 13:47:17.345: E/AndroidRuntime(670): java.lang.NullPointerException 02-12 13:47:17.345: E/AndroidRuntime(670): at android

问题 Okay full code now: DBOpenHelper: public class DBOpenHelper extends SQLiteOpenHelper { private SQLiteDatabase mDatabase; private static final int DATABASE_VERSION = 1; private static String DATABASE_NAME = "RTDB"; private static final String DB_TABLE_NAME1 = "playertable"; private static final String DB_TABLE_NAME2 = "itemtable"; private static final String DB_CREATE_TABLE_PT = "CREATE TABLE IF NOT EXISTS" + DB_TABLE_NAME1 + " (" + "ID INT(1) NOT NULL ," + "Name VARCHAR(30) ," + "HP INT(3) ,"

问题 I've been trying to fix this for the past 2 hours. Tried a lot of things. The Fragment seems to be passing a null context to my Adapter. I have tried to initialize the Context variable in onCreate and onCreateView and onActivityCreated. Same result. Here is my fragment: public class ActiveBookingsFragment extends Fragment { Context con; ArrayList<Booking> bookings; ListView activeBookings_lv; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); }

问题 There are 4 Spinnners: resiko,untung1,untung2,untung3 The user picks resiko spinner first to proceed and the app will show which Spinner will be visible (untung1/untung2/untung3) strings.xml <string-array name="spinner_resiko_string"> <item>--Pilih--</item> <item>Sangat Rendah</item> <item>Rendah</item> <item>Sedang</item> <item>Tinggi</item> </string-array> <string-array name="spinner_return_string"> <item>--Pilih--</item> <item>Rendah</item> </string-array> <string-array name="spinner

问题 There are 4 Spinnners: resiko,untung1,untung2,untung3 The user picks resiko spinner first to proceed and the app will show which Spinner will be visible (untung1/untung2/untung3) strings.xml <string-array name="spinner_resiko_string"> <item>--Pilih--</item> <item>Sangat Rendah</item> <item>Rendah</item> <item>Sedang</item> <item>Tinggi</item> </string-array> <string-array name="spinner_return_string"> <item>--Pilih--</item> <item>Rendah</item> </string-array> <string-array name="spinner

问题 This post is a Community Wiki . Edit existing answers to improve this post. It is not currently accepting new answers. 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 the following code where you