SQLiteOpenHelper: NullPointerException

Issue

I am trying to save data to SQLite database.

AddBook.java

    public class AddBook extends Activity {
        String myUrl = "";
        DownloadBook obj_Downloadbook;
        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            obj_Downloadbook = new DownloadBook(AddBook.this);//line26
    ...
    obj_Downloadbook.execute(myUrl);

This activity is calling DownloadBook.java class which extends AsyncTask. In DownloadBook.java class, I am retrieving html as string and saving to file. After saving, I am trying to record title and author into database

public class DownloadBook extends AsyncTask<String, Void, String> {
private Context context;
public DownloadBook(Context context) {
    this.context = context;
}
MyDatabase myDatabase=new MyDatabase(context);//line27
...
myDatabase.addBookInformation(title, author);

In order to manage SQLite database, I am using android-sqlite-asset-helper library. In library's github, it is written that: SQLiteAssetHelper is intended as a drop in alternative for the framework's SQLiteOpenHelper. MyDatabase.java

public class MyDatabase extends SQLiteAssetHelper {
   MyDatabase(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);//line21
        setForcedUpgradeVersion(3);
    }
   ...
   public void addBookInformation(String title, String author){
   ...

And this is giving following error:

03-24 03:13:37.248: E/AndroidRuntime(21237): Caused by:
java.lang.NullPointerException 03-24 03:13:37.248:
E/AndroidRuntime(21237):    at
com.readystatesoftware.sqliteasset.SQLiteAssetHelper.<init>(SQLiteAssetHelper.java:110)
03-24 03:13:37.248: E/AndroidRuntime(21237):    at
com.readystatesoftware.sqliteasset.SQLiteAssetHelper.<init>(SQLiteAssetHelper.java:130)
03-24 03:13:37.248: E/AndroidRuntime(21237):    at
com.joericharduz.akita.MyDatabase.<init>(MyDatabase.java:21) 03-24
03:13:37.248: E/AndroidRuntime(21237):  at
com.joericharduz.akita.DownloadBook.<init>(DownloadBook.java:27) 03-24
03:13:37.248: E/AndroidRuntime(21237):  at
com.joericharduz.akita.AddBook.onCreate(AddBook.java:26)

How to solve this problem?

Solution

Member variables are initialized before the constructor is run. So in here,

public class DownloadBook extends AsyncTask<String, Void, String> {
    private Context context;
    public DownloadBook(Context context) {
        this.context = context;
    }
    MyDatabase myDatabase=new MyDatabase(context);//line27

... myDatabase is initialized with a null context before the context is initialized in the constructor.

Move the new MyDatabase(context) initiazlization to the constructor.

Answered By - laalto