Question

I keep on getting null pointer exception while updating the table on this line-59
i.e

myDB.execSQL(updatequery);

Note: In Activity 1 the constructor has 3 edit-text fields where the 1st 2 fields has the values and 3rd one is kept as null.As soon as 2nd activity starts the 3rd field is updated in the same table.

I am inserting data in activity-1 like this

dba.createddb(data11, data22, null);

Following is my activity where I am updating the data

public class Activity2 extends Activity {

    EditText ed3;
    Button btn3;
     SQLiteDatabase myDB;
    DBAdapter dba;
    private String mRowId;
    String data3;
    String updatequery;
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.act2);
        ed3=(EditText)findViewById(R.id.data3id);
        btn3=(Button)findViewById(R.id.updatebtnid);
        //dba=new DBAdapter(Activity2.this);
        final Intent intent = getIntent();
        mRowId=intent.getStringExtra("KEYROWID");


        btn3.setOnClickListener(new OnClickListener(){

            public void onClick(View v) {


                dba = new DBAdapter(v.getContext());
                data3=ed3.getText().toString();
                updatequery  = "UPDATE "+ DBAdapter.DATABASE_TABLE+ " SET ";

                updatequery = updatequery + DBAdapter.KEY_DATA3+" = '" + data3 +"'";
                Log.v("updatequery",updatequery);
                updatequery = updatequery + " WHERE _id = '" + mRowId + "';";
                Log.v("updatequery-new",updatequery);
                Log.v("test-1","update");
                try{
                    Toast.makeText(v.getContext(), "UPDATING", Toast.LENGTH_SHORT).show();
                    Log.v("test-2","update");
                    dba.open();
                    myDB.execSQL(updatequery);
                        }catch(NullPointerException e){
                   //e.getCause();
                    e.getMessage();
                }finally{
                    Log.v("test-3","update");
                        if(myDB != null)myDB.close();
                        dba.close();
                    }
                }







        });

    }

The database which I am using:

public class DBAdapter {
    public static final String KEY_ROWID= "_id";
    public static final String KEY_DATA1="data1";
    public static final String KEY_DATA2="data2";
    public static final String KEY_DATA3="data3";


    private static String TAG="DBAdapter";

    static String DATABASE_NAME="update.db";
    static final String DATABASE_TABLE="update_table";
    private static int DATABASE_VERSION=2;


    private final Context context;
    private DatabaseHelper mDbHelper;
    private SQLiteDatabase mDb;

    private static final String DATABASE_CREATE =
      "create table update_table(_id integer primary key autoincrement, "
    + "data1 varchar, data2 varchar, data3 varchar);";




    private static class DatabaseHelper extends SQLiteOpenHelper {

        DatabaseHelper(Context context) {
            super(context, DATABASE_NAME, null, DATABASE_VERSION);
        }

        public void onCreate(SQLiteDatabase db) {

            db.execSQL(DATABASE_CREATE);
        }


        public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
            Log.w(TAG, "Upgrading database from version " + oldVersion + " to "
                    + newVersion + ", which will destroy all old data");
            db.execSQL("DROP TABLE IF EXISTS update_table");
            onCreate(db);
        }
    }




    public DBAdapter(Context ctx) {
        this.context = ctx;
        open();
    }


    public DBAdapter open() throws SQLException {
        mDbHelper = new DatabaseHelper(context);
        mDb = mDbHelper.getWritableDatabase();
        return this;
    }


    public void close() {
        mDbHelper.close();
    }





    public long createddb(String data1,String data2,String data3) {

        ContentValues initialValues = new ContentValues();


        initialValues.put(KEY_DATA1, data1);
        initialValues.put(KEY_DATA2, data2);
        initialValues.put(KEY_DATA3, data3);


        return  mDb.insert(DATABASE_TABLE, null, initialValues);




    }



    public boolean deleteSaleseditdetails(long rowId) {

        return mDb.delete(DATABASE_TABLE, KEY_ROWID + "=" + rowId, null) > 0;
    }




    public int fetchmaxId(){

        String selectQuery = "SELECT max("+KEY_ROWID+") from " + DATABASE_TABLE ;
         Cursor c= mDb.rawQuery(selectQuery, null);
        c.moveToFirst();
        return c.getInt(0);



    }








    public boolean deletedb(long rowId) {

        return mDb.delete(DATABASE_TABLE, KEY_ROWID + "=" + rowId, null) > 0;
    }



}

Following is myLogcat file:

02-04 11:53:20.216: E/AndroidRuntime(11235): FATAL EXCEPTION: main
02-04 11:53:20.216: E/AndroidRuntime(11235): java.lang.NullPointerException
02-04 11:53:20.216: E/AndroidRuntime(11235):    at com.example.testupdate.Activity2$1.onClick(Activity2.java:59)
02-04 11:53:20.216: E/AndroidRuntime(11235):    at android.view.View.performClick(View.java:2408)
02-04 11:53:20.216: E/AndroidRuntime(11235):    at android.view.View$PerformClick.run(View.java:8816)
02-04 11:53:20.216: E/AndroidRuntime(11235):    at android.os.Handler.handleCallback(Handler.java:587)
02-04 11:53:20.216: E/AndroidRuntime(11235):    at android.os.Handler.dispatchMessage(Handler.java:92)
02-04 11:53:20.216: E/AndroidRuntime(11235):    at android.os.Looper.loop(Looper.java:123)
02-04 11:53:20.216: E/AndroidRuntime(11235):    at android.app.ActivityThread.main(ActivityThread.java:4627)
02-04 11:53:20.216: E/AndroidRuntime(11235):    at java.lang.reflect.Method.invokeNative(Native Method)
02-04 11:53:20.216: E/AndroidRuntime(11235):    at java.lang.reflect.Method.invoke(Method.java:521)
02-04 11:53:20.216: E/AndroidRuntime(11235):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
02-04 11:53:20.216: E/AndroidRuntime(11235):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
02-04 11:53:20.216: E/AndroidRuntime(11235):    at dalvik.system.NativeStart.main(Native Method)

Answer 1

And from your code, I found, myDB is NULL.

As you declared SQLiteDatabase myDB;

But forgot to initialize it. So this code line myDB.execSQL(updatequery); Gives you NullPointerException.

Update: (Only pseudo code for your understanding)

Actually in your code there is no need of SQLiteDatabase myDB;

You have to just make a method executeQuery(String query) in Class DBAdapter. in That just write

mDb.execSQL(query);

Now from your Activity instead of myDB.execSQL(updatequery); call dba.executeQuery(updatequery);