Null Pointer Exception when creating SQLite Database from App

Question

I'm trying to make a simple app that can take user entered information and store it in a database from an android phone. The code I have is as follows:

import android.database.sqlite.SQLiteOpenHelper;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.EditText;
import android.widget.TextView;

import java.io.IOException;


public class MainActivity extends AppCompatActivity {

    EditText userentry;
    TextView seeuserdata;
    DataBaseHelper DataBaseHelper;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        userentry = (EditText) findViewById(R.id.userentry);
        seeuserdata = (TextView) findViewById(R.id.seeUserData);
        DataBaseHelper db = new DataBaseHelper(this, null, null, 1);
        printDatabase();
    }

    public void addButtonClicked(View view){
        Products product = new Products(userentry.getText().toString());


    }

    public void deleteButtonClicked(View view){
            String inputText = userentry.getText().toString();
            DataBaseHelper.deleteProduct(inputText);
            printDatabase();
    }

    public void printDatabase(){
        String dbString = DataBaseHelper.databaseToString();
        seeuserdata.setText(dbString);
        userentry.setText("");
    }
};

Products class

    public class Products {
    private int _id;
    private String _productname;

    public Products(String _productname){
        this._productname=_productname;
    }

    public void set_id(int _id) {
        this._id = _id;
    }

    public void set_productname(String _productname) {
        this._productname = _productname;
    }

    public int get_id() {
        return _id;
    }

    public String get_productname() {
        return _productname;
    }
}

And class DataBaseHelper

import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;

public class DataBaseHelper extends SQLiteOpenHelper {

    private static String DB_PATH = "/data/data/your.package/databases/";
    private static String DB_NAME = "products.db";
    private static int DB_VERSION = 1;
    private static final String TABLE_PRODUCTS = "products";
    public static final String COLUMN_ID = "_id";
    public static final String COLUMN_PRODUCTNAME = "productname";
    private static short WRITE_BUFFER_SIZE = 8192;
    private Context context;

    public DataBaseHelper(Context context, String name, SQLiteDatabase.CursorFactory factory, int version) {
        super(context, name, factory, version);
    }

    public void addProduct(Products product){
        ContentValues values = new ContentValues();
        values.put(COLUMN_PRODUCTNAME, product.get_productname());
        SQLiteDatabase db = getWritableDatabase();
        db.insert(TABLE_PRODUCTS, null, values);
        db.close();
    }

    public void deleteProduct(String productName){
        SQLiteDatabase db = getWritableDatabase();
        db.execSQL("DELETE FROM " + TABLE_PRODUCTS + " WHERE " + COLUMN_PRODUCTNAME + "=\"" + productName + "\";");
    }

    public String databaseToString(){
        String dbString = "";
        SQLiteDatabase db  = getWritableDatabase();
        String query = "SELECT * FROM " + TABLE_PRODUCTS + " WHERE 1";
        Cursor c = db.rawQuery(query, null);
        c.moveToFirst();
        while(!c.isAfterLast()){
            if(c.getString(c.getColumnIndex("productname"))!=null){
                dbString += c.getString(c.getColumnIndex("productname"));
                dbString += "\n";
            }
        }
        db.close();
        return dbString;
    }
    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        db.execSQL("DROP_TABLE_IF_EXISTS" + TABLE_PRODUCTS);
        onCreate(db);
    }
    @Override
    public void onCreate(SQLiteDatabase db) {
        String query = "CREATE TABLE" + TABLE_PRODUCTS + "(" + COLUMN_ID + " INTEGER PRIMARY KEY AUTOINCREMENT "+ COLUMN_PRODUCTNAME + " TEXT " + ");";
        db.execSQL(query);
    }
}

The error is:

E/AndroidRuntime: FATAL EXCEPTION: main
                  Process: com.example.barry.recordtracker, PID: 11938
                  java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.barry.recordtracker/com.example.barry.recordtracker.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String com.example.barry.recordtracker.DataBaseHelper.databaseToString()' on a null object reference
                      at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3253)
                      at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3349)
                      at android.app.ActivityThread.access$1100(ActivityThread.java:221)
                      at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1794)
                      at android.os.Handler.dispatchMessage(Handler.java:102)
                      at android.os.Looper.loop(Looper.java:158)
                      at android.app.ActivityThread.main(ActivityThread.java:7224)
                      at java.lang.reflect.Method.invoke(Native Method)
                      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230)
                      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)
                   Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String com.example.barry.recordtracker.DataBaseHelper.databaseToString()' on a null object reference
                      at com.example.barry.recordtracker.MainActivity.printDatabase(MainActivity.java:40)
                      at com.example.barry.recordtracker.MainActivity.onCreate(MainActivity.java:26)
                      at android.app.Activity.performCreate(Activity.java:6876)
                      at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1135)
                      at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3206)
                      at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3349) 
                      at android.app.ActivityThread.access$1100(ActivityThread.java:221) 
                      at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1794) 
                      at android.os.Handler.dispatchMessage(Handler.java:102) 
                      at android.os.Looper.loop(Looper.java:158) 
                      at android.app.ActivityThread.main(ActivityThread.java:7224) 
                      at java.lang.reflect.Method.invoke(Native Method) 
                      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230) 
                      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)

My understanding is that the null object the logs are referring to is the database helper which is initialized in the onCreate method. It looks to me that the database helper is created! Is it not pointing to the database helper? Is it a problem with me initializing the DB helper with (this, null, null, 1)? (meaning that it should be initialized with something else?)

score 2 · Accepted Answer · answered Jan 22 '17 at 18:12

2

You are using a local variable db instead of DataBaseHelper reference variable so you need to initialize DataBaseHelper reference

Replace this in onCreate

DataBaseHelper db = new DataBaseHelper(this, null, null, 1);

with this

DataBaseHelper = new DataBaseHelper(this, null, null, 1);

or for clarity , rename this DataBaseHelper DataBaseHelper;

to this DataBaseHelper dataBaseHelper; and use it like this

dataBaseHelper = new DataBaseHelper(this, null, null, 1);

answered Jan 22 '17 at 18:12

Pavneet_Singh

36,884
5
53
68

1

works, now onto other errors... – bdpolinsky Jan 22 '17 at 18:29
@bdpolinsky glad that i could help and good luck for happy coding :) – Pavneet_Singh Jan 23 '17 at 06:55

score 0 · Answer 2 · answered Jan 22 '17 at 18:12

0

AddbuttonClicked method is not adding entries to database. Call addProduct method of databasehelper.

answered Jan 22 '17 at 18:12

mayur newase

66
7

Null Pointer Exception when creating SQLite Database from App

2 Answers2