Android Programming SQLite

After clicking submit button, a massage arises: unfortunately SQLite_demo has stop working, Please help me... and one more thing that when the project first displayed on emulator a toast show a pop up :"constructor called " please explain why...

here is my code...........

RahulDatabaseHelper.java

public class RahulDatabaseHelper{
RahulHelper RH;
public RahulDatabaseHelper(Context context)
{
   RH=new RahulHelper(context);
}
public long insertData(String username,String userpassword)
{
    SQLiteDatabase sqLiteDatabase=RH.getWritableDatabase();**strong text**
    ContentValues Values=new ContentValues();
    Values.put(RahulHelper.NAME,username);
    Values.put(RahulHelper.PASSWORD,userpassword);
    long id=sqLiteDatabase.insert(RahulHelper.TABLE_NAME,null,Values);
    sqLiteDatabase.close();
    return id;
}


static class RahulHelper extends SQLiteOpenHelper {

    private static final  String DATABASE_NAME="vivzdatabase.db";
    private static final  String TABLE_NAME="VIVZTABLE";
    private static final  String UID="_id";
    private static final  String NAME="Name";
    private static final  String PASSWORD="Password";
    private static final  int DATABASE_VERSION=4;
    private static final String DATABASE_CREATE ="create table" +TABLE_NAME+ "("+UID+ "integer primary key autoincrement, "
            +NAME+ "VARCHAR(255)"+PASSWORD+"VARCHAR(255));";
    private static final String DROP_TABLE="DROP TABLE IF EXISTS"+TABLE_NAME;

    Context context;
    RahulHelper(Context context) {
        super(context,DATABASE_NAME,null,DATABASE_VERSION);
        this.context=context;
        Message.mess(context,"Constructor called");
    }

    @Override
    public void onCreate(SQLiteDatabase db) {

        try {
            db.execSQL(DATABASE_CREATE);
            Message.mess(context,"onCreate called");
        }catch (SQLException e)
        {Message.mess(context,""+e);}

    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

        try {
            Message.mess(context,"onUpgrade called");
            db.execSQL(DROP_TABLE);
            onCreate(db);
        }catch (SQLException e)
        {Message.mess(context,""+e);}
    }
}}        

MainActivity.java

public class MainActivity extends ActionBarActivity {

EditText et1,et2;
RahulDatabaseHelper rahulDatabaseHelper;
Context context;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);


    et1=(EditText)findViewById(R.id.username);
    et1=(EditText)findViewById(R.id.userpass);

    rahulDatabaseHelper=new RahulDatabaseHelper(this);

 }

public void method(View v)
{
  String name=et1.getText().toString();
    String pass=et2.getText().toString();

    long id=rahulDatabaseHelper.insertData(name,pass);
    if (id<0)
        Message.mess(this,"UnSuccessFull");
    else
        Message.mess(this,"Row Inserted SuccessFully");

}}

activity_main.xml

<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:textAppearance="?android:attr/textAppearanceLarge"
    android:text="Enter Name"
    android:id="@+id/textView"
    android:layout_alignParentTop="true"
    android:layout_alignParentLeft="true"
    android:layout_alignParentStart="true"
    android:layout_alignParentRight="true"
    android:layout_alignParentEnd="true" />
<EditText
    android:id="@+id/username"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:hint="enter usr name"
    android:layout_below="@+id/textView"/>

<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:textAppearance="?android:attr/textAppearanceLarge"
    android:text="Enter Password"
    android:id="@+id/textView2"
    android:layout_below="@+id/username"
    android:layout_alignParentLeft="true"
    android:layout_alignParentStart="true"
    android:layout_alignParentRight="true"
    android:layout_alignParentEnd="true" />

<EditText
    android:id="@+id/userpass"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:hint="Enter Password"
    android:layout_below="@+id/textView2"/>

<Button
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Submit"
    android:onClick="method"
    android:id="@+id/button"
    android:layout_below="@+id/userpass"
    android:layout_alignParentLeft="true"
    android:layout_alignParentStart="true"
    android:layout_alignParentRight="true"
    android:layout_alignParentEnd="true" />

Message.java

public class Message {

public static void mess(Context context,String string)
{
    Toast.makeText(context,string,Toast.LENGTH_LONG).show();
}}