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Singleton Instance returns null

In my application, I use the users password as the encryption key for encryption media. I am encrypting media using PBEWithMD5AndDES and this works fine with a password stored in shared preferences. Now to achieve a level of security I am removing the password from shared preferences and using a singleton that is only kept alive during the app session (as the app logs out automatically requiring entry of the password). Below is my singleton:
public class Credentials {
private static Credentials dataObject = null;
private Credentials() {
// left blank intentionally
}
public static Credentials getInstance() {
if (dataObject == null)
dataObject = new Credentials();
return dataObject;
}
private char[] user_password;
public char[] getUser_password() {
return user_password;
}
public void setUser_password(char[] user_password) {
this.user_password = user_password;
}
}
The password is zeroed out from memory if the app logs out, or is log out by the user or gets destroyed. However at times I am getting a null pointer when trying to retrieve the password.
char[] pswd = Credentials.getInstance().getUser_password();
What could be causing this? is there any other method I can use except a singleton?

Alternatively, you can store the password using built-in Sqlite db, though I'd still recommend you save it encrypted for max protection. You can do this in 4 steps:
2) Create an entity object to store the password:
public class Password {
int password_id; // will be auto-increamted
String password;
public Password(int password_id, String password) {
this.password_id = password_id;
this.password = password;
}
// getter/setters ...
}
2) Create an Sqlite utility object:
public class SQLiteDBAdapter {
protected static final String DATABASE_NAME = "mydb";
protected static final int DATABASE_VERSION = 1;
protected Context context;
protected static DatabaseHelper mDbHelper;
public static final String TABLE_PASSWORD = "tbl_password";
// columns
public static final String PASSWORD_ID = "_id";
public static final String PASSWORD = "password";
// create table string
private static final String CREATE_TABLE_PASSWORD =
"CREATE TABLE if not exists " + TABLE_PASSWORD + " ( " +
PASSWORD_ID + " INTEGER PRIMARY KEY AUTOINCREMENT, " +
PASSWORD + " TEXT NOT NULL);";
public SQLiteDBAdapter(Context context) {
context = context.getApplicationContext();
}
public SQLiteDatabase openDb() {
if (mDbHelper == null) {
mDbHelper = new DatabaseHelper(mContext);
}
return mDbHelper.getWritableDatabase();
}
protected static class DatabaseHelper extends SQLiteOpenHelper {
// -------------------------------------------------------------------------------------------
public DatabaseHelper(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
// -------------------------------------------------------------------------------------------
#Override
public void onCreate(SQLiteDatabase db) {
db.execSQL(CREATE_TABLE_PASSWORD);
}
// -------------------------------------------------------------------------------------------
#Override
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 routes");
onCreate(db);
}
}
}
3) Extend an Sqlite object to manipulate the table (CRUD operations):
public class PasswordDbAdapter extends SQLiteDBAdapter {
private SQLiteDatabase db;
// these are column corresponding indices
public static final int INDEX_PASSWORD_ID = 0; // an auto-increment
public static final int INDEX_PASSWORD = 1;
public PasswordDbAdapter(Context context) {
super(context);
}
public void addPassword(String password) {
db = openDb();
ContentValues values = new ContentValues();
values.put(PASSWORD, password);
db.insert(TABLE_PASSWORD, null, values);
}
public void updatePassword(String password) {
db = openDb();
ContentValues values = new ContentValues();
values.put(PASSWORD, password);
db.update(TABLE_PASSWORD, values, null);
}
public void deletePassword() {
db = openDb();
db.delete(TABLE_PASSWORD, null, null);
}
public boolean isEmpty() {
db = openDb();
boolean empty = true;
Cursor cur = db.rawQuery("SELECT COUNT(*) FROM " + TABLE_PASSWORD, null);
if (cur != null && cur.moveToFirst()) {
empty = (cur.getInt (0) == 0);
}
cur.close();
return empty;
}
public Password fetchPassword() { // ok because there's only one password record
db = openDb();
Cursor cursor = db.query(TABLE_PASSWORD, new String[]{PASSWORD_ID, PASSWORD},
null, null, null, null, null, null);
if (cursor != null &&
cursor.moveToFirst()) {
return new Password(
cursor.getString(INDEX_PASSWORD_ID),
cursor.getInt(INDEX_PASSWORD));
}
return null;
}
}
4) Finally, save/update/retrieve the password as desired:
public class MainActivity extends AppCompatActivity {
private PasswordDbAdapter passwordDB;
#Override
protected void onCreate(Bundle savedInstanceState) {
...
// initialize the password db
passwordDB = new PasswordDbAdapter(this);
// check if password record exists
if (passwordDB.isEmpty() {
// save a new copy
passwordDB.addPassword("the_password"); // more secure if it is saved encrypted
} else {
// update it
passwordDB.updatePassword("the_password");
}
}
...
public String fetchPassword() {
return passwordDB.fetchPassword(); // or first decrypt it, then return it
}
}

Android SQLite code feedback [closed]

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I have been through a few sqlite tutorials and wrote this code on my own to reinforce the principles. The tutorials I went through varied widely in a few areas so this is what I came up with as a combination of everything.
Other than the two classes I have listed below, All I have is one activity that adds, remove, inserts, update and display data from the database.
I am seeking any feedback whatsoever. However I have a few specific questions. Thanks in advance.
When should I close the helper class or does garbage collection deal with it automatically?
Should I create a Boxer POJO(Plain old java object to pass boxer data to and from the DAO?
Was the DAO implementation Efficient?
Does the code deviate from Java and Android best practices in anyway?
Any constructive advice is welcome
Helper Class
public class BoxScoresHelper extends SQLiteOpenHelper {
private static final String DB_NAME = "boxing_scores.db";
private static final int VERSION = 1;
private static BoxScoresHelper instance = null;
public static BoxScoresHelper getInstance(Context context){
if(instance == null){
instance = new BoxScoresHelper(context);
}
return instance;
}
private BoxScoresHelper(Context context) {
super(context, DB_NAME, null, VERSION);
}
#Override
public void onCreate(SQLiteDatabase db) {
db.execSQL(createBoxerSQLString());
}
#Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
db.execSQL("Drop Table If Exists " + BoxerDAO.TABLE_NAME);
onCreate(db);
}
private String createBoxerSQLString(){
String boxerCreateString = "create table " + BoxerDAO.TABLE_NAME +
"(" + BoxerDAO._ID + " Integer Primary Key AutoIncrement, " +
BoxerDAO.BOXER_NAME + " Text Not Null, " +
BoxerDAO.WEIGHT_CLASS + " Text Not Null, " +
BoxerDAO.WINS + " Integer Not Null, " +
BoxerDAO.LOSSES + " Integer Not Null);";
return boxerCreateString;
}
}
DAO Class
public class BoxerDAO {
public static final String TABLE_NAME = "Boxer";
public static final String _ID = "_id";
public static final String BOXER_NAME = "boxer_name";
public static final String WEIGHT_CLASS = "weight_class";
public static final String WINS = "wins";
public static final String LOSSES ="losses";
private final BoxScoresHelper myScoresHelper;
private SQLiteDatabase myBoxerDB;
public BoxerDAO(Context context){
myScoresHelper = BoxScoresHelper.getInstance(context);
}
public Cursor query(String[] projection,String selection,String[] selectionArgs, String orderBy){
Cursor cursor;
myBoxerDB = myScoresHelper.getReadableDatabase();
cursor = myBoxerDB.query(TABLE_NAME, projection, selection, selectionArgs, null, null, orderBy);
//myBoxerDB.close();
return cursor;
}
public Cursor queryAll(){
Cursor cursor;
myBoxerDB = myScoresHelper.getReadableDatabase();
cursor = myBoxerDB.rawQuery("Select * From " + TABLE_NAME, null);
//myBoxerDB.close();
return cursor;
}
public int delete(int id){
int rowsDel;
myBoxerDB = myScoresHelper.getWritableDatabase();
rowsDel = myBoxerDB.delete(TABLE_NAME, _ID + " = " + id , null);
//myBoxerDB.close();
return rowsDel;
}
public long insert(ContentValues values){
long insertId = -1;
myBoxerDB = myScoresHelper.getWritableDatabase();
insertId = myBoxerDB.insert(TABLE_NAME, null, values);
//myBoxerDB.close();
return insertId;
}
public int update(ContentValues values,String selection, String[] selectionArgs){
int updatedRows;
myBoxerDB = myScoresHelper.getWritableDatabase();
updatedRows = myBoxerDB.update(TABLE_NAME, values, _ID + " = " + selection, selectionArgs);
//myBoxerDB.close();
return updatedRows;
}
}

Unable to start activity in device

I'm trying to follow this tutorial, but I'm getting this error message, when I run on my device:
08-04 01:40:12.820 27896-27896/com.filipeferminiano.quiz E/AndroidRuntime﹕ FATAL EXCEPTION: main
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.filipeferminiano.quiz/com.filipeferminiano.quiz.MyActivity}: java.lang.IllegalStateException: attempt to re-open an already-closed object: SQLiteDatabase: /data/data/com.filipeferminiano.quiz/databases/triviaQuiz
How can I solve this?

Try to replace this class,hope this will help you to solve your problem.
public class DbHelper extends SQLiteOpenHelper {
private static final int DATABASE_VERSION = 1;
// Database Name
private static final String DATABASE_NAME = "triviaQuiz";
// tasks table name
private static final String TABLE_QUEST = "quest";
// tasks Table Columns names
private static final String KEY_ID = "id";
private static final String KEY_QUES = "question";
private static final String KEY_ANSWER = "answer"; //correct option
private static final String KEY_OPTA= "opta"; //option a
private static final String KEY_OPTB= "optb"; //option b
private static final String KEY_OPTC= "optc"; //option c
private SQLiteDatabase dbase;
public DbHelper(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
#Override
public void onCreate(SQLiteDatabase db) {
String sql = "CREATE TABLE IF NOT EXISTS " + TABLE_QUEST + " ( "
+ KEY_ID + " INTEGER PRIMARY KEY AUTOINCREMENT, " + KEY_QUES
+ " TEXT, " + KEY_ANSWER+ " TEXT, "+KEY_OPTA +" TEXT, "
+KEY_OPTB +" TEXT, "+KEY_OPTC+" TEXT)";
db.execSQL(sql);
addQuestions(db);
}
private void addQuestions(SQLiteDatabase db)
{
Question q1=new Question("Which company is the largest manufacturer" +
" of network equipment?","HP", "IBM", "CISCO", "C");
this.addQuestion(q1,db);
Question q2=new Question("Which of the following is NOT " +
"an operating system?", "SuSe", "BIOS", "DOS", "B");
this.addQuestion(q2,db);
Question q3=new Question("Which of the following is the fastest" +
" writable memory?","RAM", "FLASH","Register","C");
this.addQuestion(q3,db);
Question q4=new Question("Which of the following device" +
" regulates internet traffic?", "Router", "Bridge", "Hub","A");
this.addQuestion(q4,db);
Question q5=new Question("Which of the following is NOT an" +
" interpreted language?","Ruby","Python","BASIC","C");
this.addQuestion(q5,db);
}
#Override
public void onUpgrade(SQLiteDatabase db, int oldV, int newV) {
// Drop older table if existed
db.execSQL("DROP TABLE IF EXISTS " + TABLE_QUEST);
// Create tables again
onCreate(db);
}
// Adding new question
public void addQuestion(Question quest,SQLiteDatabase db) {
ContentValues values = new ContentValues();
values.put(KEY_QUES, quest.getQUESTION());
values.put(KEY_ANSWER, quest.getANSWER());
values.put(KEY_OPTA, quest.getOPTA());
values.put(KEY_OPTB, quest.getOPTB());
values.put(KEY_OPTC, quest.getOPTC());
// Inserting Row
db.insert(TABLE_QUEST, null, values);
}
public List<Question> getAllQuestions() {
List<Question> quesList = new ArrayList<Question>();
// Select All Query
String selectQuery = "SELECT * FROM " + TABLE_QUEST;
dbase=this.getReadableDatabase();
Cursor cursor = dbase.rawQuery(selectQuery, null);
// looping through all rows and adding to list
if (cursor.moveToFirst()) {
do {
Question quest = new Question();
quest.setID(cursor.getInt(0));
quest.setQUESTION(cursor.getString(1));
quest.setANSWER(cursor.getString(2));
quest.setOPTA(cursor.getString(3));
quest.setOPTB(cursor.getString(4));
quest.setOPTC(cursor.getString(5));
quesList.add(quest);
} while (cursor.moveToNext());
}
// return quest list
dbase.close();
return quesList;
}
public int rowcount()
{
int row=0;
String selectQuery = "SELECT * FROM " + TABLE_QUEST;
SQLiteDatabase db = this.getWritableDatabase();
Cursor cursor = db.rawQuery(selectQuery, null);
row=cursor.getCount();
return row;
}
}

the trace already told u the reason why it crashed:
attempt to re-open an already-closed object: SQLiteDatabase

check your database objects it closed some where in your code also check in tutorial there are not anywhere write db.close() so do not close your data base in your example..
thats it...

SQLite (1) no such table

When I run my android app I keep getting the error (1) no such table userTable, as far as I am aware I am creating the table in
TABLE_CREATE = "create table userTable("
+ USER + " text not null, " + PWD + " text not null, );";
I have two other databases in this project and the are working fine, any help is welcome.
package com.weightpro.db;
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.SQLiteDatabase.CursorFactory;
import android.database.sqlite.SQLiteOpenHelper;
public class usrPwdDB {
public static final String USER = "userName";
public static final String PWD = "password";
public static final String TABLE_NAME = "userTable";
public static final String DATA_BASE_NAME = "userdatabase";
public static final String KEY_ROWID = "_id";
public static final int DB_VERSION = 2;
private static final String TABLE_CREATE = "create table userTable("
+ USER + " text not null, " + PWD + " text not null, );";
DBHelper WDBHelper;
Context mContext;
SQLiteDatabase db;
public usrPwdDB(Context mContext) {
this.mContext = mContext;
WDBHelper = new DBHelper(mContext);
}
private static class DBHelper extends SQLiteOpenHelper
{
public DBHelper(Context context) {
super(context,DATA_BASE_NAME, null, DB_VERSION);
}
#Override
public void onCreate(SQLiteDatabase db) {
try{
db.execSQL(TABLE_CREATE);
}
catch(SQLException e)
{
e.printStackTrace();
}
}
#Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
db.execSQL("DROP TABLE IF EXISTS userTable");
onCreate(db);
}
}
public usrPwdDB open()
{
db = WDBHelper.getWritableDatabase();
return this;
}
public void close(){
WDBHelper.close();
}
public long insertInfo(String userName, String password){
ContentValues content = new ContentValues();
content.put(USER, userName);
content.put(PWD, password);
return db.insertOrThrow(TABLE_NAME, null, content);
}
public boolean getUserNameAndPassword(String userName, String Password) throws SQLException {
Cursor mCursor =
db.query(true, TABLE_NAME, new String[] {USER,
PWD},USER+"='"+userName+"' AND password='"+Password+"'", null,
null, null, null, null);
if (mCursor.getCount() > 0)
{
return true;
}
return false;}
public Cursor returnData(){
return db.query(TABLE_NAME, new String[] {USER, PWD},null,null,null,null,null);
}
}

remove the last comma , from the create table syntax,
private static final String TABLE_CREATE =
"create table userTable("
+ USER + " text not null, "
+ PWD + " text not null, );"; // remove this comma after not null
The correct syntax should be
private static final String TABLE_CREATE =
"create table userTable("
+ USER + " text not null, "
+ PWD + " text not null );";

You go wrong over here
+ USER + " text not null, " + PWD + " text not null, );"; //remove , from last text not null
correct SQL command with below
private static final String TABLE_CREATE = "create table userTable("
+ USER + " text not null, " + PWD + " text not null);" ;

private static final String TABLE_CREATE = "create table userTable("
+ USER + " text not null, " + PWD + " text not null,);" ;
remove "," after "text not null" and also remove ";"(semicolon) in the string, that is not needed i think,
then clear data or uninstall application then execute again
even though the creation of table failed i think next time onCreate() in SQLiteOpenHelper only executes once, so you will need to clear data of application
if you are using separate class for separate table and using same DB name, then all the tables in the first using class will be ok, and others will not be created since for a single database onCreate() function works only one, even if there is separate classes each with onCreate(),
onCreate() function creates a file in DB location of android file system when first called onCreate(), if the onCreate called again it check for the existence of DBNAME file in DB location and avoid creating if its exit, I think this is logic behind it...
so keep one onCreate() function for a single DB file and create all tables in that function

the table still cannot be created. what is the problem?

This is my Database class
public class ProgramDbAdapter{
public static final String KEY_ROWID = "_id";
public static final String KEY_PROGRAM_TITLE = "ProgramTitle";
public static final String KEY_PROGRAM_DATE = "ProgramDate";
public static final String KEY_PROGRAM_TIME = "ProgramTime";
public static final String KEY_PROGRAM_CHANNEL = "ProgramChannel";
private static final String DATABASE_CREATE =
"CREATE TABLE " + DATABASE_TABLE + " (" + "_id integer primary key autoincrement, "
+ "ProgramTitle text, " + "ProgramDate varchar(20), "
+ "ProgramTime varchar(20), " + "ProgramChannel text)";
private static final String DATABASE_UPGRADE = "DROP TABLE IF EXISTS " + DATABASE_TABLE;
private static class DatabaseHelper extends SQLiteOpenHelper {
DatabaseHelper(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
#Override
public void onCreate(SQLiteDatabase db){
db.execSQL(DATABASE_CREATE);
}
#Override
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(DATABASE_UPGRADE);
onCreate(db);
}
}
public ProgramDbAdapter open() throws SQLException{
mDbHelper = new DatabaseHelper(mcontext);
mDb = mDbHelper.getWritableDatabase();
return this;
}
public long CreateData(String ProgramTitle, String ProgramDate, String ProgramTime, String ProgramChannel){
ContentValues initialvalues = new ContentValues();
initialvalues.put(KEY_PROGRAM_TITLE, ProgramTitle);
initialvalues.put(KEY_PROGRAM_DATE, ProgramDate);
initialvalues.put(KEY_PROGRAM_TIME, ProgramTime);
initialvalues.put(KEY_PROGRAM_CHANNEL, ProgramChannel);
return mDb.insert(DATABASE_TABLE, null, initialvalues);
}
}
This is my main class
public class Program extends ExpandableListActivity{
public void onCreate(Bundle savedInstanceState) {
mDbHelper = new ProgramDbAdapter(this);
mDbHelper.open();
mDbHelper.CreateData("a","a","a","a");
}
}
when i call open() and createdata function, the logcat tell me no such table:Program. where is the problem is?

There is no varchar type in sqlite, see here. Use text instead.

I don't see where 'DATABASE_TABLE' is coming from.
Also, you should use the "rawQuery()", "query()"-Methods or a "SQLiteStatement" to bind parameters into your SQL-Statement.
And last but not least, SQLite doesn't know any 'varchar'. Check here for all Data types: Link

varchar is translated to text ...
from vladimir link:
If the declared type of the column
contains any of the strings "CHAR",
"CLOB", or "TEXT" then that column has
TEXT affinity. Notice that the type
VARCHAR contains the string "CHAR" and
is thus assigned TEXT affinity.
problem is that u created db in first run and there was different Create statment ...
delete app data from android settings or change DATABASE_VERSION