SQLite数据库/表突然无法创建

Question

数据库突然停止工作，我不知道我在哪里搞砸了。该数据库将不会出现在设备文件浏览器中。

public class DatabaseHelper extends SQLiteOpenHelper {

private static final String DB_NAME= "sqllitetest";
private static final int DB_VERSION = 1;

public DatabaseHelper(Context context) {
super(context, DB_NAME, null, DB_VERSION);
}

@Override
public void onCreate(SQLiteDatabase sqLiteDatabase) {
    String sqlUsers = "CREATE TABLE user_admin(user_id INTEGER PRIMARY KEY AUTOINCREMENT, user_name VARCHAR, user_password VARCHAR)";
    sqLiteDatabase.execSQL(sqlUsers);
}

public boolean addUsers(String username, String password) {
    SQLiteDatabase db = getWritableDatabase();
    String sqlString = String.format("INSERT INTO user_admin(user_name, user_password) VALUES(\"" + username + "\",\"" + password +"\");");
    db.execSQL(sqlString);
    db.close();
    return true;
}


@Override
public void onUpgrade(SQLiteDatabase sqLiteDatabase, int i, int i1) {
    String sqlUsers = "DROP TABLE IF EXISTS user_admin";
    sqLiteDatabase.execSQL(sqlUsers);
    onCreate(sqLiteDatabase);
}
}