错误：此类应提供默认构造函数，不带参数的公共构造函数

Question

我尝试过不同的代码但不起作用。我的完整代码如下。

public class CheckData extends AppCompatActivity
{
   private static final String enter_name="Name";
   private static final String enter_email="Email_id";
   private static final String enter_mob="Mobile";
   private static final String enter_song="Song_rqst";

   private static final String id="id";

   private static final String database_path="Context.getFilesDir().getPath()";
   private static final String database_name="sql_choice.db";
   private static final String table_name="check_rank";

   private static final int version = 2;

   private DbHelper dbhelper;
   private final Context ourcontext;
   private SQLiteDatabase sqldatabase;
   public CheckData(Context c)
   {
        //super();
        ourcontext=c;
   }
    /*  public CheckData()
   {
     // For the error I used this as solution but gives error           
   } */

  public class DbHelper extends SQLiteOpenHelper
  {
     public DbHelper(Context context) {
         super(context, database_name, null, version);
     }

     @Override
     public void onCreate(SQLiteDatabase db) {
     if(isDBExist())
     {

     }
     else
     {
        String execute="CREATE TABLE " + table_name +"(" +
                id + " " + "INTEGER PRIMARY KEY ," + enter_name +" TEXT NOT NULL ," + enter_email
                + " TEXT NOT NULL , " + enter_mob + " INTEGER ,"+enter_song+" TEXT NOT NULL);";
        db.execSQL(execute);
     }
}

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
    db.execSQL("DROP TABLE IF EXISTS" + database_name);
    onCreate(db);

}
public boolean isDBExist()
{
    SQLiteDatabase sql=null;
    String path=database_path + database_name;
    try
    {
        sql= SQLiteDatabase.openDatabase(path, null, SQLiteDatabase.OPEN_READWRITE);
    }
    catch(Exception e)
    {

    }
    if(sql !=null)
    {
        sql.close();
    }

    return sql !=null ? true :false;
}

public void openDatabase()
{
    String path=database_path + database_name;
    try
    {
        sqldatabase = SQLiteDatabase.openDatabase(path, null, SQLiteDatabase.OPEN_READWRITE);
    }
    catch (Exception e)
    {

    }
}

}
public CheckData open() throws SQLException
{
    dbhelper =new DbHelper(ourcontext);
    sqldatabase=dbhelper.getWritableDatabase();
    dbhelper.openDatabase();

    return this;
}

public void close()
{
    dbhelper.close();
}
public long createEntry(String name, String email, String mob, String song)
{
    ContentValues cv=new ContentValues();
    cv.put(enter_name, name);
    cv.put(enter_email,email );
    cv.put(enter_mob, mob);
    cv.put(enter_song, song);
    return sqldatabase.insert(table_name, null, cv);
}
public String getData()
{
    String column[]={id,enter_name,enter_email,enter_mob,enter_song};
    Cursor c=sqldatabase.query(table_name, column, null, null, null, null, null, null);
    String result="";
    int iid=c.getColumnIndex(id);
    int iname=c.getColumnIndex(enter_name);
    int iemail=c.getColumnIndex(enter_email);
    int imob=c.getColumnIndex(enter_mob);
    int isong=c.getColumnIndex(enter_song);

    for(c.moveToFirst();!c.isAfterLast();c.moveToNext())
    {
        result=result + " " + c.getString(iid) + " " +c.getString(iname) +" " +c.getString(iemail) + "" +
                c.getString(imob) +" " +c.getString(isong) + "" +

                "\n";
    }
    return result;
}
}

任何人都可以解决这个问题吗？以上只有在生成签名的apk时才会出错。

  

错误：此类应提供默认构造函数（不带参数的公共构造函数）