I've been recently reading a book on Java design patterns and have come across classes inheriting from other classes and being instantiated by putting  Superclass s = new Subclass()   as opposed to  Subclass s = new Subclass()   My initial thoughts were that it's more from a design point of view and due to abstraction or information hiding. However, I'm still unsure and haven't been able to find a clear explanation.   Why would someone instantiate by using Superclass s = new Subclass(), and is it ever acceptable to use Subclass s = new Subclass()?  I'd greatly appreciate any help from someone who can help shed some light on this for me.
I have seen this mentioned a few times and I am not clear on what it means. When and why would you do this?   I know what interfaces do, but the fact I am not clear on this makes me think I am missing out on using them correctly.   Is it just so if you were to do:  IInterface classRef = new ObjectWhatever()   You could use any class that implements IInterface? When would you need to do that? The only thing I can think of is if you have a method and you are unsure of what object will be passed except for it implementing IInterface. I cannot think how often you would need to do that.   Also, how could you write a method that takes in an object that implements an interface? Is that possible?
external variable in awk I am considering purchasing a Mac for my godson who will be using it to run Blender 2.8.  I know very little about this program.  All I can find are requirements for a Mac that will run earlier versions of Blender.  Would someone please recommend a list of requirements for a Mac (or a link to a list of requirements) that I could use to find a model that can run 2.8?  Thank you in advance for all your help! Sincerely, M. Lap Move EFI System Partition to another drive Don't automatically edit the post to insert "possible duplicate" links When a question is closed as a duplicate, its body is edited to auto-insert the link to that duplicate. I think there are a couple problems with that:   If the question is reopened, the auto-generated insert isn't automatically removed. It allows the poster (or anyone else) to roll back the post and protest the closure by reverting the automatic edit.    I propose that the links to the duplicate(s) are moved into a separate "header" field above the post instead of being edited into the body of the question. That way it could be removed or hidden if the question is reopened and it could not be edited or reverted without reopening the question.   There is some potential for loss of functionality there, since right now it is possible to edit the post to either include additional related links or remove obsolete/incorrect ones. That could be addressed by making the "duplicate field" editable at a certain reputation level (10k?) and enabling others to suggest edits for it that'd go through the usual approval/rejection process.  Thoughts? Why Doesn't the Adamantium Bone Covering Kill Wolverine? I've seen the  here before, as well as on many sites on the web.  I've also seen different info on what was covered.  I'm not a huge X-Men fan, but I do enjoy the characters and stories, so I know I'm probably missing out on a lot, and may have missed the obvious along the way because I didn't read a particular series or something like that.  I had a relative die from leukemia a few years ago and that reminded me of basic junior high science: that red and white blood cells are produced in the bone marrow and must be able to reach from the marrow into the blood vessels.  The leukemia my relative had was the kind where the "bad" cells would surround the marrow and prevent the new "good" blood cells from getting out to the rest of the body.  So just how much of Wolverine's skeleton is covered with Adamantium?  If it's the whole thing, there'd have to be openings for new red blood cells to get out if he is to remain alive.  I've never seen a reference to this issue, is it ever addressed?  That also raises another issue along the same line: Are hard to reach areas, such as ball and socket joints covered?  If not, then stress on other covered areas could be transferred to the weaker uncovered areas, which would lead to breakage there.  And if joints like that are covered, is there anything to say how it was done?  Are there openings or gaps in the Adamantium covering on his body?  Are there any references to any of these issues that deal with them? I have been denied a visa several times in a row. How does one deal with such serial refusals? Over the course of time here on TSE, I have observed individuals whose pattern of visa applications is best described as ''...     serial refusals - Two or more consecutive visa refusals issued by the same regime to the same person. Commonly for the same, or nearly the same, reasons. In some visa regimes Serial refusals can have a cumulative effect wherein the applicant's credibility is increasingly eroded, especially when the application pattern suggests a secondary agenda.   A common thread appears to be the need to visit the destination country (especially Schengen, the USA, or the UK) with a special sense of urgency. Also common in these cases are the following types of questions...   Should I just reapply once again? What are my chances? What can I do to improve my odds in the future? Can I somehow address the previous refusals to avoid them being a burden on all future applications? How can I break the pattern?      NB: This question is intended as a canonical about serial refusals. I have never been personally denied a visa. Unable to start Oracle database We have an Oracle database, one data file (users tablespace) of the instance got corrupt and another data file (containing application data) was deleted due to some issue.  The database is in ARCHIVELOG mode, but we neither have data file backup of both data files nor the pertaining archive logs. Hence, I guess we cannot go ahead with the recovery of data files. I am unable to open the database as the data files are not available and face.   ORA-01589: must use RESETLOGS or NORESETLOGS option for database open    I am just able to STARTUP MOUNT the database  I wanted to ask if we can somehow we can open the database by taking both the tablespaces offline after STARTUP MOUNT the database instance. Or if there is any other way I can start the database.   There was a power issue and the  server got abruptly shutdown. When we tried to restart the database and found that we were facing ORA-01589: must use RESETLOGS or NORESETLOGS option for database open. On further analysis we found that 2 of datafiles were creating problem as one got corrupt other deleted as mentioned. As of now if I try to restart the database it says one datafile which belongs to users tablespace need recovery. I wanted to confirm as if we can start the instance by bringing the tablespace offline.  I tried:  SQL&gt; select open_mode from v$database;  OPEN_MODE ---------- MOUNTED  SQL&gt; alter database open resetlogs; alter database open resetlogs * ERROR at line 1: ORA-01194: file 1 needs more recovery to be consistent ORA-01110: data file 1: '/flowsystems/oradata02/flsta02/system01.dbf'   I don't have any archive logs. How to escape quotes in shell? I'm having trouble with escaping characters in bash. I'd like to escape single and double quotes while running a command under a different user. For the purposes of this question let's say I want to echo the following on the screen:  'single quote phrase' "double quote phrase"   How can I escape all the special chars, if I also need to switch to a different user:  sudo su USER -c "echo \"'single quote phrase' \"double quote phrase\"\""   Of course, this doesn't produce the right result. Why does $1+2+3+\cdots = -\frac{1}{12}$? dynamic does not contain a definition for a property from a project reference Can I travel to the UK unaccompanied on an accompanied child visa now that I am over 18? Compute $\int_{0}^{\infty}\frac{x\sin 2x}{9+x^{2}} \, dx$ How to increase battery life on Ubuntu 20.04 and what power saving software should I install, if any? How do I create an 8 sided die from one object? Simply put, is there a way to make a cube balance solely on one point/vertex?  I'm struggling. I do not want to have to join two objects, nor have to extrude an object. I just want to have a simple eight-sided die created with one mesh. How many generator has a cyclic group of order n? We roll a die until each side appears at least once, then we stop.     What is the probability of rolling exactly $n$ dice?   I guess the answer is  $$6-6\left(\dfrac{5}{6}\right)^n\;,$$  but this may be wrong.  In trying to solve this problem, I read , but I couldn't solve the problem. I was granted a visa to Australia few months ago. I’d like to travel to Australia in few days. However, I’ve just renewed my passport and I don’t have enough time to inform them about my passport renewal. Can I travel to Australia by carrying both my old and my new passports? Proving $\frac{\sin x}{x} =\left(1-\frac{x^2}{\pi^2}\right)\left(1-\frac{x^2}{2^2\pi^2}\right) \left(1-\frac{x^2}{3^2\pi^2}\right)\cdots$ How to prove the following product? $$\frac{\sin(x)}{x}= \left(1+\frac{x}{\pi}\right) \left(1-\frac{x}{\pi}\right) \left(1+\frac{x}{2\pi}\right) \left(1-\frac{x}{2\pi}\right) \left(1+\frac{x}{3\pi}\right) \left(1-\frac{x}{3\pi}\right)\cdots$$ Show bigger amplitude of physical pendulum means bigger period Suppose you have a physical . It is true that as amplitude increases, the period increases. Can we demonstrate this fact without explicitly finding the period (which is pretty involved and pretty messy) in:    an intuitive fashion,  rigorously? Avoiding first chance exception messages when the exception is safely handled The following bit of code catches the EOS Exception  using (var reader = new BinaryReader(httpRequestBodyStream)) {      try {         while (true) {             bodyByteList.Add(reader.ReadByte());         }     } catch (EndOfStreamException) { } }   So why do I still receive first-chance exceptions in my console?      A first chance exception of type 'System.IO.EndOfStreamException' occurred in mscorlib.dll   Is there a way to hide these first chance exception messages?