Why would I instantiate an ArrayList referring to the interface List like this:  List&lt;T&gt; mylist = new ArrayList&lt;T&gt;();   Instead of simply:  ArrayList&lt;T&gt; mylist = new ArrayList&lt;T&gt;();
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?
How do I diagnose the source of focus problem in a camera? Probably a novice question, but how do I correctly diagnose from a photo for what reason that camera wasn't able to focus properly?  It can be any 1 of the following   Unsteady hand Lens issue Metering Re-Calibration required in camera or ...   Is there a set of unsaid protocols that needs to be followed by a photographer?  Goal is to get a sharp and crisp image prior to editing.  [PS: I own a Nikon D5200.] From      Every linear function on a finite-dimensional space is continuous.   I was wondering what the domain and codomain of such linear function are?   Are they any two topological vector spaces (not necessarily the same), as along as the domain is finite-dimensional? Can the codomain be a different normed space (and may not be finite-dimensional)?  I asked this because I saw elsewhere the same statement except the domain is a finite-dimensional normed space, and am also not sure if the codomain can be a different normed space (and may not be finite-dimensional).  Thanks and regards! Is there a difference between installing an application via Ubuntu Software Center or a terminal? I would like to ask a very basic question but I have never thought about it before. Well, when someone installs an application from terminal, he has to add the repository first, right? On the other side, when someone installs an application from the Ubuntu Software Center, is the repository then added automatically?  I am asking those questions to figure out this: When I run update and then upgrade, will this application be upgraded or not? Is the result same in two options? Get current editor toolbar tab via Python? Is it wrong to say $ \sqrt{x} \times \sqrt{x} =\pm x,\forall x \in \mathbb{R}$? Is it wrong to say $$ \sqrt{x} \times \sqrt{x} =\sqrt{x^2}= \pm x$$ I am quite sure that  $\sqrt{(x)^2} = \pm(x)$  But, does $\sqrt{x } \times \sqrt{x} =- (x)$ doesn't holds in $\mathbb{R}$ but if we assume $\mathbb{C}$ it holds right? Pixel Perfect 2D tiles I'm trying to make an 64x64 tilemap using Super Tilemap Editor &amp; Unity but my tiles looks terrible. I did my research about pixel perfect 2D and all of the solutions were for pixel art, they didn't work for me.  I have the following tileset I made in Adobe Illustrator as an example    Tiles looks like this when placed in game (1x zoom)    I'm pretty sure they're not 64x64 in game, they also look pixelated probably because they're smaller than they actually are on camera.  So my question is, how can I calculate the correct camera size for 64x64 tiles and do I have to make any changes in order to make sprites look pixel perfect? I'm currently using 1080/64/2=8.4375 (vertical resolution / PPU / 2) as camera size. Syntax error on print with Python 3 ...on Finnis's view all distinct instances of basic goods are incommensurable — none is of more, less, or equal value with any other. &mdash;    I expect to see more or less than any other, but then equal shows up, and is followed by with. But since with any other cannot replace than any other, do you think this sentence illegitimately omits something? How do I calculate the run rate in cricket? How could I define function with function such as Coefficient? Using dynamic where clauses in Entity Framework What does \s! do? 1st example:  \starttypescript [\s!serif] [paratype]   \definefontsynonym [ParatypeSerif-Regular] [\s!name:PTSerif-Regular] [\s!features=\s!default]   \definefontsynonym [ParatypeSerif-Italic] [\s!name:PTSerif-Italic] [\s!features=\s!default]   \definefontsynonym [ParatypeSerif-Bold] [\s!name:PTSerif-Bold] [\s!features=\s!default]   \definefontsynonym [ParatypeSerif-BoldItalic] [\s!name:PTSerif-BoldItalic] [\s!features=\s!default] \stoptypescript   2nd example:  \definefont[SerifS][\s!file:GenBkBasR at \smallfontsize]   Is \s! only related to fonts? Should I use it in my typescript files? Prove that $\sin(\theta) + \sin(\theta+2\pi/3) + \sin(\theta+4\pi/3) = 0 $ for any angle $\theta$.   This came up in the context of electricity:  It is common in electrical power engineering to use three-phase circuits with sinusoidal currents out of phase with each other by 120 degrees. The benefit of this is that the currents sum to zero at the neutral point meaning less copper is required for the system.    However, while I know that the three phasors always sum to zero, and can see visually, as in the figure that this is true at every point, how can this be shown more formally, or algebraically? How can't install a 338KB app when I have 474MB free? I have a Motorola phone, with 8GB of internal memory.  To my surprise, in a few days, I had 474MB of free space, but couldn't install a 338KB app!! So, clearly the limit of ~25MB referred to in some comments ( and ) are not always the case. A user just told me the following:     Actually it's "25MB or 10% of the storage", whichever is hit first. So   with e.g. 10 GB internal storage, it would hit you as soon as you drop   below 1 GB free. Crazy, but that's what it is.   Actually, that's not correct, because I didn't have to free up 1GB of internal memory. But anyway, half a gigabyte is enough to run a full operational system. I've seen similar complaints of hundreds of MB not enough to install apps ~ 1MB or similar small operations ( and ).  What's wrong here? How do I show apt-get package management history via command line? "Battery Health" in macOS Catalina 10.15.5? I have just installed the macOS Catalina 10.15.5 update on my 11" Mid 2013 MacBook Air. The update is working fine.  The MacBook Air specifications on the Wikipedia page says that this model has a lithium-ion battery, 'tho I haven't unscrewed the case to look. But the new Battery Health controls in System Preferences → Energy Saver don't appear.  Not a lithium-ion battery? Or perhaps other differences in this model prevent Battery Health from showing up? Something else? Comment hint not disappearing when I start to type comment If I click "add comment", the comment hint (placeholder; "Request clarification or add information.") is not a hint, but editable text. If I delete the text and click outside of the comment then the hint appears as it should and when I click back into the comment box the hint disappears as it should.   I am on Internet Explorer 10.0.7.  Am I just oblivious and this is how it has always been (having to delete the comment hint), or is this a bug? What is a lambda (function)? For a person without a comp-sci background, what is a lambda in the world of Computer Science? Proper usage of "since" and "from" with regard to duration of time Are there any rules related to the creation of a ?   I am aware of the creation method for the amulet. But I'm asking about creating the actual construct.