I am having a doubt regarding ArrayList and List. In which case we should use ArraryList like:  ArrayList obj = new ArrayList();   And in which case we should use List Interface.  List obj =  new ArrayList();   What is the difference between them?
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?
Under what conditions will healers switch targets? I've been using healers lately, which I haven't really utilized much before. I've noticed that they will sometimes switch targets, even when their original target still lives.   What conditions are needed for healers to switch targets? Selecting specific row in attribute table using ArcPy (without iterating through whole table)? This is a general, community wiki  question and answer pair intended to address any questions   concerning the reasons a site or specific site contents do not appear   in search engine results.      If your question was closed as a duplicate of this question and you   feel that the information provided here does not provide a sufficient   answer, please open a discussion on .   My site (or specific pages on my site) is not appearing in search engine results.  Why isn't my content indexed and what can I do about it? I know as a fact that I've gotten liquids larger than 3 ounces through the TSA scanner systems (such as sunscreen). I was scolded one time for bringing a shampoo container, but I was still ultimately allowed to bring that container through.  In any case, how often are liquids larger than 3 ounces ultimately confisticated, if I put them in a ziploc bag where they can be clearly seen? I would like to insert the below mathematical symbol, it looks like a big Delta but different. Is there command to obtain a similar shape? Making crafted items usable in adventure mode In a map I'm making the player has to survive while locked in a maze. To stop them from breaking out, they will be in adventure mode. However, I still want them to be able to craft items and use them with specified blocks. I have tried several methods already but they all have a flaw.  One method is to have a scoreboard objective called item and giving certain item entities a specific score using something like:  /scoreboard players set @e[type=Item] item 1 {Item:{id:"minecraft:sapling"}}   Then it is possible to select these items with:  /entitydata @e[type=Item,score_item=1,score_item_min=1] {Item:{tag:{CanPlaceOn:["dirt"],HideFlags:24}}}   This works but it requires the item to be dropped, which isn't a problem for saplings, but for tools and other craftable items, it becomes a hassle.  To fix this, I'm currently clearing tools without damage and giving the player a slightly damaged tool in return:  /clear @a minecraft:stone_axe 0 1   /give @a minecraft:stone_axe 1 1 {CanDestroy:["log","log2","leaves","leaves2"],HideFlags:24}   This doesn't work for items without damage values (e.g. torches), but I don't mind these having to be dropped as there aren't too many of these. However, there is another problem. In the nether, the player will have access to an enchantment table and an anvil. This means they can repair enchanted tools, which will cause them to be cleared and replaced with unenchanted ones as soon as they go back to the overworld.  I also thought about using a stat.craftItem scoreboard objective and giving them the usable item if they craft it. However, this would result in the player having a duplicate of every item they crafted, as I think it is impossible to select an item without NBT-data in the /clear command.  Is there any way to make this work? And if not, would it be better to have the player drop all crafted items or have duplicates of them all? Tracking down where disk space has gone on Linux? Decode escaped Url without using HttpUtility.UrlDecode Is there any function that converts an escaped Url string to its unescaped form? System.Web.HttpUtility.UrlDecode() can do that job but I don't want to add a reference to System.Web.dll. Since my app is not a web application, I don't want to add a dependency for only using a function in an assembly.  UPDATE: Check  about the same issue. Can a lambda function call itself recursively in Python? A regular function can contain a call to itself in its definition, no problem.  I can't figure out how to do it with a lambda function though for the simple reason that the lambda function has no name to refer back to.  Is there a way to do it?  How? Add desktop notifications for Chrome or Firefox What is the relationship between MIME types and File .extensions? I may have the wrong idea here, but I thought that:    MIME types are identifying codes, embedded inside a file. File .extensions are idenifying codes, suffixed to the file's name.   I thought, from something I heard in the dim dark ages, that Linux was .extension agnostic... ( maybe it was in the early days, and things have changed since then...? )  I've recently come from the Windows world, where, at the Operating-System level, a file .extension is the only way (as far as I know) to associate it with its relevant Application program.    Because I don't know why, I find it a bit disconcerting that a file named  "fred" and a file named "fred.txt" both open up in a Text Editor.    Is there a clear-cut hierarchy at work here? I've been dealing with this problem for almost 2 hours now, with hardly any progress. I'm to prove the following inequality using induction   $$\sqrt[n+1]{n+1}&lt;\sqrt[n]{n}$$ where $n≥3$, $n∈\mathbb{N}$. How can this be done? Ruby: How to iterate over a range, but in set increments? I started reading "The Mathematics of nonlinear Programming - AL peressini" recently.  Theorem : Suppose that $f(x) , f'(x) ,f''(x)$ exist on the closed interval $[a,b]$. If $x^* ,x $ are two different points of $[a,b]$ , then there exists a point $z$ strictly between $x^*$ and $x$ such that   $$f(x)=f(x^*)+f'(x^*)(x-x^*)+\frac{f''(z)}{2}(x-x^*)^2$$  I tried to prove this theorem using The Fundamental theorem of calculus. But I can not stop it at the second derivative . Do I have to use mean value theorem ? or is there a simple proof for this ? Story about encounter with hostile aliens This is a short story I read in the late 80s or early 90s in an anthology or collection.  Here are the plot points I remember:   A human spaceship encounters a ship with hostile aliens (HA). There may be friendly aliens (FA) on board the human spaceship A human (or perhaps FA) telepath scans the HA and finds they are hostile and bent on conquest of other races The captain and crew decide on a bluff: pretend they are from a large federation of many species, one so big the HA will become discouraged and drop their plans of conquest They invite one or more HA on their ship To pretend that there are many (more) races in their federation, they do things like put a fake control panel in the ships aquarium and claiming the fish in them are one of the races in their federation The HA can't conceive of multiple races cooperating and are convinced there must be some race on top controlling it all. If not, they can just be conquered one at a time This goes on for a little while until, seeing their plan isn't working (via their telepath) the humans change their plan so that when      the ship's cat (so far unseen by the HA) walks in the room, one of the humans loudly calls "The CAT!" causing everyone to stand rigidly at attention while the cat walks around more or less ignoring everyone and everything the way cats do. Having seen the "top dog" and the rigid discipline and fear he instills in everyone else, the aliens "realize" the humans are deluded into thinking all races are equal members in their 'federation", the cats are really in control of a huge empire, and they should not be messed around with. In the following question  the notation $c\in ]a,b[$ is used. What does this mean? I have never seen it before. Write a formula in an Excel Cell using VBA I'm trying to use VBA to write a formula into a cell in Excel. My problem is that when I use a semicolon (;) in my formula, I get an error:     Run-time error 1004   My macro is the following :   Sub Jours_ouvres()     Dim Feuille_Document As String     Feuille_Document = "DOCUMENT"             Application.Worksheets(Feuille_Document).Range("F2").Formula = "=SUM(D2;E2)"     End Sub So, as the title read I happened to overstayed my Schengen visa for 6 months does anyone know what the consequences could be. If I wanted to return back to Saudi Arabia. How to start a GUI application from cron? How can I change the umask for one command only? How can I interactively execute a command in Linux (zsh, if it matters) with a different umask from the default, for one command only? Perhaps a combination of commands combined in a single line? The new umask should apply only to that command and return to its default value for the next command entered.  Ideally the command would be agnostic to the default umask in force before its entered (in other words, the default umask doesn't have to specified).