SuperClass object = new SubClass();   Why use a superclass to instantiate a subclass object like above? Because the only way i learnt to instantiate an object is to:   SubClass object = new SubClass();   I'm learning java.
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?
Material Opacity in viewport? I'd like to do motion graphics type work in blender and it would be really helpful if I could see the results of keyframing material opacity to cut items in and out of view.  Blender internal is sufficient, using shadeless materials.  I could have swore there used to be something in view options.  Any ideas? MySQL Error 1093 - Can't specify target table for update in FROM clause How do I detect when someone shakes an iPhone? I want to react when somebody shakes the iPhone. I don't particularly care how they shake it, just that it was waved vigorously about for a split second. Does anyone know how to detect this? Which packages should be loaded after hyperref instead of before? Why is BigDecimal returning a weird value? surjective immersion $\mathbb{R}^2 \to \mathbb{R}^2$ which is not a diffeomorphism Does there exist a surjective immersion $\mathbb{R}^2 \to \mathbb{R}^2$ which is not a diffeomorphism?  I tried to modify $\exp: \mathbb{C} \to \mathbb{C}$ to be surjective, but I find it hard to preserve the property of being immersion.  I also noticed that if we replace $\mathbb{R}^2$ with $S^2$ or any other compact simply connected manifold, no such immersion exists, because then it would be a covering map (as a local diffeomorphism from compact space, thus proper), but since the manifold is simply connected, it must be a diffeomorphism. How do I clean up my dconf database? The topological space $X=\omega_1\cup \{\omega_1\}$ is not first countable but $\omega_1$ is. Here $\omega_1$ denotes the set of all countable ordinals and $\{\omega_1\}$ is the first uncountable ordinal. Cardinality of $\omega_1$ is $\aleph_1.$And also $\omega_1$ is called the limit ordinal meaning it is the limit point of the set $\omega_1.$  Here I want to prove two things. $1)$ $\omega_1$ is first countable. and $2)$ $\{\omega_1\}$ is the limit point of $\omega_1$. But since no sequence converges to $\{\omega_1\}$, using this I could say that our space $X$ is not first countable.  $1)$ The proof of this I got from  with just one question: it says we need to prove that such an $S(y)$ exists,and I'm thinking $S(y)=\cap\{u\in \omega_1:u\gt y\}.$ This is correct$?$ But here is a chance that the countable base around $y$ may be finite and not countably infinite.  $2)$ If possible let us assume that $\omega_1$ is not a limit point of the set $\omega_1.$ $U$ be a nbd of $\omega_1$ that does not intersect $\omega_1.$ Then what are the elements of $U$ like? The ones coming before $\omega_1$  cannot be uncountable because $\omega_1$  is the first. Then they must be countable. This is absurd so no such $U$ exists. Thus $\{\omega_1\}$ is a limit point.  Are my proofs correct? Thank you. How to execute sp_send_dbmail while limiting permissions Is there a way to provide access to users in my database to execute  msdb.dbo.sp_send_dbmail without needing to add them to the MSDB database and the DatabaseMailUserRole?  I've tried this:  ALTER PROCEDURE [dbo].[_TestSendMail] (   @To NVARCHAR(1000),   @Subject NVARCHAR(100),   @Body NVARCHAR(MAX) ) WITH EXECUTE AS OWNER AS      BEGIN         EXEC msdb.dbo.sp_send_dbmail @profile_name = N'myProfile',             @recipients = @To, @subject = @Subject, @body = @Body     END   But I get this error:  The EXECUTE permission was denied on the object 'sp_send_dbmail', database 'msdb', schema 'dbo'.   Thanks! Landscape topography from grayscale image One page website - Effect on SEO I'm considering re-designing my personal website to promote my web services in my local area.  My issue is whether to do a one page website with a scroll-to navigation system. What effect does this have on SEO. As i understand it, you set stuff like h1's and meta description on specific page content. How does this work when all of your different content is on one page? Say we have the following sample and we are trying to estimate the variance of the sample mean of the population.  X = [0, -1, 2, 10, -3]   If I take an increasing number of bootstrap (e.g. 100, 1000, 10,000, 100,0000), the bootstrap distribution of the sample mean gets narrower and narrower. In other words, I can make the bootstrap distribution arbitrarily narrow.   Given the above, what's the point of using a different number of bootstrap samples here? And wouldn't this mean that I could make the standard error of the mean arbitrarily small by just taking more and more bootstrap samples? What am I missing?  Please note that I am doing a proper bootstrap sample in the sense that each bootstrap sample has the same exact size as the original sample (input array). I have installed an Ubuntu server on a VMWare workstation with a space of 20GB storage as seen below;    After the installation I've attached another 40GB worth storage to the existing Ubuntu server installation (seen below);    Now I want to add this 40GB to my / (root) directory or to /var/ directory but my df -h result shows;  root@Userver:~# df -h Filesystem      Size  Used Avail Use% Mounted on /dev/sda1        18G  900M   16G   6% / udev            990M  4.0K  990M   1% /dev tmpfs           400M  308K  399M   1% /run none            5.0M     0  5.0M   0% /run/lock none            999M     0  999M   0% /run/shm none            100M     0  100M   0% /run/user root@Userver:~#   What should I do now? Further, I have only ssh access to the server. What's the recommended way to move a VirtualBox VM to another computer? I use VirtualBox 4.1.x on my Ubuntu machine and I’ve set up several virtual machines. Since there are several ways one can move a virtual machine in VirtualBox to another computer, I was wondering which one is the recommended way:   Use the “Import/Export utility.” Copy the entire virtual machine folder, containing the .vdi and .vbox files. Clone the VDI using “Virtual Media Manager” and then recreate a VM on the target machine but using the cloned VDI as the hard disk.   I have successfully used the 1st method several times and it has always worked. The problem is that after exporting and importing, the disk image is transformed into VMDK and not VDI anymore!  The 2nd method is probably the easiest but I’m not sure that simply copying the files will work or not on the target machine. When searching about this method, I found some people had problems in which they had to edit the VirtualBox.xml file to solve it!  At last, there’s the 3rd method, but it requires the extra work of creating a VM similar to the original VM configuration, which is not desirable.  It’s clear from the above explanation that my desired method is the 2nd one, but I need expert advice on this if it works or not. I don't want any XML editing getting in my way!  What’s the best method of safely transferring my VM’s to another computer with VirtualBox? I am supposed to integrate $f(z)=$$\frac{5}{z}$ from -3 t0 3 but I am having trouble understanding how to do this. I've done the integration the "hard" way by using parametrizations but now I need to use the fact that $f(z)$ is analytic everywhere except at $z=0$ and a different method to perform the integration but I am stumped. Is there a general rule for determining the direction of tension force? Tension, for me, is a tricky thing.  After finishing a related chapter of my book and watching a video, I still can't get a hang of it.  Here is a situation:   My knowledge is that tension, just like normal force, happens in  just the same way, but with the difference of a string attached.  It is understandable that in the picture, the string attached to the hanging mass has a tension directed upward, because it's weight is directed downward. (Action and reaction)  But what intrigues me is that applying the same logic, the horizontal mass is being pulled to the right, it would have been understandable if the tension is directed to the left.   also Can I think of tension as the reaction force when you pull, and normal force when you push?  update If I was to think tension as a reaction force in the first picture for the horizontal mass, then can the frictional force be the action force? (Ehh, I don't think that makes sentence. Friction is always reaction) I am trying to adapt an existing code to a 64 bit machine. The main problem is that in one function, the previous coder uses a void* argument that is converted into suitable type in the function itself. A short example:  void function(MESSAGE_ID id, void* param) {     if(id == FOO) {         int real_param = (int)param;         // ...     } }   Of course, on a 64 bit machine, I get the error:  error: cast from 'void*' to 'int' loses precision   I would like to correct this so that it still works on a 32 bit machine and as cleanly as possible. Any idea ? After installing Adobe PDF reader, it opens files with the .PDF file extension. Ones' default web browser opens .html files and notepad opens .txt files, etc.  Where exactly in the registry are these filetype - program associations stored in the registry?   In other words, how does Windows know with which software/program it must open a certain file(type)? The result of a Google search for &quot;error&quot; and &quot;PREP line&quot; is:  &quot;error&quot; &quot;on line&quot;: 439,000,000 results &quot;error&quot; &quot;in line&quot;: 60.600.000 results &quot;error&quot; &quot;at line&quot;: 35,800,000 results  While on is the indisputable number one, in and at have also very many hits. In the following context, which one should I use.  __ the first line you create an instance of XXX and XXX leads to the runtime error __ the last line.  I think, both prepositions are different. Although the word create refers to the action which is executed while runtime, the former part refers to the actual code that is written. In contrast, the latter part is figurative. I don't refer to the written code. The error does not really occur in the code but the code is the representation of the assembly which fails. Thus, I have two bests guess:  On the first line you create an instance of XXX and XXX leads to the runtime error at the last line. In the first line you create an instance of XXX and XXX leads to the runtime error on the last line. How does Motherboard and CPU affect RAM choice?