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  • Can you cast an object to one that implements an interface? (JAVA)

    - by DDP
    Can you cast an object to one that implements an interface? Right now, I'm building a GUI, and I don't want to rewrite the Confirm/Cancel code (A confirmation pop-up) over and over again. So, what I'm trying to do is write a class that gets passed the class it's used in and tells the class whether or not the user pressed Confirm or Cancel. The class always implements a certain interface. Code: class ConfirmFrame extends JFrame implements ActionListener { JButton confirm = new JButton("Confirm"); JButton cancel = new JButton("Cancel"); Object o; public ConfirmFrame(Object o) { // Irrelevant code here add(confirm); add(cancel); this.o = (/*What goes here?*/)o; } public void actionPerformed( ActionEvent evt) { o.actionPerformed(evt); } } I realize that I'm probably over-complicating things, but now that I've run across this, I really want to know if you can cast an object to another object that implements a certain interface.

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  • Visual Studio IDE - how do you quickly find the implementation(s) of an interface's method?

    - by Jess
    Is there a quick way to find all of the implementations of, not references to, an interface's method/property/etc? Here's some sample code: public class SomeClass : IBaseClass { public Int32 GetInt() { return 1; } } public interface IBaseClass { public Int32 GetInt(); } public class SomeOtherClass { ISomeClass _someClass; private TestMethod() { _someClass = new SomeClass(); _someClass.GetInt(); } } I want to quickly get to SomeClass.GetInt() while reviewing SomeOtherClass.TestMethod(). If I right click on _someClass.GetInt() and click 'Go To Definition', it takes me to the interface. If I click 'Find All References', I could potentially see a list of all uses ... not just the classes that implement the GetInt() method. Is there a faster way to find this? Any tips from other developers? We are using D.I. for most of our dependencies, which means that tracing through deeply nested code takes forever.

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  • Why are Objective-C instance variables declared in an interface?

    - by Chase
    I'm just getting into Objective-C (Java is my primary OO language). Defining an object's instance variables in the interface instead of the class seems strange. I'm used to an interface being a public API definition with nothing besides method signatures (not counting constants here). Is there some reason that state is defined in an interface (even if it is private) and behaviour is defined in a class. It just seems odd that since objects are state+behavior that the definition would be split into two separate places. Is it a design benefit is some way? A pain in the rear issue that you are just forced to deal with in Objective-C? A non-issue, just different? Any background on why it's done this way? Or can you put object state in a class and I just haven't hit that part in my book yet?

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  • Are there any Open source Admin Panel based on PHP and jQuery?

    - by Pablo
    I've try many CMS flavors like MODx, Drupal, Joomla for the admin Panel but they can't seem to manage my existing data, like the users. Im planing on building a admin Control Panel for my site and i was wondering if there is something out there which i can start working with instead of starting from scratch. UPDATE: To do simple tasks like: Managing my users Managing my content( the site is an image sharing site, so in this case images) I was looking more into a graphical interface more then a system as i have lots of costume content and data like the users.

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  • Unable to make admin interface connection to server when moving a mailbox.

    - by TheCodeMonk
    I have an existing Exchange 2003 server running on Windows Server 2003. I am in the process of replacing our current server infrastructure and virtualizing it all in Hyper-V. I have Essential Business Server 2008 installed in 3 separate VMs and running. Everything seems to be working fine so far. I am now trying to migrate my exchange mailboxes over to the new exchange server in the messaging server and every time I try I get this error: MapiExceptionNetworkError: Unable to make admin interface connection to server. (hr=0x80040115, ec=-2147221227) I have done some searching and found solutions like adding the computer to the exchange domain servers groups and install group, also making sure the user logged into the new server is in the proper groups. I also saw a solution in making sure that any unused NICs are disabled. I've tried all that to no avail.

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  • Bad to be logged in as admin all the time?

    - by poke
    At the office where I work, three of the other members of the IT staff are logged into their computers all the time with accounts that are members of the domain administrators group. I have serious concerns about being logged in with admin rights (either local or for the domain). As such, for everyday computer use, I use an account that just has regular user privelages. I also have an different account that is part of the domain admins group. I use this account when I need to do something that requires elevated privilages on my computer, one of the servers, or on another user's computer. What is the best practice here? Should network admins be logged in with rights to the entire network all the time (or even their local computer for that matter)?

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  • If I change Windows admin user password, then I can't login to Outlook, why?

    - by Tom
    I am seeing this strange behaviour with Windows 7 and Outlook 2010. If I change the password of User1 (Admin user), login, and start Outlook, it asks for the pasword. It keeps saying "password incorrect". I can login by using same password on the webclient. If I change User1's password back to last one, Outlook starts without any prompting and I'm able to send and receive emails. Is there any link between the user account, its password and the PST file's password?

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  • Best Practices: How can admin deploy software to 100s of PC ?

    - by Gopal
    Hi ... The Environment: I am working for a college. We have a couple of labs (about 100 PCs) for students. At the end of the semester, the PCs will be full of viruses, corrupt system files, all sorts of illegal downloads etc. (everything you can expect from a student environment). At the end of the semester, we would like to wipe out all the systems and do a clean install (WindowsXP + a set of application suites) to get ready for the next batch of students. Question: Is there any free software that will enable an admin to deploy a clean disk image to all the PCs in one go?

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  • IP KVM switch, or serial console box for remote admin?

    - by grahzny
    We have a small server farm (11 now, may add more in the future) of HP Proliant DL160 G6s. They all run either Linux (server only, no X11) or VMware ESX. We had intended to get models with iLO, in case BIOS-level remote admin became an issue, but that didn't happen. I had an IP KVM switch recommended to me (along with some sort of Remote Reboot hardware.) I've since realized that none of our machines need GUI administration, so perhaps a serial console switch would be a cheaper and more appropriate option. Something like this: http://www.kvm-switches-online.com/serimux-cs-32.html Do you folks have an opinions on which way is a better choice? Should we go for the ease of setup (plug and go, instead of turning on the feature in the BIOS and making sure the serial settings are correct) and the flexibility of an IP KVM switch even with the extra cost? Or is a serial console switch just fine?

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  • Can't Access a file I downloaded since I don't have permissions yet I am admin?

    - by chobo2
    Hi I downloaded some file and everytime I try to copy it or move it somewhere I get these errors Windows cannot access the specified device, path , or file. You may not have the appropriate permissions to access the item. You need permission to perform this action You require permission from "user(where this is my pc name/myusername)" to make changes to this file. Yet I am an admin and it is my only account on this computer and it saying to me I need permissions to open it up from "chobo2" user yet that's the account I am logged in as. I don't get it. How do I disable this stupid message so I can access every file I want. I am using windows 7 ultimate 64bit. As far as I know I have full permissions set so I don't know why I am getting this.

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  • Why does this work: Windows same local admin username and password, able to access other computer?

    - by Ankush
    I've two machines MachineA and MachineB. Both have two local accounts which have same username . Both accounts are local admin on those machines. If they have same password, I'm able to access \\MachineA\C$ from MachineB. But if I change any one password above doesn't work. And it prompts for username and password. Now if I provide MachineA\username and password, it then connects. Why isn't there a prompt for password when passwords are same? I expected passwords to be hashed with random salt, how does windows know passwords are same and authorize access? These machines are running Windows Server 2008 R2. PS. I've created following reg key to enable drive access HKLM:\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\System\LocalAccountTokenFilterPolicy to 1

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  • How to ssh to my dorm computer with shared public IP and no admin rights over the router?

    - by Aamir
    First of all, I am not a Linux or ssh newbie. I have searched for this problem on many forums extensively but nobody seemed to have discussed this. Please help me! I live in a student dorm (off-campus) and all students of the dorm share the same WAN IP (Internet or public IP), which is fortunately static. I am not an admin and have no control over the router that assigns private IP's to all of the students, so I can't really forward port 22 to my computer :( Is it still possible to establish an ssh connection to my dorm computer from a computer on campus?

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  • Windows Filtering Platform not turning off until admin logon. Win2008R2sp1

    - by rjt
    Just installed Windows Server 2008R2 SP1 to see if it would fix this problem, but it didn't. Until an administrator logs onto the domain controller, there are many events that WFP blocked a connection from Server60 to Server60 or Server60 to Server70. Both server60 and server70 are the domain controllers. One the admin logs on, the WFP events stop. The firewall is off by default GPO. Yes, i know that the WFP kicks in during the boot up sequence until the firewall takes over or in my case does not take over (since Vista), but i clearly should not have to autologon to a domain controller and call autolock or something. Example event LEVEL = Information Source = Microsoft Windows Security Auditing EventID = 5152 "Filtering Platform Packet Drop" and its evil twin id = 5157 "Filtering Platform Connection" "The Windows Filtering platform has blocked a connection." Direction %%14593 SourceAddress 192.168.10.60 SourcePort 49677 DestAddress 192.168.10.60 DestPort 389 Protocol 6 FilterRTID 65667 LayerName %%14611 LayerRTID 48 RemoteUserID S-1-0-0 RemoteMachineID S-1-0-0 windows-server-2008-r2 WFP BFE WindowsFilteringPlatform BaseFilteringEngine

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  • Change Win7 taskbar position (overriding GPO, Registry Editor, Admin. Rights)

    - by diegocavazos53
    I run the computer center of my Faculty and the problem is that users manage to change the Win7 taskbar position. I don't really know how they do this as far as I have applied many group policies that are specific to the taskbar (like locking it). I have also disallowed users from entering new registry keys or executing the command prompt (or employing scripts). They have regular user rights and many Win7 tweaking programs need administrator rights to make changes to the GUI. So in other words, the taskbar is locked, there is a policy that sets its position to the lower part of the screen, users can't see the control panel, add registry keys, use the command prompt and don't have admin. rights. How do they keep moving the taskbar position to the upper part of the screen? Any ideas would be greatly appreciated. Thank you.

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  • mod_security: How to allow ssh/http access for admin?

    - by mattesque
    I am going to be installing mod_security on my AWS EC2 Linux instance tonight and need a little help/reassurance. The only thing I am truly worried about right now is making sure my (admin) access to the instance and webserver is maintained w/o compromising security. I use ssh (port 22) and http (80) to access this and I've read horror stories from other EC2 users claiming they were locked out of their sites once they put up a firewall. So my question boils down to: What settings should I put in the mod_security conf file to make sure I can get in on those ports? IP at home is not static. (Hence the issue) Thanks so, so, so much.

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  • MOSS 2007 WSP Retraction 'Error"

    - by juanlarios
    This one is a quick post , but I thought I would post this information as I could not find anything that helped me on this specific scenario. Please read the entire article before taking action as there are some irreversable or very troublesome routes I caution about! Problem: I had a client trying to retract a WSP from Central Admin and would eventually go to an, 'Error' State. I could not retract it and after looking at event logs I figured it was a problem with security. I tried several accounts, checked the databases to see if there was some issue with readonly databases and nothing was working.   Solution: Delete the solution from central admin! Yes, I said it. With StsAdm , just delete the solution from Central Admin using this command: "C:\Program Files\Common Files\Microsoft Shared\web server extensions\12\BIN\STSADM.exe" -o deletesolution -name "yoursolution.wsp" What has just happened is that Central Admin does not know about the WSP anymore but the feature and any deployed files are still on the server. For whatever reason SharePoint was not able to retract the files as it normally does. Now you can do one of two things, you can add the solution again to central admin and deploy overtop of the deployed files so it overrides them, or simply clean up the files manually. I re-added the solution through stsadm, but then deployed through stsadm using the -force option in the command. This overrides the existing files on the server. If you deploy through Central admin it will tell you you need the -force option that is not offered as part of the UI in central admin. Use the following command: "C:\Program Files\Common Files\Microsoft Shared\web server extensions\12\BIN\STSADM.exe" -o deploysolution -name "YourSolution.wsp" -immediate -allowgacdeployment -force Just to make sure everything was good, I retracted to solution again, and it worked! then I deleted the solution from central admin alltogether. Then I checked the server and noticed all the files that were deployed with the WSP were cleaned up properly. I then re-added the new WSP the client was looking to install (an Updated WSP). Conclusion: I have no idea why it was not able to retract, but I have seen this several times. I don't know if has to do with security of certain accounts. Althought it's anoying at times, it is fairly easy to fix if you have good instructions. Hope it helps you out!   ***WORD OF CAUTION - if you clean up the files manually you might want to uninstall the features through STSADM commands as SharePOint might still recognize the features that were deployed as the WSP. You might not want to get into the mess of deleting files that are still part of activated or installed Features. THis is why I suggest doing what I did.

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  • Pros and Cons of various career paths [closed]

    - by Snitse
    What are the advantages and disadvantages of various career paths within CS? By a path I mean something like: Web Development GUI Development Sys admin/DB admin/network admin Security (maybe should be grouped with sys admin) Programming back end (like a C programmer) Algorithm Development heavy programming And any other you think should be in this list. What are the various areas in which each of these professions excels, or lags?

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  • How to give specific url using htaccess? [on hold]

    - by Dash
    I am a web developer using codeigniter.I want to give a specific url to certain pages on my website.Is it possible using htaccess?I visited following sites but couldn't find anything such there: Bluehost Tutplus and some others too. What i really wanna do is when the admin is logged in the link should be http://localhost/admin-ci/index.php/admin/index.php/dashboard and if user logs in then the link should be http://localhost/admin-ci/user/index.php/dashboard.Will htaccess be able to do this?

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  • is it possible to have duplicated folders on /home folder new partition as an error?

    - by ranna
    i move my home directory to it's own partition but i end with what it seems to be a duplicated home folders (there are 2 accounts admin and everyones account) i have "admin and everyones" folders and then i have in hide ".ecryptfs" inside i had again "admin and everyones" folder inside there is .encryptfs and .private inside each account cant read it's content as seems encrypted. which of both folders im able to delete the ones inside .encryptfs or the other showing in unhide mode "admin and everyones"? it seems is dulpicated as have the same file size.

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  • Trying to change a ubuntu user's password, Authentication token manipulation err

    - by beagleguy
    hey all, I'm trying to create a local user on a new ubuntu box my admin set up. I'm unable to change the password, I keep getting the error below. The user gets added to the shadow file but I can't get it to set a password. Any ideas? I've googled for over an hour :( thanks! admin@theserver:~$ sudo useradd jamz [sudo] password for admin: admin@theserver:~$ sudo passwd jamz passwd: Authentication token manipulation error passwd: password unchanged admin@theserver:~$

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  • How can I automatically elevate a COM interface used for automation?

    - by Jim Flood
    I have a Windows service built with ATL to expose a LocalServer32 COM interface for a set of admin commands used for configuring the service, and these can be used from VBScript for example: Set myObj = WScript.CreateObject("MySvc.Administrator") myObj.DoSomething() I want DoSomething to run elevated, and I would like the UAC prompt to come up automatically when this is called by the VBScript. Is this possible? I know I can run the script in an elevated command shell, and that I can use objShell.ShellExecute WScript.FullName, Chr(34) & WScript.ScriptFullName & Chr(34), vbNullString, "runas" for example, to run the VBScript itself elevated, and either of those work fine -- the COM method finds itself elevated. However, AFAIK getting an elevated Explorer window on the desktop is convoluted (it's not as simple as right-clicking Start/Accessories/Windows Explorer/Run as Administrator, which doesn't actually elevate.) I want a user in the local admin group to be able to drag-and-drop files and folders onto the script, and then have the script call the admin COM interface with those pathnames as arguments. (And I am hoping for something simpler than monkeying around with the args and using ShellExecute "runas".) I've tried setting UAC Execution Level to requireAdministrator in the service EXE's manifest, and setting Elevated/Enabled = 1 and LocalizedString in the registry for the MySvc.Administrator class, and these don't do the trick.

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  • C++ destructor problem with boost::scoped_ptr

    - by bb-generation
    I have a question about the following code: #include <iostream> #include <boost/scoped_ptr.hpp> class Interface { }; class A : public Interface { public: A() { std::cout << "A()" << std::endl; } virtual ~A() { std::cout << "~A()" << std::endl; } }; Interface* get_a() { A* a = new A; return a; } int main() { { std::cout << "1" << std::endl; boost::scoped_ptr<Interface> x(get_a()); std::cout << "2" << std::endl; } std::cout << "3" << std::endl; } It creates the following output: 1 A() 2 3 As you can see, it doesn't call the destructor of A. The only way I see to get the destructor of A being called, is to add a destructor for the Interface class like this: virtual ~Interface() { } But I really want to avoid any Implementation in my Interface class and virtual ~Interface() = 0; doesn't work (produces some linker errors complaining about a non existing implementation of ~Interface(). So my question is: What do I have to change in order to make the destructor being called, but (if possible) leave the Interface as an Interface (only abstract methods).

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  • How do I change the Admin password on a Ubee DVW3201B?

    - by Iszi
    I must admit that I feel rather foolish having to ask this. I recently switched ISPs, and the new one gave us a Ubee DVW3201B as our home gateway. I want to change the Administrator username/password from the defaults, but I've been having some difficulty. Every time, after I save the new username and password, I'm prompted to re-authenticate to the administration interface. It fails no matter what I try. I've tried using: New username / New password Default username / New password Default username / Default password None of the above works. This has happened twice now, with my only recourse after failure being to do a reset to factory defaults (press and hold the hard reset button for 10 seconds). Is there something I'm missing?

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  • Followup: Python 2.6, 3 abstract base class misunderstanding

    - by Aaron
    I asked a question at Python 2.6, 3 abstract base class misunderstanding. My problem was that python abstract base classes didn't work quite the way I expected them to. There was some discussion in the comments about why I would want to use ABCs at all, and Alex Martelli provided an excellent answer on why my use didn't work and how to accomplish what I wanted. Here I'd like to address why one might want to use ABCs, and show my test code implementation based on Alex's answer. tl;dr: Code after the 16th paragraph. In the discussion on the original post, statements were made along the lines that you don't need ABCs in Python, and that ABCs don't do anything and are therefore not real classes; they're merely interface definitions. An abstract base class is just a tool in your tool box. It's a design tool that's been around for many years, and a programming tool that is explicitly available in many programming languages. It can be implemented manually in languages that don't provide it. An ABC is always a real class, even when it doesn't do anything but define an interface, because specifying the interface is what an ABC does. If that was all an ABC could do, that would be enough reason to have it in your toolbox, but in Python and some other languages they can do more. The basic reason to use an ABC is when you have a number of classes that all do the same thing (have the same interface) but do it differently, and you want to guarantee that that complete interface is implemented in all objects. A user of your classes can rely on the interface being completely implemented in all classes. You can maintain this guarantee manually. Over time you may succeed. Or you might forget something. Before Python had ABCs you could guarantee it semi-manually, by throwing NotImplementedError in all the base class's interface methods; you must implement these methods in derived classes. This is only a partial solution, because you can still instantiate such a base class. A more complete solution is to use ABCs as provided in Python 2.6 and above. Template methods and other wrinkles and patterns are ideas whose implementation can be made easier with full-citizen ABCs. Another idea in the comments was that Python doesn't need ABCs (understood as a class that only defines an interface) because it has multiple inheritance. The implied reference there seems to be Java and its single inheritance. In Java you "get around" single inheritance by inheriting from one or more interfaces. Java uses the word "interface" in two ways. A "Java interface" is a class with method signatures but no implementations. The methods are the interface's "interface" in the more general, non-Java sense of the word. Yes, Python has multiple inheritance, so you don't need Java-like "interfaces" (ABCs) merely to provide sets of interface methods to a class. But that's not the only reason in software development to use ABCs. Most generally, you use an ABC to specify an interface (set of methods) that will likely be implemented differently in different derived classes, yet that all derived classes must have. Additionally, there may be no sensible default implementation for the base class to provide. Finally, even an ABC with almost no interface is still useful. We use something like it when we have multiple except clauses for a try. Many exceptions have exactly the same interface, with only two differences: the exception's string value, and the actual class of the exception. In many exception clauses we use nothing about the exception except its class to decide what to do; catching one type of exception we do one thing, and another except clause catching a different exception does another thing. According to the exception module's doc page, BaseException is not intended to be derived by any user defined exceptions. If ABCs had been a first class Python concept from the beginning, it's easy to imagine BaseException being specified as an ABC. But enough of that. Here's some 2.6 code that demonstrates how to use ABCs, and how to specify a list-like ABC. Examples are run in ipython, which I like much better than the python shell for day to day work; I only wish it was available for python3. Your basic 2.6 ABC: from abc import ABCMeta, abstractmethod class Super(): __metaclass__ = ABCMeta @abstractmethod def method1(self): pass Test it (in ipython, python shell would be similar): In [2]: a = Super() --------------------------------------------------------------------------- TypeError Traceback (most recent call last) /home/aaron/projects/test/<ipython console> in <module>() TypeError: Can't instantiate abstract class Super with abstract methods method1 Notice the end of the last line, where the TypeError exception tells us that method1 has not been implemented ("abstract methods method1"). That was the method designated as @abstractmethod in the preceding code. Create a subclass that inherits Super, implement method1 in the subclass and you're done. My problem, which caused me to ask the original question, was how to specify an ABC that itself defines a list interface. My naive solution was to make an ABC as above, and in the inheritance parentheses say (list). My assumption was that the class would still be abstract (can't instantiate it), and would be a list. That was wrong; inheriting from list made the class concrete, despite the abstract bits in the class definition. Alex suggested inheriting from collections.MutableSequence, which is abstract (and so doesn't make the class concrete) and list-like. I used collections.Sequence, which is also abstract but has a shorter interface and so was quicker to implement. First, Super derived from Sequence, with nothing extra: from abc import abstractmethod from collections import Sequence class Super(Sequence): pass Test it: In [6]: a = Super() --------------------------------------------------------------------------- TypeError Traceback (most recent call last) /home/aaron/projects/test/<ipython console> in <module>() TypeError: Can't instantiate abstract class Super with abstract methods __getitem__, __len__ We can't instantiate it. A list-like full-citizen ABC; yea! Again, notice in the last line that TypeError tells us why we can't instantiate it: __getitem__ and __len__ are abstract methods. They come from collections.Sequence. But, I want a bunch of subclasses that all act like immutable lists (which collections.Sequence essentially is), and that have their own implementations of my added interface methods. In particular, I don't want to implement my own list code, Python already did that for me. So first, let's implement the missing Sequence methods, in terms of Python's list type, so that all subclasses act as lists (Sequences). First let's see the signatures of the missing abstract methods: In [12]: help(Sequence.__getitem__) Help on method __getitem__ in module _abcoll: __getitem__(self, index) unbound _abcoll.Sequence method (END) In [14]: help(Sequence.__len__) Help on method __len__ in module _abcoll: __len__(self) unbound _abcoll.Sequence method (END) __getitem__ takes an index, and __len__ takes nothing. And the implementation (so far) is: from abc import abstractmethod from collections import Sequence class Super(Sequence): # Gives us a list member for ABC methods to use. def __init__(self): self._list = [] # Abstract method in Sequence, implemented in terms of list. def __getitem__(self, index): return self._list.__getitem__(index) # Abstract method in Sequence, implemented in terms of list. def __len__(self): return self._list.__len__() # Not required. Makes printing behave like a list. def __repr__(self): return self._list.__repr__() Test it: In [34]: a = Super() In [35]: a Out[35]: [] In [36]: print a [] In [37]: len(a) Out[37]: 0 In [38]: a[0] --------------------------------------------------------------------------- IndexError Traceback (most recent call last) /home/aaron/projects/test/<ipython console> in <module>() /home/aaron/projects/test/test.py in __getitem__(self, index) 10 # Abstract method in Sequence, implemented in terms of list. 11 def __getitem__(self, index): ---> 12 return self._list.__getitem__(index) 13 14 # Abstract method in Sequence, implemented in terms of list. IndexError: list index out of range Just like a list. It's not abstract (for the moment) because we implemented both of Sequence's abstract methods. Now I want to add my bit of interface, which will be abstract in Super and therefore required to implement in any subclasses. And we'll cut to the chase and add subclasses that inherit from our ABC Super. from abc import abstractmethod from collections import Sequence class Super(Sequence): # Gives us a list member for ABC methods to use. def __init__(self): self._list = [] # Abstract method in Sequence, implemented in terms of list. def __getitem__(self, index): return self._list.__getitem__(index) # Abstract method in Sequence, implemented in terms of list. def __len__(self): return self._list.__len__() # Not required. Makes printing behave like a list. def __repr__(self): return self._list.__repr__() @abstractmethod def method1(): pass class Sub0(Super): pass class Sub1(Super): def __init__(self): self._list = [1, 2, 3] def method1(self): return [x**2 for x in self._list] def method2(self): return [x/2.0 for x in self._list] class Sub2(Super): def __init__(self): self._list = [10, 20, 30, 40] def method1(self): return [x+2 for x in self._list] We've added a new abstract method to Super, method1. This makes Super abstract again. A new class Sub0 which inherits from Super but does not implement method1, so it's also an ABC. Two new classes Sub1 and Sub2, which both inherit from Super. They both implement method1 from Super, so they're not abstract. Both implementations of method1 are different. Sub1 and Sub2 also both initialize themselves differently; in real life they might initialize themselves wildly differently. So you have two subclasses which both "is a" Super (they both implement Super's required interface) although their implementations are different. Also remember that Super, although an ABC, provides four non-abstract methods. So Super provides two things to subclasses: an implementation of collections.Sequence, and an additional abstract interface (the one abstract method) that subclasses must implement. Also, class Sub1 implements an additional method, method2, which is not part of Super's interface. Sub1 "is a" Super, but it also has additional capabilities. Test it: In [52]: a = Super() --------------------------------------------------------------------------- TypeError Traceback (most recent call last) /home/aaron/projects/test/<ipython console> in <module>() TypeError: Can't instantiate abstract class Super with abstract methods method1 In [53]: a = Sub0() --------------------------------------------------------------------------- TypeError Traceback (most recent call last) /home/aaron/projects/test/<ipython console> in <module>() TypeError: Can't instantiate abstract class Sub0 with abstract methods method1 In [54]: a = Sub1() In [55]: a Out[55]: [1, 2, 3] In [56]: b = Sub2() In [57]: b Out[57]: [10, 20, 30, 40] In [58]: print a, b [1, 2, 3] [10, 20, 30, 40] In [59]: a, b Out[59]: ([1, 2, 3], [10, 20, 30, 40]) In [60]: a.method1() Out[60]: [1, 4, 9] In [61]: b.method1() Out[61]: [12, 22, 32, 42] In [62]: a.method2() Out[62]: [0.5, 1.0, 1.5] [63]: a[:2] Out[63]: [1, 2] In [64]: a[0] = 5 --------------------------------------------------------------------------- TypeError Traceback (most recent call last) /home/aaron/projects/test/<ipython console> in <module>() TypeError: 'Sub1' object does not support item assignment Super and Sub0 are abstract and can't be instantiated (lines 52 and 53). Sub1 and Sub2 are concrete and have an immutable Sequence interface (54 through 59). Sub1 and Sub2 are instantiated differently, and their method1 implementations are different (60, 61). Sub1 includes an additional method2, beyond what's required by Super (62). Any concrete Super acts like a list/Sequence (63). A collections.Sequence is immutable (64). Finally, a wart: In [65]: a._list Out[65]: [1, 2, 3] In [66]: a._list = [] In [67]: a Out[67]: [] Super._list is spelled with a single underscore. Double underscore would have protected it from this last bit, but would have broken the implementation of methods in subclasses. Not sure why; I think because double underscore is private, and private means private. So ultimately this whole scheme relies on a gentleman's agreement not to reach in and muck with Super._list directly, as in line 65 above. Would love to know if there's a safer way to do that.

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  • How can I define a clojure type that implements the servlet interface?

    - by Rob Lachlan
    I'm attempting to use deftype (from the bleeding-edge clojure 1.2 branch) to create a java class that implements the java Servlet interface. I would expect the code below to compile (even though it's not very useful). (ns foo [:import [javax.servlet Servlet ServletRequest ServletResponse]]) (deftype servlet [] javax.servlet.Servlet (service [this #^javax.servlet.ServletRequest request #^javax.servlet.ServletResponse response] nil)) But it doesn't compile. The compiler produces the message: Mismatched return type: service, expected: void, had: java.lang.Object [Thrown class java.lang.IllegalArgumentException] Which doesn't make sense to me, because I'm returning nil. So the fact that the return type of the method is void shouldn't be a problem. For instance, for the java.util.Set interface: (deftype bar [#^Number n] java.util.Set (clear [this] nil)) compiles without issue. So what am I doing wrong with the Servlet interface? To be clear: I know that the typical case is to subclass one of the servlet abstract classes rather than implement this interface directly, but it should still be possible to do this. Stack Trace: The stack trace for the (deftype servlet... is: Mismatched return type: service, expected: void, had: java.lang.Object [Thrown class java.lang.IllegalArgumentException] Restarts: 0: [ABORT] Return to SLIME's top level. Backtrace: 0: clojure.lang.Compiler$NewInstanceMethod.parse(Compiler.java:6461) 1: clojure.lang.Compiler$NewInstanceExpr.build(Compiler.java:6119) 2: clojure.lang.Compiler$NewInstanceExpr$DeftypeParser.parse(Compiler.java:6003) 3: clojure.lang.Compiler.analyzeSeq(Compiler.java:5289) 4: clojure.lang.Compiler.analyze(Compiler.java:5110) 5: clojure.lang.Compiler.analyze(Compiler.java:5071) 6: clojure.lang.Compiler.eval(Compiler.java:5347) 7: clojure.lang.Compiler.eval(Compiler.java:5334) 8: clojure.lang.Compiler.eval(Compiler.java:5311) 9: clojure.core$eval__4350.invoke(core.clj:2364) 10: swank.commands.basic$eval_region__673.invoke(basic.clj:40) 11: swank.commands.basic$eval_region__673.invoke(basic.clj:31) 12: swank.commands.basic$eval__686$listener_eval__687.invoke(basic.clj:54) 13: clojure.lang.Var.invoke(Var.java:365) 14: foo$eval__2285.invoke(NO_SOURCE_FILE) 15: clojure.lang.Compiler.eval(Compiler.java:5343) 16: clojure.lang.Compiler.eval(Compiler.java:5311) 17: clojure.core$eval__4350.invoke(core.clj:2364) 18: swank.core$eval_in_emacs_package__320.invoke(core.clj:59) 19: swank.core$eval_for_emacs__383.invoke(core.clj:128) 20: clojure.lang.Var.invoke(Var.java:373) 21: clojure.lang.AFn.applyToHelper(AFn.java:169) 22: clojure.lang.Var.applyTo(Var.java:482) 23: clojure.core$apply__3776.invoke(core.clj:535) 24: swank.core$eval_from_control__322.invoke(core.clj:66) 25: swank.core$eval_loop__324.invoke(core.clj:71) 26: swank.core$spawn_repl_thread__434$fn__464$fn__465.invoke(core.clj:183) 27: clojure.lang.AFn.applyToHelper(AFn.java:159) 28: clojure.lang.AFn.applyTo(AFn.java:151) 29: clojure.core$apply__3776.invoke(core.clj:535) 30: swank.core$spawn_repl_thread__434$fn__464.doInvoke(core.clj:180) 31: clojure.lang.RestFn.invoke(RestFn.java:398) 32: clojure.lang.AFn.run(AFn.java:24) 33: java.lang.Thread.run(Thread.java:637)

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