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How to add jsf components in javascript?

- by Guru

Is it possible to add JSF Components using javascript? In my case , on change of a select option , i need to display a different combination of input controls (like text box(s)). I thought i could use a element and innerHTML property to display the dynamic controls.But it seems to not work!!! <h:selectOneMenu id="browseType" class="TextBlackNormal" value="#{adminBean.browseType}" onchange="showDynamicBox(this);" valueChangeListener="#{adminBean.theValueChanged}"> <f:selectItems value="#{adminBean.browseTypeList}" /> </h:selectOneMenu>    </td> <td> <div id="dynamicBox" style="display:block"><h:inputText class="TextBlackNormal" size="32" name="browseValue" id="browseValue" value="#{adminBean.browseValue}" /></div> </td> javascript code : ~~~~~~~~~~~~~~~~ function showDynamicBox(selectObjj) { //alert('showDynamicBox ' +showDynamicBox); if(selectObjj.options[selectObjj.selectedIndex].value=='IBD/Office/IP' || selectObjj.options[selectObjj.selectedIndex].value=='APA#' ) { alert('just about to change'); document.getElementById("dynamicBox").innerHTML='<h:inputText class="TextBlackNormal" size="3" name="val1" id="val1" /> <h:inputText class="TextBlackNormal" size="3" name="val2" id="val2" /> <h:inputText class="TextBlackNormal" size="3" name="val3" id="val3" /> '; alert(' --> ' +document.getElementById("dynamicBox").innerHTML); }else{ alert('back to pavillion'); document.getElementById("dynamicBox").innerHTML='<h:inputText class="TextBlackNormal" size="32" name="browseValue" id="browseValue" value="#{adminBean.browseValue}" />'; } }

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Simplification / optimization of GPS track

- by GreyCat

I've got a GPS track, produces by gpxlogger(1) (supplied as a client for gpsd). GPS receiver updates its coordinates every 1 second, gpxlogger's logic is very simple, it writes down location (lat, lon, ele) and a timestamp (time) received from GPS every n seconds (n = 3 in my case). After writing down a several hours worth of track, gpxlogger saves several megabyte long GPX file that includes several thousands of points. Afterwards, I try to plot this track on a map and use it with OpenLayers. It works, but several thousands of points make using the map a sloppy and slow experience. I understand that having several thousands of points of suboptimal. There are myriads of points that can be deleted without losing almost anything: when there are several points making up roughly the straight line and we're moving with the same constant speed between them, we can just leave the first and the last point and throw anything else. I thought of using gpsbabel for such track simplification / optimization job, but, alas, it's simplification filter works only with routes, i.e. analyzing only geometrical shape of path, without timestamps (i.e. not checking that the speed was roughly constant). Is there some ready-made utility / library / algorithm available to optimize tracks? Or may be I'm missing some clever option with gpsbabel?

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Enum exeeding the 65535 bytes limit of static initializer... what's best to do?

- by Daniel Bleisteiner

I've started a rather large Enum of so called Descriptors that I've wanted to use as a reference list in my model. But now I've come across a compiler/VM limit the first time and so I'm looking for the best solution to handle this. Here is my error : The code for the static initializer is exceeding the 65535 bytes limit It is clear where this comes from - my Enum simply has far to much elements. But I need those elements - there is no way to reduce that set. Initialy I've planed to use a single Enum because I want to make sure that all elements within the Enum are unique. It is used in a Hibernate persistence context where the reference to the Enum is stored as String value in the database. So this must be unique! The content of my Enum can be devided into several groups of elements belonging together. But splitting the Enum would remove the unique safety I get during compile time. Or can this be achieved with multiple Enums in some way? My only current idea is to define some Interface called Descriptor and code several Enums implementing it. This way I hope to be able to use the Hibernate Enum mapping as if it were a single Enum. But I'm not even sure if this will work. And I loose unique safety. Any ideas how to handle that case?

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How do I create an inheritable Semaphore in .NET?

- by pauldoo

I am trying to create a Win32 Semaphore object which is inheritable. This means that any child processes I launch may automatically have the right to act on the same Win32 object. My code currently looks as follows: Semaphore semaphore = new Semaphore(0, 10); Process process = Process.Start(pathToExecutable, arguments); But the semaphore object in this code cannot be used by the child process. The code I am writing is a port of come working C++. The old C++ code achieves this by the following: SECURITY_ATTRIBUTES security = {0}; security.nLength = sizeof(security); security.bInheritHandle = TRUE; HANDLE semaphore = CreateSemaphore(&security, 0, LONG_MAX, NULL); Then later when CreateProcess is called the bInheritHandles argument is set to TRUE. (In both the C# and C++ case I am using the same child process (which is C++). It takes the semaphore ID on command line, and uses the value directly in a call to ReleaseSemaphore.) I suspect I need to construct a special SemaphoreSecurity or ProcessStartInfo object, but I haven't figured it out yet.

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Androids ExpandableListView - where to put the button listener for buttons that are children

- by CommonKnowledge

I have been playing around a lot with the ExpandableListView and I cannot figure out where to add the button listeners for the button that will be the children in the view. I did manage to get a button listener working that uses getChildView() below, but it seems to be the same listener for all the buttons. The best case scenario is that I would be able to implement the button listeners in the class that instantiates the ExpandableListAdapter class, and not have to put the listeners in the actual ExpandableListAdapter class. At this point I don't even know if that is possible I have been experimenting with this tutorial/code: HERE getChildView() @Override public View getChildView(int set_new, int child_position, boolean view, View view1, ViewGroup view_group1) { ChildHolder childHolder; if (view1 == null) { view1 = LayoutInflater.from(info_context).inflate(R.layout.list_group_item_lv, null); childHolder = new ChildHolder(); childHolder.section_btn = (Button)view1.findViewById(R.id.item_title); view1.setTag(childHolder); childHolder.section_btn.setOnClickListener(new OnClickListener() { @Override public void onClick(View v) { Toast.makeText(info_context, "button pushed", Toast.LENGTH_SHORT).show(); } }); }else { childHolder = (ChildHolder) view1.getTag(); } childHolder.section_btn.setText(children_collection.get(set_new).GroupItemCollection.get(child_position).section); Typeface tf = Typeface.createFromAsset(info_context.getAssets(), "fonts/AGENCYR.TTF"); childHolder.section_btn.setTypeface(tf); return view1; } Any help would be much appreciated. Thank you and I will be standing by.

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Multi-Precision Arithmetic on MIPS

- by Rob

Hi, I am just trying to implement multi-precision arithmetic on native MIPS. Assume that one 64-bit integer is in register $12 and $13 and another is in registers $14 and $15. The sum is to be placed in registers $10 and $11. The most significant word of the 64-bit integer is found in the even-numbered registers, and the least significant word is found in the odd-numbered registers. On the internet, it said, this is the shortest possible implementation. addu $11, $13, $15 # add least significant word sltu $10, $11, $15 # set carry-in bit addu $10, $10, $12 # add in first most significant word addu $10, $10, $14 # add in second most significant word I just wanna double check that I understand correctly. The sltu checks if the sum of the two least significant words is smaller or equal than one of the operands. If this is the case, than did a carry occur, is this right? To check if there occured a carry when adding the two most significant words and store the result in $9 I have to do: sltu $9, $10, $12 # set carry-in bit Does this make any sense?

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Measuring time spent in application / thread

- by Adamski

I am writing a simulation in Java whereby objects act under Newtonian physics. An object may have a force applied to it and the resulting velocity causes it to move across the screen. The nature of the simulation means that objects move in discrete steps depending on the time ellapsed between the current and previous iteration of the animation loop; e.g public void animationLoop() { long prev = System.currentTimeMillis(); long now; while(true) { long now = System.currentTimeMillis(); long deltaMillis = now - prev; prev = now; if (deltaMillis > 0) { // Some time has passed for (Mass m : masses) { m.updatePosition(deltaMillis); } // Do all repaints. } } } A problem arises if the animation thread is delayed in some way causing a large amount of time to ellapse (the classic case being under Windows whereby clicking and holding on minimise / maximise prevents a repaint), which causes objects to move at an alarming rate. My question: Is there a way to determine the time spent in the animation thread rather than the wallclock time, or can anyone suggest a workaround to avoid this problem? My only thought so far is to contstrain deltaMillis by some upper bound.

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Performance of Multiple Joins

- by geeko

Greetings Overflowers, I need to query against objects with many/complex spacial conditions. In relational databases that is translated to many joins (possibly 10+). I'm new to this business and wondering whether to go with MS SQL Server 2008 R2 or Oracle 11g or document-based solutions such as RavenDB or simply go with some spacial database (GIS)... Any thoughts ? Regards UPDATE: Thank you all for your answers. Would anybody opt for document/spatial databases ? My database would consist of tens of millions to few billion records. Mostly read-only. Almost no updates unless in case of mistakes in input. Overnight inserts and not that frequent. The join tables are predicted beforehand but the number of self joins (tables joining themselves multiple times) is not. Small pages of results from such queries are going to be viewed on an highly interactive website so response time is critical. Any predictions on how this can perform on MS SQL Server 2008 R2 or Oracle 11g ? I'm also concerned about boosting performance by adding more servers, which one scales better ? How about PostgresQL ?

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What algorithm can I use to determine points within a semi-circle?

- by khayman218

I have a list of two-dimensional points and I want to obtain which of them fall within a semi-circle. Originally, the target shape was a rectangle aligned with the x and y axis. So the current algorithm sorts the pairs by their X coord and binary searches to the first one that could fall within the rectangle. Then it iterates over each point sequentially. It stops when it hits one that is beyond both the X and Y upper-bound of the target rectangle. This does not work for a semi-circle as you cannot determine an effective upper/lower x and y bounds for it. The semi-circle can have any orientation. Worst case, I will find the least value of a dimension (say x) in the semi-circle, binary search to the first point which is beyond it and then sequentially test the points until I get beyond the upper bound of that dimension. Basically testing an entire band's worth of points on the grid. The problem being this will end up checking many points which are not within the bounds.

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How to compare two file structures in PHP?

- by OM The Eternity

I have a function which gives me the complete file structure upto n-level, function getDirectory($path = '.', $ignore = '') { $dirTree = array (); $dirTreeTemp = array (); $ignore[] = '.'; $ignore[] = '..'; $dh = @opendir($path); while (false !== ($file = readdir($dh))) { if (!in_array($file, $ignore)) { if (!is_dir("$path/$file")) { //display of file and directory name with their modification time $stat = stat("$path/$file"); $statdir = stat("$path"); $dirTree["$path"][] = $file. " === ". date('Y-m-d H:i:s', $stat['mtime']) . " Directory == ".$path."===". date('Y-m-d H:i:s', $statdir['mtime']) ; } else { $dirTreeTemp = getDirectory("$path/$file", $ignore); if (is_array($dirTreeTemp))$dirTree = array_merge($dirTree, $dirTreeTemp); } } } closedir($dh); return $dirTree; } $ignore = array('.htaccess', 'error_log', 'cgi-bin', 'php.ini', '.ftpquota'); //function call $dirTree = getDirectory('.', $ignore); //file structure array print print_r($dirTree); Now here my requirement is , I have two sites The Development/Test Site- where i do testing of all the changes The Production Site- where I finally post all the changes as per test in development site Now, for example, I have tested an image upload in the Development/test site, and i found it appropriate to publish on Production site then i will completely transfer the Development/Test DB detail to Production DB, but now I want to compare the files structure as well to transfer the corresponding image file to Production folder. There could be the situation when I update the image by editing the image and upload it with same name, now in this case the image file would be already present there, which will restrict the use of "file_exist" logic, so for these type of situations....HOW CAN I COMPARE THE TWO FILE STRUCTURE TO GET THE SYNCHRONIZATION DONE AS PER REQUIREMENT??

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Multi-module Maven build

- by Don

Hi, My project has a fairly deep graph of Maven modules. The root POM has the following plugin configured <plugins> <plugin> <groupId>org.jvnet</groupId> <artifactId>animal-sniffer</artifactId> <version>1.2</version> <configuration> <signature> <groupId>org.jvnet.animal-sniffer</groupId> <artifactId>java1.4</artifactId> <version>1.0</version> </signature> </configuration> </plugin> </plugins> If I invoke this target from the command line in the root directory via: mvn animal-sniffer:check Then it works fine as long as the current module extends (either directly or indirectly) from the root POM. However there are many children (or grandchildren) of the root module, which do not inherit from that module's POM. In this case, the goal fails because it cannot find the necessary configuration [ERROR] BUILD ERROR [INFO] ------------------------------------------------------------------------ [INFO] One or more required plugin parameters are invalid/missing for 'animal-sniffer:check' [0] Inside the definition for plugin 'animal-sniffer' specify the following: <configuration> ... <signature>VALUE</signature> </configuration>. When configuring this plugin in the root module, is there any way to exclude a list of sub-modules either by name, or by packaging type? Thanks, Donal

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Best way to unit test Collection?

- by limc

I'm just wondering how folks unit test and assert that the "expected" collection is the same/similar as the "actual" collection (order is not important). To perform this assertion, I wrote my simple assert API:- public void assertCollection(Collection<?> expectedCollection, Collection<?> actualCollection) { assertNotNull(expectedCollection); assertNotNull(actualCollection); assertEquals(expectedCollection.size(), actualCollection.size()); assertTrue(expectedCollection.containsAll(actualCollection)); assertTrue(actualCollection.containsAll(expectedCollection)); } Well, it works. It's pretty simple if I'm asserting just bunch of Integers or Strings. It can also be pretty painful if I'm trying to assert a collection of Hibernate domains, say for example. The collection.containsAll(..) relies on the equals(..) to perform the check, but I always override the equals(..) in my Hibernate domains to check only the business keys (which is the best practice stated in the Hibernate website) and not all the fields of that domain. Sure, it makes sense to check just against the business keys, but there are times I really want to make sure all the fields are correct, not just the business keys (for example, new data entry record). So, in this case, I can't mess around with the domain.equals(..) and it almost seems like I need to implement some comparators for just unit testing purposes instead of relying on collection.containsAll(..). Are there some testing libraries I could leverage here? How do you test your collection? Thanks.

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Developping an online music store

- by Simon

We need to develop an application to sell music online. No need to specify that all will be done quite legally and in so doing, we have to plan an interface to pay artists. However, we are confronted with a question: What is the best way to store music on the server? Should we save it on server's disk from a HTTP fileupload? Should we save via FTP or would it be wiser to save it in the database? No need to say that we need it to be the most safiest as possible. So maybe an https is required here. But, we what you think is the best way? Maybe other idea? Because in all HTTP case, upload songs (for administration) is quite long and boring, but easly linkable to a song that admin create in his web application comparativly to an FTP application to upload song on server and then list directory in admin part to link the correct uploaded song to the song informations in database. I know that its maybe not quite clear, it's because i'm french but tell me and I will try to explain part that you don't understand.

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Getting response status code 0 in SmartGWT webservice call using json

- by Girish

I have developed application using SmartGWT, now i need to call webservice using json to another application which is deployed in another server for submitting username and password. When i make a request with url and POST method, getting the response status code as 0 and response text as blank. Here is my code, public void sendRequest() throws Exception { // Get login json data to be sent to server. String strData = createLoginReqPacket(); String url = "some url"; RequestBuilder builder = new RequestBuilder(RequestBuilder.POST, url); builder.setHeader("Content-Type", "application/json"); builder.setHeader("Content-Length", strData.length() + ""); Request response = builder.sendRequest(strData, new RequestCallback() { @Override public void onResponseReceived(Request request, Response response) { int statusCode = response.getStatusCode(); System.out.println("Response code ----"+response.getStatusCode()+""); if (statusCode == Response.SC_OK) { String responseBody = response.getText(); System.out.println("Respose :" + responseBody); // do something with the response } else { GWT.log("Response error at server side ----",null); // do in case of server error } }// end of method. @Override public void onError(Request request, Throwable exception) { GWT.log("**** Error in service call ******",null); }// end of method. }); builder.send(); }// end of send request. Please anybody knows the solution?? Give some reference code or links for this. Thanks.

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Javascript Getting Objects to Fallback to One Another

- by Ian

Here's a ugly bit of Javascript it would be nice to find a workaround. Javascript has no classes, and that is a good thing. But it implements fallback between objects in a rather ugly way. The foundational construct should be to have one object that, when a property fails to be found, it falls back to another object. So if we want a to fall back to b we would want to do something like: a = {sun:1}; b = {dock:2}; a.__fallback__ = b; then a.dock == 2; But, Javascript instead provides a new operator and prototypes. So we do the far less elegant: function A(sun) { this.sun = sun; }; A.prototype.dock = 2; a = new A(1); a.dock == 2; But aside from elegance, this is also strictly less powerful, because it means that anything created with A gets the same fallback object. What I would like to do is liberate Javascript from this artificial limitation and have the ability to give any individual object any other individual object as its fallback. That way I could keep the current behavior when it makes sense, but use object-level inheritance when that makes sense. My initial approach is to create a dummy constructor function: function setFallback(from_obj, to_obj) { from_obj.constructor = function () {}; from_obj.constructor.prototype = to_obj; } a = {sun:1}; b = {dock:2}; setFallback(a, b); But unfortunately: a.dock == undefined; Any ideas why this doesn't work, or any solutions for an implementation of setFallback? (I'm running on V8, via node.js, in case this is platform dependent)

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When should we use Views, Temporary Tables and Direct Queries ? What are the Performance issues in a

- by Shantanu Gupta

I want to know the performance of using Views, Temp Tables and Direct Queries Usage in a Stored Procedure. I have a table that gets created every time when a trigger gets fired. I know this trigger will be fired very rare and only once at the time of setup. Now I have to use that created table from triggers at many places for fetching data and I confirms it that no one make any changes in that table. i.e ReadOnly Table. I have to use this tables data along with multiple tables to join and fetch result for further queries say select * from triggertable By Using temp table select ... into #tx from triggertable join t2 join t3 and so on select a,b, c from #tx --do something select d,e,f from #tx ---do somethign --and so on --around 6-7 queries in a row in a stored procedure. By Using Views create view viewname ( select ... from triggertable join t2 join t3 and so on ) select a,b, c from viewname --do something select d,e,f from viewname ---do somethign --and so on --around 6-7 queries in a row in a stored procedure. This View can be used in other places as well. So I will be creating at database rather than at sp By Using Direct Query select a,b, c from select ... into #tx from triggertable join t2 join t3 join ... --do something select a,b, c from select ... into #tx from triggertable join t2 join t3 join ... --do something . . --and so on --around 6-7 queries in a row in a stored procedure. Now I can create a view/temporary table/ directly query usage in all upcoming queries. What would be the best to use in this case.

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Binding value for NSTableView, but tooltip gets set as well

- by Mark

I've set up an NSTableView in Interface Builder to be populated from an NSArray. Each value of the array represents one row in the table. The value is bound correctly, but as a side effect, the table cell's tooltip is set to the string representation of the bound object. In my case, the NSArray contains NSDictiorany objects and the tooltip looks like it could be the [... description] output of that dictionary. Very ugly... I don't want the tooltip to be set at all. I have other tables that have plain NSString values bound to them and they don't have a tooltip set automatically. Is there some Interface Builder magic going on? I tried to start with a blank project - same problem. I should add that the table cell is a custom implementation of NSTextFieldCell that uses an NSButtonCell instance to draw an image and a label into the table. The values are retrieved from the dictionary bound as value. Why is the tooltip set when I only bind the "value" attribute? Thanks in advance!

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Self referencing update SQL statement for Informix

- by CheeseConQueso

Need some Informix SQL... Courses get a regular grade, but their associated labs get a grade of 'LAB'. I need to update the table so that the lab grade matches the course grade. Also, if there is no corresponding course for a lab, it means the course was canceled. In that case, I want to place a flag value of 'X' for its grade. Example data before update: id yr sess crs_no hrs grd 725 2009 FA COLL101 3.000000000000 C 725 2009 FA ENGL021 3.000000000000 FI 725 2009 FA ENGL021L 1.000000000000 LAB 725 2009 FA ENGL031 3.000000000000 FNI 725 2009 FA ENGL031L 1.000000000000 LAB 725 2009 FA MATH010 3.000000000000 FNI 725 2010 SP AOTE101 3.000000000000 C 725 2010 SP ENGL021L 1.000000000000 LAB 725 2010 SP ENGL031 3.000000000000 FI 725 2010 SP ENGL031L 1.000000000000 LAB 725 2010 SP MATH010 3.000000000000 FNI 726 2010 SP SPAN101 3.000000000000 FN Example data after update: id yr sess crs_no hrs grd 725 2009 FA COLL101 3.000000000000 C 725 2009 FA ENGL021 3.000000000000 FI 725 2009 FA ENGL021L 1.000000000000 FI 725 2009 FA ENGL031 3.000000000000 FNI 725 2009 FA ENGL031L 1.000000000000 FNI 725 2009 FA MATH010 3.000000000000 FNI 725 2010 SP AOTE101 3.000000000000 C 725 2010 SP ENGL021L 1.000000000000 X 725 2010 SP ENGL031 3.000000000000 FI 725 2010 SP ENGL031L 1.000000000000 FI 725 2010 SP MATH010 3.000000000000 FNI 726 2010 SP SPAN101 3.000000000000 FN I worked out a solution for this, but it required a lot of on-the-fly composite foreign keys built from concatenating the id, yr, sess, and substring'd crs_no. My solution is not only overkill, but it has gaps in it and it takes too long to process. I know there is an easier way to do this, but I've gone so far down one road that I am having trouble thinking of a different approach.

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Retrieve only the superclass from a class hierarchy

- by user1792724

I have an scenario as the following: @Entity @Table(name = "ANIMAL") @Inheritance(strategy = InheritanceType.JOINED) public class Animal implements Serializable { @Id @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "S_ANIMAL") @SequenceGenerator(name = "S_ANIMAL", sequenceName = "S_ANIMAL", allocationSize = 1) public int getNumero() { return numero; } public void setNumero(int numero) { this.numero = numero; } . . . } and as the subclass: @Entity @Table(name = "DOG") public class Dog extends Animal { private static final long serialVersionUID = -7341592543130659641L; . . . } I have a JPA Select statement like this: SELECT a FROM Animal a; I'm using Hibernate 3.3.1 As I can see the framework retrieves instances of Animal and also of Dog using a left outer join. Is there a way to Select only the "part" Animal? I mean, the previous Select will get all the Animals, those that are only Animals but not Dogs and those that are Dogs. I want them all, but in the case of Dogs I want to only retrieve the "Animal part" of them. I found the @org.hibernate.annotations.Entity(polymorphism = PolymorphismType.EXPLICIT) but as I could see this only works if Animal isn't an @Entity. Thanks a lot.

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BASH: How to count all the human readable files?

- by user1687406

I'm taking an intro course to UNIX and have a homework question that follows: How many files in the previous question are text files? A text file is any file containing human-readable content. (TRICK QUESTION. Run the file command on a file to see whether the file is a text file or a binary data file! If you simply count the number of files with the ".txt" extension you will get no points for this question.) The previous question simply asked how many regular files there were, which was easy to figure out by doing find . -type f | wc -l I'm just having trouble determining what "human readable content" is, since I'm assuming it means anything besides binary/assembly, but I thought that's what -type f displays. Maybe that's what the professor meant by saying "trick question"? This question has a follow up later that also asks "What text files contain the string "csc" in any mix of upper and lower case?". Obviously "text" is referring to more than just .txt files, but I need to figure out the first question to determine this!

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Is there a way to force ContourPlot re-check all the points on the each stage of it's recursion algorithm?

- by Alexey Popkov

Hello, Thanks to this excellent analysis of the Plot algorithm by Yaroslav Bulatov, I now understand the reason why Plot3D and ContourPlot fail to draw smoothly functions with breaks and discontinuities. For example, in the following case ContourPlot fails to draw contour x^2 + y^2 = 1 at all: ContourPlot[Abs[x^2 + y^2 - 1], {x, -1, 1}, {y, -1, 1}, Contours -> {0}] It is because the algorithm does not go deeply into the region near x^2 + y^2 = 1. It "drops" this region on an initial stage and do not tries to investigate it further. Increasing MaxRecursion does nothing in this sense. And even undocumented option Method -> {Refinement -> {ControlValue -> .01 \[Degree]}} does not help (but makes Plot3D a little bit smoother). The above function is just a simple example. In real life I'm working with very complicated implicit functions that cannot be solved analytically. Is there a way to get ContourPlot to go deeply into such regions near breaks and discontinuities?

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Java abstract visitor - guarantueed to succeed? If so, why?

- by disown

I was dealing with hibernate, trying to figure out the run-time class behind proxied instances by using the visitor pattern. I then came up with an AbstractVisitable approach, but I wonder if it will always produce correct results. Consider the following code: interface Visitable { public void accept(Visitor v); } interface Visitor { public void visit(Visitable visitorHost); } abstract class AbstractVisitable implements Visitable { @Override public void accept(Visitor v) { v.visit(this); } } class ConcreteVisitable extends AbstractVisitable { public static void main(String[] args) { final Visitable visitable = new ConcreteVisitable(); final Visitable proxyVisitable = (Visitable) Proxy.newProxyInstance( Thread.currentThread().getContextClassLoader(), new Class<?>[] { Visitable.class }, new InvocationHandler() { @Override public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { return method.invoke(visitable, args); } }); proxyVisitable.accept(new Visitor() { @Override public void visit(Visitable visitorHost) { System.out.println(visitorHost.getClass()); } }); } } This makes a ConcreteVisitable which inherits the accept method from AbstractVisitable. In c++, I would consider this risky, since this in AbstractVisitable could be referencing to AbstractVisitable::this, and not ConcreteVisitable::this. I was worried that the code under certain circumstances would print class AbstractVisible. Yet the code above outputs class ConcreteVisitable, even though I hid the real type behind a dynamic proxy (the most difficult case I could come up with). Is the abstract visitor approach above guaranteed to work, or are there some pitfalls with this approach? What guarantees are given in Java with respect to the this pointer?

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Is Assert.Fail() considered bad practice?

- by Mendelt

I use Assert.Fail a lot when doing TDD. I'm usually working on one test at a time but when I get ideas for things I want to implement later I quickly write an empty test where the name of the test method indicates what I want to implement as sort of a todo-list. To make sure I don't forget I put an Assert.Fail() in the body. When trying out xUnit.Net I found they hadn't implemented Assert.Fail. Of course you can always Assert.IsTrue(false) but this doesn't communicate my intention as well. I got the impression Assert.Fail wasn't implemented on purpose. Is this considered bad practice? If so why? @Martin Meredith That's not exactly what I do. I do write a test first and then implement code to make it work. Usually I think of several tests at once. Or I think about a test to write when I'm working on something else. That's when I write an empty failing test to remember. By the time I get to writing the test I neatly work test-first. @Jimmeh That looks like a good idea. Ignored tests don't fail but they still show up in a separate list. Have to try that out. @Matt Howells Great Idea. NotImplementedException communicates intention better than assert.Fail() in this case @Mitch Wheat That's what I was looking for. It seems it was left out to prevent it being abused in another way I abuse it.

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How to visually reject user input in a table?

- by FX

In the programming of a table-based application module (i.e. the user mostly enters tabular data in an already laid-out table), how would you reject user input for a given cell? The scenario is: the user edits the cell, enters something (text, picture, ...) and you want them to notice when they finish editing (hitting enter, for example) that their entry is not valid for your given "format" (in the wider meaning: it can be that they entered a string instead of a number, that their entry is too long, too short, they include a picture while it's not acceptable, ...). I can see two different things happening: You can rather easily fit their entry into your format, and you do so, but you want them to notice it so they can change if your guess is not good enough (example: they entered "15.47" in a field that needs to be an integer, so your program makes it "15") You cannot guess what to do with their entry, and want to inform them that it's not valid. My question specifically is: what visual display can you offer to inform the user that his input is invalid? Is it preferable to refuse to leave the editing mode, or not? The two things I can imagine are: using colors (red background if invalid, yellow background for my case 1 above) when you reject an input, do something like Apple does for password entry of user accounts: you make the cell "shaking" (i.e. oscillating left and right) for one second, and keep the focus/editing in their so they don't loose what they've typed. Let's hear your suggestions. PS: This question is, at least in my thought process, somehow a continuation and a specialization of my previous question on getting users to read error messages. PPS: Made this community wiki, was that the right thing to do on this kind of question or not?

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Obtaining FontMetrics before getting a Graphics instance

- by Tom Castle

Typically, I'd obtain a graphics instance something like this: BufferedImage img = new BufferedImage(width, height, BufferedImage.TYPE_INT_ARGB); Graphics2D g = img.createGraphics(); However, in the current project I'm working on, the width and height variables above are dependent upon the size of a number of text fragments that will later be drawn onto the graphics instance. But, to obtain the dimensions of the font being used I would usually use the FontMetrics that I get from the graphics object. FontMetrics metrics = g.getFontMetrics(); So, I have a nasty little dependency cycle. I cannot create the graphics object until I know the size of the text, and I cannot know the size of the text until I have a graphics object. One solution is just to create another BufferedImage/Graphics pair first in order to get the FontMetrics instance I need, but this seems unnecessary. So, is there a nicer way? Or is it the case that the width, height etc. properties for a Font are somehow dependent upon what (graphics, component...) the text is to be drawn on?

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