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  • Avoiding Object Oriented Pitfalls, Migrating from C, What Worked for You?

    - by Stephen
    I've been programming in procedural languages for quite some time now, and my first reaction to a problem is to start breaking it down into tasks to perform rather than to consider the different entities (objects) that exist and their relationships. I have had a university course in OOP, and understand the fundamentals of encapsulation, data abstraction, polymorphism, modularity and inheritance. I read Learning to think in the Object Oriented Way and Learning object oriented thinking, and will be looking at some of the books pointed to in those answers. I think that several of my medium to large sized projects will benefit from effective use of OOP but as a novice I would like to avoid time consuming, common errors. Based on your experiences, what are these pitfalls and what are reasonable ways around them? If you could explain why they are pitfalls, and how your suggestion is effective in addressing the issue it'd be appreciated. I'm thinking along the lines of something like "Is it common to have a fair number of observer and modifier methods and use private variables or are there techniques for consolidating/reducing them?" I'm not worried about using C++ as a pure OO language, if there are good reasons to mix methods. (Reminiscent of the reasons to use GOTOs, albeit sparingly.) Thank you!

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  • DB Object passing between classes singleton, static or other?

    - by Stephen
    So I'm designing a reporting system at work it's my first project written OOP and I'm stuck on the design choice for the DB class. Obviously I only want to create one instance of the DB class per-session/user and then pass it to each of the classes that need it. What I don't know it what's best practice for implementing this. Currently I have code like the following:- class db { private $user = 'USER'; private $pass = 'PASS'; private $tables = array( 'user','report', 'etc...'); function __construct(){ //SET UP CONNECTION AND TABLES } }; class report{ function __construct ($params = array(), $db, $user) { //Error checking/handling trimed //$db is the database object we created $this->db = $db; //$this->user is the user object for the logged in user $this->user = $user; $this->reportCreate(); } public function setPermission($permissionId = 1) { //Note the $this->db is this the best practise solution? $this->db->permission->find($permissionId) //Note the $this->user is this the best practise solution? $this->user->checkPermission(1) $data=array(); $this->db->reportpermission->insert($data) } };//end report I've been reading about using static classes and have just come across Singletons (though these appear to be passé already?) so what's current best practice for doing this?

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  • Recommended design pattern for object with optional and modifiable attributtes? [on hold]

    - by Ikuzen
    I've been using the Builder pattern to create objects with a large number of attributes, where most of them are optional. But up until now, I've defined them as final, as recommended by Joshua Block and other authors, and haven't needed to change their values. I am wondering what should I do though if I need a class with a substantial number of optional but non-final (mutable) attributes? My Builder pattern code looks like this: public class Example { //All possible parameters (optional or not) private final int param1; private final int param2; //Builder class public static class Builder { private final int param1; //Required parameters private int param2 = 0; //Optional parameters - initialized to default //Builder constructor public Builder (int param1) { this.param1 = param1; } //Setter-like methods for optional parameters public Builder param2(int value) { param2 = value; return this; } //build() method public Example build() { return new Example(this); } } //Private constructor private Example(Builder builder) { param1 = builder.param1; param2 = builder.param2; } } Can I just remove the final keyword from the declaration to be able to access the attributes externally (through normal setters, for example)? Or is there a creational pattern that allows optional but non-final attributes that would be better suited in this case?

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  • redoing object model construction to fit with asynchronous data fetching

    - by Andrew Patterson
    I have a modeled a set of objects that correspond with some real world concepts. TradeDrug, GenericDrug, TradePackage, DrugForm Underlying the simple object model I am trying to provide is a complex medical terminology that uses numeric codes to represent relationships and concepts, all accessible via a REST service - I am trying to hide away some of that complexity with an object wrapper. To give a concrete example I can call TradeDrug d = Searcher.FindTradeDrug("Zoloft") or TradeDrug d = new TradeDrug(34) where 34 might be the code for Zoloft. This will consult a remote server to find out some details about Zoloft. I might then call GenericDrug generic = d.EquivalentGeneric() System.Out.WriteLine(generic.ActiveIngredient().Name) in order to get back the generic drug sertraline as an object (again via a background REST call to the remote server that has all these drug details), and then perhaps find its ingredient. This model works fine and is being used in some applications that involve data processing. Recently however I wanted to do a silverlight application that used and displayed these objects. The silverlight environment only allows asynchronous REST/web service calls. I have no problems with how to make the asychhronous calls - but I am having trouble with what the design should be for my object construction. Currently the constructors for my objects do some REST calls sychronously. public TradeDrug(int code) { form = restclient.FetchForm(code) name = restclient.FetchName(code) etc.. } If I have to use async 'events' or 'actions' in order to use the Silverlight web client (I know silverlight can be forced to be a synchronous client but I am interested in asychronous approaches), does anyone have an guidance or best practice for how to structure my objects. I can pass in an action callback to the constructor public TradeDrug(int code, Action<TradeDrug> constructCompleted) { } but this then allows the user to have a TradeDrug object instance before what I want to construct is actually finished. It also doesn't support an 'event' async pattern because the object doesn't exist to add the event to until it is constructed. Extending that approach might be a factory object that itself has an asynchronous interface to objects factory.GetTradeDrugAsync(code, completedaction) or with a GetTradeDrugCompleted event? Does anyone have any recommendations?

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  • Blob object not working properly even though the class is seralized

    - by GustlyWind
    I have class which is seralized and does convert a very large amount of data object to blob to save it to database.In the same class there is decode method to convert blob to the actual object.Following is the code for encode and decode of the object. private byte[] encode(ScheduledReport schedSTDReport) { byte[] bytes = null; try { ByteArrayOutputStream bos = new ByteArrayOutputStream(); ObjectOutputStream oos = new ObjectOutputStream(bos); oos.writeObject(schedSTDReport); oos.flush(); oos.close(); bos.close(); //byte [] data = bos.toByteArray(); //ByteArrayOutputStream baos = new ByteArrayOutputStream(); //GZIPOutputStream out = new GZIPOutputStream(baos); //XMLEncoder encoder = new XMLEncoder(out); //encoder.writeObject(schedSTDReport); //encoder.close(); bytes = bos.toByteArray(); //GZIPOutputStream out = new GZIPOutputStream(bos); //out.write(bytes); //bytes = bos.toByteArray(); } catch (Exception e) { _log.error("Exception caught while encoding/zipping Scheduled STDReport", e); } decode(bytes); return bytes; } /* * Decode the report definition blob back to the * ScheduledReport object. */ private ScheduledReport decode(byte[] bytes) { ByteArrayInputStream bais = new ByteArrayInputStream(bytes); ScheduledReport sSTDR = null; try { ObjectInputStream ois = new ObjectInputStream(bais); //GZIPInputStream in = new GZIPInputStream(bais); //XMLDecoder decoder = new XMLDecoder(in); sSTDR = (ScheduledReport)ois.readObject();//decoder.readObject(); //decoder.close(); } catch (Exception e) { _log.error("IOException caught while decoding/unzipping Scheduled STDReport", e); } return sSTDR; } The problem here is whenver I change something else in this class means any other method,a new class version is created and so the new version the class is unable to decode the originally encoded blob object. The object which I am passing for encode is also seralized object but this problem exists. Any ideas thanks

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  • PHP: Next Available Value in an Array, starting with a non-indexed value

    - by Erik Smith
    I've been stumped on this PHP issue for about a day now. Basically, we have an array of hours formatted in 24-hour format, and an arbitrary value ($hour) (also a 24-hour). The problem is, we need to take $hour, and get the next available value in the array, starting with the value that immediately proceeds $hour. The array might look something like: $goodHours = array('8,9,10,11,12,19,20,21). Then the hour value might be: $hour = 14; So, we need some way to know that 19 is the next best time. Additionally, we might also need to get the second, third, or fourth (etc) available value. The issue seems to be that because 14 isn't a value in the array, there is not index to reference that would let us increment to the next value. To make things simpler, I've taken $goodHours and repeated the values several times just so I don't have to deal with going back to the start (maybe not the best way to do it, but a quick fix). I have a feeling this is something simple I'm missing, but I would be so appreciative if anyone could shed some light. Erik

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  • Encapsulate update method inside of object or have method which accepts an object to update

    - by Tom
    Hi, I actually have 2 questions related to each other: I have an object (class) called, say MyClass which holds data from my database. Currently I have a list of these objects ( List < MyClass ) that resides in a singleton in a "communal area". I feel it's easier to manage the data this way and I fail to see how passing a class around from object to object is beneficial over a singleton (I would be happy if someone can tell me why). Anyway, the data may change in the database from outside my program and so I have to update the data every so often. To update the list of the MyClass I have a method called say, Update, written in another class which accepts a list of MyClass. This updates all the instances of MyClass in the list. However would it be better instead to encapulate the Update() method inside the MyClass object, so instead I would say foreach(MyClass obj in MyClassList) { obj.update(); } What is a better implementation and why? The update method requires a XML reader. I have written an XML reader class which is basically a wrapper over the standard XML reader the language natively provides which provides application specific data collection. Should the XML reader class be in anyway in the "inheritance path" of the MyClass object - the MyClass objects inherits from the XML reader because it uses a few methods. I can't see why it should. I don't like the idea of declaring an instance of the XML Reader class inside of MyClass and an MyClass object is meant to be a simple "record" from the database and I feel giving it loads of methods, other object instances is a bit messy. Perhaps my XML reader class should be static but C#'s native XMLReader isn't static.? Any comments would be greatly appreciated Thanks Thomas

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  • Python: Access dictionary value inside of tuple and sort quickly by dict value

    - by Aquat33nfan
    I know that wasn't clear. Here's what I'm doing specifically. I have my list of dictionaries here: dict = [{int=0, value=A}, {int=1, value=B}, ... n] and I want to take them in combinations, so I used itertools and it gave me a tuple (Well, okay it gave me a memory object that I then used enumerate on so I could loop over it and enumerate gave ma tuple): for (index, tuple) in enumerate(combinations(dict, 2)): and this is where I have my problem. I want to identify which of the two items in the combination has the bigger 'int' value and which has the smaller value and assign them to variables (I'm actually using more than 2 in the combination so I can't just say if tuple[0]['int'] tuple[1]['int'] and do the assignment because I'd have to list this out a bunch of times and that's hard to manage). I was going to assign each 'int' value to a variable, sort it in a list, index the 'int' value in the list by 1, 2, 3, 4, 5 ... etc., then go back and access the dictionary I wanted by the int value and then assign the dictionary to a variable so I knew which was bigger. But I have a big list and lists and variable assignments are resource intensive and this is taking a long time (I had only a little bit of that written and it was taking forever to run). So I was hoping someone knew a fast way to do this. I actually could list out every possible combination of assignmnets using the if/thens but it's just like 5 pages of if/thens and assignments and is hard to read and manage when I want to change it. You've probably gathered this, but I"m new at programming. thx

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  • MYSQL KEY-VALUE PAIR Viability

    - by Amit
    Hi, I am new to mysql and I am looking for some answers to the follwoing questions: a) Can mysql community server can be leveraged for a key-value pair type database.?? b) Which mysql engine is best suited for a key-value pair type database ?? c) Is Mysql cluster a must for horizontal scaling of key-value based datastore or can it be acheived using MySQL replication?? d) Are there any docs or whitepapers for best practices when implementiing a kv datastore on mysql?? e) Are there any known big implementations other that friendfeed doing kv pair using MYSQL?? Would really appreciate some advise from all you Mysql gurus out there !! Thanks In Advance, Amit

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  • Store return value of function in reference C++

    - by Ruud v A
    Is it valid to store the return value of an object in a reference? class A { ... }; A myFunction() { A myObject; return A; } //myObject goes out of scope here void mySecondFunction() { A& mySecondObject = myFunction(); } Is it possible to do this in order to avoid copying myObject to mySecondObject? myObject is not needed anymore and should be exactly the same as mySecondObject so it would in theory be faster just to pass ownership of the object from one object to another. (This is also possible using boost shared pointer but that has the overhead of the shared pointer.) Thanks in advance.

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  • Bash script function return value problem

    - by Eedoh
    Hi to all. Can anyone help me return the correct value from a bash script function? Here's my function that should return first (and only) line of the file passed as an argument: LOG_FILE_CREATION_TIME() { return_value=`awk 'NR==1' $1` return return_value } And here's my call of that function in the other script: LOG_FILE_CREATION_TIME "logfile" timestamp=$? echo "Timestamp = $timestamp" I always get some random values with this code. If, for example, there's a value of 62772031 in the "logfile", I get Timestamp = 255 as an output. For some other values in the file, I get other random values as a return value, never the correct one. Any ideas?

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  • Developing a jQuery plugin that returns a given object, instead of jQuery object itself!

    - by mehdi5275
    Hi, Consider the following base code: (function($) { $.fn.myPlugin = function(settings) { return this.each(function() { //whatever }); }; }); The plugin returns a jQuery object. The question is how am I supposed to write a plugin that returns a custom object so that I can do something like this: var api = $('div.myelement').myPlugin(); api.onMyEventName(function(e, whateverParam) { //whatever }); It'd be highly appreciated if you could write some lines of code that describes me how to do that, how to call the onMyEventName function on a custom api object... Thanks.

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  • HTML Input on change of value

    - by arik-so
    Hello, I have an input tag. This tag does not have the autocomplete feature turned off, thus, one does not necessarily need to release a key to change the value of this field and focus anotehr one. My question is: how can I detect ANY value changes of this particular field, like e. g. <input onvaluechange="//do following..." /> The JavaScritp attribute onchange does not fire on change of value, only on changes like blur, focus, etc... Thanks in advance!

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  • NHibernate IUserType convert nullable DateTime to DB not-null value

    - by barakbbn
    I have legacy DB that store dates that means no-date as 9999-21-31, The column Till_Date is of type DateTime not-null="true". in the application i want to build persisted class that represent no-date as null, So i used nullable DateTime in C# //public DateTime? TillDate {get; set; } I created IUserType that knows to convert the entity null value to DB 9999-12-31 but it seems that NHibernate doesn't call SafeNullGet, SafeNullSet on my IUserType when the entity value is null, and report a null is used for not-null column. I tried to by-pass it by mapping the column as not-null="false" (changed only the mapping file, not the DB) but it still didn't help, only now it tries to insert the null value to the DB and get ADOException. Any knowledge if NHibernate doesn't support IUseType that convert null to not-null values? Thanks //Implementation public class NullableDateTimeToNotNullUserType : IUserType { private static readonly DateTime MaxDate = new DateTime(9999, 12, 31); public new bool Equals(object x, object y) { //This didn't work as well if (ReferenceEquals(x, y)) return true; //if(x == null && y == null) return false; if (x == null || y == null) return false; return x.Equals(y); } public int GetHashCode(object x) { return x == null ? 0 : x.GetHashCode(); } public object NullSafeGet(IDataReader rs, string[] names, object owner) { var value = rs.GetDateTime(rs.GetOrdinal(names[0])); return (value == MaxDate)? null : value; } public void NullSafeSet(IDbCommand cmd, object value, int index) { var dateValue = (DateTime?)value; var dbValue = (dateValue.HasValue) ? dateValue.Value : MaxDate; ((IDataParameter)cmd.Parameters[index]).Value = dbValue; } public object DeepCopy(object value) { return value; } public object Replace(object original, object target, object owner) { return original; } public object Assemble(object cached, object owner) { return cached; } public object Disassemble(object value) { return value; } public SqlType[] SqlTypes { get { return new[] { NHibernateUtil.DateTime.SqlType }; } } public Type ReturnedType { get { return typeof(DateTime?); } } public bool IsMutable { get { return false; } } } } //Final Implementation with fixes. make the column mapping in hbm.xml not-null="false" public class NullableDateTimeToNotNullUserType : IUserType { private static readonly DateTime MaxDate = new DateTime(9999, 12, 31); public new bool Equals(object x, object y) { //This didn't work as well if (ReferenceEquals(x, y)) return true; //if(x == null && y == null) return false; if (x == null || y == null) return false; return x.Equals(y); } public int GetHashCode(object x) { return x == null ? 0 : x.GetHashCode(); } public object NullSafeGet(IDataReader rs, string[] names, object owner) { var value = NHibernateUtil.Date.NullSafeGet(rs, names[0]); return (value == MaxDate)? default(DateTime?) : value; } public void NullSafeSet(IDbCommand cmd, object value, int index) { var dateValue = (DateTime?)value; var dbValue = (dateValue.HasValue) ? dateValue.Value : MaxDate; NHibernateUtil.Date.NullSafeSet(cmd, valueToSet, index); } public object DeepCopy(object value) { return value; } public object Replace(object original, object target, object owner) { return original; } public object Assemble(object cached, object owner) { return cached; } public object Disassemble(object value) { return value; } public SqlType[] SqlTypes { get { return new[] { NHibernateUtil.DateTime.SqlType }; } } public Type ReturnedType { get { return typeof(DateTime?); } } public bool IsMutable { get { return false; } } } }

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  • Using Zope object unique id ( _p_oid ) to access object itself

    - by Alex M
    Every Zope object has it's own unique id ( _p_oid ). To convert it into integer value: from Shared.DC.xml.ppml import u64 as decodeObjectId oid = decodeObjectId(getattr(<Object instance>, '_p_oid')) Is it possible to get object itself having it's _p_oid? I tried this: from ZODB.utils import p64 object = <RootObject instance>._p_jar[p64(oid)] But it seems it's a wrong way

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  • onListItemClick with Mulitple Value/Retrieving Value

    - by JuniorFlip
    Hello, I am trying to retrieve the value from a Arraylist/ArrayAdapter that I have populated. I believe my issue is at the Onitemclick event. What I would like to accomplished is that when I click on Yasmin, I can return the value of 8. Please let me know if I am on the right track import java.util.ArrayList; import android.app.Activity; import android.os.Bundle; import android.view.View; import android.widget.AdapterView; import android.widget.ArrayAdapter; import android.widget.ListView; import android.widget.TextView; import android.widget.AdapterView.OnItemClickListener; public class lister extends Activity { /** Called when the activity is first created. */ TextView txHomeTeam; protected ListView mFavlist; protected ArrayList fakeFavs = new ArrayList(); @Override public void onCreate(Bundle icicle) { super.onCreate(icicle); this.setContentView(R.layout.main); this.txHomeTeam = (TextView)this.findViewById(R.id.title); fakeFavs.add(new Favorite("John", "1")); fakeFavs.add(new Favorite("Yasmin", "8")); fakeFavs.add(new Favorite("Jack", "10")); //this.mFavlist = (ListView) this.findViewById(R.id.list_favorites); this.mFavlist = (ListView) this.findViewById(R.id.list_favorites); initListView(); mFavlist.setTextFilterEnabled(true); mFavlist.setOnItemClickListener(new OnItemClickListener() { @Override public void onItemClick(AdapterView arg0, View view, int position, long id) { // user clicked a list item, //and read the value from <Favorite>.value //txHomeTeam.setText=???? } }); } public void refreshFavListItems() { mFavlist.setAdapter(new ArrayAdapter(this, android.R.layout.simple_list_item_1, fakeFavs)); } public void initListView() { /* Loads the items to the ListView. */ refreshFavListItems(); } protected class Favorite { protected String Detail; protected String value; protected Favorite(String Detail, String value) { this.Detail = Detail; this.value = value; } public String toString() { return Detail; } } }

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  • Using AChartEngine library for graphs, not able to get value for diffrent x-axis value

    - by kundan Chaudhary
    public static ArrayList<double[]> Value = new ArrayList<double[]>(); private double[] x = new double[10]; private double[] y = new double[10]; int counter = -1; add.setOnClickListener(new OnClickListener() { @Override public void onClick(View v) { counter++; x[counter] = Double.parseDouble(income_1.getText().toString()); y[counter] = Double.parseDouble(income_2.getText().toString()); income_1.setText(""); income_2.setText(""); } }); publish.setOnClickListener(new OnClickListener() { @Override public void onClick(View v) { if (Value != null) { Value.add(x); Value.add(y); Intent intent = salesStackedBarChart.execute(BarChart.this, Value, counter); startActivity(intent); } } }); //and in SalesStackedBarChart.java class public Intent execute(Context context, ArrayList<double[]> values ,int counter) { int count = counter + 1; double fcount = counter + 1.5; String[] titles = new String[] { "Android", "iPhone" }; int[] colors = new int[] { Color.GREEN, Color.CYAN }; XYMultipleSeriesRenderer renderer = buildBarRenderer(colors); setChartSettings(renderer, "Yearly revenue in the last "+count+" years", "Years", "revenue in $", 0.5, fcount, 0, 24000, Color.GRAY, Color.LTGRAY); renderer.setXLabels(count); renderer.setYLabels(10); renderer.setDisplayChartValues(true); renderer.setXLabelsAlign(Align.LEFT); renderer.setYLabelsAlign(Align.LEFT); renderer.setZoomRate(1.1f); renderer.setBarSpacing(0.5); return ChartFactory.getBarChartIntent(context, buildBarDataset(titles, values), renderer, Type.DEFAULT); } // in AbstractDemoChart.java class protected XYMultipleSeriesDataset buildBarDataset(String[] titles, List<double[]> values) { XYMultipleSeriesDataset dataset = new XYMultipleSeriesDataset(); int length = titles.length; for (int i = 0; i < length; i++) { CategorySeries series = new CategorySeries(titles[i]); double[] v = values.get(i); int seriesLength = v.length; for (int k = 0; k < seriesLength; k++) { series.add(v[k]); } dataset.addSeries(series.toXYSeries()); } return dataset; } Run this project i get graph with x- axis value: 1,2,3,4,5.... But I want to print value: 2005,2006,2007,2008..... I changed in some code like: setChartSettings(renderer, "Yearly revenue in the last "+count+" years", "Years", "revenue in $", 2005, 2010, 0, 24000, Color.GRAY, Color.LTGRAY); and run project i get value of x-axis like: 2005,2006,2007.... but not get graph bar value. Values of all x-axis are null. How can I make this work?

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  • How to get a cell value in JQGrid?

    - by dev
    How to get a cell value in JQGrid? If I use the following syntax – var ret = jQuery("#MyGrid").jqGrid('getRowData', id); ret = ret.ProductId; it returns the following HTML. I actually need the value of the cell. Thanks. Dev

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  • Textbox Wrong Value

    - by user181421
    Hello, I have an asp.net page with a datalist with few textboxes, and a submit button. when i cahnge the text in the textbox, and click submit, the value i get in the vb code is the old value and not the one i just entered. Any idea? thanks

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  • Default value of a type

    - by viky
    For any given type i want to know its default value. In C#, there is a keyword called default for doing this like object obj = default(Decimal); but I have an instance of Type (called myType) and if I say this, object obj = default(myType); it doesn't work Is there any good way of doing this? I know that a huge switch block will work but thats not a good choice.

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