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  • which situation abstract class i should use

    - by Bharanikumar
    Hi , Am not worked on extream level of oops in my projects , So i have little doubts , In which situation should i use abstract method or classes , Basically i know about abstract class definition and flow, I got details from this URL Doubt is which situation should i use abstract class and methods ,

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  • java array pass by reference does not work?

    - by stdnoit
    guys i thought almost all language including java pass array into function as reference (modifiable) but somehow it does not work here. and the testArray is still 1,2,3 with size of 3 strange enough, when if i change result[i] = 2 to a[1] =2; it work . it did pass by reference what is wrong with this code? at the end, i had a = result; (which update the a). did result get removed from stack. that is why a still get to the original a ? i am confused. thanks class Test { public static void main(String[] args) { int[] testArray = {1,2,3}; equalize(testArray, 6); System.out.println("test Array size :" + testArray.length); for(int i = 0; i < testArray.length; i++) System.out.println(testArray[i]); } public static void equalize(int[] a, int biggerSize) { if(a.length > biggerSize) throw new Error("Array size bigger than biggerSize"); int[] result = new int[biggerSize]; // System.arraycopy(a, 0, result, 0, a.length); // int array default value should be 0 for(int i = 0; i < biggerSize; i++) result[i] = 2; a = result; } }

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  • Best way to run multiple queries per second on database, performance wise?

    - by Michael Joell
    I am currently using Java to insert and update data multiple times per second. Never having used databases with Java, I am not sure what is required, and how to get the best performance. I currently have a method for each type of query I need to do (for example, update a row in a database). I also have a method to create the database connection. Below is my simplified code. public static void addOneForUserInChannel(String channel, String username) throws SQLException { Connection dbConnection = null; PreparedStatement ps = null; String updateSQL = "UPDATE " + channel + "_count SET messages = messages + 1 WHERE username = ?"; try { dbConnection = getDBConnection(); ps = dbConnection.prepareStatement(updateSQL); ps.setString(1, username); ps.executeUpdate(); } catch(SQLException e) { System.out.println(e.getMessage()); } finally { if(ps != null) { ps.close(); } if(dbConnection != null) { dbConnection.close(); } } } And my DB connection private static Connection getDBConnection() { Connection dbConnection = null; try { Class.forName(DB_DRIVER); } catch (ClassNotFoundException e) { System.out.println(e.getMessage()); } try { dbConnection = DriverManager.getConnection(DB_CONNECTION, DB_USER,DB_PASSWORD); return dbConnection; } catch (SQLException e) { System.out.println(e.getMessage()); } return dbConnection; } This seems to be working fine for now, with about 1-2 queries per second, but I am worried that once I expand and it is running many more, I might have some issues. My questions: Is there a way to have a persistent database connection throughout the entire run time of the process? If so, should I do this? Are there any other optimizations that I should do to help with performance? Thanks

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  • Is possible to generate constant value during compilation?

    - by AOI Karasu
    I would like my classes to be identified each type by an unique hash code. But I don't want these hashed to be generated every time a method, eg. int GetHashCode(), is invoked during runtime. I'd like to use already generated constants and I was hoping there is a way to make the compiler do some come computing and set these constants. Can it be done using templates? Could you give me some example, if it is possible.

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  • Selecting all elements

    - by Eelke
    This should be really simple but I'm a javascript/jQuery rookie, so here we go: With the following code I can select a certain element var user = $(".ui-selected .user-name").html(); But if there are multiple elements with the above classes, only the first value gets selected. What I would like to accomplish is a variable with all the elements seperated by a , like: user1,user2,user3 ... etc. Any help would be greatly appreciated, thanks in advance!

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  • Measuring the CPU frequency scaling effect

    - by Bryan Fok
    Recently I am trying to measure the effect of the cpu scaling. Is it accurate if I use this clock to measure it? template<std::intmax_t clock_freq> struct rdtsc_clock { typedef unsigned long long rep; typedef std::ratio<1, clock_freq> period; typedef std::chrono::duration<rep, period> duration; typedef std::chrono::time_point<rdtsc_clock> time_point; static const bool is_steady = true; static time_point now() noexcept { unsigned lo, hi; asm volatile("rdtsc" : "=a" (lo), "=d" (hi)); return time_point(duration(static_cast<rep>(hi) << 32 | lo)); } }; Update: According to the comment from my another post, I believe redtsc cannot use for measure the effect of cpu frequency scaling because the counter from the redtsc does not affected by the CPU frequency, am i right?

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  • Make instance of class in java at runtime

    - by Milan
    In my program I generate classes dynamically but when I try: Class service = Class.forName("com.MyClass"); I recieve java.lang.ClassNotFoundException If I run one more time the program (in Eclipse), then it is working. Does anybody see the problem

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  • php OOP, full sample

    - by lolalola
    Hi, On this site I found a lot of cool examples of PHP OOP. Maybe you know where to find complete examples? Guest books, registration forms, blog... When I look at the full model is much easier to understand OOP PHP. As different classes interacting with each other, exchange data How to use the generic class for sending data to the database Thanks

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  • Visual Studio Default Open File Action

    - by Kleinux
    I am using Visual Studio 2008 with C#. Is there a way to set the default editor for a class file containing a DataTable derived class? Whenever I double click on one of these classes to open the file VS attempts to open a component designer. Since my class isn't compatible with that editor this is a rather useless default. I would like these files to open up in the normal code editor.

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  • Why strings behave like ValueType

    - by AJP
    I was perplexed after executing this piece of code, where strings seems to behave as if they are value types. I am wondering whether the assignment operator is operating on values like equality operator for strings. Here is the piece of code I did to test this behavior. using System; namespace RefTypeDelimma { class Program { static void Main(string[] args) { string a1, a2; a1 = "ABC"; a2 = a1; //This should assign a1 reference to a2 a2 = "XYZ"; //I expect this should change the a1 value to "XYZ" Console.WriteLine("a1:" + a1 + ", a2:" + a2);//Outputs a1:ABC, a2:XYZ //Expected: a1:XYZ, a2:XYZ (as string being a ref type) Proc(a2); //Altering values of ref types inside a procedure //should reflect in the variable thats being passed into Console.WriteLine("a1: " + a1 + ", a2: " + a2); //Outputs a1:ABC, a2:XYZ //Expected: a1:NEW_VAL, a2:NEW_VAL (as string being a ref type) } static void Proc(string Val) { Val = "NEW_VAL"; } } } In the above code if I use a custom classes instead of strings, I am getting the expected behavior. I doubt is this something to do with the string immutability? welcoming expert views on this.

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  • What's the Flash equivalent of FlexEvent.CREATION_COMPLETE

    - by John
    I'm moving some Flex classes to pure Flash/AS3 to be part of a shared library. I have an event listener on FlexEvent.CREATION_COMPLETE to create and add display-objects once things are running, but I don't know the right way to do this in Flash? edit: Maybe if my class subclasses Sprite rather than a Flex class, I can add children in the constructor, I don't need to wait for a "construction complete" event?

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  • How to check if an entityset is populated

    - by TheQ
    How can i check if an entityset of a linq-object is populated or not? Example code below. My model have two methods, one joins data, and the other does not: public static Member GetMemberWithSettings(Guid memberId) { using (DataContext db = new DataContext()) { DataLoadOptions dataLoadOptions = new DataLoadOptions(); dataLoadOptions.LoadWith<Member>(x => x.Settings); db.LoadOptions = dataLoadOptions; var query = from x in db.Members where x.MemberId == memberId select x; return query.FirstOrDefault(); } } public static Member GetMember(Guid memberId) { using (DataContext db = new DataContext()) { var query = from x in db.Members where x.MemberId == memberId select x; return query.FirstOrDefault(); } } Then my control have the following code: Member member1 = Member.GetMemberWithSettings(memberId); Member member2 = Member.GetMember(memberId); Debug.WriteLine(member1.Settings.Count); Debug.WriteLine(member2.Settings.Count); The last line will generate a "Cannot access a disposed object" exception. I know that i can get rid of that exception just by not disposing the datacontext, but then the last line will generate a new query to the database, and i don't want that. What i would like is something like: Debug.WriteLine((member1.Settings.IsPopulated()) ? member1.Settings.Count : -1); Debug.WriteLine((member2.Settings.IsPopulated()) ? member2.Settings.Count : -1); Is it possible?

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  • Can I have two names for the same variable?

    - by Roman
    The short version of the question: I do: x = y. Then I change x, and y is unchanged. What I want is to "bind" x and y in such a way that I change y whenever I change x. The extended version (with some details): I wrote a class ("first" class) which generates objects of another class ("second" class). In more details, every object of the second class has a name as a unique identifier. I call a static method of the first class with a name of the object from the second class. The first class checks if such an object was already generated (if it is present in the static HashMap of the first class). If it is already there, it is returned. If it is not yet there, it is created, added to the HashMap and returned. And then I have the following problem. At some stage of my program, I take an object with a specific name from the HashMap of the first class. I do something with this object (for example change values of some fields). But the object in the HashMap does not see these changes! So, in fact, I do not "take" an object from the HashMap, I "create a copy" of this object and this is what I would like to avoid.

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  • Any way in C++ to forward declare a function prototype?

    - by jsyjr
    I make regular use of forward class declarations and pointers to such classes. I now have a need to pass a function pointer through a number of layers. I would prefer to include the header that declares my function pointer's prototype only into the module that dereferences a function pointer rather than into each layer that simply passes along that pointer value. Is this possible?

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  • Why cant we create Object if constructor is in private section?

    - by Abhi
    Dear all I want to know why cant we create object if the constructor is in private section. I know that if i make a method static i can call that method using <classname> :: <methodname(...)>; But why cant we create object is my doubt... I also know if my method is not static then also i can call function by the following... class A { A(); public: void fun1(); void fun2(); void fun3(); }; int main() { A *obj =(A*)malloc(sizeof(A)); //Here we can't use new A() because constructor is in private //but we can use malloc with it, but it will not call the constructor //and hence it is harmful because object may not be in usable state. obj->fun1(); obj->fun2(); obj->fun3(); } So only doubt is why cant we create object when constructor is in private section? Thanks in advance

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  • Where does that randomness come from ?

    - by Jules Olléon
    I'm working on a data mining research project and use code from a big svn. Apparently one of the methods I use from that svn uses randomness somewhere without asking for a seed, which makes 2 calls to my program return different results. That's annoying for what I want to do, so I'm trying to locate that "uncontrolled" randomness. Since the classes I use depend on many other, that's pretty painful to do by hand. Any idea how I could find where that randomness comes from ?

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  • Why can't I dynamically add rows to a HTML table using JavaScript in Internet Explorer?

    - by karlthorwald
    In Firefox it works, in my Internet Explorer 6 or 7 it doesn't: <html> <head> <script type="text/javascript"> function newLine() { var tdmod = document.createElement('td'); tdmod.appendChild(document.createTextNode("dynamic")); var tr = document.createElement('tr'); tr.appendChild(tdmod); var tt = document.getElementById("t1"); tt.appendChild(tr); } </script> </head> <body> <a href="#" onclick="newLine()">newLine</a> <table id="t1" border="1"> <tr> <td> static </td> </tr> </table> </body> The user clicks on the link "newLine" and new rows should be added to the table. How to make this work also in IE? Edit: Thanks to the accepted answer I changed it like this and now it works: <table border="1"> <tbody id="t1"> <tr> <td> static </td> </tr> </tbody> </table>

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  • Clear listview content?

    - by Slash
    I have a little problem with listview. How do i clear a listview content, knowing that it has a custom adapter? edit : the custom adapter class extends BaseAdapter, it looks like this : import android.app.Activity; import android.content.Context; import android.view.LayoutInflater; import android.view.View; import android.view.ViewGroup; import android.widget.BaseAdapter; import android.widget.TextView; public class MyAdapter extends BaseAdapter { private Activity activity; private String[] data; private static LayoutInflater inflater=null; public MyAdapter(Activity _a, String[] _str) { activity = _a; data = _str; inflater = (LayoutInflater)activity.getSystemService(Context.LAYOUT_INFLATER_SERVICE); } public static class ViewHolder{ public TextView text; } @Override public int getCount() { return data.length; } @Override public Object getItem(int position) { return position; } @Override public long getItemId(int position) { return position; } @Override public View getView(int position, View view, ViewGroup parent) { View v = view; ViewHolder holder; if(v == null) { v = inflater.inflate(R.layout.rowa, null); holder=new ViewHolder(); holder.text=(TextView)v.findViewById(R.id.dexter); v.setTag(holder); }else{ holder=(ViewHolder)v.getTag(); } holder.text.setText(data[position]); return v; } }

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