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  • Java Thread - Synchronization issue

    - by Yatendra Goel
    From Sun's tutorial: Synchronized methods enable a simple strategy for preventing thread interference and memory consistency errors: if an object is visible to more than one thread, all reads or writes to that object's variables are done through synchronized methods. (An important exception: final fields, which cannot be modified after the object is constructed, can be safely read through non-synchronized methods, once the object is constructed) This strategy is effective, but can present problems with liveness, as we'll see later in this lesson. Q1. Is the above statements mean that if an object of a class is going to be shared among multiple threads, then all instance methods of that class (except getters of final fields) should be made synchronized, since instance methods process instance variables?

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  • How to put Listview items into String Array?

    - by user2851687
    Im developing an app and as the title says how to put items of listview into String array, not string array to listview but listview to string array. I've been searching for this but what I only found is putting String array items into listview. Please help me thank you in advance. To clarify this thread, the question is how to put listview items into String array. Thanks. :D Codes public class DailyPlanTab extends Activity implements OnItemClickListener { ListView dailyPlanList; ArrayList<DailyManager> taskList = new ArrayList<DailyManager>(); DatabaseDailyPlan db; @Override protected void onCreate(Bundle savedInstanceState) { // TODO Auto-generated method stub super.onCreate(savedInstanceState); setContentView(R.layout.dailyplan_layout); dailyPlanList = (ListView) findViewById(R.id.lvDailyPlanList); dailyPlanList.setOnItemClickListener(this); ImageView add = (ImageView) findViewById(R.id.ivDailyPlanAdd); add.setOnClickListener(new OnClickListener() { @Override public void onClick(View v) { // TODO Auto-generated method stub Intent newDailyIntent = new Intent(getApplicationContext(), NewDailyPlan.class); startActivity(newDailyIntent); } }); } @Override protected void onResume() { // TODO Auto-generated method stub super.onResume(); taskList.clear(); db = new DatabaseDailyPlan(getApplicationContext()); db.getWritableDatabase(); ArrayList<DailyManager> tempList = db.getTask(); for (int i = 0; i < tempList.size(); i++) { String getTask = tempList.get(i).getDaily_name(); String getDate = tempList.get(i).getDaily_date(); int getId = tempList.get(i).getDaily_id(); DailyManager dm = new DailyManager(); dm.setDaily_name(getTask); dm.setDaily_date(getDate); dm.setDaily_id(getId); taskList.add(dm); } dailyPlanList.setAdapter(new ListAdapter(this)); // db.close(); } public class ListAdapter extends BaseAdapter { LayoutInflater inflater; ViewHolder viewHolder; public ListAdapter(Context c) { // TODO Auto-generated constructor stub inflater = LayoutInflater.from(c); } @Override public int getCount() { // TODO Auto-generated method stub return taskList.size(); } @Override public Object getItem(int position) { // TODO Auto-generated method stub return position; } @Override public long getItemId(int position) { // TODO Auto-generated method stub return position; } @Override public View getView(int position, View convertView, ViewGroup parent) { // TODO Auto-generated method stub if (convertView == null) { convertView = inflater.inflate(R.layout.row_checklist_item, null); viewHolder = new ViewHolder(); viewHolder.taskTitle = (TextView) convertView .findViewById(R.id.tvCheckListItem); convertView.setTag(viewHolder); } else { viewHolder = (ViewHolder) convertView.getTag(); } viewHolder.taskTitle.setText("" + taskList.get(position).getDaily_name()); return convertView; } } public class ViewHolder { TextView taskTitle, taskDate; } @Override public void onItemClick(AdapterView<?> arg0, View arg1, int position, long arg3) { // TODO Auto-generated method stub int taskId = taskList.get(position).getDaily_id(); String taskName = taskList.get(position).getDaily_name(); String taskDate = taskList.get(position).getDaily_date(); Intent newPlan = new Intent(getApplicationContext(), DailyPlan.class); newPlan.putExtra("task_id", taskId); newPlan.putExtra("task_name", taskName); startActivity(newPlan); } next is the information of the item inside the listview public class DailyPlan extends Activity implements OnItemClickListener { final ArrayList<DailyManager> savedItems = new ArrayList<DailyManager>(); ListView checkList; Boolean nextItem = false; TempManager tm; DatabaseTemp dbTemp; Intent i; int taskId = -1; String taskName = " ", taskDate = null; DatabaseDailyPlan db; DailyManager dm; @Override protected void onCreate(Bundle savedInstanceState) { // TODO Auto-generated method stub super.onCreate(savedInstanceState); setContentView(R.layout.saved_dailyplan); checkList = (ListView) findViewById(R.id.lvCheckList); // checkList.setOnItemClickListener(this); try { i = getIntent(); taskId = i.getExtras().getInt("task_id"); taskName = i.getExtras().getString("task_name"); Toast.makeText(getApplicationContext(), "From new id is" + taskId, 5000).show(); } catch (Exception e) { } Button addList = (Button) findViewById(R.id.bAddList); addList.setOnClickListener(new OnClickListener() { @Override public void onClick(View v) { // TODO Auto-generated method stub // openDialog("", false, -1); } }); if (nextItem) { // openDialog("", false, -1); } } public void refresh() { DailyPlan.this.onResume(); } @Override protected void onResume() { // TODO Auto-generated method stub super.onResume(); savedItems.clear(); dbTemp = new DatabaseTemp(getApplicationContext()); dbTemp.getWritableDatabase(); db = new DatabaseDailyPlan(getApplicationContext()); db.getWritableDatabase(); if (taskId != -1) { // / For Load ArrayList<DailyManager> savedList = db.getList(taskId); for (int i = 0; i < savedList.size(); i++) { String savedListItems = savedList.get(i).getDaily_list(); String savedListTitle = savedList.get(i).getDaily_name(); String savedListDate = savedList.get(i).getDaily_date(); int savedListId = savedList.get(i).getDaily_id(); DailyManager dm = new DailyManager(); dm.setDaily_list(savedListItems); dm.setDaily_name(savedListTitle); dm.setDaily_date(savedListDate); dm.setDaily_id(savedListId); savedItems.add(dm); } } else { // / For New } checkList.setAdapter(new ListAdapter(this)); } public class ListAdapter extends BaseAdapter { LayoutInflater inflater; ViewHolder viewHolder; public ListAdapter(Context c) { // TODO Auto-generated constructor stub inflater = LayoutInflater.from(c); } @Override public int getCount() { // TODO Auto-generated method stub return savedItems.size(); } @Override public Object getItem(int position) { // TODO Auto-generated method stub return position; } @Override public long getItemId(int position) { // TODO Auto-generated method stub return position; } @Override public View getView(int position, View convertView, ViewGroup parent) { // TODO Auto-generated method stub if (convertView == null) { convertView = inflater.inflate(R.layout.row_checklist_item, null); viewHolder = new ViewHolder(); viewHolder.checkListItem = (TextView) convertView .findViewById(R.id.tvCheckListItem); convertView.setTag(viewHolder); } else { viewHolder = (ViewHolder) convertView.getTag(); } viewHolder.checkListItem.setText(savedItems.get(position) .getDaily_list() + position); final int temp = position; return convertView; } } private class ViewHolder { TextView checkListItem; } @Override public void onItemClick(AdapterView<?> arg0, View arg1, int item, long arg3) { // TODO Auto-generated method stub // openDialog(savedItems.get(item).getDaily_name(), true, // savedItems.get(item).getDaily_id()); } }

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  • Which is the best Linux C/C++ debugger (or front-end to gdb) to help teaching programming?

    - by omer.gimenez
    I teach a sort of "lite" C++ programming course to novices ("lite" meaning no pointers, no classes, just plain old C, plus references and STL string and vectors). Students have no previous experience in programming, so I believe that using an interactive debugger would help them understand program flow, variables, and recursion. The course is taught in Linux. Teaching them to use gdb is just overkill (they will not use nor understand most features). I just need something simple but easy to use: to see at which line the program is now, what is in the stack (local variables, previous calls, etc.). I look something similar to old Turbo Pascal or Turbo C++ Borland's debugger, or Visual Studio debugger. Thank you,

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  • Is there a better way to do SELECT queries in MySQL and sort them in PHP than this way?

    - by Kent
    I am just learning PHP/MySQL, one this I am having to do a lot is displaying data that was previously inserted into the database out to the user's browser. So I am doing this: $select = mysql_query('SELECT * FROM pages'); while ($return = mysql_fetch_assoc($select)) { $title = $return['title']; $author = $return['author']; $content = $return['content']; } then I can use these variables through out the page. Now, doing it the above way isn't an issue when I only have 3 columns in a database but what if I am dealing with a huge database with many more columns. I have a nagging feeling that the pros do it in some more efficient way where they maybe loop through the table they are selecting from to find all columns it has and associate them with variables automatically. Is that the case? or is the above how you guys do it too?

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  • Linked lists in Java - Help with writing methods

    - by user368241
    Representation of a string in linked lists In every intersection in the list there will be 3 fields : The letter itself. The number of times it appears consecutively. A pointer to the next intersection in the list. The following class CharNode represents a intersection in the list : public class CharNode { private char _data; private int _value; private charNode _next; public CharNode (char c, int val, charNode n) { _data = c; _value = val; _next = n; } public charNode getNext() { return _next; } public void setNext (charNode node) { _next = node; } public int getValue() { return _value; } public void setValue (int v) { value = v; } public char getData() { return _data; } public void setData (char c) { _data = c; } } The class StringList represents the whole list : public class StringList { private charNode _head; public StringList() { _head = null; } public StringList (CharNode node) { _head = node; } } Add methods to the class StringList according to the details : (I will add methods gradually according to my specific questions) (Pay attention, these are methods from the class String and we want to fulfill them by the representation of a string by a list as explained above) Pay attention to all the possible error cases. Write what is the time complexity and space complexity of every method that you wrote. Make sure the methods you wrote are effective. It is NOT allowed to use ready classes of Java. It is NOT allowed to move to string and use string operations. 1) public int indexOf (int ch) - returns the index in the string it is operated on of the first appeareance of the char "ch". If the char "ch" doesn't appear in the string, returns -1. If the value of fromIndex isn't in the range, returns -1. Here is my try : public int indexOf (int ch) { int count = 0; charNode pos = _head; if (pos == null ) { return -1; } for (pos = _head; pos!=null && pos.getData()!=ch; pos = pos.getNext()) { count = count + pos.getValue(); } if (pos==null) return -1; return count; } Time complexity = O(N) Space complexity = O(1) EDIT : I have a problem. I tested it in BlueJ and if the char ch doesn't appear it returns -1 but if it does, it always returns 0 and I don't understand why... I am confused. How can the compiler know that the value is the number of times the letter appears consecutively? Can I assume this because its given on the question or what? If it's true and I can assume this, then my code should be correct right? Ok I just spoke with my instructor and she said it isn't required to write it in the exercise but in order for me to test that it indeed works, I need to open a new class and write a code for making a list so that the the value of every node is the number of times the letter appears consecutively. Can someone please assist me? So I will copy+paste to BlueJ and this way I will be able to test all the methods. Meanwhile I am moving on to the next methods. 2) public int indexOf (int ch, int fromIndex) - returns the index in the string it is operated on of the first appeareance of the char "ch", as the search begins in the index "fromIndex". If the char "ch" doesn't appear in the string, returns -1. If the value of fromIndex doesn't appear in the range, returns -1. Here is my try: public int indexOf (int ch, int fromIndex) { int count = 0, len=0, i; charNode pos = _head; CharNode cur = _head; for (pos = _head; pos!=null; pos = pos.getNext()) { len = len+1; } if (fromIndex<0 || fromIndex>=len) return -1; for (i=0; i<fromIndex; i++) { cur = cur.getNext(); } if (cur == null ) { return -1; } for (cur = _head; cur!=null && cur.getData()!=ch; cur = cur.getNext()) { count = count + cur.getValue(); } if (cur==null) return -1; return count; } Time complexity = O(N) ? Space complexity = O(1) 3) public StringList concat (String str) - returns a string that consists of the string that it is operated on and in its end the string "str" is concatenated. Here is my try : public StringList concat (String str) { String str = ""; charNode pos = _head; if (str == null) return -1; for (pos = _head; pos!=null; pos = pos.getNext()) { str = str + pos.getData(); } str = str + "str"; return str; } Time complexity = O(N) Space complexity = O(1)

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  • Ensuring all waiting threads complete

    - by Daniel
    I'm building a system where the progress of calling threads is dependent on the state of two variables. One variable is updated sporadically by an external source (separate from the client threads) and multiple client threads block on a condition of both variables. The system is something like this TypeB waitForB() { // Can be called by many threads. synchronized (B) { while (A <= B) { B.wait(); } A = B; return B; { } void updateB(TypeB newB) { // Called by one thread. synchronized (B) { B.update(newB); B.notifyAll(); // All blocked threads must receive new B. } } I need all the blocked threads to receive the new value of B once it has been updated. But the problem is once a single thread finishes and updates A, the waiting condition becomes true again so some of the other threads become blocked and don't receive the new value of B. Is there a way of ensuring that only the last thread that was blocked on B updates A, or another way of getting this behaviour?

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  • Write to a binary file?

    - by rick irby
    Here is data structure w/ variables: struct Part_record { char id_no[3]; int qoh; string desc; double price: }; --- (Using "cin" to input data) --- Part_record null_part = {" ", 0," ",0.0}; --- --- file.seekg( -(long)sizeof(Part_record), ios::cur); file.write( ( char *)&part, sizeof(Part_record) ); The three variables, qoh, Id_no & price, write out correctly, but the "desc" variable is not right. Do I need to initialize Part_record some other way? It should be 20 characters in length. If you have enough info here, pls share your advice,thanks.

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  • Why use constants in programming?

    - by Adam N
    I've just been going back over a bit of C studying using Ivor Horton's Beginning C book. I got to the bit about declaring constants which seems to get mixed up with variables in the same sentence. Just to clarify, what is the difference in specifying constants and variables in C, and really, when do you need to use a constant instead of a variable? I know folks say to use a constant when the information doesn't change during program execution but I can't really think of a time when a variable couldn't be used instead. Thanks

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  • Codeigniter pre_system hook for DB driven dynamic controller selection - best approach?

    - by Andy
    Although I can tentatively see a solution to this, I was wondering if there may be a glaringly obvious simpler approach. My aim is to use the first segment of a given URI to query the DB as to which controller should be run. I assume I would have to reform the URI with the resultant controller name in segment 1, then allow the system to continue processing as normal (hence a pre_system hook). Although not essential I would also like to hold a couple of other variables from the same DB request to be used later in the call stack, and assume this would have to be done using global variables? Any better suggestions would be gladly received. Thanks.

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  • Find a variable with a given value in VS2008

    - by Aaron
    I have an instance variable with several members, many of which have their own members and so on. Using the debugger and watch variables, I found a string variable with a specific value that I need by diving into this variable's members. However, after spending some time on other things and coming back to this, I am now unable to find where this value is located. When I have my application paused, is there a way to search the values of variables in the current context for a given value? To clarify, if I have the given structure: myVariable | |--aMember1 | |--subMember = "A value" | |--aMember2 |--subMember = "Another value" Is there a way (possibly using the watch list in VS debugger) to search myVariable for any member or submember with the value "A value", returning to me the path myVariable->aMember->subMember?

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  • Propor usage of double and single quotes?

    - by Phox
    I'm talking about the performance increase here. From all I know you can echo variables in double quotes ("), like so: <?php echo "You are $yourAge years old"; ?> But single quotes will just return You are $yourAge years old. But what about performance differences? I've always gone by the rule that single quotes are faster because the PHP interpreter doesn't have to search through the string for variables. But I'm seeing more and more blog and forum posts on the web saying differently. Does anyone actually have any information on this subject? Perhaps benchmark tests or something? Cheers.

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  • Remembering Form information

    - by Pete Herbert Penito
    Hi everyone! I'm sorry if this has been asked before but I feel my situation is a little different... I have a huge form (like 50 questions involving checkboxes, drop downs, text boxes and textareas) When a user submits a form and the validation page throws an error, is there an easy way to keep the info they entered? My intitial form is on form.php and then the form action is form_posted.php, before anything is run on form_posted.php I have my validation code which sends the user back to form.php with an error number (eg. form.php?error=3) if there was a problem with any in particular. This is done with header("form.php?error=3") so on form.php do the posted variables exist? even tho the page wasn't specifically sent with any posted variables. Also if this is the case, is it completely secure to be making the value of a textbox what it was before? like <input type="text" value="php echo $_POSTED["username"] ?>">

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  • Turkish characters are not displayed correctly

    - by tfeseas
    MySql database uses utf-8 encoding and data are stored correctly.I use set_name utf8 query to make sure the data called are utf-8 encoded.all variables from database works fine as long as the header charset is utf-8,but the static html characters do not work properly.When i set header charset to ISO-8859-9 variables are displayed differenly while html characters work ok.can anyone help me? <?php header('Content-Type: text/html; charset=ISO-8859-9'); ?> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head><title>noname</title> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />

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  • How to obtain listview information without refreshing the page?

    - by user1808098
    I am currently developing an Android Application for my Final Year Project. But to be honest I do not have any basic knowledges and everything started from scratch and referring to online tutorials a lot. Here is my question, I was trying to retrieve data from listview activity. There are two listview in my page using button. I was able to display the first listview but when it get data for the second listview, the data for first listview is disappeared because the page is refreshed, vice versa. What code should I modified to get both the data in the page? (Database not implemented yet) Please help, thanks a lot. Below are my codings. Codings for XML. <!-- Location --> <TextView android:id="@+id/TextViewLocation" android:layout_width="fill_parent" android:layout_height="wrap_content" android:layout_marginTop="5dip" android:layout_marginBottom="10dip" android:text="Location Information" android:gravity="center" android:textSize="15dip" android:textColor="#025f7c"/> <!-- Condition Label --> <TextView android:layout_width="fill_parent" android:layout_height="wrap_content" android:textColor="#372c24" android:text="Traffic Condition"/> <Button android:id="@+id/inputListView" android:layout_width="fill_parent" android:layout_height="wrap_content" android:layout_marginTop="5dip" android:layout_marginBottom="10dip" android:text="choose one..."/> <!-- Comment Label --> <TextView android:layout_width="fill_parent" android:layout_height="wrap_content" android:textColor="#372c24" android:text="What's Happening?"/> <Button android:id="@+id/inputListView2" android:layout_width="fill_parent" android:layout_height="wrap_content" android:layout_marginTop="5dip" android:layout_marginBottom="10dip" android:text="choose one..."/> <!-- Suggestion Label --> <TextView android:layout_width="fill_parent" android:layout_height="wrap_content" android:textColor="#372c24" android:text="Comments / Suggestion"/> <EditText android:layout_width="fill_parent" android:layout_height="80dp" android:layout_marginTop="5dip" android:layout_marginBottom="10dip" android:singleLine="true"/> <!-- Image button --> <Button android:id="@+id/btnImage" android:layout_width="fill_parent" android:layout_height="wrap_content" android:layout_marginTop="5dip" android:text="Upload Image"/> <!-- Report button --> <Button android:id="@+id/btnReportCheckin" android:layout_width="fill_parent" android:layout_height="wrap_content" android:layout_marginTop="5dip" android:text="Report"/> <!-- Link to Logout --> <TextView android:id="@+id/linkLogout" android:layout_width="fill_parent" android:layout_height="wrap_content" android:layout_marginTop="5dip" android:layout_marginBottom="40dip" android:text="Log Out" android:gravity="center" android:textSize="20dip" android:textColor="#025f7c"/> </LinearLayout> <!-- Check or Report Form Ends --> Codings for Activity Class public class CheckinActivity extends Activity { @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); // Set View to checkin.xml setContentView(R.layout.checkin); /* TextView LocationView = (TextView) findViewById(R.id.TextViewLocation); Intent h = getIntent(); // getting attached intent data String address = h.getStringExtra("address"); // displaying selected product name LocationView.setText(address); */ Button ListViewScreen = (Button) findViewById(R.id.inputListView); //Listening to Button ListViewScreen.setOnClickListener(new View.OnClickListener() { public void onClick(View v) { //Switching to ListView Screen Intent i = new Intent(getApplicationContext(), ListViewActivity.class); startActivity(i); } } ); Button SelectedView = (Button) findViewById(R.id.inputListView); Intent i = getIntent(); // getting attached intent data String product = i.getStringExtra("product"); // displaying selected product name SelectedView.setText(product); Button ListView2Screen = (Button) findViewById(R.id.inputListView2); //Listening to Button ListView2Screen.setOnClickListener(new View.OnClickListener() { public void onClick(View v) { //Switching to ListView Screen Intent j = new Intent(getApplicationContext(), ListView2Activity.class); startActivity(j); } } ); Button SelectedView2 = (Button) findViewById(R.id.inputListView2); Intent j = getIntent(); // getting attached intent data String product2 = j.getStringExtra("product2"); // displaying selected product name SelectedView2.setText(product2); TextView Logout = (TextView) findViewById(R.id.linkLogout); // Listening to Log out Logout.setOnClickListener(new View.OnClickListener() { public void onClick(View arg0) { // Closing menu screen // Switching to Login Screen/closing register screen finish(); } }); } } Coding for listview class public class ListViewActivity extends ListActivity { @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); // storing string resources into Array String[] traffic_condition = getResources().getStringArray(R.array.traffic_condition); // Binding resources Array to ListAdapter this.setListAdapter(new ArrayAdapter<String>(this, R.layout.listitem, R.id.listViewLayout, traffic_condition)); ListView lv = getListView(); // listening to single list item on click lv.setOnItemClickListener(new OnItemClickListener() { public void onItemClick(AdapterView<?> parent, View view, int position, long id) { // selected item String product = ((TextView) view).getText().toString(); // Launching new Activity on selecting single List Item Intent i = new Intent(getApplicationContext(), CheckinActivity.class); // sending data to new activity i.putExtra("product", product); startActivity(i); } }); } } Hope I made myself clear, I can provide a screen shot of my apps if it is required, thanks!

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  • Is it a good idea to define a variable in a local block for a case of a switch statement?

    - by Paperflyer
    I have a rather long switch-case statement. Some of the cases are really short and trivial. A few are longer and need some variables that are never used anywhere else, like this: switch (action) { case kSimpleAction: // Do something simple break; case kComplexAction: { int specialVariable = 5; // Do something complex with specialVariable } break; } The alternative would be to declare that variable before going into the switch like this: int specialVariable = 5; switch (action) { case kSimpleAction: // Do something simple break; case kComplexAction: // Do something complex with specialVariable break; } This can get rather confusing since it is not clear to which case the variable belongs and it uses some unnecessary memory. However, I have never seen this usage anywhere else. Do you think it is a good idea to declare variables locally in a block for a single case?

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  • Call an anonymous function defined in a setInterval

    - by Tominator
    Hi, I've made this code: window.setInterval(function(){ var a = doStuff(); var b = a + 5; }, 60000) The actual contents of the anonymous function is of course just for this small example as it doesn't matter. What really happens is a bunch of variables get created in the scope of the function itself, because I don't need/want to pollute the global space. But as you all know, the doStuff() function won't be called until 60 seconds in the page. I would also like to call the function right now, as soon as the page is loaded, and from then on every 60 seconds too. Is it somehow possible to call the function without copy/pasting the inside code to right after the setInterval() line? As I said, I don't want to pollute the global space with useless variables that aren't needed outside the function.

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  • ok.. what's with this 'var' thing in C#?? [closed]

    - by KevinDeus
    Possible Duplicate: Use of var keyword in C# I have ReSharper, which is a pretty good tool to remind me of some good programming practices.. for example it always recommends that I use the most narrowed convention I can use when passing variables to functions (such as recommending IEnumerable instead of List when I fail to use any of List's specific function. Awesome. However, one of its new behaviors (for C# 4.0) is to remind me at every opportunity to use 'var' when declaring variables. Now I know that there are some valid uses of 'var', but do I really want to use it all the time? I'm sure that ReSharper has a reason for this, but I can't figure it out.. for me it makes the code less readable..

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  • How can I improve my select query for storing large versioned data sets?

    - by Jason Francis
    At work, we build large multi-page web applications, consisting mostly of radio and check boxes. The primary purpose of each application is to gather data, but as users return to a page they have previously visited, we report back to them their previous responses. Worst-case scenario, we might have up to 900 distinct variables and around 1.5 million users. For several reasons, it makes sense to use an insert-only approach to storing the data (as opposed to update-in-place) so that we can capture historical data about repeated interactions with variables. The net result is that we might have several responses per user per variable. Our table to collect the responses looks something like this: CREATE TABLE [dbo].[results]( [id] [bigint] IDENTITY(1,1) NOT NULL, [userid] [int] NULL, [variable] [varchar](8) NULL, [value] [tinyint] NULL, [submitted] [smalldatetime] NULL) Where id serves as the primary key. Virtually every request results in a series of insert statements (one per variable submitted), and then we run a select to produce previous responses for the next page (something like this): SELECT t.id, t.variable, t.value FROM results t WITH (NOLOCK) WHERE t.userid = '2111846' AND (t.variable='internat' OR t.variable='veteran' OR t.variable='athlete') AND t.id IN (SELECT MAX(id) AS id FROM results WITH (NOLOCK) WHERE userid = '2111846' AND (t.variable='internat' OR t.variable='veteran' OR t.variable='athlete') GROUP BY variable) Which, in this case, would return the most recent responses for the variables "internat", "veteran", and "athlete" for user 2111846. We have followed the advice of the database tuning tools in indexing the tables, and against our data, this is the best-performing version of the select query that we have been able to come up with. Even so, there seems to be significant performance degradation as the table approaches 1 million records (and we might have about 150x that). We have a fairly-elegant solution in place for sharding the data across multiple tables which has been working quite well, but I am open for any advice about how I might construct a better version of the select query. We use this structure frequently for storing lots of independent data points, and we like the benefits it provides. So the question is, how can I improve the performance of the select query? I assume the nested select statement is a bad idea, but I have yet to find an alternative that performs as well. Thanks in advance. NB: Since we emphasize creating over reading in this case, and since we never update in place, there doesn't seem to be any penalty (and some advantage) for using the NOLOCK directive in this case.

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  • Keep a javascript variable after an ajax call

    - by Guillaume le Floch
    I'm new in javascript and jQuery. I'm using ajax calls to get data from my server. The fact is, I'm losing my javascript variables after the call .. Here is what I did : the variable is define outside any function and treat in an other function. var a = 0; function myfunction(url){ $.ajax({ url: url, timeout: 20000, success: function(data){ // Do some stuff // The a variable is now undefined }, error: function(){ // Do some stuff } }); } Everything is working fine, the only thing is that I need to keep my variables ... but it looks like it's gone .. Does anyone know why? Thanks

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  • Proper usage of double and single quotes?

    - by Phox
    I'm talking about the performance increase here. From all I know you can echo variables in double quotes ("), like so: <?php echo "You are $yourAge years old"; ?> But single quotes will just return You are $yourAge years old. But what about performance differences? I've always gone by the rule that single quotes are faster because the PHP interpreter doesn't have to search through the string for variables. But I'm seeing more and more blog and forum posts on the web saying differently. Does anyone actually have any information on this subject? Perhaps benchmark tests or something?

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  • WCF Service returning 400 error: The body of the message cannot be read because it is empty

    - by Josh
    I have a WCF service that is causing a bit of a headache. I have tracing enabled, I have an object with a data contract being built and passed in, but I am seeing this error in the log: <TraceData> <DataItem> <TraceRecord xmlns="http://schemas.microsoft.com/2004/10/E2ETraceEvent/TraceRecord" Severity="Error"> <TraceIdentifier>http://msdn.microsoft.com/en-US/library/System.ServiceModel.Diagnostics.ThrowingException.aspx</TraceIdentifier> <Description>Throwing an exception.</Description> <AppDomain>efb0d0d7-1-129315381593520544</AppDomain> <Exception> <ExceptionType>System.ServiceModel.ProtocolException, System.ServiceModel, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089</ExceptionType> <Message>There is a problem with the XML that was received from the network. See inner exception for more details.</Message> <StackTrace> at System.ServiceModel.Channels.HttpRequestContext.CreateMessage() at System.ServiceModel.Channels.HttpChannelListener.HttpContextReceived(HttpRequestContext context, Action callback) at System.ServiceModel.Activation.HostedHttpTransportManager.HttpContextReceived(HostedHttpRequestAsyncResult result) at System.ServiceModel.Activation.HostedHttpRequestAsyncResult.HandleRequest() at System.ServiceModel.Activation.HostedHttpRequestAsyncResult.BeginRequest() at System.ServiceModel.Activation.HostedHttpRequestAsyncResult.OnBeginRequest(Object state) at System.Runtime.IOThreadScheduler.ScheduledOverlapped.IOCallback(UInt32 errorCode, UInt32 numBytes, NativeOverlapped* nativeOverlapped) at System.Runtime.Fx.IOCompletionThunk.UnhandledExceptionFrame(UInt32 error, UInt32 bytesRead, NativeOverlapped* nativeOverlapped) at System.Threading._IOCompletionCallback.PerformIOCompletionCallback(UInt32 errorCode, UInt32 numBytes, NativeOverlapped* pOVERLAP) </StackTrace> <ExceptionString> System.ServiceModel.ProtocolException: There is a problem with the XML that was received from the network. See inner exception for more details. ---&amp;gt; System.Xml.XmlException: The body of the message cannot be read because it is empty. --- End of inner exception stack trace --- </ExceptionString> <InnerException> <ExceptionType>System.Xml.XmlException, System.Xml, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089</ExceptionType> <Message>The body of the message cannot be read because it is empty.</Message> <StackTrace> at System.ServiceModel.Channels.HttpRequestContext.CreateMessage() at System.ServiceModel.Channels.HttpChannelListener.HttpContextReceived(HttpRequestContext context, Action callback) at System.ServiceModel.Activation.HostedHttpTransportManager.HttpContextReceived(HostedHttpRequestAsyncResult result) at System.ServiceModel.Activation.HostedHttpRequestAsyncResult.HandleRequest() at System.ServiceModel.Activation.HostedHttpRequestAsyncResult.BeginRequest() at System.ServiceModel.Activation.HostedHttpRequestAsyncResult.OnBeginRequest(Object state) at System.Runtime.IOThreadScheduler.ScheduledOverlapped.IOCallback(UInt32 errorCode, UInt32 numBytes, NativeOverlapped* nativeOverlapped) at System.Runtime.Fx.IOCompletionThunk.UnhandledExceptionFrame(UInt32 error, UInt32 bytesRead, NativeOverlapped* nativeOverlapped) at System.Threading._IOCompletionCallback.PerformIOCompletionCallback(UInt32 errorCode, UInt32 numBytes, NativeOverlapped* pOVERLAP) </StackTrace> <ExceptionString>System.Xml.XmlException: The body of the message cannot be read because it is empty.</ExceptionString> </InnerException> </Exception> </TraceRecord> </DataItem> </TraceData> So, here is my service interface: [ServiceContract] public interface IRDCService { [OperationContract] Response<Customer> GetCustomer(CustomerRequest request); [OperationContract] Response<Customer> GetSiteCustomers(CustomerRequest request); } And here is my service instance public class RDCService : IRDCService { ICustomerService customerService; public RDCService() { //We have to locate the instance from structuremap manually because web services *REQUIRE* a default constructor customerService = ServiceLocator.Locate<ICustomerService>(); } public Response<Customer> GetCustomer(CustomerRequest request) { return customerService.GetCustomer(request); } public Response<Customer> GetSiteCustomers(CustomerRequest request) { return customerService.GetSiteCustomers(request); } } The configuration for the web service (server side) looks like this: <system.serviceModel> <diagnostics> <messageLogging logMalformedMessages="true" logMessagesAtServiceLevel="true" logMessagesAtTransportLevel="true" /> </diagnostics> <services> <service behaviorConfiguration="MySite.Web.Services.RDCServiceBehavior" name="MySite.Web.Services.RDCService"> <endpoint address="http://localhost:27433" binding="wsHttpBinding" contract="MySite.Common.Services.Web.IRDCService"> <identity> <dns value="localhost:27433" /> </identity> </endpoint> <endpoint address="mex" binding="mexHttpBinding" contract="IMetadataExchange" /> </service> </services> <behaviors> <serviceBehaviors> <behavior name="MySite.Web.Services.RDCServiceBehavior"> <!-- To avoid disclosing metadata information, set the value below to false and remove the metadata endpoint above before deployment --> <serviceMetadata httpGetEnabled="true"/> <!-- To receive exception details in faults for debugging purposes, set the value below to true. Set to false before deployment to avoid disclosing exception information --> <serviceDebug includeExceptionDetailInFaults="true"/> <dataContractSerializer maxItemsInObjectGraph="6553600" /> </behavior> </serviceBehaviors> </behaviors> </system.serviceModel> Here is what my request object looks like [DataContract] public class CustomerRequest : RequestBase { [DataMember] public int Id { get; set; } [DataMember] public int SiteId { get; set; } } And the RequestBase: [DataContract] public abstract class RequestBase : IRequest { #region IRequest Members [DataMember] public int PageSize { get; set; } [DataMember] public int PageIndex { get; set; } #endregion } And my IRequest interface public interface IRequest { int PageSize { get; set; } int PageIndex { get; set; } } And I have a wrapper class around my service calls. Here is the class. public class MyService : IMyService { IRDCService service; public MyService() { //service = new MySite.RDCService.RDCServiceClient(); EndpointAddress address = new EndpointAddress(APISettings.Default.ServiceUrl); BasicHttpBinding binding = new BasicHttpBinding(BasicHttpSecurityMode.None); binding.TransferMode = TransferMode.Streamed; binding.MaxBufferSize = 65536; binding.MaxReceivedMessageSize = 4194304; ChannelFactory<IRDCService> factory = new ChannelFactory<IRDCService>(binding, address); service = factory.CreateChannel(); } public Response<Customer> GetCustomer(CustomerRequest request) { return service.GetCustomer(request); } public Response<Customer> GetSiteCustomers(CustomerRequest request) { return service.GetSiteCustomers(request); } } and finally, the response object. [DataContract] public class Response<T> { [DataMember] public IEnumerable<T> Results { get; set; } [DataMember] public int TotalResults { get; set; } [DataMember] public int PageIndex { get; set; } [DataMember] public int PageSize { get; set; } [DataMember] public RulesException Exception { get; set; } } So, when I build my CustomerRequest object and pass it in, for some reason it's hitting the server as an empty request. Any ideas why? I've tried upping the object graph and the message size. When I debug it stops in the wrapper class with the 400 error. I'm not sure if there is a serialization error, but considering the object contract is 4 integer properties I can't imagine it causing an issue.

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  • Java - Does null variable require space in memory

    - by Yatendra Goel
    class CheckStore { private String displayText; private boolean state; private String meaningfulText; private URL url; public CheckStore(String text, boolean state) { this.displayText = text; this.state = state; } : : } As I am initializing only two variables (displayText and state) in the constructor, Will the rest two variables (meaningfulText and url which will have the value null) will require space in memory to store null value. Q1. I think they will require space. If they will, then how much memory does a null value takes in the memory (like int takes 4 bytes). Q2. How much space a string takes in memory. I guess it will depend on the length of the string. So how much space a string takes of how much length?

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  • What is the Sql Server equivalent for Oracle's DBMS_ASSERT?

    - by dotNetYum
    DBMS_ASSERT is one of the keys to prevent SQL injection attacks in Oracle. I tried a cursory search...is there any SQL Server 2005/2008 equivalent for this functionality? I am looking for a specific implementation that has a counterpart of all the respective Oracle package members of DBMS_ASSERT. NOOP SIMPLE_SQL_NAME QUALIFIED_SQL_NAME SCHEMA_NAME I know the best-practices of preventing injection...bind variables...being one of them. But,in this question I am specifically looking for a good way to sanitize input...in scenarios where bind-variables were not used. Do you have any specific implemetations? Is there a library that actually is a SQL Server Port of the Oracle package?

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  • How to setup Math program

    - by Miles
    I'm needing to write a program (C#) that will allow the user to create generic formulas with variables and numbers. For example: D = A + (A - C / X)(7.8 - 6.6) F = E + (E - C / X)(7.8 - 6.6) FinalResult = (A + D)(0.9) + (E + F)(0.32) + B(0.1) + .023 where all variables would mean for me to go to a database and look something up based on values and return a number in its place. So A would be 2.12 for example (and the same for C and E) Whats the best way to structure this program? How would I make my program read these formulas? I've seen a little bit of the MathML but not sure how to get that started (or an example of it)

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