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  • Java: opening and reading from a file without locking it.

    - by rogue780
    I need to be able to mimic 'tail -f' with Java. I'm trying to read a log file as it's being written by another process, but when I open the file to read it, it locks the file and the other process can't write to it anymore. Any help would be greatly appreciated! Here is the code that I'm using currently: public void read(){ Scanner fp = null; try{ fp = new Scanner(new FileReader(this.filename)); fp.useDelimiter("\n"); }catch(java.io.FileNotFoundException e){ System.out.println("java.io.FileNotFoundException e"); } while(true){ if(fp.hasNext()){ this.parse(fp.next()); } } }

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  • Is it faster to do the pages first and CSS second, or should I do them at the same time?

    - by Fred Haslam
    I have been tasked with building a new web project from scratch, with the exception of reusing CSS files (the look and feel) from an existing project. In the past I have always completed development of the functionality and the web-ui before considering the appearance. This is mostly due to CSS development overlapping with the tail end of the project. I now have the opportunity to integrate a static set of CSS as I build the application. I have no experience with this circumstance. Would it be faster to develop the project and web-pages first, then integrate the CSS; or would it be faster to integrate the CSS as part of page development?

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  • How do I implement a fibonacci sequence in java using try/catch logic?

    - by Lars Flyger
    I know how to do it using simple recursion, but in order to complete this particular assignment I need to be able to accumulate on the stack and throw an exception that holds the answer in it. So far I have: public static int fibo(int index) { int sum = 0; try { fibo_aux(index, 1, 1); } catch (IntegerException me) { sum = me.getIntValue(); } return sum; } fibo_aux is supposed to throw an IntegerException (which holds the value of the answer that is retireved via getIntValue) and accumulates the answer on the stack, but so far I can't figure it out. Can anyone help?

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  • Fibonacci Sequence using loop and recur

    - by AdamJMTech
    I am doing the Project Euler challenge in Clojure and I want to find the sum of all the even numbers in a fibonacci sequence up to a certain number. The code for a function that does this is below. I know there are quicker and easier ways of doing this, I am just experimenting with recursion using loop and recur. However the code doesn't seem to work it never returns an answer. (defn fib-even-sum [upto] (loop [previous 1 nxt 1 sum 0] (if (or (<= upto 1) (>= nxt upto)) sum) (if (= (mod nxt 2) 0) (recur nxt (+ previous nxt) (+ sum nxt)) (recur nxt (+ previous nxt) sum)))) I was not sure if I could do recur twice in the same loop or not. I'm not sure if this is causing the problem?

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  • Disallow using comma operator

    - by RiaD
    I never use the comma operator. But sometimes, when I write some recursions, I make a stupid mistake: I forget the function name. That's why the last operand is returned, not the result of a recursion call. Simplified example: int binpow(int a,int b){ if(!b) return 1; if(b&1) return a*binpow(a,b-1); return (a*a,b/2); // comma operator } Is it possible get a compilation error instead of incorrect, hard to debug code?

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  • Is there a better way to avoid an infinite loop using winforms?

    - by Hamish Grubijan
    I am using .Net 3.5 for now. Right now I am using a using trick to disable and enable events around certain sections of code. The user can change either days, hours, minutes or total minutes, and that should not cause an infinite cascade of events (e.g. minutes changing total, total changing minutes, etc.) While the code does what I want, there might be a better / more straight-forward way. Do you know of any? For brawny points: This control will be used by multiple teams - I do not want to make it embarrassing. I suspect that I do not need to reinvent the wheel when defining hours in a day, days in week, etc. Some other standard .Net library out there must have it. Any other remarks regarding code? This using (EventHacker.DisableEvents(this)) business - that must be a common pattern in .Net ... changing the setting temporarily. What is the name of it? I'd like to be able to refer to it in a comment and also read up more on current implementations. In the general case not only a handle to the thing being changed needs to be remembered, but also the previous state (in this case previous state does not matter - events are turned on and off unconditionally). Then there is also a possibility of multi-threaded hacking. One could also utilize generics to make the code arguably cleaner. Figuring all this out can lead to a multi-page blog post. I'd be happy to hear some of the answers. P.S. Does it seem like I suffer from obsessive compulsive disorder? Some people like to get things finished and move on; I like to keep them open ... there is always a better way. // Corresponding Designer class is omitted. using System; using System.Windows.Forms; namespace XYZ // Real name masked { interface IEventHackable { void EnableEvents(); void DisableEvents(); } public partial class PollingIntervalGroupBox : GroupBox, IEventHackable { private const int DAYS_IN_WEEK = 7; private const int MINUTES_IN_HOUR = 60; private const int HOURS_IN_DAY = 24; private const int MINUTES_IN_DAY = MINUTES_IN_HOUR * HOURS_IN_DAY; private const int MAX_TOTAL_DAYS = 100; private static readonly decimal MIN_TOTAL_NUM_MINUTES = 1; // Anything faster than once per minute can bog down our servers. private static readonly decimal MAX_TOTAL_NUM_MINUTES = (MAX_TOTAL_DAYS * MINUTES_IN_DAY) - 1; // 99 days should be plenty. // The value above was chosen so to not cause an overflow exception. // Watch out for it - numericUpDownControls each have a MaximumValue setting. public PollingIntervalGroupBox() { InitializeComponent(); InitializeComponentCustom(); } private void InitializeComponentCustom() { this.m_upDownDays.Maximum = MAX_TOTAL_DAYS - 1; this.m_upDownHours.Maximum = HOURS_IN_DAY - 1; this.m_upDownMinutes.Maximum = MINUTES_IN_HOUR - 1; this.m_upDownTotalMinutes.Maximum = MAX_TOTAL_NUM_MINUTES; this.m_upDownTotalMinutes.Minimum = MIN_TOTAL_NUM_MINUTES; } private void m_upDownTotalMinutes_ValueChanged(object sender, EventArgs e) { setTotalMinutes(this.m_upDownTotalMinutes.Value); } private void m_upDownDays_ValueChanged(object sender, EventArgs e) { updateTotalMinutes(); } private void m_upDownHours_ValueChanged(object sender, EventArgs e) { updateTotalMinutes(); } private void m_upDownMinutes_ValueChanged(object sender, EventArgs e) { updateTotalMinutes(); } private void updateTotalMinutes() { this.setTotalMinutes( MINUTES_IN_DAY * m_upDownDays.Value + MINUTES_IN_HOUR * m_upDownHours.Value + m_upDownMinutes.Value); } public decimal TotalMinutes { get { return m_upDownTotalMinutes.Value; } set { m_upDownTotalMinutes.Value = value; } } public decimal TotalHours { set { setTotalMinutes(value * MINUTES_IN_HOUR); } } public decimal TotalDays { set { setTotalMinutes(value * MINUTES_IN_DAY); } } public decimal TotalWeeks { set { setTotalMinutes(value * DAYS_IN_WEEK * MINUTES_IN_DAY); } } private void setTotalMinutes(decimal nTotalMinutes) { if (nTotalMinutes < MIN_TOTAL_NUM_MINUTES) { setTotalMinutes(MIN_TOTAL_NUM_MINUTES); return; // Must be carefull with recursion. } if (nTotalMinutes > MAX_TOTAL_NUM_MINUTES) { setTotalMinutes(MAX_TOTAL_NUM_MINUTES); return; // Must be carefull with recursion. } using (EventHacker.DisableEvents(this)) { // First set the total minutes this.m_upDownTotalMinutes.Value = nTotalMinutes; // Then set the rest this.m_upDownDays.Value = (int)(nTotalMinutes / MINUTES_IN_DAY); nTotalMinutes = nTotalMinutes % MINUTES_IN_DAY; // variable reuse. this.m_upDownHours.Value = (int)(nTotalMinutes / MINUTES_IN_HOUR); nTotalMinutes = nTotalMinutes % MINUTES_IN_HOUR; this.m_upDownMinutes.Value = nTotalMinutes; } } // Event magic public void EnableEvents() { this.m_upDownTotalMinutes.ValueChanged += this.m_upDownTotalMinutes_ValueChanged; this.m_upDownDays.ValueChanged += this.m_upDownDays_ValueChanged; this.m_upDownHours.ValueChanged += this.m_upDownHours_ValueChanged; this.m_upDownMinutes.ValueChanged += this.m_upDownMinutes_ValueChanged; } public void DisableEvents() { this.m_upDownTotalMinutes.ValueChanged -= this.m_upDownTotalMinutes_ValueChanged; this.m_upDownDays.ValueChanged -= this.m_upDownDays_ValueChanged; this.m_upDownHours.ValueChanged -= this.m_upDownHours_ValueChanged; this.m_upDownMinutes.ValueChanged -= this.m_upDownMinutes_ValueChanged; } // We give as little info as possible to the 'hacker'. private sealed class EventHacker : IDisposable { IEventHackable _hackableHandle; public static IDisposable DisableEvents(IEventHackable hackableHandle) { return new EventHacker(hackableHandle); } public EventHacker(IEventHackable hackableHandle) { this._hackableHandle = hackableHandle; this._hackableHandle.DisableEvents(); } public void Dispose() { this._hackableHandle.EnableEvents(); } } } }

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  • t-sql recursive query

    - by stackoverflowuser
    Based on an existing table I used CTE recursive query to come up with following data. But failing to apply it a level further. Data is as below id name parentid -------------------------- 1 project 0 2 structure 1 3 path_1 2 4 path_2 2 5 path_3 2 6 path_4 3 7 path_5 4 8 path_6 5 I want to recursively form full paths from the above data. Means the recursion will give the following output. FullPaths ------------- Project Project\Structure Project\Structure\Path_1 Project\Structure\Path_2 Project\Structure\Path_3 Project\Structure\Path_1\path_4 Project\Structure\Path_2\path_5 Project\Structure\Path_3\path_6 Thanks

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  • C# two classes with static members referring to each other

    - by Jerry
    Hi, I wonder why this code doesn't end up in endless recursion. I guess it's connected to the automatic initialization of static members to default values, but can someone tell me "step by step" how does 'a' get the value of 2 and 'b' of 1? public class A { public static int a = B.b + 1; } public class B { public static int b = A.a + 1; } static void Main(string[] args) { Console.WriteLine("A.a={0}, B.b={1}", A.a, B.b); //A.a=2, B.b=1 Console.Read(); }

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  • Fatal error with php code

    - by basma
    hello i have a problem in my php code that use recursion: <?php solveTowers(5, "A", "B", "C"); function solveTowers($count, $src, $dest, $spare) { if (count == 1) { echo "Move a disk from ".$src." to ".$dest ; } else { solveTowers($count - 1, $src, $spare, $dest); solveTowers(1, $src, $dest, $spare); solveTowers($count - 1, $spare, $dest, $src); } } ?> but it doesnt run !! this error accures : Fatal error: Allowed memory size of 134217728 bytes exhausted (tried to allocate 261904 bytes) in C:\xampp\htdocs\cap492\towers.php on line 13 line 13 is the first call to the function in the else statment can you please help me with that ?!

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  • Building 'flat' rather than 'tree' LINQ expressions

    - by Ian Gregory
    I'm using some code (available here on MSDN) to dynamically build LINQ expressions containing multiple OR 'clauses'. The relevant code is var equals = values.Select(value => (Expression)Expression.Equal(valueSelector.Body, Expression.Constant(value, typeof(TValue)))); var body = equals.Aggregate<Expression>((accumulate, equal) => Expression.Or(accumulate, equal)); This generates a LINQ expression that looks something like this: (((((ID = 5) OR (ID = 4)) OR (ID = 3)) OR (ID = 2)) OR (ID = 1)) I'm hitting the recursion limit (100) when using this expression, so I'd like to generate an expression that looks like this: (ID = 5) OR (ID = 4) OR (ID = 3) OR (ID = 2) OR (ID = 1) How would I modify the expression building code to do this?

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  • car and cdr in scheme is driving me crazy ...

    - by kristian Roger
    Hi Im facing a probem with the car and cdr functions for example: first I defined a list caled it x (define x (a (bc) d ( (ef) g ) )) so x now is equal to (a (bc) d ( (ef) g ) now for example I need to get the g from this list using only car and cdr (!! noshortcuts as caddr cddr !!) the correct answer is: (car(cdr(car(cdr(cdr(cdr x)))))) BUT how ? :-( I work according to the rule (the car gives the head of list and cdr gives the tail) and instead of getting the answer above I keep reaching wronge answers can any one help me in understanding this ... give me step or a way to solve it step by step thanx in advance Im really sick of scheme language.

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  • MS SQL replace sequence of same characters inside Text Field (TSQL only)

    - by zmische
    I have a text column varchar(4000) with text: 'aaabbaaacbaaaccc' and I need to remove all duplicated chars - so only one from sequence left: 'abacbac' It should not be a function, Procedure or CLR - Regex solution. Only true SQL select. Currently I think about using recursive WITH clause with replace 'aa'-'a', 'bb'-'b', 'cc'-'c'. So recursion should cycle until all duplicated sequences of that chars would be replaced. DO you have another solution, perhaps more Permormant one? PS: I searched through this site about different replace examples - they didnt suit to this case.

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  • How do you solve this Haskell problem using a fold map and take?

    - by Linda Cohen
    Define a function replicate which given a list of numbers returns a list with each number duplicated its value. Use a fold, map, and take .. replicate [5,1,3,2,8,1,2] output: [5,5,5,5,5,1,3,3,3,2,2,8,8,8,8,8,8,8,8,1,2,2] I've figure this out using List comprehension and recursion: replicate2 [] = [] replicate2 (n:nn) = take n(repeat n) ++ replicate2 nn but how would you use fold and map to do this? so far I have: replicate n = map (foldl1 (take n(repeat n)) n) n which is obviously wrong, but I think I am close.. so any help would be nice, THANKS!

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  • Where to find Android Development Homework Problems

    - by antonlavey
    Ok so I am starting off with android development and I have found a bunch of useful tutorials so I am set there. What I am looking for is a resource that provides homework style problems to do and has the answers downloadable so I can check my solution against the "official" solution. So for example instead of the notepad tutorial it would be: "Build an application that you can create, edit, delete notes, ...etc.". Ideally the "official" solution would have some explanation as to why they built it the way they did. (so a tutorial at the tail end) Anyone know of any resources that provide their tutorials in this format? Thanks.

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  • Calling same function until it connect to server

    - by user171523
    I am in the process of designing a system where i need to keep on trying to connect to MQ server unitl i get a connection. By default if the MQ is not availlble it will thorugh exception. How can call the same method again and again until i get the connection. I know i can use recursion, is there any better way to do it . Becuase i would like to avoid infinite loops. I also want to wait the the furthere processing until i get connection. I am using .net 2.0 with C#. It is window Service application.

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  • What is the most efficient way to store a mapping "key -> event stream"?

    - by jkff
    Suppose there are ~10,000's of keys, where each key corresponds to a stream of events. I'd like to support the following operations: push(key, timestamp, event) - pushes event to the event queue for key, marked with the given timestamp. It is guaranteed that event timestamps for a particular key are pushed in sorted or almost sorted order. tail(key, timestamp) - get all events for key since the given timestamp. Usually the timestamp requests for a given key are almost monotonically increasing, almost synchronously with pushes for the same key. This stuff has to be persistent (although it is not absolutely necessary to persist pushes immediately and to keep tails with pushes strictly in sync), so I'm going to use some kind of database. What is the optimal kind of database structure for this task? Would it be better to use a relational database, a key-value storage, or something else?

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  • car and cdr in Scheme are driving me crazy ...

    - by kristian Roger
    Hi Im facing a problem with the car and cdr functions for example: first I defined a list called it x (define x (a (bc) d ( (ef) g ) )) so x now is equal to (a (bc) d ( (ef) g ) ) now for example I need to get the g from this list using only car and cdr (!! noshortcuts as caddr cddr !!) the correct answer is: (car(cdr(car(cdr(cdr(cdr x)))))) BUT how ? :-( I work according to the rules (the car gives the head of list and cdr gives the tail) and instead of getting the answer above I keep reaching wrong answers. Can any one help me in understanding this ... give me step or a way to solve it step by step Thanks in advance. I'm really sick of Scheme.

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  • How does functional programming work?

    - by Headcrab
    I'm used to imperative/OO programming (know C, C++, Python, PHP, etc.). I wanted to get into functional programming but there are some things unclear to me. Take for example the languages F# and Haskell: How do you implement loops? By recursion? Eew. What about conditions? How can you get by without variables? I mean.. What do we have RAM for.. storing variables, right?

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  • A Simulator for a non-deterministic Push-Down Automaton

    - by shake
    Well, i need to make simulator for non-deterministic Push-Down Automaton. Everything is okey, i know i need to do recursion or something similar. But i do not know how to make that function which would simulate automaton. I got everything else under control, automaton generator, stack ... I am doing it in java, so this is maybe only issue that man can bump on, and i did it. So if anyone have done something similar, i could use advices. This is my current organisation of code: C lasses: class transit: list -contains non deterministic transitions state input sign stack sign class generator it generate automaton from file clas NPA public boolean start() - this function i am having trouble with Of course problem of separate stacks, and input for every branch. I tried to solve it with collection of objects NPA and try to start every object, but it doesn work :((..

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  • Stopping httpd causes a process started from perl CGI script to receive SIGTERM

    - by Pranav Pal
    I am running a shell script from a perl CGI script: #!/usr/bin/perl my $command = "./script.sh &"; my $pid = fork(); if (defined($pid) && $pid==0) { # background process system( $command ); } The shell script looks like this: #!/bin/sh trap 'echo trapped' 15 tail -f test.log When I run the CGI script from browser, and then stop httpd using /etc/init.d/httpd stop, the script receives a SIGTERM signal. I was expecting the script to run as a separate process and not be tied in anyway to httpd. Though I can trap the SIGTERM, I would like to understand why the script is receiving SIGTERM at all. What wrong am I doing here? I am running RHEL 5.8 and Apache HTTP server 2.4. Thanks, Pranav

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  • Is ReaderWriterLockSlim.EnterUpgradeableReadLock() essentially the same as Monitor.Enter()?

    - by Neil Barnwell
    So I have a situation where I may have many, many reads and only the occasional write to a resource shared between multiple threads. A long time ago I read about ReaderWriterLock, and have read about ReaderWriterGate which attempts to mitigate the issue where many writes coming in trump reads and hurt performance. However, now I've become aware of ReaderWriterLockSlim... From the docs, I believe that there can only be one thread in "upgradeable mode" at any one time. In a situation where the only access I'm using is EnterUpgradeableReadLock() (which is appropriate for my scenario) then is there much difference to just sticking with lock(){}? Here's the excerpt: A thread that tries to enter upgradeable mode blocks if there is already a thread in upgradeable mode, if there are threads waiting to enter write mode, or if there is a single thread in write mode. Or, does the recursion policy make any difference to this?

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  • top-k selection/merge

    - by tcurdt
    I have n sorted lists. These lists are quite long (300000+ tuples). Selecting the top 10 of the individual lists is of course trivial - they are right at the head of the lists. Where it gets more interesting is when I want the top 10 of all the sorted lists. The question is whether there is an algorithm to calculate the combined top 10 having the correct order while cutting off the long tail of the lists. The goal is to reduce the required space. And if there is: How does one find the limit where is is safe to cut? Note: The actual counts are not important. Only the order is.

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  • Why do SQL connection leave parameters in?

    - by acidzombie24
    While coding with sqlite everytime i always had the exact number of parameters and when i executed the query i always had 0 parameters after it. I kept using the cmd object and it worked fine. Now while porting to use sql server (2008) my SqlConnection has parameters left over from a successful command. Why? I seem to be able to create tables without the problem (then again i may have use a clone of an empty cmd since i use recursion). Does SqlCommand always leave the parameters in after a query? This always breaks the following query unless i do parameter.clear(). Should i create a new SqlCommand object? or use parameter.clear() each time? I'm somewhat confused.

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  • Bind can only work for the DNS server inside zone

    - by Bob
    I got a big problem when I added a new zone to my current Bind configuration. ===============/etc/named.conf=============== include "/etc/rndc.key"; controls { inet 127.0.0.1 port 953 allow { 127.0.0.1; } keys { "rndckey"; }; }; acl "trusted" { 127.0.0.1; 208.43.81.157; 69.4.236.88; }; options { directory "/var/named"; allow-query { any; }; recursion yes; allow-recursion { trusted; }; }; zone "." { type hint; file "root.hints"; }; zone "2comu.com" { type master; file "2comu.com.db"; allow-update { none; }; }; zone "usa-diamond.com" { type master; file "usa-diamond.com.db"; allow-update { none; }; }; ===============/var/named/2comu.com.db=============== $TTL 86400 @ IN SOA ns1.2comu.com. root.2comu.com. ( 2011011101 3600 300 3600000 3600 ) IN NS ns1.2comu.com. IN NS ns2.2comu.com. IN MX 10 email.2comu.com. ns1.2comu.com. IN A 208.43.81.157 ns2.2comu.com. IN A 69.4.236.88 www.2comu.com. IN A 208.43.81.157 ftp.2comu.com. IN A 208.43.81.157 email.2comu.com. IN A 208.43.81.157 ===============/var/named/usa-diamond.com=============== $TTL 86400 @ IN SOA ns1.2comu.com. root.usa-diamond.com. ( 2011011115 3600 300 3600000 3600 ) IN NS ns1.2comu.com. IN NS ns2.2comu.com. www.usa-diamond.com. IN A 208.43.81.157 ================================================================ All of the configurations inside domain 2comu.com work well. But when www.usa-diamond.com doesn't work at all. When I tried "dig +trace www.usa-diamond.com", I got the following message ================================================================ ; <<>> DiG 9.3.6-P1-RedHat-9.3.6-4.P1.el5_4.2 <<>> +trace usa-diamond.com ;; global options: printcmd . 517603 IN NS c.root-servers.net. . 517603 IN NS d.root-servers.net. . 517603 IN NS e.root-servers.net. . 517603 IN NS f.root-servers.net. . 517603 IN NS g.root-servers.net. . 517603 IN NS h.root-servers.net. . 517603 IN NS i.root-servers.net. . 517603 IN NS j.root-servers.net. . 517603 IN NS k.root-servers.net. . 517603 IN NS l.root-servers.net. . 517603 IN NS m.root-servers.net. . 517603 IN NS a.root-servers.net. . 517603 IN NS b.root-servers.net. ;; Received 500 bytes from 208.43.81.157#53(208.43.81.157) in 0 ms com. 172800 IN NS j.gtld-servers.net. com. 172800 IN NS d.gtld-servers.net. com. 172800 IN NS e.gtld-servers.net. com. 172800 IN NS i.gtld-servers.net. com. 172800 IN NS f.gtld-servers.net. com. 172800 IN NS m.gtld-servers.net. com. 172800 IN NS b.gtld-servers.net. com. 172800 IN NS k.gtld-servers.net. com. 172800 IN NS l.gtld-servers.net. com. 172800 IN NS c.gtld-servers.net. com. 172800 IN NS h.gtld-servers.net. com. 172800 IN NS a.gtld-servers.net. com. 172800 IN NS g.gtld-servers.net. ;; Received 505 bytes from 192.33.4.12#53(c.root-servers.net) in 3 ms usa-diamond.com. 172800 IN NS ns1.2comu.com. usa-diamond.com. 172800 IN NS ns2.2comu.com. ;; Received 107 bytes from 192.48.79.30#53(j.gtld-servers.net) in 177 ms ;; Received 33 bytes from 208.43.81.157#53(ns1.2comu.com) in 0 ms ========================================================================= It seems I can't get any answer from ns1.2comu.com. Can anyone give some suggestions? Thanks a lot. Bob

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  • Forbid GridView to load all views at once

    - by efpies
    I have about 700 items to display in the grid view. On a Samsung Galaxy Tab 10.1 this is not a problem: it has enough memory. On a HTC Explorer the heap is overflown. So I want to load data dynamically regarding current scroll position (N rows for screen + 5 rows as a tail). And I want to show a scrollbar which represents the position in total rows. But I don't want to draw items that I don't see. In other words, I want to create something similar to UITableView in iOS. How can I do this?

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