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• Suggestions for connecting .NET WPF GUI with Java SE Server

  - by Sam Goldberg

  BACKGROUND We are building a Java (SE) trading application which will be monitoring market data and sending trade messages based on the market data, and also on user defined configuration parameters. We are planning to provide the user with a thin client, built in .NET (WPF) for managing the parameters, controlling the server behavior, and viewing the current state of the trading. The client doesn't need real-time updates; it will instead update the view once every few seconds (or whatever interval is configured by the user). The client has about 6 different operations it needs to perform with the server, for example: CRUD with configuration parameters query subset of the data receive updates of current positions from server It is possible that most of the different operations (except for receiving data) are just different flavors of managing the configuration parameters, but it's too early in our analysis for us to be sure. To connect the client with the server, we have been considering using: SOAP Web Service RESTful service building a custom TCP/IP based API (text or xml) (least preferred - but we use this approach with other applications we have) As best as I understand, pros and cons of the different web service flavors are: SOAP pro: totally automated in .NET (and Java), modifying server side interface require no code changes in communication layer, just running refresh on Web Service reference to regenerate the classes. con: more overhead in the communication layer sending more text, etc. We're not using J2EE container so maybe doesn't work so well with J2SE REST pro: lighter weight, less data. Has good .NET and Java support. (I don't have any real experience with this, so don't know what other benefits it has.) con: client will not be automatically aware if there are any new operations or properties added (?), so communication layer needs to be updated by developer if server interface changes. con: (both approaches) Server cannot really push updates to the client at regular intervals (?) (However, we won't mind if client polls the server to get updates.) QUESTION What are your opinions on the above options or suggestions for other ways to connect the 2 parts? (Ideally, we don't want to put much work into the communication layer, because it's not the significant part of the application so the more off-the-shelf and automated the better.)

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• Is SHA-1 secure for password storage?

  - by Tgr

  Some people throw around remarks like "SHA-1 is broken" a lot, so I'm trying to understand what exactly that means. Let's assume I have a database of SHA-1 password hashes, and an attacker whith a state of the art SHA-1 breaking algorithm and a botnet with 100,000 machines gets access to it. (Having control over 100k home computers would mean they can do about 10^15 operations per second.) How much time would they need to find out the password of any one user? find out the password of a given user? find out the password of all users? find a way to log in as one of the users? find a way to log in as a specific user? How does that change if the passwords are salted? Does the method of salting (prefix, postfix, both, or something more complicated like xor-ing) matter? Here is my current understanding, after some googling. Please correct in the answers if I misunderstood something. If there is no salt, a rainbow attack will immediately find all passwords (except extremely long ones). If there is a sufficiently long random salt, the most effective way to find out the passwords is a brute force or dictionary attack. Neither collision nor preimage attacks are any help in finding out the actual password, so cryptographic attacks against SHA-1 are no help here. It doesn't even matter much what algorithm is used - one could even use MD5 or MD4 and the passwords would be just as safe (there is a slight difference because computing a SHA-1 hash is slower). To evaluate how safe "just as safe" is, let's assume that a single sha1 run takes 1000 operations and passwords contain uppercase, lowercase and digits (that is, 60 characters). That means the attacker can test 1015*60*60*24 / 1000 ~= 1017 potential password a day. For a brute force attack, that would mean testing all passwords up to 9 characters in 3 hours, up to 10 characters in a week, up to 11 characters in a year. (It takes 60 times as much for every additional character.) A dictionary attack is much, much faster (even an attacker with a single computer could pull it off in hours), but only finds weak passwords. To log in as a user, the attacker does not need to find out the exact password; it is enough to find a string that results in the same hash. This is called a first preimage attack. As far as I could find, there are no preimage attacks against SHA-1. (A bruteforce attack would take 2160 operations, which means our theoretical attacker would need 1030 years to pull it off. Limits of theoretical possibility are around 260 operations, at which the attack would take a few years.) There are preimage attacks against reduced versions of SHA-1 with negligible effect (for the reduced SHA-1 which uses 44 steps instead of 80, attack time is down from 2160 operations to 2157). There are collision attacks against SHA-1 which are well within theoretical possibility (the best I found brings the time down from 280 to 252), but those are useless against password hashes, even without salting. In short, storing passwords with SHA-1 seems perfectly safe. Did I miss something?

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• WebCenter Customer Spotlight: Ferrous Resources do Brasil S.A.

  - by me

  Author: Peter Reiser - Social Business Evangelist, Oracle WebCenter  Solution SummaryFerrous Resources do Brasil S.A. (Ferrous) is a startup company whose core business is the exploration, prospection, exploitation, and commercialization of iron ore. They wanted to create an effective, secure and scalable document management system to support the company’s new iron ore exploration operations in Brazil. Ferrous worked with the Oracle Partner 2D Tecnologia to implement a centralized document management system using  Oracle WebCenter Content. The single repository hold almost 220,000 files with an expected to growth to 8 million files in the next two years.  The solution has reduced  financial audit reporting from two weeks to only four days. Company OverviewFounded in 2007, Ferrous Resources do Brasil S.A. (Ferrous) is a startup company whose core business is the exploration, prospection, exploitation, and commercialization of iron ore. Ferrous intends to become one of the five largest iron ore mining companies in the world within the next few years.  Business ChallengesFerrous wanted to create an effective, secure and scalable document management system to support the company’s new iron ore exploration operations in Brazil. Solution DeployedFerrous worked with the Oracle Partner 2D Tecnologia to implement a centralized document management system using  Oracle WebCenter Content. They consolidated all company documents into a single repository to hold almost 220,000 files, including iron-ore project layout and pictures for a repository that is expected to grow to 8 million files in the next two years. Business Results Gained access to reports on individual files of pictures, project layouts, text files, spreadsheets, and slides–enabling the company to find out who opened and altered each  file and when, as well as to access previous versions Enabled investors and board of directors abroad to access all company documents via a Web portal, something that was previously achieved only through e-mails or CD file transfers Enabled the company to consolidate all files, which were mostly disseminated in pen drives and desktops, so that they are now available to more than 500 system users, including investors, lawyers, partners, and 320 in-company users Reduced time to search specific documents, saving several days in financial audit reporting, an activity that previously took two weeks and now requires only four days  “With Oracle WebCenter Content, we managed to organize, control, and protect the company’s files since the beginning of operations and, as a consequence, can offer rapid and transparent access to all company documents.” Frederico Samartini, Business Performance Manager, Ferrous Resources do Brasil S.A. Additional Information Ferrous Customer Snapshot Oracle WebCenter Content

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• Design pattern for isomorphic trees

  - by Peregring-lk

  I want to create a data structure to work with isomorphic tree. I don't search for a "algorithms" or methods to check if two or more trees are isomorphic each other. Just to create various trees with the same structure. Example: 2 - - - - - - - 'a' - - - - - - - 3.5 / \ / \ / \ 3 3 'f' 'y' 1.0 3.1 / \ / \ / \ 4 7 'e' 'f' 2.3 7.7 The first "layer" or tree is the "natural tree" (a tree with natural numbers), the second layer is the "character tree" and the third one is the "float tree". The data structure has a method or iterator to traverse the tree and to make diferent operations with its values. These operations could change the value of nodes, but never its structure (first I create the structure and then I configure the tree with its diferent layers). In case of that I add a new node, this would be applied to each layer. Which known design pattern fits with this description or is related with it?

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• Remote synchronization

  - by Tomas Mysik

  Hi all, today we would like to show you another improvement we have prepared for NetBeans 7.2. Today, let's talk a little bit about remote synchronization. If you already use our simple (S)FTP client, this enhancement could be useful for you. Simply right click on Source Files and select Synchronize. Please notice that the remote synchronization works better only on the whole project (it means that the Source Files must be selected). The Synchronize action is also available on individual files (more files can be selected at once) but the suggested operation (download, upload etc.) does not work so precisely. Also please notice that the suggested operations are not 100% reliable since the timestamps provided by FTP servers are not exact. Once the remote files (their names and paths only, of course) are fetched, the main dialog appears: As you can see, NetBeans tries to suggest you operations (upload, download etc.) which should be done for each individual file of your project. If you are interested only in some particular changes, you can simply filter the list: Since we have a file conflict, we need to resolve it first. Fortunately this is very easy because we just select the desired file and click the Diff button . The remote version of our file is downloaded and compared with the local version. The resut is displayed in the dialog where you can easily apply and/or refuse the remote changes or even simply type manually to the local version of the selected file: Once we are done with our changes, the operation for the selected file changes to Upload and the file is marked with * (since we made some changes). Please notice that if you now click the Cancel button, in fact no changes are done in our local file. As you can see, if we have one or more files selected, we can change their operation to: no operation (file won't be synchronized) download upload delete (both local and remote file) reset (the operation is resetted to the original one suggested by NetBeans and also all changes done via Diff action are discarded) Now we are ready to synchronize our project. NetBeans will show us the synchronization summary (this dialog can be omitted, see the Show Summary checkbox on the previous image). The synchronization itself starts and we can see its progress and of course its result. As always, all the operations can be reviewed in the Output window. That's all for today, as always, please test it and report all the issues or enhancements you find in NetBeans BugZilla (component php, subcomponent FTP support).

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• MySQL Enterprise Backup 3.8.2 - Overview

  - by Priya Jayakumar

    MySQL Enterprise Backup (MEB) is the ideal solution for backing up MySQL databases. MEB 3.8.2 is released in June 2013. MySQL Enterprise Backup 3.8.2 release’s main goal is to improve usability. With this release, users can know the progress of backup completed both in terms of size and as a percentage of the total. This release also offers options to be able to manage the behavior of MEB in case the space on the secondary storage is completely exhausted during backup. The progress indicator is a (short) string that indicates how far the execution of a time-consuming MEB command has progressed. It consists of one or more "meters" that measures the progress of the command. There are two options introduced to control the progress reporting function of mysqlbackup command (1) –show-progress (2) –progress-interval. The user can control the progress indicator by using “--show-progress” option in any of the MEB operations. This option instructs MEB to output periodically short reports on the progress of time-consuming commands. The argument of this option instructs where the output could be sent. For example it could be stderr, stdout, file, fifo and table. With the “--show-progress” option both the total size of the backup to be copied and the size that’s already copied will be shown. Along with this, the state of the operation for example data or meta-data being copied or tables being locked and other such operations will also be reported. This gives more clear information to the DBA on the progress of the backup that’s happening. Interval between progress report in seconds is controlled by “--progress-interval” option. For more information on this please refer progress-report-options. MEB can also be accessed through GUI from MySQL WorkBench’s next version. This can be used as the front end interface for MEB users to perform backup operations at the click of a button. This feature was highly requested by DBAs and will be very useful. Refer http://insidemysql.com/mysql-workbench-6-0-a-sneak-preview/ for WorkBench upcoming release info. Along with the progress report feature some of the important issues like below are also addressed in MEB 3.8.2. In MEB 3.8.2 a new command line option “--on-disk-full” is introduced to abort or warn the user when a backup process encounters a full disk condition. When no option is given, by default it would abort. A few issues related to “incremental-backup” are also addressed in this release. Please refer 3.8.2 documentation for more details. It would be good for MEB users to move to 3.8.2 to take incremental backups. Overall the added usability and the important defects fixed in this release makes MySQL Enterprise Backup 3.8.2 a promising release.  

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• Abstract Data Type and Data Structure

  - by mark075

  It's quite difficult for me to understand these terms. I searched on google and read a little on Wikipedia but I'm still not sure. I've determined so far that: Abstract Data Type is a definition of new type, describes its properties and operations. Data Structure is an implementation of ADT. Many ADT can be implemented as the same Data Structure. If I think right, array as ADT means a collection of elements and as Data Structure, how it's stored in a memory. Stack is ADT with push, pop operations, but can we say about stack data structure if I mean I used stack implemented as an array in my algorithm? And why heap isn't ADT? It can be implemented as tree or an array.

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• Java Synchronized List Deadlock

  - by portoalet

  From Effective Java 2nd edition item 67 page 266-268: The background thread calls s.removeObserver, which attempts to lock observers, but it can’t acquire the lock, because the main thread already has the lock. All the while, the main thread is waiting for the background thread to finish removing the observer, which explains the deadlock. I am trying to find out which threads deadlock in the main method by using ThreadMXBean (http://stackoverflow.com/questions/1102359/programmatic-deadlock-detection-in-java) , but why does it not return the deadlocked threads? I used a new Thread to run the ThreadMXBean detection. public class ObservableSet<E> extends ForwardingSet<E> { public ObservableSet(Set<E> set) { super(set); } private final List<SetObserver<E>> observers = new ArrayList<SetObserver<E>>(); public void addObserver(SetObserver<E> observer) { synchronized(observers) { observers.add(observer); } } public boolean removeObserver(SetObserver<E> observer) { synchronized(observers) { return observers.remove(observer); } } private void notifyElementAdded(E element) { synchronized(observers) { for (SetObserver<E> observer : observers) observer.added(this, element); } } @Override public boolean add(E element) { boolean added = super.add(element); if (added) notifyElementAdded(element); return added; } @Override public boolean addAll(Collection<? extends E> c) { boolean result = false; for (E element : c) result|=add(element); //callsnotifyElementAdded return result; } public static void main(String[] args) { ObservableSet<Integer> set = new ObservableSet<Integer>(new HashSet<Integer>()); final ThreadMXBean threadMxBean = ManagementFactory.getThreadMXBean(); Thread t = new Thread(new Runnable() { @Override public void run() { while( true ) { long [] threadIds = threadMxBean.findDeadlockedThreads(); if( threadIds != null) { ThreadInfo[] infos = threadMxBean.getThreadInfo(threadIds); for( ThreadInfo threadInfo : infos) { StackTraceElement[] stacks = threadInfo.getStackTrace(); for( StackTraceElement stack : stacks ) { System.out.println(stack.toString()); } } } try { System.out.println("Sleeping.."); TimeUnit.MILLISECONDS.sleep(1000); } catch (InterruptedException e) { // TODO Auto-generated catch block e.printStackTrace(); } } } }); t.start(); set.addObserver(new SetObserver<Integer>() { public void added(ObservableSet<Integer> s, Integer e) { ExecutorService executor = Executors.newSingleThreadExecutor(); final SetObserver<Integer> observer = this; try { executor.submit(new Runnable() { public void run() { s.removeObserver(observer); } }).get(); } catch (ExecutionException ex) { throw new AssertionError(ex.getCause()); } catch (InterruptedException ex) { throw new AssertionError(ex.getCause()); } finally { executor.shutdown(); } } }); for (int i = 0; i < 100; i++) set.add(i); } } public interface SetObserver<E> { // Invoked when an element is added to the observable set void added(ObservableSet<E> set, E element); } // ForwardingSet<E> simply wraps another Set and forwards all operations to it.

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• A Quantity class with units

  - by Ryan Ohs

  Goals Create a class that associates a numeric quantity with a unit of measurement. Provide support for simple arithmetic and comparison operations. Implementation An immutable class (Could have been struct but I may try inheritance later) Unit is stored in an enumeration Supported operations: Addition w/ like units Subtraction w/ like units Multiplication by scalar Division by scalar Modulus by scalar Equals() >, >=, <, <=, == IComparable ToString() Implicit cast to Decimal The Source The souce can be downloaded from Github. Notes This class does not support any arithmetic that would modify the unit. This class is not suitable for manipulating currencies. Future Ideas Have a CompositeQuantity class that would allow quantities with unlike units to be combined. Similar currency class with support for allocations/distributions. Provide conversion between units. (Actually I think this would be best placed in an external service. Many situations I deal with require some sort of dynamic conversion ratio.)

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• Difference between EJB Persist & Merge operation

  - by shantala.sankeshwar

  This article gives the difference between EJB Persist & Merge operations with scenarios.Use Case Description Users working on EJB persist & merge operations often have this question in mind " When merge can create new entity as well as modify existing entity,then why do we have 2 separate operations - persist & merge?" The reason is very simple.If we use merge operation to create new entity & if the entity exists then it does not throw any exception,but persist throws exception if the entity already exists.Merge should be used to modify the existing entity.The sql statement that gets executed on persist operation is insert statement.But in case of merge first select statement gets executed & then update sql statement gets executed.Scenario 1: Persist operation to create new Emp recordLet us suppose that we have a Java EE Web Application created with Entities from Emp table & have created session bean with data control. Drop Emp Object(Expand SessionEJBLocal->Constructors under Data Controls) as ADF Parameter form in jspx pageDrop persistEmp(Emp) as ADF CommandButton & provide #{bindings.EmpIterator.currentRow.dataProvider} as the value for emp parameter.Then run this page & provide values for Emp,click on 'persistEmp' button.New Emp record gets created.So when we execute persist operation only insert sql statement gets executed :INSERT INTO EMP (EMPNO, COMM, HIREDATE, ENAME, JOB, DEPTNO, SAL, MGR) VALUES (?, ?, ?, ?, ?, ?, ?, ?)    bind => [2, null, null, e2, null, 10, null, null]Scenario 2: Merge operation to modify existing Emp recordLet us suppose that we have a Java EE Web Application created with Entities from Emp table & have created session bean with data control.Drop empFindAll() Object as ADF form on jspx page.Drop mergeEmp(Emp) operation as commandButton & provide #{bindings.EmpIterator.currentRow.dataProvider} as the value for emp parameter.Then run this page & modify values for Emp record,click on 'mergeEmp' button.The respective Emp record gets modified.So when we execute merge operation select & update sql statements gets executed :SELECT EMPNO, COMM, HIREDATE, ENAME, JOB, DEPTNO, SAL, MGR FROM EMP WHERE (EMPNO = ?) bind => [7566]UPDATE EMP SET ENAME = ? WHERE (EMPNO = ?) bind => [KINGS, 7839]

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• What is the correct way to handle debug output in Java?

  - by Federico Zancan

  As my current Java projects grow bigger and bigger, I feel a likewise growing need to insert debug output in several points of my code. To enable or disable this feature appropriately, depending on the opening or closure of the test sessions, I usually put a private static final boolean DEBUG = false at the beginning of the classes my tests are inspecting, and trivially use it this way (for example): public MyClass { private static final boolean DEBUG = false; ... some code ... public void myMethod(String s) { if (DEBUG) { System.out.println(s); } } } and the like. But that doesn't bliss me out, because of course it works but there could be too many classes in which to set DEBUG to true, if you are not staring at just a couple of them. Conversely, I (like - I think - many others) wouldn't love to put the whole application in debug mode, as the amount of text being output could be overwhelming. So, is there a correct way to architecturally handle such situation or the most correct way is to use the DEBUG class member?

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• Can a recursive function have iterations/loops?

  - by Omega

  I've been studying about recursive functions, and apparently, they're functions that call themselves, and don't use iterations/loops (otherwise it wouldn't be a recursive function). However, while surfing the web for examples (the 8-queens-recursive problem), I found this function: private boolean placeQueen(int rows, int queens, int n) { boolean result = false; if (row < n) { while ((queens[row] < n - 1) && !result) { queens[row]++; if (verify(row,queens,n)) { ok = placeQueen(row + 1,queens,n); } } if (!result) { queens[row] = -1; } }else{ result = true; } return result; } There is a while loop involved. ... so I'm a bit lost now. Can I use loops or not?

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• Unit testing time-bound code

  - by maasg

  I'm currently working on an application that does a lot of time-bound operations. That is, based on long now = System.currentTimeMillis();, and combined with an scheduler, it will calculate periods of time that parametrize the execution of some operations. e.g.: public void execute(...) { // executed by an scheduler each x minutes final int now = (int) TimeUnit.MILLISECONDS.toSeconds(System.currentTimeMillis()); final int alignedTime = now - now % getFrequency() ; final int startTime = alignedTime - 2 * getFrequency(); final int endTimeSecs = alignedTime - getFrequency(); uploadData(target, startTime, endTimeSecs); } Most parts of the application are unit-tested independently of time (in this case, uploadData has a natural unit test), but I was wondering about best practices for testing time-bound parts that rely on System.currentTimeMillis() ?

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• Google App Engine JDO how to define class fields ?

  - by Frank

  I have a class like this : import java.io.*; import java.util.*; public class Contact_Info_Entry implements Serializable { public static final long serialVersionUID=26362862L; String Contact_Id,First_Name="",Last_Name="",Company_Name="",Branch_Name="",Address_1="",Address_2="",City="",State="",Zip="",Country="",E_Mail="",Phone; int I_1,I_2; float F_1,F_2; boolean B_1,B_2; GregorianCalendar Date_1, Date_2; Vector<String> A_Vector=new Vector<String>(); public Contact_Info_Entry() { } ...... } If I want to translate it to a class for JDO, do I need to define each field by it self or can I do a group at a time ? For instance do I have to make it like this : @PersistenceCapable(identityType=IdentityType.APPLICATION) public class Contact_Info_Entry implements Serializable { @PrimaryKey @Persistent(valueStrategy=IdGeneratorStrategy.IDENTITY) private Long id; @Persistent public static final long serialVersionUID=26362862L; @Persistent String Contact_Id; @Persistent String First_Name; @Persistent String Last_Name; ...... @Persistent int I_1; @Persistent int I_2; ... @Persistent float F_1; ... @Persistent boolean B_1; @Persistent boolean B_2; @Persistent GregorianCalendar Date_1; ... @Persistent Vector<String> A_Vector=new Vector<String>(); public Contact_Info_Entry() { } ...... } Or can I do a group at a time like this : @PersistenceCapable(identityType=IdentityType.APPLICATION) public class Contact_Info_Entry implements Serializable { @PrimaryKey @Persistent(valueStrategy=IdGeneratorStrategy.IDENTITY) private Long id; @Persistent public static final long serialVersionUID=26362862L; @Persistent String Contact_Id,First_Name,Last_Name=""; ...... @Persistent int I_1=0,I_2=1; ... @Persistent float F_1; ... @Persistent boolean B_1,B_2; @Persistent GregorianCalendar Date_1; ... @Persistent Vector<String> A_Vector=new Vector<String>(); public Contact_Info_Entry() { } ...... } Or can I skip the "@Persistent" all together like this : import java.io.*; import java.util.*; @PersistenceCapable(identityType=IdentityType.APPLICATION) public class Contact_Info_Entry implements Serializable { public static final long serialVersionUID=26362862L; String Contact_Id,First_Name="",Last_Name="",Company_Name="",Branch_Name="",Address_1="",Address_2="",City="",State="",Zip="",Country="", E_Mail="",Phone; int I_1,I_2; float F_1,F_2; boolean B_1,B_2; GregorianCalendar Date_1, Date_2; Vector<String> A_Vector=new Vector<String>(); public Contact_Info_Entry() { } ...... } Which are correct ? Frank

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• Trying to implement fling events on an object

  - by Adam Short

  I have a game object, well a bitmap, which I'd like to "fling". I'm struggling to get it to fling ontouchlistener due to it being a bitmap and not sure how to proceed and I'm struggling to find the resources to help. Here's my code so far: https://github.com/addrum/Shapes GameActivity class: package com.main.shapes; import android.app.Activity; import android.content.Context; import android.graphics.Bitmap; import android.graphics.BitmapFactory; import android.graphics.Canvas; import android.os.Bundle; import android.view.GestureDetector; import android.view.MotionEvent; import android.view.SurfaceHolder; import android.view.SurfaceView; import android.view.View.OnTouchListener; import android.view.Window; public class GameActivity extends Activity { private GestureDetector gestureDetector; View view; Bitmap ball; float x, y; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); //Remove title bar this.requestWindowFeature(Window.FEATURE_NO_TITLE); view = new View(this); ball = BitmapFactory.decodeResource(getResources(), R.drawable.ball); gestureDetector = new GestureDetector(this, new GestureListener()); x = 0; y = 0; setContentView(view); ball.setOnTouchListener(new OnTouchListener() { @Override public boolean onTouch(android.view.View v, MotionEvent event) { // TODO Auto-generated method stub return false; } }); } @Override protected void onPause() { super.onPause(); view.pause(); } @Override protected void onResume() { super.onResume(); view.resume(); } public class View extends SurfaceView implements Runnable { Thread thread = null; SurfaceHolder holder; boolean canRun = false; public View(Context context) { super(context); holder = getHolder(); } public void run() { while (canRun) { if (!holder.getSurface().isValid()) { continue; } Canvas c = holder.lockCanvas(); c.drawARGB(255, 255, 255, 255); c.drawBitmap(ball, x - (ball.getWidth() / 2), y - (ball.getHeight() / 2), null); holder.unlockCanvasAndPost(c); } } public void pause() { canRun = false; while (true) { try { thread.join(); } catch (InterruptedException e) { e.printStackTrace(); } break; } thread = null; } public void resume() { canRun = true; thread = new Thread(this); thread.start(); } } } GestureListener class: package com.main.shapes; import android.view.GestureDetector.SimpleOnGestureListener; import android.view.MotionEvent; public class GestureListener extends SimpleOnGestureListener { private static final int SWIPE_MIN_DISTANCE = 120; private static final int SWIPE_THRESHOLD_VELOCITY = 200; @Override public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX, float velocityY) { if (e1.getX() - e2.getX() > SWIPE_MIN_DISTANCE && Math.abs(velocityX) > SWIPE_THRESHOLD_VELOCITY) { //From Right to Left return true; } else if (e2.getX() - e1.getX() > SWIPE_MIN_DISTANCE && Math.abs(velocityX) > SWIPE_THRESHOLD_VELOCITY) { //From Left to Right return true; } if (e1.getY() - e2.getY() > SWIPE_MIN_DISTANCE && Math.abs(velocityY) > SWIPE_THRESHOLD_VELOCITY) { //From Bottom to Top return true; } else if (e2.getY() - e1.getY() > SWIPE_MIN_DISTANCE && Math.abs(velocityY) > SWIPE_THRESHOLD_VELOCITY) { //From Top to Bottom return true; } return false; } @Override public boolean onDown(MotionEvent e) { //always return true since all gestures always begin with onDown and<br> //if this returns false, the framework won't try to pick up onFling for example. return true; } }

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• Google App Engine JDO how to define instance fields ?

  - by Frank

  I have a class like this : import java.io.*; import java.util.*; public class Contact_Info_Entry implements Serializable { public static final long serialVersionUID=26362862L; String Contact_Id,First_Name="",Last_Name="",Company_Name="",Branch_Name="",Address_1="",Address_2="",City="",State="",Zip="",Country="",E_Mail="",Phone; int I_1,I_2; float F_1,F_2; boolean B_1,B_2; GregorianCalendar Date_1, Date_2; Vector<String> A_Vector=new Vector<String>(); public Contact_Info_Entry() { } ...... } If I want to translate it to a class for JDO, do I need to define each field by it self or can I do a group at a time ? For instance do I have to make it like this : @PersistenceCapable(identityType=IdentityType.APPLICATION) public class Contact_Info_Entry implements Serializable { @PrimaryKey @Persistent(valueStrategy=IdGeneratorStrategy.IDENTITY) private Long id; @Persistent public static final long serialVersionUID=26362862L; @Persistent String Contact_Id; @Persistent String First_Name; @Persistent String Last_Name; ...... @Persistent int I_1; @Persistent int I_2; ... @Persistent float F_1; ... @Persistent boolean B_1; @Persistent boolean B_2; @Persistent GregorianCalendar Date_1; ... @Persistent Vector<String> A_Vector=new Vector<String>(); public Contact_Info_Entry() { } ...... } Or can I do a group at a time like this : @PersistenceCapable(identityType=IdentityType.APPLICATION) public class Contact_Info_Entry implements Serializable { @PrimaryKey @Persistent(valueStrategy=IdGeneratorStrategy.IDENTITY) private Long id; @Persistent public static final long serialVersionUID=26362862L; @Persistent String Contact_Id,First_Name,Last_Name=""; ...... @Persistent int I_1=0,I_2=1; ... @Persistent float F_1; ... @Persistent boolean B_1,B_2; @Persistent GregorianCalendar Date_1; ... @Persistent Vector<String> A_Vector=new Vector<String>(); public Contact_Info_Entry() { } ...... } Or can I skip the "@Persistent" all together like this : import java.io.*; import java.util.*; @PersistenceCapable(identityType=IdentityType.APPLICATION) public class Contact_Info_Entry implements Serializable { public static final long serialVersionUID=26362862L; String Contact_Id,First_Name="",Last_Name="",Company_Name="",Branch_Name="",Address_1="",Address_2="",City="",State="",Zip="",Country="", E_Mail="",Phone; int I_1,I_2; float F_1,F_2; boolean B_1,B_2; GregorianCalendar Date_1, Date_2; Vector<String> A_Vector=new Vector<String>(); public Contact_Info_Entry() { } ...... } Which are correct ? Frank

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• Suggestions for connecting .NET WPF GUI with Java SE Server aoo

  - by Sam Goldberg

  BACKGROUND We are building a Java (SE) trading application which will be monitoring market data and sending trade messages based on the market data, and also on user defined configuration parameters. We are planning to provide the user with a thin client, built in .NET (WPF) for managing the parameters, controlling the server behavior, and viewing the current state of the trading. The client doesn't need real-time updates; it will instead update the view once every few seconds (or whatever interval is configured by the user). The client has about 6 different operations it needs to perform with the server, for example: CRUD with configuration parameters query subset of the data receive updates of current positions from server It is possible that most of the different operations (except for receiving data) are just different flavors of managing the configuration parameters, but it's too early in our analysis for us to be sure. To connect the client with the server, we have been considering using: SOAP Web Service RESTful service building a custom TCP/IP based API (text or xml) (least preferred - but we use this approach with other applications we have) As best as I understand, pros and cons of the different web service flavors are: SOAP pro: totally automated in .NET (and Java), modifying server side interface require no code changes in communication layer, just running refresh on Web Service reference to regenerate the classes. con: more overhead in the communication layer sending more text, etc. We're not using J2EE container so maybe doesn't work so well with J2SE REST pro: lighter weight, less data. Has good .NET and Java support. (I don't have any real experience with this, so don't know what other benefits it has.) con: client will not be automatically aware if there are any new operations or properties added (?), so communication layer needs to be updated by developer if server interface changes. con: (both approaches) Server cannot really push updates to the client at regular intervals (?) (However, we won't mind if client polls the server to get updates.) QUESTION What are your opinions on the above options or suggestions for other ways to connect the 2 parts? (Ideally, we don't want to put much work into the communication layer, because it's not the significant part of the application so the more off-the-shelf and automated the better.)

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• About insertion sort and especially why it's said that copy is much faster than swap?

  - by Software Engeneering Learner

  From Lafore's "Data Structures and Algorithms in Java": (about insertion sort (which uses copy + shift instead of swap (used in bubble and selection sort))) However, a copy isn’t as time-consuming as a swap, so for random data this algo- rithm runs twice as fast as the bubble sort and faster than the selectionsort. Also author doesn't mention how time consuming shift is. From my POV copy is the simplest pointer assignment operation. While swap is 3x pointer assignment operations. Which doesn't take much time. Also shift of N elemtns is Nx pointer assignment operations. Please correct me if I'm wrong. Please explain, why what author says is true? I don't understand.

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• Can static and dynamically typed languages be seen as different tools for different types of jobs?

  - by Erik Reppen

  Yes, similar questions have been asked but always with the aim of finding out 'which one is better.' I'm asking because I came up as a dev primarily in JavaScript and don't really have any extensive experience writing in statically typed languages. In spite of this I definitely see value in learning C for handling demanding operations at lower levels of code (which I assume has a lot to do with static vs dynamic at the compiler level), but what I'm trying to wrap my head around is whether there are specific project contexts (maybe certain types of dynamic data-intensive operations?) involving things other than performance where it makes a lot more sense to go with Java or C# vs. something like Python.

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• Partitioning tutorial - new features in Oracle Database 12c

  - by KLaker

  For data warehousing projects Oracle Partitioning really is a must-have feature because it delivers so many important benefits such as: Dramatically improves query performance and speeds up database maintenance operations Lowers costs by enabling a tiered storage approach that allows data to be stored on the most cost-effective storage for better resource utilisation Combined with Oracle Advanced Compression, it provides an automated approach to information lifecycle management using a simple, efficient, yet powerful way to manage data growth and reduce complexity and costs To help you get the most from partitioning we have released a new tutorial that covers the 12c new features. Topics include how to: Use Interval Reference Partitioning Perform Cascading TRUNCATE and EXCHANGE Operations Move Partitions Online Maintain Multiple Partitions Maintain Global Indexes Asynchronously Use Partial Indexes For more information about this tutorial follow this link to the Oracle Learning Library: http://apex.oracle.com/pls/apex/f?p=44785:24:0::NO:24:P24_CONTENT_ID,P24_PREV_PAGE:8408,2 where you can begin your tutorial right now! For more information about Oracle Partitioning visit our home page on OTN: http://www.oracle.com/technetwork/database/bi-datawarehousing/dbbi-tech-info-part-100980.html

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• effect and model vertex declaration compatibility

  - by Vodácek

  I have normal model drawing code. When I try to draw model without UV coordinates I got this exception: System.InvalidOperationException: The current vertex declaration does not include all the elements required by the current vertex shader. TextureCoordinate0 is missing. at Microsoft.Xna.Framework.Graphics.GraphicsDevice.VerifyCanDraw( Boolean bUserPrimitives, Boolean bIndexedPrimitives) at Microsoft.Xna.Framework.Graphics.GraphicsDevice.DrawIndexedPrimitives( PrimitiveType primitiveType, Int32 baseVertex, Int32 minVertexIndex, Int32 numVertices, Int32 startIndex, Int32 primitiveCount) at Microsoft.Xna.Framework.Graphics.ModelMeshPart.Draw() at Microsoft.Xna.Framework.Graphics.ModelMesh.Draw() ... I know what cause the exception, but is possible to avoid it? Is possible to check model before drawing it with current shader for vertex declaration compatibility?

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• Consumer Electronics Show (CES) Summit:Best Practices in Transforming Channels and Partnerships

  - by charles.knapp

  Expanding consumer demand is driving the entire high technology industry, accompanied by product lifecycles as short as a few months, continued pricing and promotion pressures, and increased globalization. Unifying global channel management, operations, and execution flow will increase efficiency and growth. IT can help, but one must think beyond generic ERP and CRM. Please join Oracle and IBM at the Bellagio Hotel in Las Vegas, Wednesday January 5, 1-7 pm. Learn from IBM, VTech, Plantronics, Cisco, Symantec and Oracle High Tech Product Strategy how to improve:Channel sales, marketing, and operations management - enhance NPI, sales, forecasts, training, promotion planning, execution and settlement Winning the deal - determining the right price for the right deal for the "perfect quote", capturing the order and order management Collaborative and rapid supply chain planning - improve agility, inventory turns, and profits Register now for this FREE event. We hope you'll join us for our Oracle High Technology CES Summit and networking reception with your peers.

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• Liskov substitution and abstract classes / strategy pattern

  - by Kolyunya

  I'm trying to follow LSP in practical programming. And I wonder if different constructors of subclasses violate it. It would be great to hear an explanation instead of just yes/no. Thanks much! P.S. If the answer is no, how do I make different strategies with different input without violating LSP? class IStrategy { public: virtual void use() = 0; }; class FooStrategy : public IStrategy { public: FooStrategy(A a, B b) { c = /* some operations with a, b */ } virtual void use() { std::cout << c; } private: C c; }; class BarStrategy : public IStrategy { public: BarStrategy(D d, E e) { f = /* some operations with d, e */ } virtual void use() { std::cout << f; } private: F f; };

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• Two interfaces with identical signatures

  - by corsiKa

  I am attempting to model a card game where cards have two important sets of features: The first is an effect. These are the changes to the game state that happen when you play the card. The interface for effect is as follows: boolean isPlayable(Player p, GameState gs); void play(Player p, GameState gs); And you could consider the card to be playable if and only if you can meet its cost and all its effects are playable. Like so: // in Card class boolean isPlayable(Player p, GameState gs) { if(p.resource < this.cost) return false; for(Effect e : this.effects) { if(!e.isPlayable(p,gs)) return false; } return true; } Okay, so far, pretty simple. The other set of features on the card are abilities. These abilities are changes to the game state that you can activate at-will. When coming up with the interface for these, I realized they needed a method for determining whether they can be activated or not, and a method for implementing the activation. It ends up being boolean isActivatable(Player p, GameState gs); void activate(Player p, GameState gs); And I realize that with the exception of calling it "activate" instead of "play", Ability and Effect have the exact same signature. Is it a bad thing to have multiple interfaces with an identical signature? Should I simply use one, and have two sets of the same interface? As so: Set<Effect> effects; Set<Effect> abilities; If so, what refactoring steps should I take down the road if they become non-identical (as more features are released), particularly if they're divergent (i.e. they both gain something the other shouldn't, as opposed to only one gaining and the other being a complete subset)? I'm particularly concerned that combining them will be non-sustainable as soon as something changes. The fine print: I recognize this question is spawned by game development, but I feel it's the sort of problem that could just as easily creep up in non-game development, particularly when trying to accommodate the business models of multiple clients in one application as happens with just about every project I've ever done with more than one business influence... Also, the snippets used are Java snippets, but this could just as easily apply to a multitude of object oriented languages.

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• Which is the most practical way to add functionality to this piece of code?

  - by Adam Arold

  I'm writing an open source library which handles hexagonal grids. It mainly revolves around the HexagonalGrid and the Hexagon class. There is a HexagonalGridBuilder class which builds the grid which contains Hexagon objects. What I'm trying to achieve is to enable the user to add arbitrary data to each Hexagon. The interface looks like this: public interface Hexagon extends Serializable { // ... other methods not important in this context <T> void setSatelliteData(T data); <T> T getSatelliteData(); } So far so good. I'm writing another class however named HexagonalGridCalculator which adds some fancy pieces of computation to the library like calculating the shortest path between two Hexagons or calculating the line of sight around a Hexagon. My problem is that for those I need the user to supply some data for the Hexagon objects like the cost of passing through a Hexagon, or a boolean flag indicating whether the object is transparent/passable or not. My question is how should I implement this? My first idea was to write an interface like this: public interface HexagonData { void setTransparent(boolean isTransparent); void setPassable(boolean isPassable); void setPassageCost(int cost); } and make the user implement it but then it came to my mind that if I add any other functionality later all code will break for those who are using the old interface. So my next idea is to add annotations like @PassageCost, @IsTransparent and @IsPassable which can be added to fields and when I'm doing the computation I can look for the annotations in the satelliteData supplied by the user. This looks flexible enough if I take into account the possibility of later changes but it uses reflection. I have no benchmark of the costs of using annotations so I'm a bit in the dark here. I think that in 90-95% of the cases the efficiency is not important since most users wont't use a grid where this is significant but I can imagine someone trying to create a grid with a size of 5.000.000.000 X 5.000.000.000. So which path should I start walking on? Or are there some better alternatives? Note: These ideas are not implemented yet so I did not pay too much attention to good names.

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