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• Median calculation in ActionScript 3

  - by Gabor Kako

  I have a number array and I'd like to calculate the median. When the array is odd, the calculation is OK, when it's even strange number comes up. private var numbers:String = "2,5,3,4,6,1"; private var array:Array = numbers.split(","); private function getMedian(array:Array):Number { var sortnums:Array = array.sort(Array.NUMERIC); var length:Number = sortnums.length; var mid1:Number; var mid2:Number; var median:Number; if(length % 2 == 0){ mid1 = length / 2; trace("mid1: "+mid1); mid2= ((length - 1) / 2)-0.5; trace("mid2: "+mid2); trace ("mid1: "+sortnums[mid1]+", mid2: "+sortnums[mid2]); median = (sortnums[mid1] + sortnums[mid2]) / 2; }else{ mid1 = (length / 2)-0.5 median = sortnums[mid1] } trace (median); return median; } The result is 21.5, but should be 3.5 mid1 and mid2 are a position in the array. Could somebody help?

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• java: retrieving the "canonical value" from a Set<T> where T has a custom equals()

  - by Jason S

  I have a class Foo which overrides equals() and hashCode() properly. I would like to also would like to use a HashSet<Foo> to keep track of "canonical values" e.g. I have a class that I would like to write like this, so that if I have two separate objects that are equivalent I can coalesce them into references to the same object: class Canonicalizer<T> { final private Set<T> values = new HashSet<T>(); public T findCanonicalValue(T value) { T canonical = this.values.get(value); if (canonical == null) { // not in the set, so put it there for the future this.values.add(value); return value; } else { return canonical; } } } except that Set doesn't have a "get" method that would return the actual value stored in the set, just the "contains" method that returns true or false. (I guess that it assumes that if you have an object that is equal to a separate object in the set, you don't need to retrieve the one in the set) Is there a convenient way to do this? The only other thing I can think of is to use a map and a list: class Canonicalizer<T> { // warning: neglects concurrency issues final private Map<T, Integer> valueIndex = new HashMap<T, Integer>(); final private List<T> values = new ArrayList<T>(); public T findCanonicalValue(T value) { Integer i = this.valueIndex.get(value); if (i == null) { // not in the set, so put it there for the future i = this.values.size(); this.values.add(value); this.valueIndex.put(value, i); return value; } else { // in the set return this.values.get(i); } } }

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• How to create custom query for CollectionOfElements

  - by Shervin

  Hi. I have problems creating a custom query. This is what entities: @Entity public class ApplicationProcess { @CollectionOfElements private Set<Template> defaultTemplates; //more fields } And Template.java @Embeddable @EqualsAndHashCode(exclude={"file", "selected", "used"}) public class Template implements Comparable<Template> { @Setter private ApplicationProcess applicationProcess; @Setter private Boolean used = Boolean.valueOf(false); public Template() { } @Parent public ApplicationProcess getApplicationProcess() { return applicationProcess; } @Column(nullable = false) @NotNull public String getName() { return name; } @Column(nullable = true) public Boolean isUsed() { return used; } public int compareTo(Template o) { return getName().compareTo(o.getName()); } } I want to create a update statement. I have tried these two: int v = entityManager.createQuery("update ApplicationProcess_defaultTemplates t set t.used = true " + "WHERE t.applicationProcess.id=:apId").setParameter("apId", ap.getId()) .executeUpdate(); ApplicationProcess_defaultTemplates is not mapped [update ApplicationProcess_defaultTemplates t set t.used = true WHERE t.applicationProcess.id=:apId] And I have tried int v = entityManager.createQuery("update Template t set t.used = true " + "WHERE t.applicationProcess.id=:apId").setParameter("apId", ap.getId()) .executeUpdate(); With the same error: Template is not mapped [update Template t set t.used = true WHERE t.applicationProcess.id=:apId] Any ideas? UPDATE I fixed it by creating native query int v = entityManager.createNativeQuery("update ApplicationProcess_defaultTemplates t set t.used=true where t.ApplicationProcess_id=:apId").setParameter("apId", ap.getId()).executeUpdate();

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• Are there any garanties in JLS about order of execution static initialization blocks?

  - by Roman

  I wonder if it's reliable to use a construction like: private static final Map<String, String> engMessages; private static final Map<String, String> rusMessages; static { engMessages = new HashMap<String, String> () {{ put ("msgname", "value"); }}; rusMessages = new HashMap<String, String> () {{ put ("msgname", "????????"); }}; } private static Map<String, String> msgSource; static { msgSource = engMessages; } public static String msg (String msgName) { return msgSource.get (msgName); } Is there a possibility that I'll get NullPointerException because msgSource initialization block will be executed before the block which initializes engMessages? (about why don't I do msgSource initialization at the end of upper init. block: just the matter of taste; I'll do so if the described construction is unreliable)

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• Google App Engine datastore encoding?

  - by sernaferna

  I'm using the GAE datastore for a Java application, and storing some text that will be in numerous languages. In my servlet, I'm first checking to see if there's any data in the data store, and, if not, I'm creating some, similar to the following: ArrayList<Lang> list = new ArrayList<Lang>(); list.add(new Lang("EN", "English", 1)); list.add(new Lang("ES", "Español", 0)); //more languages here... PersistenceManager pm = PMF.get().getPersistenceManager(); for(Lang l : list) { pm.makePersistent(l); } Since this is using JDO, I guess I should include the relevent parts of the Lang class too: @PersistenceCapable public class Lang { @PrimaryKey private String code; @Persistent private String name; @Persistent private int popularity; // getters & setters & constructors... } However, the non-ASCII characters are giving me grief. I've set my Eclipse project to use the UTF-8 encoding instead of the default Cp1252, so I think I'm okay from that perspective, but when I use the App Engine Data Viewer to look at my data, that Español entry becomes Español, and when I click on it to view it, I get a 500 Server Error. (There are some other entries with right-to-left text that don't even show up in the Data Viewer at all, but one problem at a time...) Is there anything special I can do in my code to set the character encoding, or specify to GAE that the data I'm storing is UTF-8? Or is the problem on the Eclipse side, and is there something I should be doing with my Java code?

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• How to decide between using PLINQ and LINQ at runtime?

  - by Hamish Grubijan

  Or decide between a parallel and a sequential operation in general. It is hard to know without testing whether parallel or sequential implementation is best due to overhead. Obviously it will take some time to train "the decider" which method to use. I would say that this method cannot be perfect, so it is probabilistic in nature. The x,y,z do influence "the decider". I think a very naive implementation would be to give both 1/2 chance at the beginning and then start favoring them according to past performance. This disregards x,y,z, however. I suspect that this question would be better answered by academics than practitioners. Anyhow, please share your heuristic, your experience if any, your tips on this. Sample code: public interface IComputer { decimal Compute(decimal x, decimal y, decimal z); } public class SequentialComputer : IComputer { public decimal Compute( ... // sequential implementation } public class ParallelComputer : IComputer { public decimal Compute( ... // parallel implementation } public class HybridComputer : IComputer { private SequentialComputer sc; private ParallelComputer pc; private TheDecider td; // Helps to decide between the two. public HybridComputer() { sc = new SequentialComputer(); pc = new ParallelComputer(); td = TheDecider(); } public decimal Compute(decimal x, decimal y, decimal z) { decimal result; decimal time; if (td.PickOneOfTwo() == 0) { // Time this and save result into time. result = sc.Compute(...); } else { // Time this and save result into time. result = pc.Compute(); } td.Train(time); return result; } }

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• How to collect and inject all beans of a given type in Spring XML configuration

  - by GrzegorzOledzki

  One of the strongest accents of the Spring framework is the Dependency Injection concept. I understand one of the advices behind that is to separate general high-level mechanism from low-level details (as announced by Dependency Inversion Principle). Technically, that boils down to having a bean implementation to know as little as possible about a bean being injected as a dependency, e.g. public class PrintOutBean { private LogicBean logicBean; public void action() { System.out.println(logicBean.humanReadableDetails()); } //... } <bean class="PrintOutBean"> <property name="loginBean" ref="ShoppingCartBean"/> </bean> But what if I wanted to a have a high-level mechanism operating on multiple dependent beans? public class MenuManagementBean { private Collection<Option> options; public void printOut() { for (Option option:options) { // do something for option } //... } } I know one solution would be to use @Autowired annotation in the singleton bean, that is... @Autowired private Collection<Option> options; But doesn't it violate the separation principle? Why do I have to specify what dependents to take in the very same place I use them (i.e. MenuManagementBean class in my example)? Is there a way to inject collections of beans in the XML configuration like this (without any annotation in the MMB class)? <bean class="MenuManagementBean"> <property name="options"> <xxx:autowire by-type="MyOptionImpl"/> </property> </bean>

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• How to print each object in a collection in a separate page in Silverlight

  - by Ash

  I would like to know if its possible to print each object in a collection in separate pages using Silverlight printing API. Suppose I have a class Label public class Label { public string Address { get; set; } public string Country { get; set; } public string Name { get; set; } public string Town { get; set; } } I can use print API and print like this. private PrintDocument pd; private void PrintButton_Click(object sender, RoutedEventArgs e) { pd.Print("Test Print"); } private void pd_PrintPage(object sender, PrintPageEventArgs e) { Label labelToPrint = new Label() { Name = "Fake Name", Address = "Fake Address", Country = "Fake Country", Town = "Town" }; var printpage = new LabelPrint(); printpage.DataContext = new LabelPrintViewModel(labelToPrint); e.PageVisual = printpage; } LabelPrint Xaml <StackPanel x:Name="LayoutRoot" VerticalAlignment="Center" HorizontalAlignment="Center"> <TextBlock Text="{Binding Name}" /> <TextBlock Text="{Binding Address}" /> <TextBlock Text="{Binding Town}" /> <TextBlock Text="{Binding Country}" /> </StackPanel> Now, say I've a collection of Label objects, List<Label> labels = new List<Label>() { labelToPrint, labelToPrint, labelToPrint, labelToPrint }; How can I print each object in the list in separate pages ? Thanks for any suggestions ..

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• How do I correct feature envy in this case?

  - by RMorrisey

  I have some code that looks like: class Parent { private Intermediate intermediateContainer; public Intermediate getIntermediate(); } class Intermediate { private Child child; public Child getChild() {...} public void intermediateOp(); } class Child { public void something(); public void somethingElse(); } class Client { private Parent parent; public void something() { parent.getIntermediate().getChild().something(); } public void somethingElse() { parent.getIntermediate().getChild().somethingElse(); } public void intermediate() { parent.getIntermediate().intermediateOp(); } } I understand that is an example of the "feature envy" code smell. The question is, what's the best way to fix it? My first instinct is to put the three methods on parent: parent.something(); parent.somethingElse(); parent.intermediateOp(); ...but I feel like this duplicates code, and clutters the API of the Parent class (which is already rather busy). Do I want to store the result of getIntermediate(), and/or getChild(), and keep my own references to these objects?

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• Message Handlers and the WeakReference issue

  - by user1058647

  The following message Handler works fine receiving messages from my service... private Handler handler = new Handler() { public void handleMessage(Message message) { Object path = message.obj; if (message.arg1 == 5 && path != null) //5 means its a single mapleg to plot on the map { String myString = (String) message.obj; Gson gson = new Gson(); MapPlot mapleg = gson.fromJson(myString, MapPlot.class); myMapView.getOverlays().add(new DirectionPathOverlay(mapleg.fromPoint, mapleg.toPoint)); mc.animateTo(mapleg.toPoint); } else { if (message.arg1 == RESULT_OK && path != null) { Toast.makeText(PSActivity.this, "Service Started" + path.toString(), Toast.LENGTH_LONG).show(); } else { Toast.makeText(PSActivity.this,"Service error" + String.valueOf(message.arg1), Toast.LENGTH_LONG).show(); } } }; }; However, even though it tests out alright in the AVD (I'm feeding it a large KML file via DDMS) the "object path = message.obj;" line has a WARNING saying "this Handler class should be static else leaks might occur". But if I say "static Handler handler = new Handler()" it won't compile complaining that I "cannot make a static reference to a non-static field myMapView. If I can't make such references, I can't do anything useful. This led me into several hours of googling around on this issue and learning more about weakReferences than I ever wanted to know. The often found reccomendation I find is that I should replace... private Handler handler = new Handler() with static class handler extends Handler { private final WeakReference<PSActivity> mTarget; handler(PSActivity target) { mTarget = new WeakReference<PSActivity>(target); } But this won't compile still complaining that I can't make a static reference to a non-dtatic field. So, my question a week or to ago was "how can I write a message handler for android so my service can send data to my activity. Even though I have working code, the question still stands with the suffix "without leaking memory". Thanks, Gary

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• Getting an updated location in Android

  - by jul

  Hi, I'm using the code shown below to get an updated value for location every time a button is clicked. When my activity is resumed I get an update every second, so that when I call getLastKnownLocation I expect to have a location that have been updated in the last second. Is that the correct way to do that? I would expect the onLocationChanged event to be triggered every time I execute a 'geo fix' command (or max after 1s since I request update every 1s), but it's only triggered the first time. Why? Any help/suggestion welcome! Thanks package org.digitalfarm.atable; ... public class Atable extends Activity { private Button mSearchButton; private TextView mytext; private LocationManager locationManager; public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); mSearchButton = (Button)this.findViewById(R.id.button); mytext = (TextView) findViewById(R.id.dude); locationManager = (LocationManager)getSystemService(Context.LOCATION_SERVICE); final Criteria criteria = new Criteria(); criteria.setAccuracy(Criteria.ACCURACY_FINE); mSearchButton.setOnClickListener(new OnClickListener() { @Override public void onClick(View v) { String provider = locationManager.getBestProvider(criteria, true); Location location = locationManager.getLastKnownLocation(provider); } }); } //Start a location listener LocationListener onLocationChange=new LocationListener() { public void onLocationChanged(Location loc) { //sets and displays the lat/long when a location is provided String latlong = "Lat: " + loc.getLatitude() + " Long: " + loc.getLongitude(); mytext.setText(latlong); } public void onProviderDisabled(String provider) { // required for interface, not used } public void onProviderEnabled(String provider) { // required for interface, not used } public void onStatusChanged(String provider, int status, Bundle extras) { // required for interface, not used } }; //pauses listener while app is inactive @Override public void onPause() { super.onPause(); locationManager.removeUpdates(onLocationChange); } //reactivates listener when app is resumed @Override public void onResume() { super.onResume(); locationManager.requestLocationUpdates(LocationManager.GPS_PROVIDER,1000,100.0f,onLocationChange); } }

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• android opengl es texture mapping into polygons

  - by kamil

  I wrote opengl es code for android to map textures on a square but i want to draw texture on polygons. When user moved the image, texture will be mapped on polygons have more vertexes. I tried the arrays combination below for pentagon but i could not find the correct triangle combination in indices array. public float vertices[] = { // -1.0f, 1.0f, 0.0f, //Top Left // -1.0f, -1.0f, 0.0f, //Bottom Left // 1.0f, -1.0f, 0.0f, //Bottom Right // 1.0f, 1.0f, 0.0f //Top Right -1.0f, 1.0f, 0.0f, //Top Left -1.0f, -1.0f, 0.0f, //Bottom Left 1.0f, -1.0f, 0.0f, //Bottom Right 1.0f, 1.0f, 0.0f, //Top Right 0.4f, 1.4f, 0.0f }; /** Our texture pointer */ private int[] textures = new int[1]; /** The initial texture coordinates (u, v) */ private float texture[] = { //Mapping coordinates for the vertices // 1.0f, 0.0f, // 1.0f, 1.0f, // 0.0f, 1.0f, // 0.0f, 0.0f, // 0.0f, 1.0f, // 0.0f, 0.0f, // 1.0f, 0.0f, // 1.0f, 1.0f, 0.0f, 0.0f, 0.0f, 1.0f, 1.0f, 1.0f, 1.0f, 0.0f, 1.0f, 0.7f, }; /** The initial indices definition */ private byte indices[] = { //2 triangles // 0,1,2, 2,3,0, 0,1,2, 2,3,4, 3,4,0, //triangles for five vertexes }; i draw with the code below gl.glDrawElements(GL10.GL_TRIANGLES, indices.length, GL10.GL_UNSIGNED_BYTE, indexBuffer);

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• ListView causing OutOfMemory Error

  - by Michael

  So I am not really given a reason to the right of this error message. I am not exactly sure why this is happening but my guess though is that it has to do with the fact that there are around ~50 good quality drawables. Upon scrolling really fast, the app crashes. I feel as if I am mitigating most common issues with ListView and crashing such as using View Holders as well as only initiating the inflater once. Process: com.example.michael.myandroidappactivity, PID: 20103 java.lang.OutOfMemoryError at android.graphics.BitmapFactory.nativeDecodeAsset(Native Method) Here is the code public class ImageAdapter extends BaseAdapter { private Context context; private ArrayList<Integer> imageIds; private static LayoutInflater inflater; public ImageAdapter(Context _context, ArrayList<Integer> _imageIds) { context = _context; imageIds = _imageIds; } @Override public int getCount() { return imageIds.size(); } @Override public Object getItem(int position) { return null; } @Override public long getItemId(int position) { return 0; } static class ViewHolder{ ImageView img; } @Override public View getView(int position, View convertView, ViewGroup parent) { ViewHolder holder = null; View rowView = null; if(rowView==null) { LayoutInflater inflater = (LayoutInflater) context .getSystemService(Context.LAYOUT_INFLATER_SERVICE); rowView = inflater.inflate(R.layout.listview_layout, parent, false); holder = new ViewHolder(); holder.img = (ImageView) rowView.findViewById(R.id.flag); rowView.setTag(holder); } else { holder = (ViewHolder) rowView.getTag(); } holder.img.setImageResource(imageIds.get(position)); return rowView; } }

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• Why the HelloWorld of opennlp library works fine on Java but doesn't work with Jruby?

  - by 0x90

  I am getting this error: SyntaxError: hello.rb:13: syntax error, unexpected tIDENTIFIER public HelloWorld( InputStream data ) throws IOException { The HelloWorld.rb is: require "java" import java.io.FileInputStream; import java.io.InputStream; import java.io.IOException; import opennlp.tools.postag.POSModel; import opennlp.tools.postag.POSTaggerME; public class HelloWorld { private POSModel model; public HelloWorld( InputStream data ) throws IOException { setModel( new POSModel( data ) ); } public void run( String sentence ) { POSTaggerME tagger = new POSTaggerME( getModel() ); String[] words = sentence.split( "\\s+" ); String[] tags = tagger.tag( words ); double[] probs = tagger.probs(); for( int i = 0; i < tags.length; i++ ) { System.out.println( words[i] + " => " + tags[i] + " @ " + probs[i] ); } } private void setModel( POSModel model ) { this.model = model; } private POSModel getModel() { return this.model; } public static void main( String args[] ) throws IOException { if( args.length < 2 ) { System.out.println( "HelloWord <file> \"sentence to tag\"" ); return; } InputStream is = new FileInputStream( args[0] ); HelloWorld hw = new HelloWorld( is ); is.close(); hw.run( args[1] ); } } when running ruby HelloWorld.rb "I am trying to make it work" when I run the HelloWorld.java "I am trying to make it work" it works perfectly, of course the .java doesn't contain the require java statement. EDIT: I followed the following steps. The output for jruby -v : jruby 1.6.7.2 (ruby-1.8.7-p357) (2012-05-01 26e08ba) (Java HotSpot(TM) 64-Bit Server VM 1.6.0_35) [darwin-x86_64-java]

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• Trying to write priority queue in Java but getting "Exception in thread "main" java.lang.ClassCastEx

  - by Dan

  For my data structure class, I am trying to write a program that simulates a car wash and I want to give fancy cars a higher priority than regular ones using a priority queue. The problem I am having has something to do with Java not being able to type cast "Object" as an "ArrayQueue" (a simple FIFO implementation). What am I doing wrong and how can I fix it? public class PriorityQueue<E> { private ArrayQueue<E>[] queues; private int highest=0; private int manyItems=0; public PriorityQueue(int h) { highest=h; queues = (ArrayQueue[]) new Object[highest+1]; <----problem is here } public void add(E item, int priority) { queues[priority].add(item); manyItems++; } public boolean isEmpty( ) { return (manyItems == 0); } public E remove() { E answer=null; int counter=0; do { if(!queues[highest-counter].isEmpty()) { answer = queues[highest-counter].remove(); counter=highest+1; } else counter++; }while(highest-counter>=0); return answer; } }

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• Various way to stop a thread - which is the correct way

  - by Yan Cheng CHEOK

  I had came across different suggestion of stopping a thread. May I know, which is the correct way? Or it depends? Using Thread Variable http://download.oracle.com/javase/1.4.2/docs/guide/misc/threadPrimitiveDeprecation.html private volatile Thread blinker; public void stop() { blinker = null; } public void run() { Thread thisThread = Thread.currentThread(); while (blinker == thisThread) { try { thisThread.sleep(interval); } catch (InterruptedException e){ } repaint(); } } Using boolean flag private volatile boolean flag; public void stop() { flag = false; } public void run() { while (flag) { try { thisThread.sleep(interval); } catch (InterruptedException e){ } repaint(); } } Using Thread Variable together with interrupt private volatile Thread blinker; public void stop() { blinker.interrupt(); blinker = null; } public void run() { Thread thisThread = Thread.currentThread(); while (!thisThread.isInterrupted() && blinker == thisThread) { try { thisThread.sleep(interval); } catch (InterruptedException e){ } repaint(); } }

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• Java Class<T> static method forName() IncompatibleClassChangeError

  - by matt

  Hi, i have this code: private static Importable getRightInstance(String s) throws Exception { Class<? extends Importable> c = Class.forName(s).asSubclass(Importable.class); Importable i = c.newInstance(); return i; } which i can also write private static Importable getRightInstance(String s) throws Exception { Class<? extends Importable> c = (Class<? extends Importable>)Class.forName(s); Importable i = c.newInstance(); return i; } or private static Importable getRightInstance(String s) throws Exception { Class<?> c = Class.forName(s); Importable i = (Importable)c.newInstance(); return i; } where Importable is an interface and s is a string representing an implementing class. Well, in any case it gives the following: Exception in thread "main" java.lang.IncompatibleClassChangeError: class C1 has interface Importable as super class Here is the last snippet of the stack trace: at java.lang.Class.forName(Class.java:169) at Importer.getRightImportable(Importer.java:33) at Importer.importAll(Importer.java:44) at Test.main(Test.java:16) Now, class C1 actually implemens Importable and i totally don't understand why it complaints. Thanks in advance.

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• Problem with moving a winform using C#

  - by karthik

  My form doesn't have a title bar, so I am implementing the code to drag the entire form around the screen. I am using the below code to do it, which works fine. I have two panels in my form, PanelA and PanelB. During the startup I show PanelA where the dragging works perfectly. Later when the user clicks the button in PanelA, I need to make PanelA invisible and show PanelB However, the dragging does not work when PanelB is shown. What's the problem here? private void SerialPortScanner_MouseUp(object sender, MouseEventArgs e) { this.drag = false; } private void SerialPortScanner_MouseDown(object sender, MouseEventArgs e) { this.drag = true; this.start_point = new Point(e.X, e.Y); } private void SerialPortScanner_MouseMove(object sender, MouseEventArgs e) { if (this.drag) { Point p1 = new Point(e.X, e.Y); Point p2 = this.PointToScreen(p1); Point p3 = new Point(p2.X - this.start_point.X, p2.Y - this.start_point.Y); this.Location = p3; } }

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• Hibernate Transient Extends problem

  - by mrvreddy

  @MappedSuperclass public abstract class BaseAbstract implements Serializable{ private static final long serialVersionUID = 1L; protected String test = //some random value; public String getTest() { return test; } public void setTest(String test){ this.test = test; } } @Entity public class Artist extends BaseAbstract { private static final long serialVersionUID = 1L; private Integer id; @override @Transient public String getTest() { return test; } ..... } My question is... when i am trying to do any operation on the artist, along with id and name, test is also getting saved which should not be the case... if i add the same transient on the baseabstract class getTest() method, i see test column NOT getting created(ideally what it should happen) but if i try to override the method with adding annotaion in the sub class it creates the test column... I dont know why this is happening since when hibernate is creating the artist object and checks for annotations, it should see the transient annotation present on the getTest() of artist method...and should not create a column in the database... Let me know if you need any clarification.... Any response on this is greatly appreciated.... Thank you

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• How to "wrap" implementation in C#

  - by igor

  Hello, I have these classes in C# (.NET Framework 3.5) described below: public class Base { public int State {get; set;} public virtual int Method1(){} public virtual string Method2(){} ... public virtual void Method10(){} } public class B: Base { // some implementation } public class Proxy: Base { private B _b; public class Proxy(B b) { _b = b; } public override int Method1() { if (State == Running) return _b.Method1(); else return base.Method1(); } public override string Method2() { if (State == Running) return _b.Method2(); else return base.Method2(); } public override void Method10() { if (State == Running) _b.Method10(); else base.Method10(); } } I want to get something this: public Base GetStateDependentImplementation() { if (State == Running) // may be some other rule return _b; else return base; // compile error } and my Proxy's implementation will be: public class Proxy: Base { ... public override int Method1() { return GetStateDependentImplementation().Method1(); } public override string Method2() { return GetStateDependentImplementation().Method2(); } ... } Of course, I can do this (aggregation of base implementation): public RepeaterOfBase: Base // no any overrides, just inheritance { } public class Proxy: Base { private B _b; private RepeaterOfBase _Base; public class Proxy(B b, RepeaterOfBase aBase) { _b = b; _base = aBase; } } ... public Base GetStateDependentImplementation() { if (State == Running) return _b; else return _Base; } ... But instance of Base class is very huge and I have to avoid to have other additional copy in memory. So I have to simplify my code have to "wrap" implementation have to avoid a code duplication have to avoid aggregation of any additional instance of Base class (duplication) Is it possible to reach these goals?

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• Java - Calling all methods of a class

  - by Thomas Eschemann

  I'm currently working on an application that has to render several Freemarker templates. So far I have a Generator class that handles the rendering. The class looks more or less like this: public class Generator { public static void generate(…) { renderTemplate1(); renderTemplate2(); renderTemplate3(); } private static void render(…) { // renders the template } private static void renderTemplate1() { // Create config object for the rendering // and calls render(); }; private static void renderTemplate1() { // Create config object for the rendering // and calls render(); }; … } This works, but it doesn't really feel right. What I would like to do is create a class that holds all the renderTemplate...() methods and then call them dynamically from my Generator class. This would make it cleaner and easier to extend. I was thinking about using something like reflection, but it doesn't really feel like a good solution either. Any idea on how to implement this properly ?

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• Efficient database access when dealing with multiple abstracted repositories

  - by Nathan Ridley

  I want to know how most people are dealing with the repository pattern when it involves hitting the same database multiple times (sometimes transactionally) and trying to do so efficiently while maintaining database agnosticism and using multiple repositories together. Let's say we have repositories for three different entities; Widget, Thing and Whatsit. Each repository is abstracted via a base interface as per normal decoupling design processes. The base interfaces would then be IWidgetRepository, IThingRepository and IWhatsitRepository. Now we have our business layer or equivalent (whatever you want to call it). In this layer we have classes that access the various repositories. Often the methods in these classes need to do batch/combined operations where multiple repositories are involved. Sometimes one method may make use of another method internally, while that method can still be called independently. What about, in this scenario, when the operation needs to be transactional? Example: class Bob { private IWidgetRepository _widgetRepo; private IThingRepository _thingRepo; private IWhatsitRepository _whatsitRepo; public Bob(IWidgetRepository widgetRepo, IThingRepository thingRepo, IWhatsitRepository whatsitRepo) { _widgetRepo = widgetRepo; _thingRepo= thingRepo; _whatsitRepo= whatsitRepo; } public void DoStuff() { _widgetRepo.StoreSomeStuff(); _thingRepo.ReadSomeStuff(); _whatsitRepo.SaveSomething(); } public void DoOtherThing() { _widgetRepo.UpdateSomething(); DoStuff(); } } How do I keep my access to that database efficient and not have a constant stream of open-close-open-close on connections and inadvertent invocation of MSDTS and whatnot? If my database is something like SQLite, standard mechanisms like creating nested transactions are going to inherently fail, yet the business layer should not have to be concerning itself with such things. How do you handle such issues? Does ADO.Net provide simple mechanisms to handle this or do most people end up wrapping their own custom bits of code around ADO.Net to solve these types of problems?

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• Is this a correct way to stop Execution Task

  - by Yan Cheng CHEOK

  I came across code to stop execution's task. private final ExecutorService executor = Executors.newSingleThreadExecutor(); public void stop() { executor.shutdownNow(); try { executor.awaitTermination(100, TimeUnit.DAYS); } catch (InterruptedException ex) { log.error(null, ex); } } public Runnable getRunnable() { return new Runnable() { public void run() { while (!Thread.currentThread().isInterrupted()) { // What if inside fun(), someone try to clear the interrupt flag? // Say, through Thread.interrupted(). We will stuck in this loop // forever. fun(); } } }; } I realize that, it is possible for Runnable to be in forever loop, as Unknown fun may Thread.sleep, clear the interrupt flag and ignore the InterruptedException Unknown fun may Thread.interrupted, clear the interrupt flag. I was wondering, is the following way correct way to fix the code? private final ExecutorService executor = Executors.newSingleThreadExecutor(); private volatile boolean flag = true; public void stop() { flag = false; executor.shutdownNow(); try { executor.awaitTermination(100, TimeUnit.DAYS); } catch (InterruptedException ex) { log.error(null, ex); } } public Runnable getRunnable() { return new Runnable() { public void run() { while (flag && !Thread.currentThread().isInterrupted()) { // What if inside fun(), someone try to clear the interrupt flag? // Say, through Thread.interrupted(). We will stuck in this loop // forever. fun(); } } }; }

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• Need a refresher course on property access...

  - by Code Sherpa

  Hi. I need help with accessing class properties within a given class. For example, take the below class: public partial class Account { private Profile _profile; private Email _email; private HostInfo _hostInfo; public Profile Profile { get { return _profile; } set { _profile = value; } } public Email Email { get { return _email; } set { _email = value; } } public HostInfo HostInfo { get { return _hostInfo; } set { _hostInfo = value; } } In the class "Account" exists a bunch of class properties such as Email or Profile. Now, when I want to access those properties at run-time, I do something like this (for Email): _accountRepository = ObjectFactory.GetInstance<IAccountRepository>(); string username = Cryptography.Decrypt(_webContext.UserNameToVerify, "verify"); Account account = _accountRepository.GetAccountByUserName(username); if(account != null) { account.Email.IsConfirmed = true; But, I get "Object reference not set..." for account.Email... Why is that? How do I access Account such that account.Email, account.Profile, and so on returns the correct data for a given AccountId or UserName. Here is a method that returns Account: public Account GetAccountByUserName(string userName) { Account account = null; using (MyDataContext dc = _conn.GetContext()) { try { account = (from a in dc.Accounts where a.UserName == userName select a).FirstOrDefault(); } catch { //oops } } return account; } The above works but when I try: account = (from a in dc.Accounts join em in dc.Emails on a.AccountId equals em.AccountId join p in dc.Profiles on em.AccountId equals p.AccountId where a.UserName == userName select a).FirstOrDefault(); I am still getting object reference exceptions for my Email and Profile properties. Is this simply a SQL problem or is there something else I need to be doing to be able to fully access all the properties within my Account class? Thanks!

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• C++ member template for boost ptr_vector

  - by Ivan

  Hi there, I'm trying to write a container class using boost::ptr_vector. Inside the ptr_vector I would like to include different classes. I'm trying to achieve that using static templates, but so far I'm not able to do that. For example, the container class is class model { private: boost::ptr_vector<elem_type> elements; public: void insert_element(elem_type *a) { element_list.push_back(a); } }; and what I'm trying to achieve is be able to use different elem_type classes. The code below doesn't satisfy my requirements: template <typename T>class model { private: boost::ptr_vector<T> elements; public: void insert_element(T *a) { element_list.push_back(a); } }; because when I initialize the container class I can only use one class as template: model <elem_type_1> model_thing; model_thing.insert_element(new elem_type_1) but not elem_type_2: model_thing.insert_element(new elem_type_2)//error, of course It is possible to do something like using templates only on the member? class model { private: template <typename T> boost::ptr_vector<T> elements; public: void insert_element(T *a) { element_list.push_back(a); } }; //wrong So I can call the insert_element on the specific class that I want to insert? Note that I do not want to use virtual members. Thanks!

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