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  • How to properly mix generics and inheritance to get the desired result?

    - by yamsha
    My question is not easy to explain using words, fortunately it's not too difficult to demonstrate. So, bear with me: public interface Command<R> { public R execute();//parameter R is the type of object that will be returned as the result of the execution of this command } public abstract class BasicCommand<R> { } public interface CommandProcessor<C extends Command<?>> { public <R> R process(C<R> command);//this is my question... it's illegal to do, but you understand the idea behind it, right? } //constrain BasicCommandProcessor to commands that subclass BasicCommand public class BasicCommandProcessor implements CommandProcessor<C extends BasicCommand<?>> { //here, only subclasses of BasicCommand should be allowed as arguments but these //BasicCommand object should be parameterized by R, like so: BasicCommand<R> //so the method signature should really be // public <R> R process(BasicCommand<R> command) //which would break the inheritance if the interface's method signature was instead: // public <R> R process(Command<R> command); //I really hope this fully illustrates my conundrum public <R> R process(C<R> command) { return command.execute(); } } public class CommandContext { public static void main(String... args) { BasicCommandProcessor bcp = new BasicCommandProcessor(); String textResult = bcp.execute(new BasicCommand<String>() { public String execute() { return "result"; } }); Long numericResult = bcp.execute(new BasicCommand<Long>() { public Long execute() { return 123L; } }); } } Basically, I want the generic "process" method to dictate the type of generic parameter of the Command object. The goal is to be able to restrict different implementations of CommandProcessor to certain classes that implement Command interface and at the same time to able to call the process method of any class that implements the CommandProcessor interface and have it return the object of type specified by the parametarized Command object. I'm not sure if my explanation is clear enough, so please let me know if further explanation is needed. I guess, the question is "Would this be possible to do, at all?" If the answer is "No" what would be the best work-around (I thought of a couple on my own, but I'd like some fresh ideas)

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  • How to introduce multi-column constraint with JPA annotations?

    - by plouh
    I am trying to introduce a multi-key constraint on a JPA-mapped entity: public class InventoryItem { @Id private Long id; @Version private Long version; @ManyToOne @JoinColumn("productId") private Product product; @Column(nullable=false); private long serial; } Basically (product, serial) pair should be unique, but I only found a way to say that serial should be unique. This obviously isn't a good idea since different products might have same serial numbers. Is there a way to generate this constraint via JPA or am I forced to manually create it to DB?

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  • Joining tables with composite keys in a legacy system in hibernate

    - by Steve N
    Hi, I'm currently trying to create a pair of Hibernate annotated classes to load (read only) from a pair of tables in a legacy system. The legacy system uses a consistent (if somewhat dated) approach to keying tables. The tables I'm attempting to map are as follows: Customer CustomerAddress -------------------------- ---------------------------- customerNumber:string (pk) customerNumber:string (pk_1) name:string sequenceNumber:int (pk_2) street:string postalCode:string I've approached this by creating a CustomerAddress class like this: @Entity @Table(name="CustomerAddress") @IdClass(CustomerAddressKey.class) public class CustomerAddress { @Id @AttributeOverrides({ @AttributeOverride(name = "customerNumber", column = @Column(name="customerNumber")), @AttributeOverride(name = "sequenceNumber", column = @Column(name="sequenceNumber")) }) private String customerNumber; private int sequenceNumber; private String name; private String postalCode; ... } Where the CustomerAddressKey class is a simple Serializable object with the two key fields. The Customer object is then defined as: @Entity @Table(name = "Customer") public class Customer { private String customerNumber; private List<CustomerAddress> addresses = new ArrayList<CustomerAddress>(); private String name; ... } So, my question is: how do I express the OneToMany relationship on the Customer table?

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  • Android sql creating database once

    - by semajhan
    One thing i'm not understanding is how to create the database and data just once in an android application. I extend SQLiteOpenHelper and use a DataHelper class that to manipulate data. Now, I have addEvent() and updateEvent() within the DataHelper class. I create an instance of DataHelper in my Activity and addEvent() a couple of times to insert data. Well, now I don't know how to just do that once. If I restart the app, its just going to "addEvent()" again and so the data is being reset every time. Sorry for the probably really REALLY noob question. The only solution I found was not using the DataHelper class and just adding data "manually" within the onCreate() method in SQLiteOpenHelper.

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  • When to use new layouts and when to use new activities?

    - by cmdfrg
    I'm making a game in Android and I'm trying to add a set of menu screens. Each screen takes up the whole display and has various transitions available to other screens. As a rough summary, the menu screens are: Start screen Difficult select screen Game screen. Pause screen. Game over screen. And there are several different ways you can transition between screen: 1 - 2 2 - 3 3 - 4 (pause game) 4 - 1 (exit game) 4 - 3 (resume game) 3 - 5 (game ends) Obviously, I need some stored state when moving between screens, such as the difficulty level select when starting a game and what the player's score is when the game over screen is shown. Can anyone give me some advice for the easiest way to implement the above screens and transitions in Android? All the create/destroy/pause/resume methods make me nervous about writing brittle code if I'm not careful. I'm not fond of using an Activity for each screen. It seems too heavy weight, having to pass data around using intents seems like a real pain and each screen isn't a useful module by itself. As the "back" button doesn't always go back to the previous screen either, my menu layout doesn't seem to fit the activity model well. At the moment, I'm representing each screen as an XML layout file and I have one activity. I set the different buttons on each layout to call setContentView to update the screen the main activity is showing (e.g. the pause button changes the layout to the pause screen). The activity holds onto all the state needed (e.g. the current difficulty level and the game high score), which makes it easy to share data between screens. This seems roughly similar to the LunarLander sample, except I'm using multiple screens. Does what I have at the moment sound OK or am I not doing things the typical Android way? Is there a class I can use (e.g. something like ViewFlipper) that could make my life easier? By the way, my game screen is implemented as a SurfaceView that stores the game state. I need the state in this view to persist between calls to setContentView (e.g. to resume from paused). Is the right idea to create the game view when the activity starts, keep a reference to it and then use this reference with setContentView whenever I want the game screen to appear?

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  • Hibernate - Persisting polymorphic joins

    - by Marty Pitt
    Hi I'm trying to understand how to best implement a polymorphic one-to-many in hibernate. Eg: @MappedSuperclass public class BaseEntity { Integer id; // etc... } @Entity public class Author extends BaseEntity {} @Entity public class Post extends BaseEntity {} @Entity public class Comment extends BaseEntity {} And now, I'd like to also persist audit information, with the following class: @Entity public class AuditEvent { @ManyToOne // ? BaseEntity entity; } What is the appropriate mapping for auditEvent.entity? Also, how will Hibernate actually persist this? Would a series of join tables be generated (AuditEvent_Author , AuditEvent_Post, AuditEvent_Comment), or is there a better way? Note, I'd rather not have my other entity classes expose the other side of the join (eg., List<AuditEvent> events on BaseEntity) - but if that's the cleanest way to implement, then it will suffice.

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  • How to set message when I get Exception

    - by user1748932
    public class XMLParser { // constructor public XMLParser() { } public String getXmlFromUrl(String url) { String responseBody = null; getset d1 = new getset(); String d = d1.getData(); // text String y = d1.getYear(); // year String c = d1.getCircular(); String p = d1.getPage(); List<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>(); nameValuePairs.add(new BasicNameValuePair("YearID", y)); nameValuePairs.add(new BasicNameValuePair("CircularNo", c)); nameValuePairs.add(new BasicNameValuePair("SearchText", d)); nameValuePairs.add(new BasicNameValuePair("pagenumber", p)); try { HttpClient httpclient = new DefaultHttpClient(); HttpPost httppost = new HttpPost(url); httppost.setEntity(new UrlEncodedFormEntity(nameValuePairs)); HttpResponse response = httpclient.execute(httppost); HttpEntity entity = response.getEntity(); responseBody = EntityUtils.toString(entity); } catch (UnsupportedEncodingException e) { e.printStackTrace(); } catch (ClientProtocolException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } // return XML return responseBody; } public Document getDomElement(String xml) { Document doc = null; DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance(); try { DocumentBuilder db = dbf.newDocumentBuilder(); InputSource is = new InputSource(); is.setCharacterStream(new StringReader(xml)); doc = db.parse(is); } catch (ParserConfigurationException e) { Log.e("Error: ", e.getMessage()); return null; } catch (SAXException e) { Log.e("Error: ", e.getMessage()); // i m getting Exception here return null; } catch (IOException e) { Log.e("Error: ", e.getMessage()); return null; } return doc; } /** * Getting node value * * @param elem * element */ public final String getElementValue(Node elem) { Node child; if (elem != null) { if (elem.hasChildNodes()) { for (child = elem.getFirstChild(); child != null; child = child .getNextSibling()) { if (child.getNodeType() == Node.TEXT_NODE) { return child.getNodeValue(); } } } } return ""; } /** * Getting node value * * @param Element * node * @param key * string * */ public String getValue(Element item, String str) { NodeList n = item.getElementsByTagName(str); return this.getElementValue(n.item(0)); } } I am getting Exception in this class for parsing data. I want print this message in another class which extends from Activity. Can you please tell me how? I tried much but not able to do.. public class AndroidXMLParsingActivity extends Activity { public int currentPage = 1; public ListView lisView1; static final String KEY_ITEM = "docdetails"; static final String KEY_NAME = "heading"; public Button btnNext; public Button btnPre; public static String url = "http://dev.taxmann.com/TaxmannService/TaxmannService.asmx/GetNotificationList"; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); // listView1 lisView1 = (ListView) findViewById(R.id.listView1); // Next btnNext = (Button) findViewById(R.id.btnNext); // Perform action on click btnNext.setOnClickListener(new View.OnClickListener() { public void onClick(View v) { currentPage = currentPage + 1; ShowData(); } }); // Previous btnPre = (Button) findViewById(R.id.btnPre); // Perform action on click btnPre.setOnClickListener(new View.OnClickListener() { public void onClick(View v) { currentPage = currentPage - 1; ShowData(); } }); ShowData(); } public void ShowData() { XMLParser parser = new XMLParser(); String xml = parser.getXmlFromUrl(url); // getting XML Document doc = parser.getDomElement(xml); // getting DOM element NodeList nl = doc.getElementsByTagName(KEY_ITEM); int displayPerPage = 5; // Per Page int TotalRows = nl.getLength(); int indexRowStart = ((displayPerPage * currentPage) - displayPerPage); int TotalPage = 0; if (TotalRows <= displayPerPage) { TotalPage = 1; } else if ((TotalRows % displayPerPage) == 0) { TotalPage = (TotalRows / displayPerPage); } else { TotalPage = (TotalRows / displayPerPage) + 1; // 7 TotalPage = (int) TotalPage; // 7 } int indexRowEnd = displayPerPage * currentPage; // 5 if (indexRowEnd > TotalRows) { indexRowEnd = TotalRows; } // Disabled Button Next if (currentPage >= TotalPage) { btnNext.setEnabled(false); } else { btnNext.setEnabled(true); } // Disabled Button Previos if (currentPage <= 1) { btnPre.setEnabled(false); } else { btnPre.setEnabled(true); } // Load Data from Index int RowID = 1; ArrayList<HashMap<String, String>> menuItems = new ArrayList<HashMap<String, String>>(); HashMap<String, String> map; // RowID if (currentPage > 1) { RowID = (displayPerPage * (currentPage - 1)) + 1; } for (int i = indexRowStart; i < indexRowEnd; i++) { Element e = (Element) nl.item(i); // adding each child node to HashMap key => value map = new HashMap<String, String>(); map.put("RowID", String.valueOf(RowID)); map.put(KEY_NAME, parser.getValue(e, KEY_NAME)); // adding HashList to ArrayList menuItems.add(map); RowID = RowID + 1; } SimpleAdapter sAdap; sAdap = new SimpleAdapter(AndroidXMLParsingActivity.this, menuItems, R.layout.list_item, new String[] { "RowID", KEY_NAME }, new int[] { R.id.ColRowID, R.id.ColName }); lisView1.setAdapter(sAdap); } } This my class where I want to Print that message

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  • Problem loading a contents URL into a string

    - by bebeTech
    I've been using this method for a few weeks now as suggested on my previous question and the app now keeps crashing with a Protocol 443 error - something about unable to resolve the address. Worked fine when first installed and then just stopped. The same with on the device itself, worked fine until this morning and now the same issue?? Nothing wrong with the URL as I can still load in a browser. If I leave it for a couple of days it starts working again?? Is there a more effecient way of using the Http POST and GET functions? All I am trying to do is perform a login and save the resulting page to a string. Is there a more Android friendly way?

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  • Read a file to multiple array byte[]

    - by hankol
    I have an encryption algorithm (AES) that accepts file converted to array byte and encrypt it. Since I am going to process a very big size files, the JVM may go out of memory. I am planing to read the files in multiple array byte. each containing some part of the file. Then I teratively feed the algorithm. Finally merge them to produce encrypted file. So my question is: there any way to read a file part by part to multiple array byte? I thought I can use the following to read the file to array byte: IOUtils.toByteArray(InputStream input). And then split the array into multiple bytes using: Arrays.copyOfRange(). But I am afraid that the first code that reads file to byte will make the JVM to go out of memory. any suggestion please ? thanks

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  • Is this technically thread safe despite being mutable?

    - by Finbarr
    Yes, the private member variable bar should be final right? But actually, in this instance, it is an atomic operation to simply read the value of an int. So is this technically thread safe? class foo { private int bar; public foo(int bar) { this.bar = bar; } public int getBar() { return bar; } } // assume infinite number of threads repeatedly calling getBar on the same instance of foo.

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  • from Hibernate hbm to JPA annotations, a challenging one

    - by nodje
    Hi, I've been struggling with this one for quite some time already. It appears a lot less simple than I thought it'd be: This is included in the "COTISATION" table mapping an uses SynchroDataType, extending Hibernate UserType. This works really great, and I can't find a way to translate it to proper JPA, while keeping the convenience of it. Does someone has a solution for that kind of one-to-one mapping? cheers

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  • Should we or should we not check in the classes folder in WEB-INF directory into SVN?

    - by Vatsala
    I use SVN, and am learning how to use it along with eclipse IDE. The first time I add classes to my package, there is no problem, the generated class files get into SVN smoothly. The moment I edit them, I get this message - "WEB-INF/classes" is obstructed. I try the "clean-up" command and the clean up command says "WEB-INF/classes" folder is locked. I use TortoiseSVN as my SVN client. I know why this is happening. It probably because the Eclipse overwrites all the files while generating classes and then causes this - Is it inappropriate to commit the class files into SVN? If not, what should I do to commit these class files smoothly?

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  • connection.setRequestProperty and excplicitly writing to the urloutputstream are they same ?

    - by Bunny Rabbit
    URL url = new URL("http://www.example.com/comment"); HttpURLConnection connection = (HttpURLConnection) url.openConnection(); connection.setDoOutput(true); connection.setRequestMethod("POST"); Is connection.setRequestProperty(key, value); same as OutputStreamWriter writer = new OutputStreamWriter(connection.getOutputStream()); writer.write("key=" + value); writer.close(); if not please correct me .

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  • How do I manipulate a tree of immutable objects?

    - by Frederik
    I'm building an entire application out of immutable objects so that multi-threading and undo become easier to implement. I'm using the Google Collections Library which provides immutable versions of Map, List, and Set. My application model looks like a tree: Scene is a top-level object that contains a reference to a root Node. Each Node can contain child Nodes and Ports. An object graph might look like this: Scene | +-- Node | +-- Node | +- Port +-- Node | +- Port +- Port If all of these objects are immutable, controlled by a top-level SceneController object: What is the best way to construct this hierarchy? How would I replace an object that is arbitrarily deep in the object tree? Is there a way to support back-links, e.g. a Node having a "parent" attribute?

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  • HTML/CSS Rendering to Image

    - by Steve
    Is there a library or tool that can take an html page and some css, and then render an image? I would like to define some templates server side using html code snippets, and some CSS to define the layout. Then using the template and CSS, I would like to essentially render an image of how this would display in a browser, and pass the image back to the client. Thanks.

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  • Inheritance question / problem

    - by Itsik
    I'm creating a custom Layout for android. The layout implementation is exactly the same, but once I need to extend from RelativeLayout, and once from LinearLayout. class Layout1 extends LinearLayout { // methods and fields } class Layout2 extends RelativeLayout { // the same EXACT methods and fields } How can I use inheritance to avoid DRY and implement my methods once.

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  • Is there some way to assume @Nullable as default? (using FindBugs or any other free tool).

    - by alex2k8
    Consider such code public void m1(String text) { if(text == null) text = "<empty>"; System.out.println(text.toLowerCase()); } And this is a buggy version: public void m1(String text) { System.out.println(text.toLowerCase()); } If null value passed, the NullPointerException may be thrown. I would like the static-analysis tool (e.g. FindBugs) to report this issue. Unsuccessfully the FindBugs (at least by default) requires me to specify @Nullable annotation explicitly. public void m1(@Nullable String text) { System.out.println(text.toLowerCase()); // FindBugs: text must be nonnull but is marked as nullable } The problem is that if I forget to annotate it, the bug will be missed!!! How can I make the FindBugs (or any other free tool) to assume @Nullable by default?

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  • Good article about File- and Folder Permissions on production server?

    - by Camran
    I have a classifieds website, and users may post classifieds, add images, remove classifieds etc etc... I have no idea what to set the permissions to on folders. For instance, a php script which I have uploads a file to a directory. What would you have set the directory permissions to? Nobody need access to the directory, only the php script... Just wonder if anybody has a good (brief) article about setting the "right" permissions? Thanks

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