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  • Compare class objects

    - by reto
    I have to compare a class object against a list of pre defined classes. Is it safe to use == or should I use equals()? if (klass == KlassA.class) { } else if (klass == KlassB.class) { } else if (klass == KlassC.class) { } else { } Note: I cannot use instanceof, I don't have an object, I just have the class object. I (mis)use it like an enum in this situation! Thanks!

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  • Is it a good idea to close and open hibernate sessions frequently?

    - by Gaurav
    Hi, I'm developing an application which requires that state of entities be read from a database at frequent intervals or triggers. However, once hibernate reads the state, it doesn't re-read it unless I explicitly close the session and read the entity in a new session. Is it a good idea to open a session everytime I want to read the entity and then close it afterwards? How much of an overhead does this put on the application and the database (we use a c3p0 connection pool also)? Will it be enough to simply evict the entity from the session before reading it again?

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  • Design pattern: polymorphisim for list of objects

    - by ziang
    Suppose I have a class A, and A1, A2 inherits from A. There are 2 functions: List<A1> getListA1(){...} List<A2> getListA2(){...} Now I want to do something similar to both A1 and A2 in another function public void process(List<A>){...} If I want to pass the instance of either ListA1 or ListA2, of course the types doesn't match because the compiler doesn't allow the coercion from List< A1 to List< A. I can't do something like this: List<A1> listA1 = getListA1(); List<A> newList = (List<A>)listA1; //this is not allowed. So what is the best approach to the process()? Is there any way to do it in a universal way rather than write the similar code to both List and List?

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  • Contacts & Autocomplete

    - by Vince
    First post. I'm new to android and programming in general. What I'm attempting to is to have an autocomplete text box pop up with auto complete names from the contact list. IE, if they type in "john" it will say "John Smith" or any john in their contacts. The code is basic, I pulled it from a few tutorials. private void autoCompleteBox() { ContentResolver cr = getContentResolver(); Uri contacts = Uri.parse("content://contacts/people"); Cursor managedCursor1 = cr.query(contacts, null, null, null, null); if (managedCursor1.moveToFirst()) { String contactname; String cphoneNumber; int nameColumn = managedCursor1.getColumnIndex("name"); int phoneColumn = managedCursor1.getColumnIndex("number"); Log.d("int Name", Integer.toString(nameColumn)); Log.d("int Number", Integer.toString(phoneColumn)); do { // Get the field values contactname = managedCursor1.getString(nameColumn); cphoneNumber = managedCursor1.getString(phoneColumn); if ((contactname != " " || contactname != null) && (cphoneNumber != " " || cphoneNumber != null)) { c_Name.add(contactname); c_Number.add(cphoneNumber); Toast.makeText(this, contactname, Toast.LENGTH_SHORT) .show(); } } while (managedCursor1.moveToNext()); } name_Val = (String[]) c_Name.toArray(new String[c_Name.size()]); phone_Val = (String[]) c_Number.toArray(new String[c_Name.size()]); ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, android.R.layout.simple_dropdown_item_1line, name_Val); personName.setAdapter(adapter); } personName is my autocompletetextbox. So it actually works when I use it in the emulator (4.2) with manually entered contacts through the people app, but when I use it on my device, it will not pop up with any names. I'm sure it's something ridiculous but I've tried to find the answer and I'm getting nowhere. Can't learn if I don't ask.

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  • JPA and aggregate functions. How do I use the result of the query?

    - by Bogdan
    Hey guys, I'm new to ORM stuff and I need some help understanding something. Let's assume I have the following standard SQL query: SELECT *, COUNT(test.testId) AS noTests FROM inspection LEFT JOIN test ON inspection.inspId = test.inspId GROUP BY inspection.inspId which I want to use in JPA. I have an Inspection entity with a one-to-many relationship to a Test entity. (an inspection has many tests) I tried writing this in JPQL: Query query = em.createQuery("SELECT insp, COUNT(???what???) FROM Inspection insp LEFT JOIN insp.testList " + "GROUP BY insp.inspId"); 1) How do I write the COUNT clause? I'd have to apply count to elements from the test table but testList is a collection, so I can't do smth like COUNT(insp.testList.testId) 2) Assuming 1 is resolved, what type of object will be returned. It will definitely not be an Inspection object... How do I use the result?

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  • Hibernate is performing unwanted SELECTs on call to saveOrUpdate

    - by digiarnie
    Let's say I have a House entity which maps to many Person entities. I then load an existing House which has 20 occupants. beginTransaction(); House house = houseDao.find(1L); commitTransaction(); Later in the code, I can then add a new Person to the House: ... List<Person> people = house.getPeople(); people.add(new Person("Dilbert")); .... When I make the call: session.saveOrUpdate(house); Hibernate performs 21 queries: 1 to SELECT the House and 20 to SELECT each existing Person in the House. I'm sure it's a small issue on my part, however, what should I do so that I can add a new Person to the house without having such a heavy hit on the database in this situation? This is all done within the same session.

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  • FindBugs and CheckForNull on classes vs. interfaces

    - by ndn
    Is there any way to let FindBugs check and warn me if a CheckForNull annotation is present on the implementation of a method in a class, but not on the declaration of the method in the interface? import javax.annotation.CheckForNull; interface Foo { public String getBar(); } class FooImpl implements Foo { @CheckForNull @Override public String getBar() { return null; } } public class FindBugsDemo { public static void main(String[] args) { Foo foo = new FooImpl(); System.out.println(foo.getBar().length()); } } I just discovered a bug in my application due to a missing null check that was not spotted by FindBugs because CheckForNull was only present on FooImpl, but not on Foo, and I don't want to spot all other locations of this problem manually.

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  • OnClickListener onClick=true and selector

    - by azerto00
    I have not found any answer for my problem, so I need your help ... I have an LinearLayout which I want to be clickable in order to lunch another activity. So I implement an onClickListener to it. I created an selector for this LinearLayout in order that what someone click on it, the background change. I just don't understand that : If my LinearLayout doesn't have android:clickable="true" in the xml, I'm able to click on it and get what I want but the selector doesn't work. If I remove this line, it is the opposite .. the selector work but not the onClick event. So, can anyone can explain me why ? Just in case, here is my the content of my selector file : <selector xmlns:android="http://schemas.android.com/apk/res/android"> <item android:drawable="@drawable/btn_restaurants_background_state_pressed" android:state_pressed="true"></item> <item android:drawable="@drawable/btn_restaurants_background_state_pressed" android:state_focused="true"></item> <item android:drawable="@drawable/btn_restaurants_background_state_pressed" android:state_selected="true"></item> <item android:drawable="@drawable/btn_restaurants_background_state_normal"></item> </selector> Thanks you in advance

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  • Implementing clone on a LinkedList

    - by devoured elysium
    I am trying to implement a clone() method on a DoubleLinkedList. Now, the problem is that implementing it by "the convention" is a lot more troublesome than just creating a new DoubleLinkedList and filling it with all the elements of my current DoubleLinkedList. Is there any inconvenient I am not seeing when doing that? Here is my current approach: @Override public DoubleLinkedList<T> clone() { DoubleLinkedList<T> dll = new DoubleLinkedList<T>(); for (T element : dll) { dll.add(element); } return dll; } Here is what it would be by the convention: @Override public DoubleLinkedList<T> clone() { try { DoubleLinkedList<T> dll = (DoubleLinkedList<T>)super.clone(); //kinda complex code to copy elements return dll; } catch (CloneNotSupportedException e) { throw new InternalError(e.toString()); } }

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  • Tuning garbage collections for low latency

    - by elec
    I'm looking for arguments as to how best to size the young generation (with respect to the old generation) in an environment where low latency is critical. My own testing tends to show that latency is lowest when the young generation is fairly large (eg. -XX:NewRatio <3), however I cannot reconcile this with the intuition that the larger the young generation the more time it should take to garbage collect. The application runs on linux, jdk 6 before update 14, i.e G1 not available.

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  • Generics in return types of static methods and inheritance

    - by Axel
    Generics in return types of static methods do not seem to get along well with inheritance. Please take a look at the following code: class ClassInfo<C> { public ClassInfo(Class<C> clazz) { this(clazz,null); } public ClassInfo(Class<C> clazz, ClassInfo<? super C> superClassInfo) { } } class A { public static ClassInfo<A> getClassInfo() { return new ClassInfo<A>(A.class); } } class B extends A { // Error: The return type is incompatible with A.getClassInfo() public static ClassInfo<B> getClassInfo() { return new ClassInfo<B>(B.class, A.getClassInfo()); } } I tried to circumvent this by changing the return type for A.getClassInfo(), and now the error pops up at another location: class ClassInfo<C> { public ClassInfo(Class<C> clazz) { this(clazz,null); } public ClassInfo(Class<C> clazz, ClassInfo<? super C> superClassInfo) { } } class A { public static ClassInfo<? extends A> getClassInfo() { return new ClassInfo<A>(A.class); } } class B extends A { public static ClassInfo<? extends B> getClassInfo() { // Error: The constructor ClassInfo<B>(Class<B>, ClassInfo<capture#1-of ? extends A>) is undefined return new ClassInfo<B>(B.class, A.getClassInfo()); } } What is the reason for this strict checking on static methods? And how can I get along? Changing the method name seems awkward.

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  • Write to text file using ArrayList

    - by Ugochukwutubelum Chiemenam
    The program is basically about reading from a text file, storing the current data into an ArrayList, then writing data (from user input) into the same text file. Kindly let me know where I am going wrong in this sub-part? The data inside the text file is as follows: abc t1 1900 xyz t2 1700 The compiler is showing an error at the line output.format("%s%s%s%n", public class justTesting { private Scanner input; private Formatter output; private ArrayList<Student> tk = new ArrayList<Student>(); public static void main(String[] args) { justTesting app = new justTesting(); app.create(); app.writeToFile(); } public void create() { Text entry = new Text(); Scanner input = new Scanner(System.in); System.out.printf("%s\n", "Please enter your name, ID, and year: "); while (input.hasNext()) { try { entry.setName(input.next()); entry.setTelNumber(input.next()); entry.setDOB(input.next()); for (int i = 0; i < tk.size(); i++) { output.format("%s%s%s%n", tk.get(i).getName(), tk.get(i) .getTelNumber(), tk.get(i).getDOB()); } } catch (FormatterClosedException fce) { System.err.println("Error writing to file."); return; } catch (NoSuchElementException nsee) { System.err.println("Invalid input. Try again: "); input.nextLine(); } System.out.printf("%s\n", "Please enter your name, ID, and year: "); } } public void writeToFile() { try { output = new Formatter("testing.txt"); } catch (SecurityException se) { System.err .println("You do not have write access permission to this file."); System.exit(1); } catch (FileNotFoundException fnfe) { System.err.println("Error opening or creating file."); System.exit(1); } } }

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  • How to test unescaped &nbsps; as a whitespace

    - by gleery
    I use apache common lang to unescape a block of html text which contains &nbsp;, I want to filter out blocks that contains only whitespaces. But I can't test the   as a whitespace. It's not in the normal whitespace list(http://en.wikipedia.org/wiki/Whitespace_character), and I try to print its Hex form by calling Character.getNumericValue which return -1. &nbsp should be a whitespace,isn't? But How can I test it?

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  • when get pagecontent from URL the connect alway return nopermistion ?

    - by tiendv
    I have a methor to return pagecontent of link but when it run, alway return "Do not perrmisson ", plesea check it here is code to return string pagecontent public static String getPageContent(String targetURL) throws Exception { Hashtable contentHash = new Hashtable(); URL url; URLConnection conn; // The data streams used to read from and write to the URL connection. DataOutputStream out; DataInputStream in; // String returned as the result . String returnString = ""; // Create the URL object and make a connection to it. url = new URL(targetURL); conn = url.openConnection(); // check out permission of acess URL if (conn.getPermission() != null) { returnString = "Do not Permission access URL "; } else { // Set connection parameters. We need to perform input and output, // so set both as true. conn.setDoInput(true); conn.setDoOutput(true); // Disable use of caches. conn.setUseCaches(false); // Set the content type we are POSTing. We impersonate it as // encoded form data conn.setRequestProperty("Content-Type", "application/x-www-form-urlencoded"); // get the output stream . out = new DataOutputStream(conn.getOutputStream()); String content = ""; // Create a single String value pairs for all the keys // in the Hashtable passed to us. Enumeration e = contentHash.keys(); boolean first = true; while (e.hasMoreElements()) { // For each key and value pair in the hashtable Object key = e.nextElement(); Object value = contentHash.get(key); // If this is not the first key-value pair in the hashtable, // concantenate an "&" sign to the constructed String if (!first) content += "&"; // append to a single string. Encode the value portion content += (String) key + "=" + URLEncoder.encode((String) value); first = false; } // Write out the bytes of the content string to the stream. out.writeBytes(content); out.flush(); out.close(); // check if can't read from URL // Read input from the input stream. in = new DataInputStream(conn.getInputStream()); String str; while (null != ((str = in.readLine()))) { returnString += str + "\n"; } in.close(); } // return the string that was read. return returnString; }

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  • Use the serialVersionUID or suppress warnings?

    - by Okami
    Dear all, first thing to note is the serialVersionUID of a class implementing Interface Serializable is not in question. What if we create a class that for example extends HttpServlet? It also should have a serialVersionUID. If someone knows that this object will never be serialized should he define it or add an annotation to suppress those warnings? What would you do and why? Thanks for sharing your thoughts. Okami

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